WO2022157725A1 - Silver nano-ink composition comprising mixed-phase capped nanoparticles, methods of preparation, kit and applications thereof - Google Patents

Silver nano-ink composition comprising mixed-phase capped nanoparticles, methods of preparation, kit and applications thereof Download PDF

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Publication number
WO2022157725A1
WO2022157725A1 PCT/IB2022/050582 IB2022050582W WO2022157725A1 WO 2022157725 A1 WO2022157725 A1 WO 2022157725A1 IB 2022050582 W IB2022050582 W IB 2022050582W WO 2022157725 A1 WO2022157725 A1 WO 2022157725A1
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silver
nanoparticles
phase
present disclosure
vol
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PCT/IB2022/050582
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French (fr)
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Mitta DIVYA
Subho Dasgupta
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Indian Institute Of Science
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/52—Electrically conductive inks
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/30—Inkjet printing inks
    • C09D11/32—Inkjet printing inks characterised by colouring agents
    • C09D11/322—Pigment inks
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/30—Inkjet printing inks
    • C09D11/36—Inkjet printing inks based on non-aqueous solvents
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/30—Inkjet printing inks
    • C09D11/38—Inkjet printing inks characterised by non-macromolecular additives other than solvents, pigments or dyes

Definitions

  • the present disclosure generally relates to the field of printed electronics and conducting nano-inks.
  • the present disclosure relates to a nano-ink composition suitable for use as printable ink in commercial printers.
  • the said nano-ink composition comprises mixed- phase capped nanoparticles that lend many advantages to the nano-ink containing them.
  • the present disclosure also provides for methods of preparing the said nanoparticles and inks, a kit and applications thereof.
  • TCO transparent conducting oxide
  • ITO Sn-doped Indium Oxide
  • inkjet printable silver inks typically require higher temperature of annealing/curing and are hence not suitable for paper or inexpensive polymer (e.g. PET) substrates. Further, the shelf life of commercially available silver inks is limited, and varies from about one to a few months. Furthermore, inks that can be low temperature curable are either precursor based, and are highly basic, having high pH, that is typically not suitable for inkjet print heads or have very limited shelf life.
  • inks that can be chemically cured at room temperatures have organic and ionic contaminants in the printed films from the residues of the stabilizer and flocculation agent, especially due to the large concentration of ionic contaminants, group-I cation and halide ions.
  • This technology has not seen a great commercial success.
  • the present disclosure aims to address the same.
  • the present disclosure relates to a silver nano-ink composition comprising mixed-phase capped nanoparticles.
  • each of the mixed-phase capped nanoparticle comprises of about 5% to about 95% silver phase, and of about 5% to about 95% silver oxide phase.
  • the silver nano-ink composition also comprises at least one solvent and at least one excipient.
  • the present disclosure also relates to the capped nanoparticles comprising a mixture of silver and silver oxide phases.
  • the nanoparticles of the present disclosure are capped by one or more stabilizing/capping agent.
  • the present disclosure also provides for a method of preparing said capped nanoparticles, and their use in preparing the silver nano-ink composition of the present disclosure.
  • the method of preparing the silver nano-ink composition comprises mixing plurality of mixed-phase capped nanoparticles with at least one solvent and at least one excipient.
  • the method of preparing the capped nanoparticles comprises acts of: contacting silver salt solution with stabilizing agent, adding a reducing agent at a rate suitable to obtain a mixture/ mixed phase of silver and silver oxide nanoparticles, and optionally isolating/separating the nanoparticles thus obtained.
  • the present disclosure also provides for a kit for obtaining the silver nano-ink composition, comprising plurality of mixed-phase capped nanoparticles, at least one solvent and at least one excipient, optionally along with user instructions for obtaining the said composition.
  • the present disclosure also provides for use of the silver nano-ink composition of the present disclosure for preparing a substrate comprising a conductive silver pattern.
  • the present disclosure also provides for a substrate having the conductive silver pattern formed by the silver nano-ink composition of the present disclosure; and a method of obtaining the same.
  • the silver nano-ink composition is applied on to a substrate through inkjet printing, to form the conductive silver pattern.
  • the present disclosure also pertains to a method of making a conductive silver pattern on a substrate, said method comprising applying the silver nano-ink composition of the present disclosure on a substrate followed by curing the substrate to form the conductive silver pattern.
  • the curing is carried out through thermal curing at a temperature ranging from about 40 °C to about 150 °C, or through photonic curing.
  • the curing results in phase change of silver oxide to silver in the mixed-phase capped nanoparticles causing a volume change driven removal of the capping agent from the nanoparticles and facilitating formation of the conductive silver pattern.
  • the silver nano-ink has a long shelf-life of at least about 6 to 12 months.
  • Figure 1 depicts (a) XRD patterns of the as-synthesised Batch A, B and C nanoparticles (with different addition rate of the reducing agent NaOH) showing a mixture/mixed phase of both Ag and Ag 2 O phases with NaOH as the reducing agent and PVA as the capping agent and (b) their annealed (80 °C for 1 hour for Batch A and 120 °C for 1 hour for Batch B and C respectively) counterparts showing pure Ag phase in case of Batch A and B, whereas Batch C still contains minor traces of silver oxide present after annealing at 120 °C for 1 hour.
  • the standard Ag and Ag 2 O patterns are also shown at the bottom for reference.
  • Figure 2 depicts (a) As-synthesised mixed phase of Ag and Ag 2 O nanoparticles with NaOH as the reducing agent and capped with PVA. (b) Stable nano-ink of the mixed phase of Ag and Ag 2 O nanoparticles dispersed in NMP. (c) Comparison of DLS measurement of both Batch A and Batch B nano-inks soon after ink preparation and after 3 months of shelf life.
  • Figure 3 depicts SEM micrographs of (a) as-prepared Batch A nanoparticles and its (b) inkjet-printed nano-ink layer, with NaOH as the reducing agent, PVA as the capping agent and NMP as the solvent.
  • Figure 4 depicts SEM micrographs of (a) as-prepared Batch B nanoparticles and its (b-d) inkjet-printed nano-ink layer, with NaOH as the reducing agent, PVA as the capping agent and NMP as the solvent.
  • Figure 5 depicts (a) Optical microscope image of a printed silver square which is used for the four-probe measurement, (b) Variability of sheet resistance with number of bending cycles, where the solid and dashed lines represent tension and compression conditions and the hollow circle, triangle, and square represent the 1%, 2% and 4% strain conditions of Batch A ink, whereas the solid shapes represent Batch B ink, respectively.
  • Figure 6 depicts (a) XRD and (b,c) SEM micrographs of inkjet-printed phase pure silver oxide (Ag 2 O) nanoparticles capped by PVA.
  • the nanoparticles are synthesised by adding first the reducing agent NaOH to AgNO 3 solution, followed by the addition of PVA solution.
  • Image in (b) represents the inkjet-printed film from freshly prepared ink and (c) depicts the film printed using a ink stored for 72 hours where the nanoparticles eventually had a reaction with the solvent NMP and developed an insulating shell around the nanoparticles.
  • Figure 7 depicts (a) the XRD patterns of the as-synthesised nanoparticles (using KOH as reducing agent and PVA as the capping agent) showing a mixture/mixed phase of both Ag and Ag 2 O phases; and (b) the XRD patterns of the annealed ink showing a pure Ag phase.
  • Figure 8 depicts (a) the XRD patterns of the as-synthesised nanoparticles (using LiOH as reducing agent and PVA as the capping agent) showing a mixture/mixed phase of both Ag and Ag 2 O phases; and (b) the XRD patterns of the annealed ink showing a pure Ag phase.
  • Figure 9 depicts (a) the XRD patterns of the as-synthesised nanoparticles (using PVP as surfactant/stabilizing agent and NaOH as the reducing agent) showing a mixture/mixed phase of both Ag and Ag 2 O phases; and (b) the XRD patterns of the annealed ink showing a pure Ag phase.
  • Figure 10 depicts (a) the stable nano-ink of the Ag+Ag 2 O mixed-phase nanoparticles prepared with NaOH as the reducing agent and PVA as the capping agent and dispersed in DMSO; and (b) provides a comparison of DLS measurements of the as-prepared nano-ink synthesised using NMP and DMSO as the solvents.
  • Figure 11 depicts the XRD pattern of the Batch A nanoparticles with NaOH as the reducing agent and PVA as the capping agent, just after their preparation, and after storing them for 6 months.
  • the present disclosure aims to address the drawbacks of the art and provides for novel nanoparticles having high shelf life, low temperature curable silver ink, kits, methods for their preparations and applications thereof.
  • the terms "method” and “process” are employed interchangeably and are meant to convey their commonly known dictionary meaning.
  • the terms “annealing”, “curing” and “sintering” are employed interchangeably and refer to their ordinary meaning known to a person skilled in the art with respect to the field of the present disclosure. Generally, these terms are meant to describe ways through which toughening or hardening of a material takes place through cross-linking and can be used for all the processes where a solid product is obtained from a liquid solution.
  • annealing is employed for thermal curing or photonic curing of the silver nano-ink composition of the present disclosure on a substrate, resulting in formation of conductive silver pattern on the substrate.
  • thermal curing within the context of the present disclosure is also alternatively used with the term “heating”.
  • the term “mixed-phase nanoparticle” or the like refers to nanoparticles having a particle size ranging from about 2 nm to about 500 nm and comprising a mixed phase of silver and silver oxide.
  • both silver phase and silver oxide phase coexist in each nanoparticle of the present disclosure.
  • each nanoparticle is made up of a mixture of silver and silver oxide phase, and the presence and percentage of each phase depends on the stage of preparation/curing of the nanoparticle.
  • the nanoparticles are capped by a suitable stabilizing/capping agent, to give rise to “mixed-phase capped nanoparticles”.
  • the term “mixed phase” or “mixed-phase” refers to a phase mixture or a combination of silver and silver oxide phases.
  • phase change refers to phase transition of silver oxide (Ag 2 O) to metallic silver (Ag).
  • capping agent and “stabilizing agent” are used interchangeably, and are meant to convey their ordinary meaning known to a person skilled in the field of the present disclosure.
  • the “capping agent” or “stabilizing agent” is employed for capping of the mixed-phase nanoparticles of the present disclosure.
  • nano-ink is meant to describe an ink composition formed from nanoparticles as the primary constituting component.
  • excipient and “industrially acceptable excipient” are used interchangeably, and are meant to convey their ordinary meaning known to a person skilled in the field of the present disclosure. In the context of the present disclosure, these terms are meant to describe additional components present in the nano-ink, in addition to the mixed- phase nanoparticles of the present disclosure, and which play a role in improving printability, flowability and/or dispersion quality of the ink, and include components that are useful in viscosity modification, de-wetting, curing, drying, film formation and densification control.
  • the industrially acceptable excipients used herein thus also include any conventionally employed component/excipient in silver nano-inks.
  • the present disclosure solves the unmet need of the prior art, by providing a silver nano-ink composition comprising mixed-phase capped nanoparticles, that is capable of being applied onto a substrate for forming conductive silver patterns at relatively low temperature thermal curing or photonic curing. Further, the nano-ink composition of the present disclosure is also capable of being directly printed on to the substrate through techniques like inkjet printing and has high shelf-life that allows efficient storage of the ink, without any undesirable or detrimental effect.
  • the silver nano-ink composition comprises capped nanoparticles comprising a mixed phase of silver and silver oxide.
  • the silver nano-ink composition comprises of mixed-phase capped nanoparticles
  • the mixed- phase nanoparticles of the present disclosure are capped by one or more capping or stabilizing agent, as is described in more detail in further embodiments of the present disclosure.
  • each of the mixed-phase capped nanoparticle within the silver nano-ink comprises of about 5 vol.% to about 95 vol.% silver phase, and of about 5 vol.% to about 95 vol.% silver oxide phase.
  • the nanoparticles comprise about 15 vol.% to about 85 vol.% of silver and about 15 vol.% to about 85 vol.% of silver oxide.
  • the nanoparticles comprise about 5 vol.%, 6 vol.%, 7 vol.%, 8 vol.%, 9 vol.%, 10 vol.%, 11 vol.%, 12 vol.%, 13 vol.%, 14 vol.%, 15 vol.%, 16 vol.%, 17 vol.%, 18 vol.%, 19 vol.%, 20 vol.%, 21 vol.%, 22 vol.%, 23 vol.%, 24 vol.%, 25 vol.%, 26 vol.%, 27 vol.%, 28 vol.%, 29 vol.%, 30 vol.%, 31 vol.%, 32 vol.%, 33 vol.%, 34 vol.%, 35 vol.%, 36 vol.%, 37 vol.%, 38 vol.%, 39 vol.%, 40 vol.%, 41 vol.%, 42 vol.%, 43 vol.%, 44 vol.%, 45 vol.%, 46 vol.%, 47 vol.%, 48 vol.%, 49 vol.%, 50 vol.%, 51 vol.%, 52 vol.%
  • the nanoparticles comprise about 5 vol.%, 6 vol.%, 7 vol.%, 8 vol.%, 9 vol.%, 10 vol.%, 11 vol.%, 12 vol.%, 13 vol.%, 14 vol.%, 15 vol.%, 16 vol.%, 17 vol.%, 18 vol.%, 19 vol.%, 20 vol.%, 21 vol.%, 22 vol.%, 23 vol.%, 24 vol.%, 25 vol.%, 26 vol.%, 27 vol.%, 28 vol.%, 29 vol.%, 30 vol.%, 31 vol.%, 32 vol.%, 33 vol.%, 34 vol.%, 35 vol.%, 36 vol.%, 37 vol.%, 38 vol.%, 39 vol.%, 40 vol.%, 41 vol.%, 42 vol.%, 43 vol.%, 44 vol.%, 45 vol.%, 46 vol.%, 47 vol.%, 48 vol.%, 49 vol.%, 50 vol.%, 51 vol.%, 52 vol.%
  • each of the mixed-phase capped nanoparticle within the silver nano-ink comprises of about 36 vol.% silver phase and of about 64 vol.% silver oxide phase.
  • each of the mixed-phase capped nanoparticle within the silver nano-ink comprises of about 20 vol.% silver phase and of about 80 vol.% silver oxide phase.
  • each of the mixed-phase capped nanoparticle within the silver nano-ink comprises of about 16 vol.% silver phase and of about 84 vol.% silver oxide phase.
  • the silver nano-ink in addition to the plurality of the mixed- phase capped nanoparticles, also comprises at least one solvent and at least one excipient. In some embodiments of the present disclosure, the silver nano-ink composition comprises about 1 wt.% to about 55 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
  • the silver nano-ink composition comprises about 5 wt.% to about 25 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
  • the amount of nanoparticles is 20 wt.% of the solvent used, i.e., approx. 0.2 g of nanoparticles for 1 ml of solvent (in case of NMP, density is about 1.03 g/ml).
  • the silver nano-ink composition comprises about 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%,
  • the silver nano-ink composition comprises about 45 wt.% to about 99 wt.% of the solvent.
  • the silver nano-ink composition comprises about 45 wt.%, 46 wt.%, 47 wt.%, 48 wt.%, 49 wt.%, 50 wt.%, 51 wt.%, 52 wt.%, 53 wt.%,
  • the solvent employed as part of the silver nano-ink composition is a polar or non-polar solvent.
  • the solvent employed as part of the silver nano-ink composition is selected from a group comprising but not limited N-Methyl-2- Pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile, ethyl acetate, dichloromethane, hexamethylphosphoric triamide, cyclohexyl-pyrrolidinone, chlorobenzene, dimethylformamide, N-vinyl-pyrrolidinone, N-methyl formamide and cyclohexanone, or any combination thereof.
  • NMP N-Methyl-2- Pyrrolidone
  • DMSO dimethyl sulfoxide
  • acetonitrile ethyl acetate
  • dichloromethane hexamethylphosphoric triamide
  • cyclohexyl-pyrrolidinone chlorobenzene
  • dimethylformamide N-vinyl-pyrrolidinone
  • N-methyl formamide and cyclohexanone
  • the solvent employed as part of the silver nano-ink composition is N-Methyl-2 -Pyrrolidone (NMP).
  • the solvent employed as part of the silver nano-ink composition is dimethyl sulfoxide (DMSO).
  • the silver nano-ink composition comprises about 0.1 wt.% to about 20 wt.% of the excipient with respect to weight of the nanoparticles.
  • the silver nano-ink composition comprises about 0.1 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, or about 20 wt.% of the excipient with respect to weight of the nanoparticles.
  • the excipient employed as part of the silver nano-ink composition is selected from a group comprising but not limited to capping agent, viscosity modifier, wetting/de-wetting agent, curing agent, adhesion promoter, anti-foaming agent and humectant, or a combination thereof.
  • the excipient employed as part of the silver nano-ink composition is selected from a group comprising but not limited to terpineol, glycol, glycerol, glycol ether and cellulose ether, tripropylene glycol mono methyl ether, diethylene glycol mono butyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, hydroxypropyl methylcellulose, ethyl cellulose, hydroxy ethyl cellulose, methyl cellulose, sodium carboxy methyl cellulose and benzyl cellulose, or any combination thereof.
  • the excipient employed as part of the silver nano-ink composition is terpineol.
  • the excipient employed as part of the silver nano-ink composition is a capping agent selected from a group comprising but not limited to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1-hexadecylamine and octadecyl-p-vinylbenzyldimethyl ammonium chloride, or any combination thereof.
  • PVA poly vinyl alcohol
  • PVP polyvinyl chloride
  • PMMA poly(methyl methacrylate)
  • the silver nano-ink composition of the present disclosure comprises mixed-phase capped nanoparticles, poly vinyl alcohol (PVA) and terpineol.
  • the silver nano-ink composition of the present disclosure comprises mixed-phase capped nanoparticles, polyvinyl pyrrolidone (PVP) and terpineol.
  • PVP polyvinyl pyrrolidone
  • the mixed-phase capped nanoparticles of the present disclosure have a size ranging from about 2 nm to about 500 nm.
  • the mixed-phase capped nanoparticles of the present disclosure have a size ranging from about 3 nm to about 200 nm.
  • the nanoparticle size is ranging from about 5 nm to about 100 nm. In some embodiments, the nanoparticle size is ranging from about 10 nm and about 50 nm.
  • the nanoparticles of the present disclosure are capped with one or more stabilizing agent (also called as capping agent).
  • Capping prevents large/ extensive aggregation/agglomeration of the nanoparticles for a sustained period of time and increases their stability as individual/isolated nanoparticles or as small sized agglomerates. Absence of capping agent would result in heavy agglomeration of the nanoparticles leading to large sized agglomerates which will either settle down due to gravity and unable to function as a free flowing ink, or clog the nozzles of any jetting type printing process and thus the same would not be suitable for jetting -type printing applications.
  • the stabilizing agent is a surfactant or a polymer molecule used to stabilize the nanoparticles during or after their synthesis.
  • the stabilizing or the capping agent is selected from a group comprising but not limiting to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1- hexadecylamine and octadecyl-p-vinylbenzyldimethyl ammonium chloride, or any combination thereof.
  • the stabilizing or the capping agent is poly vinyl alcohol (PVA).
  • the stabilizing or the capping agent is polyvinyl pyrrolidone (PVP).
  • the silver nano-ink of the present disclosure comprises capped nanoparticles comprising a mixed phase of silver and silver oxide (the mixed-phase capped nanoparticles).
  • An advantage of the nano-ink of the present disclosure is that it requires lower heating/curing/sintering temperature (or energy, in case of photonic curing) to form a conductive pattern upon application on a suitable substrate.
  • the silver oxide phase Upon curing, which can be through thermal curing/heating using low temperatures or photonic curing, the silver oxide phase will undergo a phase change which facilitates the nanoparticles to uncap from its stabilizing or capping agents. This establishes an interparticle contact between the newly transformed silver nanoparticles.
  • sintering/curing at relatively low temperatures is sufficient to convert the remaining oxide phase in the ink/ particles to silver, leading to removal of the stabilizer/capping molecule to obtain interparticle contact, which in turn results in formation of a high conducting silver pattern.
  • the silver nano-ink composition of the present disclosure requires relatively lower sintering temperature (low temperature thermal curing) to convert to conducting phase than conventional silver based nano-inks which require high thermal sintering temperatures to remove the capping agent.
  • Commercial nano-inks suitable for use in ink jet/R&D printers, having only silver nanoparticles are heavily stabilized by stabilizing/capping agents, and therefore require high temperatures (such as those over 150 °C and typically between 150 °C- 300 °C, depending on the ink variety) to remove the capping agent and allow silver particle- particle interaction for formation of conductive layers/lines/fdms.
  • the phase change of silver oxide to silver in the nano-ink of the present disclosure causes a large volume change (Pilling-Bedworth ratio ⁇ 1.56) which helps to remove the capping agents from the nanoparticles, without the need of high sintering temperatures.
  • the thermal sintering at low temperature is sufficient to initiate the phase change of the silver oxide which catalyses the removal of capping agent from the nanoparticles.
  • the removal of capping agent in the present disclosure is not via decomposition of the capping agent at high temperatures, but by physical separation facilitated by the phase change of the silver oxide phase present in the nano-ink of the present disclosure.
  • heating at even low temperature converts the remaining oxide phase in the ink/ particles into pure silver, leading to removal of stabilizer/capping molecules to obtain interparticle contact. Therefore, conducting fdms/lines/layers can be achieved at temperatures as low as 80-85 °C or lower to about 150 °C or lower. This is particularly beneficial in use of the nano-ink of the present disclosure for printing even on inexpensive, paper/ polymer substrates and at a low cost.
  • the nano-ink of the present disclosure is also suitable for applications that would use photonic curing for the formation of conductive metallic silver particles.
  • the silver nano-ink composition of the present disclosure requires relatively lower curing temperature (thermal curing) or relatively lower curing energy (photonic curing) to form conducting pattern on a substrate.
  • the present disclosure accordingly also relates to the method of preparing the silver nano-ink composition as described above.
  • the method of preparing the silver nano-ink composition as described above comprises act of mixing plurality of mixed-phase capped nanoparticles with at least one solvent and at least one excipient.
  • the mixing of plurality of mixed-phase capped nanoparticles with at least one solvent and at least one excipient is carried out by sonication or vigorous mixing.
  • the method of preparing the silver nano-ink composition as described above is carried out by sonication or vigorous mixing of the mixed- phase capped nanoparticles dispersed in at least one solvent and at least one excipient.
  • the method of preparing the silver nano-ink composition as described above comprises: a) preparing a reaction mixture by dissolving a capping/stabilizing agent in a solvent, followed by adding mixed-phase capped nanoparticles to the reaction mixture; and b) subjecting the mixture comprising the nanoparticles to sonication or vigorous mixing, followed by addition of an excipient to obtain the silver nano-ink composition.
  • the method of preparing the silver nano-ink composition as described above comprises employing the same amounts or concentrations of the nanoparticles, capping agent, solvent and excipient, as the amounts or concentrations at which they are finally present in the silver nano-ink composition of the present disclosure.
  • the method of preparing the silver nano-ink composition as described above comprises employing about 45 wt.% to about 99 wt.% of the solvent.
  • the method of preparing the silver nano-ink composition as described above comprises employing about 0.1 wt.% to about 10 wt.% of capping agent with respect to weight of the solvent used.
  • the method of preparing the silver nano-ink composition as described above comprises employing about 1 wt.% to about 55 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
  • the method of preparing the silver nano-ink composition as described above comprises employing about 0.1 wt.% to about 20 wt.% of the excipient with respect to weight of the nanoparticles.
  • the method of preparing the silver nano-ink composition as described above comprises: a) preparing a reaction mixture by dissolving a capping agent in a solvent at a temperature ranging from about 100 °C to about 200 °C for about 1 hour to about 2 hours, followed by adding mixed-phase capped nanoparticles to the reaction mixture; and b) subjecting the mixture comprising the nanoparticles to sonication or vigorous mixing, followed by addition of an excipient to obtain the silver nano-ink composition.
  • the method of preparing the silver nano-ink composition as described above comprises: a) preparing a reaction mixture by dissolving a capping agent in a solvent at a temperature of about 100 °C for about 1 hour, followed by adding mixed- phase capped nanoparticles to the reaction mixture; and b) subjecting the mixture comprising the nanoparticles to sonication or vigorous mixing, followed by addition of an excipient to obtain the silver nano-ink composition.
  • the sonication is carried out at a frequency ranging from about 5 kHz to about 300 kHz; and wherein the sonication or the vigorous mixing is carried out for a time period ranging from about 2 minutes to about 120 minutes.
  • the solvent employed as part of the method for preparing the silver nano-ink composition is selected from a group comprising but not limited to N-Methyl-2-Pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile, ethyl acetate, dichloromethane, hexamethylphosphoric triamide, cyclohexyl-pyrrolidinone, chlorobenzene, dimethylformamide, N-vinyl-pyrrolidinone, N-methyl formamide and cyclohexanone, or any combination thereof.
  • NMP N-Methyl-2-Pyrrolidone
  • DMSO dimethyl sulfoxide
  • acetonitrile ethyl acetate
  • dichloromethane hexamethylphosphoric triamide
  • cyclohexyl-pyrrolidinone chlorobenzene
  • dimethylformamide N-vinyl-pyrrolidinone
  • the solvent employed as part of the method for preparing the silver nano-ink composition is N-Methyl-2-Pyrrolidone (NMP).
  • the solvent employed as part of the method for preparing the silver nano-ink composition is dimethyl sulfoxide (DMSO).
  • the excipient employed as part of the method for preparing the silver nano-ink composition is selected from a group comprising but not limited to capping agent, viscosity modifier, wetting/de-wetting agent, curing agent, adhesion promoter, anti-foaming agent and humectant, or a combination thereof.
  • the excipient employed as part of the method for preparing the silver nano-ink composition is selected from a group comprising but not limited to terpineol, glycol, glycerol, glycol ether and cellulose ether, tripropylene glycol mono methyl ether, diethylene glycol mono butyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, hydroxypropyl methylcellulose, ethyl cellulose, hydroxy ethyl cellulose, methyl cellulose, sodium carboxy methyl cellulose and benzyl cellulose, or any combination thereof.
  • the excipient employed as part of the method for preparing the silver nano-ink composition is terpineol.
  • the excipient employed as part of the method for preparing the silver nano-ink composition is a capping agent selected from a group comprising but not limited to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1 -hexadecylamine and octadecyl-p- vinylbenzyldimethyl ammonium chloride, or any combination thereof.
  • the method of preparing the silver nano-ink composition comprises dissolving the stabilizing agent such as PVA or PVP in solvent such as NMP or DMSO by heating at a temperature ranging from about 100 °C to about 200 °C for about 1 hour to about 2 hours.
  • the nanoparticles are added to the reaction mixture which is subjected to sonication to obtain the nano-ink / nano-ink composition of the present disclosure.
  • Other excipients such as terpineol are thereafter added, either along with the nanoparticles or subsequently post the sonication step and further subjected to mixing and sonication.
  • the stabilizing agent such as PVA or PVP
  • solvent such as NMP or DMSO
  • nanoparticles and excipients such as terpineol
  • the silver nano-ink composition comprises about 1 wt.% to about 55 wt.% of the aforesaid nanoparticles.
  • the method of preparing the silver nano-ink composition as described above comprises employing about 45 wt.% to about 99 wt.% of the solvent such as NMP or DMSO.
  • the method of preparing the silver nano-ink composition as described above comprises employing about 95 wt.% of the solvent such as NMP or DMSO.
  • the method of preparing the silver nano-ink composition as described above comprises employing about 0.1 wt.% to about 10_wt.% of capping agent such as PVA or PVP, with respect to weight of the solvent used.
  • capping agent such as PVA or PVP
  • the method of preparing the silver nano-ink composition as described above comprises employing about 5 wt.% of capping agent such as PVA or PVP, with respect to weight of the solvent used. In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing about 1 wt.% to about 55 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
  • the method of preparing the silver nano-ink composition as described above comprises employing about 20 wt.% of the mixed-phase nanoparticles.
  • the method of preparing the silver nano-ink composition as described above comprises employing about 0.1 wt.% to about 20 wt.% of the excipient such as terpineol with respect to weight of the nanoparticles.
  • the method of preparing the silver nano-ink composition as described above comprises employing about 10 wt.% of the excipient such as terpineol.
  • Dynamic light scattering (DLS) measurement is performed to determine the particle/ agglomerate size distribution of the silver nano-ink, immediately post preparation of the ink and post a period of time to assess the shelf life of the ink.
  • DLS Dynamic light scattering
  • the nano-ink composition of the present disclosure has a long shelf life.
  • a simple step of vigorous shaking and/or sonication for a short period of time makes the nano-ink ready for printing.
  • a simple step of sonication for about 15 mins makes the nano-ink ready for printing through narrow nozzle (down to 20 ⁇ m or lower) inkjet printer even after 3 months of preparation.
  • the nano-ink composition of the present disclosure has a shelf life of at least 3 months, preferably at least 6 months, more preferably at least 9 months or at least 12 months.
  • the present disclosure allows for commercialising the nanoparticles per se to provide a higher shelf life.
  • the present nano-ink has extremely long -lifetime as the particles would be stored (at a cool, dry and dark place) and not the nanodispersions; the ink can easily be formulated with short time ultrasonic agitation of the particles in a chosen solvent.
  • the mixed-phase capped nanoparticles can be stored in cold, dry and dark place for very long time ranging from months to several years.
  • commercializing the mixed-phase capped nanoparticles per se instead of a nano-ink comprising the same further increases the shelf-life and additionally also reduces the cost of the ink.
  • the mixed-phase capped nanoparticles of the present disclosure can be constituted to a silver nano-ink composition, in a form suitable for use as ink in printing applications, at the user’s end by employing a simple and short method (such as addition of suitable industrially acceptable excipients like solvents etc., and sonicating the mixture).
  • a simple and short method such as addition of suitable industrially acceptable excipients like solvents etc., and sonicating the mixture.
  • This additionally allows the user to customise the nano-ink composition by employing solvents/other excipients suitable for their intended application, and allows for using the nanoparticles in various applications.
  • the present disclosure also provides for a method of preparing the said nanoparticles comprising a mixed phase of silver and silver oxide, wherein the nanoparticles are capped by one or more stabilizing or capping agent.
  • method of sonochemistry is employed to develop a mixture/mixed phase of silver and silver oxide within the nanoparticles.
  • all the solutions used during the synthesis of the nanoparticles were prepared in de-ionized water.
  • the capping of the nanoparticles with the stabilizing agent is carried out either during the synthesis of the nanoparticles or after their synthesis.
  • the method of preparing the mixed-phase capped nanoparticles comprises combining: a solvent, a silver salt, stabilizing agent, and a reducing agent; and subjecting to ultrasonication.
  • the method of preparing the mixed-phase capped nanoparticles comprises acts of: a) contacting a silver salt solution with a capping agent to obtain a mixture; and b) adding a reducing agent at a rate suitable to obtain the mixed-phase nanoparticle comprising the silver and silver oxide phases.
  • the method of preparing the mixed-phase capped nanoparticles as described above comprises employing the silver salt solution and the reducing agent in equi-molar amounts.
  • a person skilled in the art understand the amount of capping agent that is needed to be added, to cap the nanoparticles prepared by the above method.
  • the method of preparing the mixed-phase capped nanoparticles comprises acts of: contacting silver salt solution with stabilizing or capping agent, adding a reducing agent at a rate suitable to obtain a mixture/ mixed phase of silver and silver oxide nanoparticles (mixed phase capped nanoparticles), and isolating/ separating the nanoparticles comprising a mixed phase of silver and silver oxide, by a suitable technique such as but not limited to centrifugation and optionally crushing the nanoparticles obtained.
  • the method of preparing the mixed-phase capped nanoparticles comprises acts of: contacting a silver salt solution with a stabilizing or capping agent to obtain a reaction mixture, optionally sonicating the reaction mixture, contacting the reaction mixture with a reducing agent, optionally sonicating the mixture thus obtained, to obtain the nanoparticles comprising a mixed phase of silver and silver oxide, and separating the nanoparticles formed to obtain the said nanoparticles.
  • the method of preparing the mixed-phase capped nanoparticles comprises acts of: a. contacting a silver salt solution with a stabilizing agent and optionally sonicating the mixture, b. this is followed with addition of reducing agent to the mixture and optionally sonicating the mixture thus obtained, c. centrifuging the mixture of step b) to obtain the nanoparticles comprising a mixed phase of silver and silver oxide, and d. optionally crushing the nanoparticles to obtain a fine powdery form.
  • the method of preparing the mixed-phase capped nanoparticles comprises acts of: a. subjecting silver salt solution to sonication in an ultrasonic bath; b. adding stabilizing or capping agent (such as but not limited to a polymeric agent solution like PVA or PVP) obtained by continuous stirring on a hot plate to the silver salt solution in the presence of ultrasonic waves and subjected to continuous sonication, c. adding a reducing agent solution to the reactant mixture, d. sonicating the mixture for an optimal time period such as for about 8 to about 12 hours, e.
  • stabilizing or capping agent such as but not limited to a polymeric agent solution like PVA or PVP
  • the silver salt is selected from a group comprising but not limiting to silver nitrate, silver acetate and silver chloride, or any combination thereof.
  • the silver salt is silver nitrate.
  • molarity of the silver nitrate may be varied in between 0.0001 M to saturated molar concentration. In some embodiments of the present disclosure, the optimal molar ratio of the silver nitrate is about 0.5 M.
  • the silver salt solution is prepared by adding the desired silver salt to a solvent selected from a group comprising but not limiting to water (preferably distilled water), alcohol and toluene, or any combination thereof.
  • the silver salt solution is prepared by adding the desired silver salt to water. In some embodiments of the present disclosure, the silver salt solution is prepared by adding the desired silver salt to alcohol.
  • the silver salt solution is prepared by adding the desired silver salt to any suitable strong solvent, as an alternative to water, alcohol and/or toluene, such as those including but not limited to acetonitrile, chloroform, methyl ethyl ketone, and chlorobenzene.
  • suitable strong solvent as an alternative to water, alcohol and/or toluene, such as those including but not limited to acetonitrile, chloroform, methyl ethyl ketone, and chlorobenzene.
  • the alcohol used as a solvent for preparing the silver salt solution in the present disclosure is selected from a group comprising but not limited to ethanol, 2-methoxy ethanol, 2-propanol, and ethylene glycol, or any combination thereof.
  • the solvent used for preparing the silver salt solution in the present disclosure is water.
  • the reducing agent employed for preparing the mixed-phase capped nanoparticles is selected from a group comprising but not limiting to sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium borohydride, hydroxylamine, and hydrazine hydrate, or any combination thereof.
  • the reducing agent employed for preparing the mixed-phase capped nanoparticles is sodium hydroxide.
  • the reducing agent employed for preparing the mixed-phase capped nanoparticles is potassium hydroxide.
  • the reducing agent employed for preparing the mixed-phase capped nanoparticles is lithium hydroxide.
  • the reducing agent is added to the capping agent and silver salt solution at a rate ranging between 0.1 ml/min to about 90 ml/min for a batch size of 90 ml to about 180 ml of the reducing agent to be added.
  • the reducing agent is added to the capping agent and silver salt solution at a rate ranging between 0.1 ml/min to about 20 ml/min for a batch size of 90 ml to about 180 ml of the reducing agent to be added.
  • the rate of addition of reducing agent ranges from about 0.1 ml/min to about 90 ml/min for a batch size of 90 ml to about 180 ml of the reducing agent is merely illustrative and relative in nature, as the said rate at which the reducing agent is added to the capped silver salt solution can vary based on the final amount of the nanoparticles required to be prepared.
  • the above rate of addition acts as a guidance to a person skilled in the art, who in possession of this knowledge, can easily modify the rate of the addition of the reducing agent depending on the final amount/volume of the nanoparticles and/or nano-ink composition that is desired.
  • the rate of addition of the reducing agent controls the amount of silver and silver oxide phases in the final product.
  • the method of preparing the mixed-phase capped nanoparticles is carried out under continuous sonication in an ultrasonic bath operating at a frequency ranging from about 5 kHz to about 300 kHz, at ultrasonic power ranging from about 15 W to about 150 W, and wherein the ultrasonic bath is maintained at a temperature ranging from about 5 °C to about 15 °C.
  • the sonication is carried out in an ultrasonic bath operating at a frequency ranging from about 5 kHz to about 300 kHz.
  • the sonication is carried out in an ultrasonic bath operating at a frequency ranging from about 10 kHz to about 250 kHz, from about 10 kHz to about 200 kHz, from about 10 kHz to about 150 kHz, from about 10 kHz to about 100 kHz or from about 15 kHz to about 50 kHz.
  • maintaining the ultrasonic bath temperature between temperatures ranging from about 5 °C to about 15 °C is critical to obtain the desired particle size of the nanoparticles.
  • the mixture is sonicated for a time period of about 1 hour; and wherein post addition of the reducing agent to the mixture, the mixture is sonicated for a time period of about 8 hours.
  • the stabilizing agent (also called as capping agent) is a surfactant/ polymer molecule used to stabilize the nanoparticles.
  • an equal and optimal weight ratio of stabilizing agent as that of the silver salt is used for the preparation of the nanoparticles.
  • the method for preparation of the mixed- phase capped nanoparticles employs about 0.1 g to about 10 g, preferably about 1.53 g of silver salt in about 90 ml of DI water.
  • the method for preparation of the mixed- phase capped nanoparticles employs about 0.01 g to about 10 g, preferably about 0.153 g to about 1.53 g of stabilizing agent in about 90 ml of DI water.
  • the method for preparation of the mixed- phase capped nanoparticles employs about 0.05 g to about 5 g, preferably about 0.36 g of reducing agent in about 90 ml of DI water.
  • the stabilizing or the capping agent is selected from a group comprising but not limiting to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1- hexadecylamine and octadecyl-p-vinylbenzyldimethyl ammonium chloride, or any combination thereof.
  • PVA poly vinyl alcohol
  • PVP polyvinyl pyrrolidone
  • PMMA poly(methyl methacrylate)
  • the stabilizing or the capping agent is poly vinyl alcohol (PVA).
  • the surfactant poly vinyl alcohol (PVA) having an average molecular weight of about 2000 to 1 million Da is used as a capping agent for the nanoparticles.
  • the average molecular weight of the PVA is ranging from about 13,000 to about 23,000 Da.
  • the stabilizing or the capping agent is polyvinyl pyrrolidone (PVP).
  • the stabilizing agent is prepared by continuous stirring on a hot plate at temperature ranging from about 100 °C to about 120 °C for about 1 hour to about 2 hour.
  • the method of preparation of the mixed-phase capped nanoparticles comprises addition of the stabilizing agent (such as but not limited to PVA or PVP) before the reducing agent to aid in formation of a mixed phase of silver and silver oxide. This also prevents the formed nanoparticles to agglomerate and thus controls their size.
  • the stabilizing agent such as but not limited to PVA or PVP
  • the method of preparing the mixed-phase capped nanoparticles as described above comprises employing the silver salt solution such as the AgNO 3 solution and the reducing agent such as NaOH, KOH or the Li OH, in equimolar amounts.
  • addition of the stabilizing agent towards the end of the process fails to give a mixed phase of silver and silver oxide nanoparticles.
  • the continuous ultrasonication during the addition and/or mixing of reactants in the method of preparation of nanoparticles is critical for obtaining the desired size and constituent of nanoparticles.
  • the mixed-phase capped nanoparticle is isolated or separated from the solution by centrifugation, and wherein the centrifugation is carried out at a speed ranging from about 1000 rpm to about 20000 rpm for about 1 to about 60 minutes.
  • the centrifugation results in formation of a precipitate and wherein the precipitate obtained is washed and dried for removal of unreacted agents.
  • the washing and/or drying is done gently so as to not cause dislodging of the nanoparticle capping.
  • centrifugation is carried out at a speed ranging from about 1000 rpm to about 20000 rpm for about 10 to about 20 minutes.
  • the precipitate obtained may be washed by any suitable solvent such as but not limited to distilled water, alcohol (e.g. ethanol) etc. and optionally dried in an oven at temperature ranging from about 35 °C to about 40 °C for about 10 to about 12 hours.
  • the method of sonochemistry was employed to develop a mixture of silver and silver oxide nanoparticles capped by a polymeric agent such as PVA or PVP.
  • about 90 ml to about 180 ml of 0.1 M aqueous silver salt solution (such as AgNO 3 solution) was taken in a glass beaker and subjected to sonication in an ultrasonic bath operating at a frequency of about 5 kHz to about 300 kHz and ultrasonic power of about 80 W to about 150 W.
  • About 90 ml to about 180 ml of stabilizing agent (such as PVA solution) was obtained by continuous stirring on a hot plate at about 100 °C to about 120 °C for about 1 hour to about 2 hour, which was then added to the silver salt solution in the presence of ultrasonic waves.
  • aqueous reducing agent such as NaOH solution
  • the mixture was henceforth sonicated for an optimal time of about 8 hours to about 12 hours during which no colour change was observed.
  • the resulting solution was then centrifuged at an optimum speed of about 1000 rpm to about 20000 rpm for about 10 to about 20 minutes and the precipitate was washed with a suitable solvent (such as but not limited to water (preferably distilled water) and alcohol (e.g.
  • the precipitated nanoparticles are washed with excess amount of de-ionized water or alcohol or a mixture thereof in order to remove any unreacted silver salt, reducing agent or capping agent present.
  • the precipitated nanoparticles are dried carefully either at room temperature or at temperature ranging from about 35 °C to about 40 °C or in a vacuum desiccator to obtain dry mixed phase nanoparticles.
  • the temperature during the drying process must not exceed 40 °C in order to avoid any unwanted conversion of silver oxide to silver.
  • the mixed phase nanoparticles are then stored in dark and cool place in order to avoid light and temperature assisted conversion of Ag 2 O to Ag.
  • the present disclosure also pertains to a kit comprising the mixed-phase capped nanoparticles of the present disclosure, and a method of preparation thereof.
  • the kit comprises:
  • the mixed-phase capped nanoparticles comprising a mixed phase of silver and silver oxide, wherein the nanoparticles are capped by one or more stabilizing agent, at least one solvent, at least one excipient, and optionally along with user instructions for obtaining the said composition.
  • the user instructions provide direction to obtain the nano-ink composition of the present disclosure by employing the mixed-phase capped nanoparticles of the present disclosure.
  • the present disclosure also provides a method of manufacturing the kit that comprises combining/assembling:
  • the mixed-phase capped nanoparticles of the present disclosure comprising a mixed phase of silver and silver oxide, wherein the nanoparticles are capped by one or more stabilizing agent, at least one solvent, at least one industrially acceptable excipient, and optionally user instructions for obtaining the said composition.
  • each of the mixed-phase capped nanoparticle within the kit comprises of about 5 vol.% to about 95 vol.% silver phase, and of about 5 vol.% to about 95 vol.% silver oxide phase.
  • the silver nano-ink composition obtained as a result of using the kit comprises about 1 wt.% to about 55 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
  • the silver nano-ink composition obtained as a result of using the kit comprises about 45 wt.% to about 99 wt.% of the solvent.
  • the solvent employed as part of the kit is a polar or non-polar solvent.
  • the solvent employed as part of the kit is selected from a group comprising but not limited N-Methyl-2-Pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile, ethyl acetate, dichloromethane, hexamethylphosphoric triamide, cyclohexyl-pyrrolidinone, chlorobenzene, dimethylformamide, N-vinyl- pyrrolidinone, N-methyl formamide and cyclohexanone, or any combination thereof.
  • NMP N-Methyl-2-Pyrrolidone
  • DMSO dimethyl sulfoxide
  • acetonitrile ethyl acetate
  • dichloromethane hexamethylphosphoric triamide
  • cyclohexyl-pyrrolidinone chlorobenzene
  • dimethylformamide N-vinyl- pyrrolidinone
  • N-methyl formamide and cyclohexanone
  • the solvent employed as part of the kit is N- Methyl-2-Pyrrolidone (NMP).
  • the solvent employed as part of the kit is dimethyl sulfoxide (DMSO).
  • the kit comprises about 0. 1 wt.% to about 20 wt.% of the excipient with respect to weight of the nanoparticles.
  • the excipient employed as part of the kit is selected from a group comprising but not limited to capping agent, viscosity modifier, wetting/de-wetting agent, curing agent, adhesion promoter, anti-foaming agent and humectant, or a combination thereof.
  • the excipient employed as part of the kit is selected from a group comprising but not limited to terpineol, glycol, glycerol, glycol ether and cellulose ether, tripropylene glycol mono methyl ether, diethylene glycol mono butyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, hydroxypropyl methylcellulose, ethyl cellulose, hydroxy ethyl cellulose, methyl cellulose, sodium carboxy methyl cellulose and benzyl cellulose, or any combination thereof.
  • the excipient employed as part of the kit is terpineol.
  • the excipient employed as part of the kit is a capping agent selected from a group comprising but not limited to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1- hexadecylamine and octadecyl-p-vinylbenzyldimethyl ammonium chloride, or any combination thereof.
  • a capping agent selected from a group comprising but not limited to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1- hexadecylamine and octadecyl-p-vinylbenzyldimethyl ammonium chloride, or any combination thereof.
  • the kit of the present disclosure comprises mixed-phase capped nanoparticles, poly vinyl alcohol (PVA) and terpineol.
  • the kit of the present disclosure comprises mixed-phase capped nanoparticles, polyvinyl pyrrolidone (PVP) and terpineol.
  • the present disclosure also pertains to use of the silver nano-ink composition of the present disclosure for preparing a substrate comprising a conductive silver pattern.
  • the silver nano-ink composition of the present disclosure is used for making a conductive silver pattern on a substrate.
  • the silver nano-ink composition of the present disclosure is used for making a conductive silver pattern on a substrate, by applying the silver nano-ink composition of the present disclosure on the substrate followed by curing the substrate to obtain the conductive silver pattern.
  • the present disclosure also relates to a method of making a conductive silver pattern on a substrate, said method comprising applying the silver nano-ink composition of the present disclosure on the substrate followed by curing the substrate to obtain the conductive silver pattern.
  • the silver nano-ink composition is applied onto the substrate using commercially or industrially known solution processing or printing technology.
  • the pattern formed by curing of the silver nano-ink of the present disclosure could be of any given geometry and size, depending on the respective end use/application; and each such pattern is formed on a substrate as a whole or any part thereof. All permutation-combinations with respect to size and geometry of the pattern and the size and geometry of the substrate are envisaged within the purview of the present disclosure.
  • the silver nano-ink composition is applied onto the substrate using inkjet printing.
  • the thickness of the silver conductive pattern printed using inkjet printing ranges from about 0.05 ⁇ m to about 5 ⁇ m.
  • the nano-ink composition of the present disclosure is thus suitable for use in printers selected from a group comprising but not limited to R&D printers, inkjet printers, gravure printers, offset printers, flexo printers and any commercial functional ink printer.
  • the silver nano-ink of the present disclosure suitable for use in any printer with nozzle diameter 20 ⁇ m. In some embodiments, the silver nano-ink of the present disclosure suitable for use in any printer with nozzle diameter lower than 20 ⁇ m.
  • the curing temperature or energy required in the present disclosure is relatively low.
  • the thermal curing can be performed at 150 °C or less, for example, at a temperature ranging from about 80 °C to about 120 °C for about 1 hour to about 2 hours. Heating at a said low temperature converts the remaining oxide phase in the ink/particles into pure silver phase, and in that process the stabilizer molecules get removed to obtain interparticle contact. As a result, a silver conductive layer/film/lines having high conductivity and low resistance is formed.
  • the curing is carried out through thermal curing or photonic curing.
  • the thermal curing is a low temperature thermal curing.
  • the thermal curing is a low temperature thermal curing, carried out at a temperature ranging from about 40 °C to about 150 °C, for time period ranging from about 10 minutes to about 120 minutes.
  • the thermal curing is carried out at a temperature lower than or equal to 150 °C. In some embodiments, the heating is carried out at a temperature lower to or equal to about 150 °C, 140 °C, 130 °C, 120 °C, 110 °C, 100 °C, 90 °C, 85 °C, 80 °C, 75 °C, 70 °C, 65 °C, 60 °C, 55 °C, 50 °C, 45 °C, or about 40 °C.
  • the photonic curing is carried out at room temperature or slightly elevated temperature thereof.
  • photonic curing is a well-known technique, a person skilled in the art will readily know and understand how it is to be applied in the context of the present disclosure, to obtain a conductive silver layer from the nano-ink of the present disclosure.
  • curing results in phase change of silver oxide to silver in the mixed-phase capped nanoparticles causing a volume change driven removal of the capping agent from the nanoparticles and facilitating formation of the conductive silver pattern.
  • thickness of the conductive silver pattern applied through inkjet printing ranges from about 0.05 ⁇ m to about 5 ⁇ m.
  • thickness of the conductive silver pattern applied through processes or technologies other than inkjet printing could deviate from the abovementioned range of 0.05 ⁇ m to 5 ⁇ m, and a person skilled in the art would be aware of the same.
  • the thickness of the conductive silver pattern formed after curing could vary accordingly, and all such variations are meant to be included and incorporated as part of the present disclosure.
  • the present disclosure also envisages and encompasses all variations possible with respect to thickness or no. of patterns or no. of layers of patterns formed through the curing of the silver nano-ink of the present disclosure. All such permutation-combinations are also within the ambit of the present disclosure.
  • the substrate on which the conductive silver pattern can be formed by use of the silver nano-ink herein is selected from a group comprising but not limited to photopaper, cellulose, polyethylene terephthalate (PET), textile and glass, or any combination thereof.
  • a person skilled in the art is fully aware of the kind of substrates that can be employed for forming a conductive silver pattern.
  • the list of substrates described herein is not exhaustive and only provides a very small representation for the purposes of understanding. Any such substrate capable of being used for forming a conductive silver pattern, but not listed explicitly herein, also falls under the purview of the present disclosure.
  • the substrate on which the conductive silver pattern can be formed by use of the silver nano-ink herein is employed in applications selected from a group comprising but not limited to printed circuit boards, RFID tags, thin film transistors, memristors, flexible e-readers, reflective displays, capacitive displays, sensors, conductive tracers, capacitor and resistor elements, resistive tracers on windshield defrosters, automotive sensors, touch screens, and thin film photovoltaic solar cells.
  • applications selected from a group comprising but not limited to printed circuit boards, RFID tags, thin film transistors, memristors, flexible e-readers, reflective displays, capacitive displays, sensors, conductive tracers, capacitor and resistor elements, resistive tracers on windshield defrosters, automotive sensors, touch screens, and thin film photovoltaic solar cells.
  • a person skilled in the art is fully aware of the applications of substrates that carry a conductive silver pattern.
  • the list of applications or uses described herein is not exhaustive and only provides a very small representation for the purposes of
  • the present disclosure also pertains to a printed substrate having the conductive silver pattern formed by the silver nano-ink composition of the present disclosure.
  • sheet resistance of printed substrate is assessed using the four-probe van der Pauw method.
  • the sheet resistance of the film is obtained as per the equation, where ⁇ /ln2, ⁇ V and I are the van der Pauw constant, voltage difference measured between two contact points and current injected between two other contact points, respectively .
  • the resistivity of the printed silver films was calculated using the following equation, where, R and t are the sheet resistance and thickness of the films (measured by optical profilometry), respectively .
  • the printed nanoparticulate silver film has a resistivity of ⁇ about 4.5 x 10 - 5 ⁇ cm.
  • tire printed nanoparticulate silver film has a resistivity of ⁇ about 3x 10 - 5 ⁇ cm .
  • the mechanical flexibility of the printed nanoparticulate silver film is also high, and printed films can endure different strain conditions (compressive stress, tensile stress etc.) even after 10,000 cycles.
  • the present disclosure allows usage of wide variety of substrate including heat-resistant substrates.
  • the substrate include photopaper, cellulose, polyethylene terephthalate (PET), textile, glass etc.
  • advantages of the present disclosure include but are not limited to:
  • the capped nanoparticles (mixed phase of silver and silver oxide) of the present disclosure can be stored at cold, dry and dark place for very long time ranging from months to years and they can be easily converted to functional printable nano-ink in a short time. While silver nanoparticles have a tendency to sinter (when not heavily capped) and agglomerate at room temperature, the nanoparticles of the present disclosure comprising a mixed phase of silver oxide and silver have a lower tendency of agglomeration as each particle is capped by a capping agent.
  • the present disclosure allows a user to customise the nano-ink composition by employing solvents or other industrially acceptable excipient suitable for the intended application.
  • the nano-ink composition of the present disclosure is a particle based ink having a long shelf life, low temperature thermal curing, and high conductivity.
  • the nano-ink is suitable for use in printers which require very low agglomerate size to avoid clogging.
  • the silver inks of the present disclosure require low annealing/curing temperatures.
  • a high conducting silver pattern can be achieved upon heating the silver nano-ink compositions of the present disclosure at a very low temperature (as low as 80-85 °C or even lower) or by a small energy photonic curing that would not damage/ physically alter even a low temperature stable substrate.
  • the nano-ink composition of the present application can thus be employed on various substrates (including temperature sensitive substrates) such as photopaper, cellulose, polyethylene terephthalate (PET) etc.
  • the silver nano-ink of the present disclosure forms conductive layer having high conductivity and low resistance.
  • the molar concentration of the reagents for synthesis of nanoparticles is: 0.1 M each of analytical grade aqueous silver nitrate ( AgNO 3 ) (S D Fine-Chem Ltd.) and aqueous sodium hydroxide (NaOH) (S D Fine-Chem Ltd.) solution and an equal weight ratio (as that of AgNO 3 ) of a surfactant poly(vinyl alcohol) (PVA) (average molecular weight ⁇ 13,000- 23,000); Sigma-Aldrich Chemie GmbH).
  • AgNO 3 analytical grade aqueous silver nitrate
  • NaOH sodium hydroxide
  • PVA surfactant poly(vinyl alcohol)
  • Batch A represents the nanoparticles and nano-ink containing a mixed phase of silver and silver oxide nanoparticles that are produced using a reducing agent flow rate of 14 ml/min and can be cured and converted to complete silver at a temperature as low as 80 °C.
  • Batch B represents the nanoparticles and nano-ink containing mixed phase of silver and silver oxide nanoparticles that are produced using a reducing agent flow rate of 8 ml/min and can be cured and converted to complete silver at a temperature as low as 120 °C.
  • Batch C represents the nanoparticles and nano-ink containing mixed phase of silver and silver oxide nanoparticles that are produced using an extremely slow reducing agent addition rate of 0.4 ml/min and it partially converts to silver at a temperature as low as 120 °C.
  • Example 1A Synthesis of nanoparticles with NaOH as reducing agent
  • the method of sonochemistry was employed to develop a mixed phase of silver and silver oxide nanoparticles capped by a polymeric agent PVA.
  • 90 ml of 0.1 M aqueous AgNO 3 solution was taken in a glass beaker and was subjected to sonication in an ultrasonic bath operating at a frequency of 40 kHz and ultrasonic power of 100 W.
  • 90 ml of PVA solution was obtained by continuous stirring on a hot plate at 100 °C for 1 hour on a hot plate with magnetic stirrer, which was then added to the AgNO 3 solution in the presence of ultrasonic waves.
  • the flow rate during the addition of PVA and NaOH to the reactant mixture is controlled and varied as 14 ml/min (Batch A), 8 ml/min (Batch B) and 0.4 ml/min (Batch C), which thereby result in a mixture of Ag 2 O and Ag in the final resulting precipitate.
  • the addition rate of PVA and NaOH mixture to the silver salt controls the relative composition of silver and silver oxide in the final product [see Figure 1(a)].
  • the silver content is relatively the highest in the case of Batch A, thereby can transform to complete silver and a high conducting film at a temperature of 80-85 °C or lower.
  • a highly conductive printed silver pattern has been achieved at 120 °C or lower.
  • a very low content of silver was obtained, which gave rise to a very high sheet resistance at a curing temperature of 120 °C (above which the paper substrate starts to degrade).
  • a significant decrease in the amount of silver was evident which inherently affects the curing temperature and the sheet resistance.
  • Example IB Synthesis of nanoparticles with KOH as the reducing agent
  • the method of sonochemistry was employed to develop a mixed phase of silver and silver oxide nanoparticles capped by a polymeric agent PVA.
  • 135 ml of 0.1 M aqueous AgNO 3 solution was taken in a glass beaker and was subjected to sonication in an ultrasonic bath operating at a frequency of 100 kHz and ultrasonic power of 100 W.
  • 135 ml of PVA solution was obtained by continuous stirring on a hot plate at 100 °C for 1.5 hours on a hot plate with magnetic stirrer, which was then added to the AgNO 3 solution in the presence of ultrasonic waves.
  • Example 1C Synthesis of nanoparticles with LiOH as the reducing agent
  • the method of sonochemistry was employed to develop a mixed phase of silver and silver oxide nanoparticles capped by a polymeric agent PVA.
  • 180 ml of 0.1 M aqueous AgNO 3 solution was taken in a glass beaker and was subjected to sonication in an ultrasonic bath operating at a frequency of 300 kHz and ultrasonic power of 100 W.
  • 180 ml of PVA solution was obtained by continuous stirring on a hot plate at 100 °C for 2 hours on a hot plate with magnetic stirrer, which was then added to the AgNO 3 solution in the presence of ultrasonic waves.
  • Example ID Synthesis of nanoparticles with polyvinyl pyrrolidone (PVP) as the capping agent
  • the method of sonochemistry was employed to develop a mixed phase of silver and silver oxide nanoparticles capped by a polymeric agent polyvinyl pyrrolidone (PVP).
  • PVP polyvinyl pyrrolidone
  • 90 ml of 0.1 M aqueous AgNO 3 solution was taken in a glass beaker and was subjected to sonication in an ultrasonic bath operating at a frequency of 40 kHz and ultrasonic power of 100 W.
  • 90 ml of PVA solution was obtained by continuous stirring on a hot plate at 100 °C for 1 hour on a hot plate with magnetic stirrer, which was then added to the AgNO 3 solution in the presence of ultrasonic waves.
  • the silver and silver oxide mixed phase nanoparticles synthesized as per Example 1A were crushed to a fine powder with a mortar and pestle prior to ink preparation.
  • the solvent of the ink was N-Methyl-2-Pyrrolidone (NMP) (Sigma-Aldrich Chemie GmbH). 5 wt% of PVA (with respect to the weight of nanoparticles) is dissolved in NMP by heating at 100 °C for 1 hour on a hot plate with magnetic stirrer, prior to the addition of silver nanoparticles.
  • NMP N-Methyl-2-Pyrrolidone
  • the inks were converted to pure metallic silver by heating/sintering at about 80 °C or about 120 °C on a hot plate for about 1 hour.
  • the phase mixture has been characterized as a mixture of silver and silver oxide following the JCPDS database for Ag (JCPDS 04-0783) and Ag 2 O (JCPDS 75-1532), respectively ( Figure 1).
  • Figure 1 depicts (a) XRD patterns of the as-synthesised Batch C, Batch B and Batch A nanoparticles showing a mixture of both Ag and Ag 2 O phases and (b) their annealed counterparts (Batch A at 80 °C and Batches B & C at 120 °C for 1 hour) showing pure Ag phase in case of Batch A and B, whereas Batch C contains minor traces of silver oxide still present after annealing at 120 °C for 1 hour.
  • the standard Ag and Ag 2 O patterns are also shown at the bottom for reference.
  • Figure 2 ⁇ depicts the comparison of DLS measurement of both Batch A and Batch B nano- inks soon after ink preparation and after 3 months. It was found that sonication for 15 mins makes the ink ready for printing through narrow nozzle (down to 20 ⁇ m or lower) inkjet printer even after 3 months of preparation. Therefore, the synthesized nano-ink also shows a long shelf life.
  • FIG. 3 depicts SEM micrographs of (a) as- prepared Batch A nanoparticles and its (b) inkjet-printed nano-ink layer.
  • Figure 4 depicts SEM micrographs of (a) as-prepared Batch B nanoparticles and its (b-d) inkjet-printed nano- ink layer. It is observed that the nanoparticles exhibit almost a spherical shape with a narrow size range. The clear boundary between the nanoparticles reveals that the particles are barely accumulated, instead they are fairly separated, which means the nanoparticles are covered by the capping agent PVA, and hence the particles cannot interact with each other.
  • Comparison of shelf life of the mixed-phase nanoparticles was carried out by measuring the XRD pattern of the Batch A nanoparticles just after their preparation, and after storing them for 6 months. As can be seen from Figure 11, the two sets showed very similar XRD patterns, confirming that the nanoparticles of the present disclosure have high shelflife.
  • the silver and silver oxide mixed phase nanoparticles synthesized as per Example IB were crushed to a fine powder with a mortar and pestle prior to ink preparation.
  • the solvent of the ink was N-Methyl-2-Pyrrolidone (NMP) (Sigma-Aldrich Chemie GmbH). 5 wt.% of PVA (with respect to the weight of nanoparticles) is dissolved in NMP by heating at 100 °C for 1 hour on a hot plate with magnetic stirrer, prior to the addition of silver nanoparticles.
  • NMP N-Methyl-2-Pyrrolidone
  • the silver and silver oxide mixed phase nanoparticles synthesized as per Example 1C were crushed to a fine powder with a mortar and pestle prior to ink preparation.
  • the solvent of the ink was N-Methyl-2-Pyrrolidone (NMP) (Sigma-Aldrich Chemie GmbH). 5 wt% of PVA (with respect to the weight of nanoparticles) is dissolved in NMP by heating at 100 °C for 1 hour on a hot plate with magnetic stirrer, prior to the addition of silver nanoparticles.
  • NMP N-Methyl-2-Pyrrolidone
  • the silver and silver oxide mixed phase nanoparticles synthesized as per Example ID were crushed to a fine powder with a mortar and pestle prior to ink preparation.
  • the solvent of the ink was N-Methyl-2-Pyrrolidone (NMP) (Sigma-Aldrich Chemie GmbH). 5 wt.% of PVA (with respect to the weight of nanoparticles) is dissolved in NMP by heating at 100 °C for 1 hour on a hot plate with magnetic stirrer, prior to the addition of silver nanoparticles.
  • NMP N-Methyl-2-Pyrrolidone
  • Example 2E Preparation of nano-ink and conductive ink
  • the silver and silver oxide mixed phase nanoparticles synthesized as per Example 1A were crushed to a fine powder with a mortar and pestle prior to ink preparation.
  • the solvent of the ink was Dimethyl sulfoxide (DMSO) (Sigma-Aldrich Chemie GmbH). 5 wt% of PVA (with respect to the weight of nanoparticles) is dissolved in DMSO by heating at 100 °C for 1 hour on a hot plate with magnetic stirrer, prior to the addition of silver nanoparticles.
  • DMSO Dimethyl sulfoxide
  • FIG. 10(a) depicts the stable nano-ink of the Ag+Ag 2 O mixed-phase nanoparticles dispersed in DMSO.
  • Figure 10(b) provides a comparison of DLS measurements of the as-prepared nano-ink synthesised using NMP (example 2A) and DMSO (this example) as the solvents.
  • the nanoparticles were obtained as per Example 1, wherein the flow rate during the addition of PVA and NaOH to the reactant mixture is controlled and varied as 14 ml/min (Batch A), 8 ml/min (Batch B), and 0.4 ml/min (Batch C), which thereby helped to control the amounts of Ag 2 O and Ag in the final resulting precipitate.
  • the obtained nanoparticles were protected from direct light exposure to avoid their degradation.
  • Figure 1 depicts (a) XRD patterns of the as-synthesised Batch C, Batch B and Batch A nanoparticles showing a mixture of both Ag and Ag 2 O phases and (b) their annealed counterparts (Batch A at 80 °C and Batches B & C at 120 °C for 1 hour) showing pure Ag phase in case of Batch A and B, whereas Batch C contains minor traces of silver oxide still present after annealing at 120 °C for 1 hour.
  • the standard Ag and Ag 2 O patterns are also shown at the bottom for reference.
  • the silver content is relatively the highest in the case of Batch A, which thereby can transform to complete silver and a high conducting film at a temperature of 80-85 °C or lower.
  • Batch B a highly conductive printed silver pattern has been achieved at 120 °C or lower.
  • Batch C a very low content of silver was obtained, which gave rise to a very high sheet resistance at a curing temperature of 120 °C (above which the Epson photographic paper substrate starts to degrade).
  • a significant decrease in the amount of silver was evident which inherently affects the curing temperature and the sheet resistance.
  • a square of 3 layers was inkjet-printed on the paper substrate by employing the nano-inks obtained from Example 2, which was further used to measure the sheet resistance using the four-probe van der Pauw method.
  • Hie sheet resistance of the film is obtained as per the equation, where, ⁇ /ln2, ⁇ V and I are the van der Pauw constant, voltage difference measured between inner contact points and current injected between two outer contact points, respectively.
  • Tire resistivity of the printed silver films was calculated using the following equation, where, R and t are the sheet resistance and thickness of the films (measured by optical profilometry), respectively.
  • the mechanical flexibility of the printed nanoparticulate film was also investigated.
  • Inkjet- printed silver films were subjected to different bending fatigue tests under compressive and tensile stress.
  • the bending diameters has been varied as 25 mm, 12.5 mm and 6.25 mm to achieve a strain of 1%, 2% and 4%, respectively for both the conditions of compression and tension and for both the nano-inks (Batch A and Batch B).
  • the number of bending cycles were also varied as 10, 100, 1000 and 10,000 in each of the strain conditions and the sheet resistance values were compared with the as-printed sample.
  • Figure 5(b) depicts the variability of sheet resistance with the number of bending cycles, where the solid and dashed lines represent tension and compression conditions and the hollow circle, triangle, and square represent the 1%, 2% and 4% strain conditions of Batch A ink, whereas the solid shapes represent Batch B ink, respectively. It is observed that the films subjected to different strain conditions have shown more or less no change in their sheet resistance even after 10,000 cycles.
  • Example 5 Effect of capping the precipitated nanoparticles by addition of capping agent post addition of the reducing agent
  • the nanoparticles were synthesized as per Example 1 with the exception that the reducing agent NaOH was first added to the silver nitrate solution, which was followed by the addition of the polymeric agent PVA solution. Adding the reducing agent to the silver salt solution resulted in phase pure silver oxide nanoparticles, which were then capped by a stabilizing agent by the addition of PVA solution.
  • Figure 6(a) represents the XRD of the as-synthesised nanoparticles showing phase pure silver oxide phase.
  • the nanoparticles were further used in the preparation of nano-ink in the presence of the solvent NMP, and SEM micrograph of the printed film is shown in Figure 6(b).
  • This nano-ink on storage for 72 hours results in the formation of a shell around the nanoparticles as shown in Figure 6(c) of the printed film.
  • This shell thereby deteriorates the conductivity of the film. It is due to the formation of ⁇ -bond by the lone pairs of electrons on oxygen or nitrogen atoms of the solvent NMP with the silver species. Also, oxygen atom can act as a ⁇ -donor, and both the ⁇ - and ⁇ - bond, along with the donation of electrons to the d-orbitals of silver lowers its energy and hence increases its catalytic reactivity. (X. Y. Toy et al., Royal Society of Chemistry, 2014, 4, 516). This leads to the formation of a shell, which thus hinders the conductivity of the silver layer.

Abstract

The present disclosure generally relates to the field of printed electronics and conducting nano-inks. Particularly, the present disclosure provides for a printable nano-ink composition comprising plurality of mixed-phase capped nanoparticles. Each of the capped nanoparticles of the disclosure have a mixed phase of silver and silver oxide, that results in desirable properties for the nano-ink The present disclosure also provides for a method of preparing the said nanoparticles and the nano-ink composition, and applications thereof. The nanoparticles have good shelf life and can thus be stored unchanged for long time. Further, the ink can be flawlessly printed and can be converted to high conducting metallic silver at temperatures of about 150 °C or lower.

Description

“SILVER NANO-INK COMPOSITION COMPRISING MIXED-PHASE CAPPED NANOPARTICLES, METHODS OF PREPARATION, KIT AND APPLICATIONS THEREOF”
TECHNICAL FIELD
The present disclosure generally relates to the field of printed electronics and conducting nano-inks. Particularly, the present disclosure relates to a nano-ink composition suitable for use as printable ink in commercial printers. The said nano-ink composition comprises mixed- phase capped nanoparticles that lend many advantages to the nano-ink containing them. The present disclosure also provides for methods of preparing the said nanoparticles and inks, a kit and applications thereof.
BACKGROUND OF THE DISCLOSURE
In the recent years, printed electronics has made a surge into multiple application domains. A technology that has seen substantial commercial success in the field of printed electronics is the various printable conductive inks, among which silver, copper and several transparent conducting oxide (TCO) inks, such as, Sn-doped Indium Oxide (ITO) are already being used to print touch panels, transparent displays etc.
The inkjet printable silver inks that are commercially available or reported in scientific literature typically require higher temperature of annealing/curing and are hence not suitable for paper or inexpensive polymer (e.g. PET) substrates. Further, the shelf life of commercially available silver inks is limited, and varies from about one to a few months. Furthermore, inks that can be low temperature curable are either precursor based, and are highly basic, having high pH, that is typically not suitable for inkjet print heads or have very limited shelf life.
On the other hand, inks that can be chemically cured at room temperatures have organic and ionic contaminants in the printed films from the residues of the stabilizer and flocculation agent, especially due to the large concentration of ionic contaminants, group-I cation and halide ions. This technology has not seen a great commercial success. Thus, there is an unmet need in the art for obtaining silver inks having high shelf life by employing low annealing/curing temperatures. The present disclosure aims to address the same.
SUMMARY OF THE DISCLOSURE
The present disclosure relates to a silver nano-ink composition comprising mixed-phase capped nanoparticles.
In some embodiments of the present disclosure, each of the mixed-phase capped nanoparticle comprises of about 5% to about 95% silver phase, and of about 5% to about 95% silver oxide phase.
The silver nano-ink composition also comprises at least one solvent and at least one excipient.
The present disclosure also relates to the capped nanoparticles comprising a mixture of silver and silver oxide phases. The nanoparticles of the present disclosure are capped by one or more stabilizing/capping agent.
The present disclosure also provides for a method of preparing said capped nanoparticles, and their use in preparing the silver nano-ink composition of the present disclosure.
In some embodiments of the present disclosure, the method of preparing the silver nano-ink composition comprises mixing plurality of mixed-phase capped nanoparticles with at least one solvent and at least one excipient.
In some embodiments of the present disclosure, the method of preparing the capped nanoparticles comprises acts of: contacting silver salt solution with stabilizing agent, adding a reducing agent at a rate suitable to obtain a mixture/ mixed phase of silver and silver oxide nanoparticles, and optionally isolating/separating the nanoparticles thus obtained. The present disclosure also provides for a kit for obtaining the silver nano-ink composition, comprising plurality of mixed-phase capped nanoparticles, at least one solvent and at least one excipient, optionally along with user instructions for obtaining the said composition.
The present disclosure also provides for use of the silver nano-ink composition of the present disclosure for preparing a substrate comprising a conductive silver pattern.
The present disclosure also provides for a substrate having the conductive silver pattern formed by the silver nano-ink composition of the present disclosure; and a method of obtaining the same.
In some embodiments of the present disclosure, the silver nano-ink composition is applied on to a substrate through inkjet printing, to form the conductive silver pattern.
The present disclosure also pertains to a method of making a conductive silver pattern on a substrate, said method comprising applying the silver nano-ink composition of the present disclosure on a substrate followed by curing the substrate to form the conductive silver pattern.
In some embodiments of the present disclosure, the curing is carried out through thermal curing at a temperature ranging from about 40 °C to about 150 °C, or through photonic curing.
In some embodiments of the present disclosure, the curing results in phase change of silver oxide to silver in the mixed-phase capped nanoparticles causing a volume change driven removal of the capping agent from the nanoparticles and facilitating formation of the conductive silver pattern.
In some embodiments of the present disclosure, the silver nano-ink has a long shelf-life of at least about 6 to 12 months.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE
In order to ensure that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure where:
Figure 1 depicts (a) XRD patterns of the as-synthesised Batch A, B and C nanoparticles (with different addition rate of the reducing agent NaOH) showing a mixture/mixed phase of both Ag and Ag2O phases with NaOH as the reducing agent and PVA as the capping agent and (b) their annealed (80 °C for 1 hour for Batch A and 120 °C for 1 hour for Batch B and C respectively) counterparts showing pure Ag phase in case of Batch A and B, whereas Batch C still contains minor traces of silver oxide present after annealing at 120 °C for 1 hour. The standard Ag and Ag2O patterns are also shown at the bottom for reference.
Figure 2 depicts (a) As-synthesised mixed phase of Ag and Ag2O nanoparticles with NaOH as the reducing agent and capped with PVA. (b) Stable nano-ink of the mixed phase of Ag and Ag2O nanoparticles dispersed in NMP. (c) Comparison of DLS measurement of both Batch A and Batch B nano-inks soon after ink preparation and after 3 months of shelf life.
Figure 3 depicts SEM micrographs of (a) as-prepared Batch A nanoparticles and its (b) inkjet-printed nano-ink layer, with NaOH as the reducing agent, PVA as the capping agent and NMP as the solvent.
Figure 4 depicts SEM micrographs of (a) as-prepared Batch B nanoparticles and its (b-d) inkjet-printed nano-ink layer, with NaOH as the reducing agent, PVA as the capping agent and NMP as the solvent.
Figure 5 depicts (a) Optical microscope image of a printed silver square which is used for the four-probe measurement, (b) Variability of sheet resistance with number of bending cycles, where the solid and dashed lines represent tension and compression conditions and the hollow circle, triangle, and square represent the 1%, 2% and 4% strain conditions of Batch A ink, whereas the solid shapes represent Batch B ink, respectively.
Figure 6 depicts (a) XRD and (b,c) SEM micrographs of inkjet-printed phase pure silver oxide (Ag2O) nanoparticles capped by PVA. Here, the nanoparticles are synthesised by adding first the reducing agent NaOH to AgNO3 solution, followed by the addition of PVA solution. Image in (b) represents the inkjet-printed film from freshly prepared ink and (c) depicts the film printed using a ink stored for 72 hours where the nanoparticles eventually had a reaction with the solvent NMP and developed an insulating shell around the nanoparticles.
Figure 7 depicts (a) the XRD patterns of the as-synthesised nanoparticles (using KOH as reducing agent and PVA as the capping agent) showing a mixture/mixed phase of both Ag and Ag2O phases; and (b) the XRD patterns of the annealed ink showing a pure Ag phase.
Figure 8 depicts (a) the XRD patterns of the as-synthesised nanoparticles (using LiOH as reducing agent and PVA as the capping agent) showing a mixture/mixed phase of both Ag and Ag2O phases; and (b) the XRD patterns of the annealed ink showing a pure Ag phase.
Figure 9 depicts (a) the XRD patterns of the as-synthesised nanoparticles (using PVP as surfactant/stabilizing agent and NaOH as the reducing agent) showing a mixture/mixed phase of both Ag and Ag2O phases; and (b) the XRD patterns of the annealed ink showing a pure Ag phase.
Figure 10 depicts (a) the stable nano-ink of the Ag+Ag2O mixed-phase nanoparticles prepared with NaOH as the reducing agent and PVA as the capping agent and dispersed in DMSO; and (b) provides a comparison of DLS measurements of the as-prepared nano-ink synthesised using NMP and DMSO as the solvents.
Figure 11 depicts the XRD pattern of the Batch A nanoparticles with NaOH as the reducing agent and PVA as the capping agent, just after their preparation, and after storing them for 6 months.
DESCRIPTION OF THE DISCLOSURE
The present disclosure aims to address the drawbacks of the art and provides for novel nanoparticles having high shelf life, low temperature curable silver ink, kits, methods for their preparations and applications thereof.
Before going into the detailed description, while the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate better understanding of the presently disclosed subject matter.
As used herein, the terms "method" and “process” are employed interchangeably and are meant to convey their commonly known dictionary meaning. As used herein, the terms “annealing”, “curing” and “sintering” are employed interchangeably and refer to their ordinary meaning known to a person skilled in the art with respect to the field of the present disclosure. Generally, these terms are meant to describe ways through which toughening or hardening of a material takes place through cross-linking and can be used for all the processes where a solid product is obtained from a liquid solution. In the context of the present disclosure, “annealing”, “curing” and “sintering” is employed for thermal curing or photonic curing of the silver nano-ink composition of the present disclosure on a substrate, resulting in formation of conductive silver pattern on the substrate. In-tum, the term “thermal curing” within the context of the present disclosure is also alternatively used with the term “heating”.
As used herein, the term “mixed-phase nanoparticle” or the like, refers to nanoparticles having a particle size ranging from about 2 nm to about 500 nm and comprising a mixed phase of silver and silver oxide. Thus, both silver phase and silver oxide phase coexist in each nanoparticle of the present disclosure. In other words, each nanoparticle is made up of a mixture of silver and silver oxide phase, and the presence and percentage of each phase depends on the stage of preparation/curing of the nanoparticle. Further, the nanoparticles are capped by a suitable stabilizing/capping agent, to give rise to “mixed-phase capped nanoparticles”. Thus, as used herein, the term “mixed phase” or “mixed-phase” refers to a phase mixture or a combination of silver and silver oxide phases.
As used herein, the term “phase change” refers to phase transition of silver oxide (Ag2O) to metallic silver (Ag).
As used herein, the terms “capping agent” and “stabilizing agent” are used interchangeably, and are meant to convey their ordinary meaning known to a person skilled in the field of the present disclosure. In the context of the present disclosure, the “capping agent” or “stabilizing agent” is employed for capping of the mixed-phase nanoparticles of the present disclosure.
As used herein, the term “nano-ink” is meant to describe an ink composition formed from nanoparticles as the primary constituting component.
As used herein, the terms “excipient” and “industrially acceptable excipient” are used interchangeably, and are meant to convey their ordinary meaning known to a person skilled in the field of the present disclosure. In the context of the present disclosure, these terms are meant to describe additional components present in the nano-ink, in addition to the mixed- phase nanoparticles of the present disclosure, and which play a role in improving printability, flowability and/or dispersion quality of the ink, and include components that are useful in viscosity modification, de-wetting, curing, drying, film formation and densification control. The industrially acceptable excipients used herein thus also include any conventionally employed component/excipient in silver nano-inks.
Accordingly, to reiterate, the present disclosure solves the unmet need of the prior art, by providing a silver nano-ink composition comprising mixed-phase capped nanoparticles, that is capable of being applied onto a substrate for forming conductive silver patterns at relatively low temperature thermal curing or photonic curing. Further, the nano-ink composition of the present disclosure is also capable of being directly printed on to the substrate through techniques like inkjet printing and has high shelf-life that allows efficient storage of the ink, without any undesirable or detrimental effect.
In some embodiments of the present disclosure, the silver nano-ink composition comprises capped nanoparticles comprising a mixed phase of silver and silver oxide. In other words, the silver nano-ink composition comprises of mixed-phase capped nanoparticles The mixed- phase nanoparticles of the present disclosure are capped by one or more capping or stabilizing agent, as is described in more detail in further embodiments of the present disclosure.
In some embodiments of the present disclosure, each of the mixed-phase capped nanoparticle within the silver nano-ink comprises of about 5 vol.% to about 95 vol.% silver phase, and of about 5 vol.% to about 95 vol.% silver oxide phase.
In some embodiments of the present disclosure, the nanoparticles comprise about 15 vol.% to about 85 vol.% of silver and about 15 vol.% to about 85 vol.% of silver oxide.
In some embodiments of the present disclosure, the nanoparticles comprise about 5 vol.%, 6 vol.%, 7 vol.%, 8 vol.%, 9 vol.%, 10 vol.%, 11 vol.%, 12 vol.%, 13 vol.%, 14 vol.%, 15 vol.%, 16 vol.%, 17 vol.%, 18 vol.%, 19 vol.%, 20 vol.%, 21 vol.%, 22 vol.%, 23 vol.%, 24 vol.%, 25 vol.%, 26 vol.%, 27 vol.%, 28 vol.%, 29 vol.%, 30 vol.%, 31 vol.%, 32 vol.%, 33 vol.%, 34 vol.%, 35 vol.%, 36 vol.%, 37 vol.%, 38 vol.%, 39 vol.%, 40 vol.%, 41 vol.%, 42 vol.%, 43 vol.%, 44 vol.%, 45 vol.%, 46 vol.%, 47 vol.%, 48 vol.%, 49 vol.%, 50 vol.%, 51 vol.%, 52 vol.%, 53 vol.%, 54 vol.%, 55 vol.%, 56 vol.%, 57 vol.%, 58 vol.%, 59 vol.%, 60 vol.%, 61 vol.%, 62 vol.%, 63 vol.%, 64 vol.%, 65 vol.%, 66 vol.%, 67 vol.%, 68 vol.%, 69 vol.%, 70 vol.%, 71 vol.%, 72 vol.%, 73 vol.%, 74 vol.%, 75 vol.%, 76 vol.%, 77 vol.%, 78 vol.%, 79 vol.%, 80 vol.%, 81 vol.%, 82 vol.%, 83 vol.%, 84 vol.%, 85 vol.%, 86 vol.%, 87 vol.%, 88 vol.%, 89 vol.%, 90 vol.%, 91 vol.%, 92 vol.%, 93 vol.%, 94 vol.%, or about 95 vol.% of silver phase.
In some embodiments of the present disclosure, the nanoparticles comprise about 5 vol.%, 6 vol.%, 7 vol.%, 8 vol.%, 9 vol.%, 10 vol.%, 11 vol.%, 12 vol.%, 13 vol.%, 14 vol.%, 15 vol.%, 16 vol.%, 17 vol.%, 18 vol.%, 19 vol.%, 20 vol.%, 21 vol.%, 22 vol.%, 23 vol.%, 24 vol.%, 25 vol.%, 26 vol.%, 27 vol.%, 28 vol.%, 29 vol.%, 30 vol.%, 31 vol.%, 32 vol.%, 33 vol.%, 34 vol.%, 35 vol.%, 36 vol.%, 37 vol.%, 38 vol.%, 39 vol.%, 40 vol.%, 41 vol.%, 42 vol.%, 43 vol.%, 44 vol.%, 45 vol.%, 46 vol.%, 47 vol.%, 48 vol.%, 49 vol.%, 50 vol.%, 51 vol.%, 52 vol.%, 53 vol.%, 54 vol.%, 55 vol.%, 56 vol.%, 57 vol.%, 58 vol.%, 59 vol.%, 60 vol.%, 61 vol.%, 62 vol.%, 63 vol.%, 64 vol.%, 65 vol.%, 66 vol.%, 67 vol.%, 68 vol.%, 69 vol.%, 70 vol.%, 71 vol.%, 72 vol.%, 73 vol.%, 74 vol.%, 75 vol.%, 76 vol.%, 77 vol.%, 78 vol.%, 79 vol.%, 80 vol.%, 81 vol.%, 82 vol.%, 83 vol.%, 84 vol.%, 85 vol.%, 86 vol.%, 87 vol.%, 88 vol.%, 89 vol.%, 90 vol.%, 91 vol.%, 92 vol.%, 93 vol.%, 94 vol.%, or about 95 vol.% of silver oxide phase.
In some embodiments of the present disclosure, each of the mixed-phase capped nanoparticle within the silver nano-ink comprises of about 36 vol.% silver phase and of about 64 vol.% silver oxide phase.
In some embodiments of the present disclosure, each of the mixed-phase capped nanoparticle within the silver nano-ink comprises of about 20 vol.% silver phase and of about 80 vol.% silver oxide phase.
In some embodiments of the present disclosure, each of the mixed-phase capped nanoparticle within the silver nano-ink comprises of about 16 vol.% silver phase and of about 84 vol.% silver oxide phase.
In some embodiments of the present disclosure, in addition to the plurality of the mixed- phase capped nanoparticles, the silver nano-ink also comprises at least one solvent and at least one excipient. In some embodiments of the present disclosure, the silver nano-ink composition comprises about 1 wt.% to about 55 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
In some embodiments of the present disclosure, the silver nano-ink composition comprises about 5 wt.% to about 25 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used. In an exemplary embodiment, the amount of nanoparticles is 20 wt.% of the solvent used, i.e., approx. 0.2 g of nanoparticles for 1 ml of solvent (in case of NMP, density is about 1.03 g/ml).
In some embodiments of the present disclosure, the silver nano-ink composition comprises about 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%,
21 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, 25 wt.%, 26 wt.%, 27 wt.%, 28 wt.%, 29 wt.%, 30 wt.%, 31 wt.%, 32 wt.%, 33 wt.%, 34 wt.%, 35 wt.%, 36 wt.%, 37 wt.%, 38 wt.%, 39 wt.%,
40 wt.%, 41 wt.%, 42 wt.%, 43 wt.%, 44 wt.%, 45 wt.%, 46 wt.%, 47 wt.%, 48 wt.%, 49 wt.%, 50 wt.%, 51 wt.%, 52 wt.%, 53 wt.%, 54 wt.%, or about 55 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
In some embodiments of the present disclosure, the silver nano-ink composition comprises about 45 wt.% to about 99 wt.% of the solvent.
In some embodiments of the present disclosure, the silver nano-ink composition comprises about 45 wt.%, 46 wt.%, 47 wt.%, 48 wt.%, 49 wt.%, 50 wt.%, 51 wt.%, 52 wt.%, 53 wt.%,
54 wt.%, 55 wt.%, 56 wt.%, 57 wt.%, 58 wt.%, 59 wt.%, 60 wt.%, 61 wt.%, 62 wt.%, 63 wt.%, 64 wt.%, 65 wt.%, 66 wt.%, 67 wt.%, 68 wt.%, 69 wt.%, 70 wt.%, 71 wt.%, 72 wt.%,
73 wt.%, 74 wt.%, 75 wt.%, 76 wt.%, 77 wt.%, 78 wt.%, 79 wt.%, 80 wt.%, 81 wt.%, 82 wt.%, 83 wt.%, 84 wt.%, 85 wt.%, 86 wt.%, 87 wt.%, 88 wt.%, 89 wt.%, 90 wt.%, 91 wt.%,
92 wt.%, 93 wt.%, 94 wt.%, 95 wt.%, 96 wt.%, 97 wt.%, 98 wt.%, or about 99 wt.% of the solvent.
In some embodiments of the present disclosure, the solvent employed as part of the silver nano-ink composition is a polar or non-polar solvent.
In some embodiments of the present disclosure, the solvent employed as part of the silver nano-ink composition is selected from a group comprising but not limited N-Methyl-2- Pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile, ethyl acetate, dichloromethane, hexamethylphosphoric triamide, cyclohexyl-pyrrolidinone, chlorobenzene, dimethylformamide, N-vinyl-pyrrolidinone, N-methyl formamide and cyclohexanone, or any combination thereof.
In some embodiments of the present disclosure, the solvent employed as part of the silver nano-ink composition is N-Methyl-2 -Pyrrolidone (NMP).
In some embodiments of the present disclosure, the solvent employed as part of the silver nano-ink composition is dimethyl sulfoxide (DMSO).
In some embodiments of the present disclosure, the silver nano-ink composition comprises about 0.1 wt.% to about 20 wt.% of the excipient with respect to weight of the nanoparticles.
In some embodiments of the present disclosure, the silver nano-ink composition comprises about 0.1 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, or about 20 wt.% of the excipient with respect to weight of the nanoparticles.
In some embodiments of the present disclosure, the excipient employed as part of the silver nano-ink composition is selected from a group comprising but not limited to capping agent, viscosity modifier, wetting/de-wetting agent, curing agent, adhesion promoter, anti-foaming agent and humectant, or a combination thereof.
In some embodiments of the present disclosure, the excipient employed as part of the silver nano-ink composition is selected from a group comprising but not limited to terpineol, glycol, glycerol, glycol ether and cellulose ether, tripropylene glycol mono methyl ether, diethylene glycol mono butyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, hydroxypropyl methylcellulose, ethyl cellulose, hydroxy ethyl cellulose, methyl cellulose, sodium carboxy methyl cellulose and benzyl cellulose, or any combination thereof.
In some embodiments of the present disclosure, the excipient employed as part of the silver nano-ink composition is terpineol.
In some embodiments of the present disclosure, the excipient employed as part of the silver nano-ink composition is a capping agent selected from a group comprising but not limited to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1-hexadecylamine and octadecyl-p-vinylbenzyldimethyl ammonium chloride, or any combination thereof.
Thus, in some embodiments, the silver nano-ink composition of the present disclosure comprises mixed-phase capped nanoparticles, poly vinyl alcohol (PVA) and terpineol.
Similarly, in some embodiments, the silver nano-ink composition of the present disclosure comprises mixed-phase capped nanoparticles, polyvinyl pyrrolidone (PVP) and terpineol.
In some embodiments of the present disclosure, the mixed-phase capped nanoparticles of the present disclosure have a size ranging from about 2 nm to about 500 nm.
In some embodiments of the present disclosure, the mixed-phase capped nanoparticles of the present disclosure have a size ranging from about 3 nm to about 200 nm.
In some embodiments, the nanoparticle size is ranging from about 5 nm to about 100 nm. In some embodiments, the nanoparticle size is ranging from about 10 nm and about 50 nm.
As mentioned above, the nanoparticles of the present disclosure are capped with one or more stabilizing agent (also called as capping agent). Capping prevents large/ extensive aggregation/agglomeration of the nanoparticles for a sustained period of time and increases their stability as individual/isolated nanoparticles or as small sized agglomerates. Absence of capping agent would result in heavy agglomeration of the nanoparticles leading to large sized agglomerates which will either settle down due to gravity and unable to function as a free flowing ink, or clog the nozzles of any jetting type printing process and thus the same would not be suitable for jetting -type printing applications.
In some embodiments of the present disclosure, the stabilizing agent is a surfactant or a polymer molecule used to stabilize the nanoparticles during or after their synthesis.
In some embodiments of the present disclosure, the stabilizing or the capping agent is selected from a group comprising but not limiting to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1- hexadecylamine and octadecyl-p-vinylbenzyldimethyl ammonium chloride, or any combination thereof. In some embodiments of the present disclosure, the stabilizing or the capping agent is poly vinyl alcohol (PVA). In some embodiments of the present disclosure, the stabilizing or the capping agent is polyvinyl pyrrolidone (PVP).
The silver nano-ink of the present disclosure comprises capped nanoparticles comprising a mixed phase of silver and silver oxide (the mixed-phase capped nanoparticles). An advantage of the nano-ink of the present disclosure is that it requires lower heating/curing/sintering temperature (or energy, in case of photonic curing) to form a conductive pattern upon application on a suitable substrate. Upon curing, which can be through thermal curing/heating using low temperatures or photonic curing, the silver oxide phase will undergo a phase change which facilitates the nanoparticles to uncap from its stabilizing or capping agents. This establishes an interparticle contact between the newly transformed silver nanoparticles. Thus, sintering/curing at relatively low temperatures (which alternately may also be achieved by low power photonic curing) is sufficient to convert the remaining oxide phase in the ink/ particles to silver, leading to removal of the stabilizer/capping molecule to obtain interparticle contact, which in turn results in formation of a high conducting silver pattern.
The silver nano-ink composition of the present disclosure requires relatively lower sintering temperature (low temperature thermal curing) to convert to conducting phase than conventional silver based nano-inks which require high thermal sintering temperatures to remove the capping agent. Commercial nano-inks suitable for use in ink jet/R&D printers, having only silver nanoparticles are heavily stabilized by stabilizing/capping agents, and therefore require high temperatures (such as those over 150 °C and typically between 150 °C- 300 °C, depending on the ink variety) to remove the capping agent and allow silver particle- particle interaction for formation of conductive layers/lines/fdms. Without being bound to a theory, the phase change of silver oxide to silver in the nano-ink of the present disclosure causes a large volume change (Pilling-Bedworth ratio ≃1.56) which helps to remove the capping agents from the nanoparticles, without the need of high sintering temperatures. The thermal sintering at low temperature is sufficient to initiate the phase change of the silver oxide which catalyses the removal of capping agent from the nanoparticles. Thus, the removal of capping agent in the present disclosure is not via decomposition of the capping agent at high temperatures, but by physical separation facilitated by the phase change of the silver oxide phase present in the nano-ink of the present disclosure. Therefore, heating at even low temperature (such as about 150 °C or lower, or about 80-85 °C) converts the remaining oxide phase in the ink/ particles into pure silver, leading to removal of stabilizer/capping molecules to obtain interparticle contact. Therefore, conducting fdms/lines/layers can be achieved at temperatures as low as 80-85 °C or lower to about 150 °C or lower. This is particularly beneficial in use of the nano-ink of the present disclosure for printing even on inexpensive, paper/ polymer substrates and at a low cost.
The nano-ink of the present disclosure is also suitable for applications that would use photonic curing for the formation of conductive metallic silver particles. In some embodiments, the silver nano-ink composition of the present disclosure requires relatively lower curing temperature (thermal curing) or relatively lower curing energy (photonic curing) to form conducting pattern on a substrate.
The present disclosure accordingly also relates to the method of preparing the silver nano-ink composition as described above.
In some embodiments of the present disclosure, the method of preparing the silver nano-ink composition as described above comprises act of mixing plurality of mixed-phase capped nanoparticles with at least one solvent and at least one excipient.
In some embodiments of the present disclosure, the mixing of plurality of mixed-phase capped nanoparticles with at least one solvent and at least one excipient is carried out by sonication or vigorous mixing.
In some embodiments of the present disclosure, the method of preparing the silver nano-ink composition as described above is carried out by sonication or vigorous mixing of the mixed- phase capped nanoparticles dispersed in at least one solvent and at least one excipient.
In some embodiments of the present disclosure, the method of preparing the silver nano-ink composition as described above comprises: a) preparing a reaction mixture by dissolving a capping/stabilizing agent in a solvent, followed by adding mixed-phase capped nanoparticles to the reaction mixture; and b) subjecting the mixture comprising the nanoparticles to sonication or vigorous mixing, followed by addition of an excipient to obtain the silver nano-ink composition. In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing the same amounts or concentrations of the nanoparticles, capping agent, solvent and excipient, as the amounts or concentrations at which they are finally present in the silver nano-ink composition of the present disclosure.
In some embodiments of the present disclosure, the method of preparing the silver nano-ink composition as described above comprises employing about 45 wt.% to about 99 wt.% of the solvent.
In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing about 0.1 wt.% to about 10 wt.% of capping agent with respect to weight of the solvent used.
In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing about 1 wt.% to about 55 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing about 0.1 wt.% to about 20 wt.% of the excipient with respect to weight of the nanoparticles.
In some embodiments of the present disclosure, the method of preparing the silver nano-ink composition as described above comprises: a) preparing a reaction mixture by dissolving a capping agent in a solvent at a temperature ranging from about 100 °C to about 200 °C for about 1 hour to about 2 hours, followed by adding mixed-phase capped nanoparticles to the reaction mixture; and b) subjecting the mixture comprising the nanoparticles to sonication or vigorous mixing, followed by addition of an excipient to obtain the silver nano-ink composition.
In some embodiments of the present disclosure, the method of preparing the silver nano-ink composition as described above comprises: a) preparing a reaction mixture by dissolving a capping agent in a solvent at a temperature of about 100 °C for about 1 hour, followed by adding mixed- phase capped nanoparticles to the reaction mixture; and b) subjecting the mixture comprising the nanoparticles to sonication or vigorous mixing, followed by addition of an excipient to obtain the silver nano-ink composition.
In some embodiments of the present disclosure, the sonication is carried out at a frequency ranging from about 5 kHz to about 300 kHz; and wherein the sonication or the vigorous mixing is carried out for a time period ranging from about 2 minutes to about 120 minutes.
In some embodiments of the present disclosure, the solvent employed as part of the method for preparing the silver nano-ink composition is selected from a group comprising but not limited to N-Methyl-2-Pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile, ethyl acetate, dichloromethane, hexamethylphosphoric triamide, cyclohexyl-pyrrolidinone, chlorobenzene, dimethylformamide, N-vinyl-pyrrolidinone, N-methyl formamide and cyclohexanone, or any combination thereof.
In some embodiments of the present disclosure, the solvent employed as part of the method for preparing the silver nano-ink composition is N-Methyl-2-Pyrrolidone (NMP).
In some embodiments of the present disclosure, the solvent employed as part of the method for preparing the silver nano-ink composition is dimethyl sulfoxide (DMSO).
In some embodiments of the present disclosure, the excipient employed as part of the method for preparing the silver nano-ink composition is selected from a group comprising but not limited to capping agent, viscosity modifier, wetting/de-wetting agent, curing agent, adhesion promoter, anti-foaming agent and humectant, or a combination thereof.
In some embodiments of the present disclosure, the excipient employed as part of the method for preparing the silver nano-ink composition is selected from a group comprising but not limited to terpineol, glycol, glycerol, glycol ether and cellulose ether, tripropylene glycol mono methyl ether, diethylene glycol mono butyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, hydroxypropyl methylcellulose, ethyl cellulose, hydroxy ethyl cellulose, methyl cellulose, sodium carboxy methyl cellulose and benzyl cellulose, or any combination thereof.
In some embodiments of the present disclosure, the excipient employed as part of the method for preparing the silver nano-ink composition is terpineol. In some embodiments of the present disclosure, the excipient employed as part of the method for preparing the silver nano-ink composition is a capping agent selected from a group comprising but not limited to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1 -hexadecylamine and octadecyl-p- vinylbenzyldimethyl ammonium chloride, or any combination thereof.
In some embodiments of the present disclosure, the method of preparing the silver nano-ink composition comprises dissolving the stabilizing agent such as PVA or PVP in solvent such as NMP or DMSO by heating at a temperature ranging from about 100 °C to about 200 °C for about 1 hour to about 2 hours. After dissolving the stabilizing agent in the solvent, the nanoparticles are added to the reaction mixture which is subjected to sonication to obtain the nano-ink / nano-ink composition of the present disclosure. Other excipients such as terpineol are thereafter added, either along with the nanoparticles or subsequently post the sonication step and further subjected to mixing and sonication.
In some embodiments of the present disclosure, the stabilizing agent (such as PVA or PVP) is dissolved in solvent (such as NMP or DMSO) and stored, and when needed, nanoparticles and excipients (such as terpineol) can be added, and sonicated to obtain the nano-ink.
In some embodiments of the present disclosure, the silver nano-ink composition comprises about 1 wt.% to about 55 wt.% of the aforesaid nanoparticles.
In some embodiments of the present disclosure, the method of preparing the silver nano-ink composition as described above comprises employing about 45 wt.% to about 99 wt.% of the solvent such as NMP or DMSO.
In some embodiments of the present disclosure, the method of preparing the silver nano-ink composition as described above comprises employing about 95 wt.% of the solvent such as NMP or DMSO.
In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing about 0.1 wt.% to about 10_wt.% of capping agent such as PVA or PVP, with respect to weight of the solvent used.
In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing about 5 wt.% of capping agent such as PVA or PVP, with respect to weight of the solvent used. In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing about 1 wt.% to about 55 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing about 20 wt.% of the mixed-phase nanoparticles.
In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing about 0.1 wt.% to about 20 wt.% of the excipient such as terpineol with respect to weight of the nanoparticles.
In some embodiments, the method of preparing the silver nano-ink composition as described above comprises employing about 10 wt.% of the excipient such as terpineol.
In some embodiments of the present disclosure, Dynamic light scattering (DLS) measurement is performed to determine the particle/ agglomerate size distribution of the silver nano-ink, immediately post preparation of the ink and post a period of time to assess the shelf life of the ink.
In some embodiments of the present disclosure, the nano-ink composition of the present disclosure has a long shelf life.
In some embodiments of the present disclosure, a simple step of vigorous shaking and/or sonication for a short period of time (such as about 10-15 mins) makes the nano-ink ready for printing.
In some embodiments of the present disclosure, a simple step of sonication for about 15 mins makes the nano-ink ready for printing through narrow nozzle (down to 20 μm or lower) inkjet printer even after 3 months of preparation.
In some embodiments of the present disclosure, the nano-ink composition of the present disclosure has a shelf life of at least 3 months, preferably at least 6 months, more preferably at least 9 months or at least 12 months.
In some embodiments, the present disclosure allows for commercialising the nanoparticles per se to provide a higher shelf life. The present nano-ink has extremely long -lifetime as the particles would be stored (at a cool, dry and dark place) and not the nanodispersions; the ink can easily be formulated with short time ultrasonic agitation of the particles in a chosen solvent. The mixed-phase capped nanoparticles can be stored in cold, dry and dark place for very long time ranging from months to several years. Thus, commercializing the mixed-phase capped nanoparticles per se instead of a nano-ink comprising the same further increases the shelf-life and additionally also reduces the cost of the ink. Further, the mixed-phase capped nanoparticles of the present disclosure can be constituted to a silver nano-ink composition, in a form suitable for use as ink in printing applications, at the user’s end by employing a simple and short method (such as addition of suitable industrially acceptable excipients like solvents etc., and sonicating the mixture). This additionally allows the user to customise the nano-ink composition by employing solvents/other excipients suitable for their intended application, and allows for using the nanoparticles in various applications.
Since the mixed-phase capped nanoparticles form the primary component of the silver nano- ink of the present disclosure, the present disclosure also provides for a method of preparing the said nanoparticles comprising a mixed phase of silver and silver oxide, wherein the nanoparticles are capped by one or more stabilizing or capping agent.
In some embodiments of the present disclosure, method of sonochemistry is employed to develop a mixture/mixed phase of silver and silver oxide within the nanoparticles. In some embodiments, all the solutions used during the synthesis of the nanoparticles (mixture/mixed phase of silver and silver oxide) were prepared in de-ionized water.
In some embodiments of the present disclosure, the capping of the nanoparticles with the stabilizing agent is carried out either during the synthesis of the nanoparticles or after their synthesis.
In some embodiments of the present disclosure, the method of preparing the mixed-phase capped nanoparticles comprises combining: a solvent, a silver salt, stabilizing agent, and a reducing agent; and subjecting to ultrasonication.
In some embodiments of the present disclosure, the method of preparing the mixed-phase capped nanoparticles comprises acts of: a) contacting a silver salt solution with a capping agent to obtain a mixture; and b) adding a reducing agent at a rate suitable to obtain the mixed-phase nanoparticle comprising the silver and silver oxide phases. In some embodiments of the present disclosure, the method of preparing the mixed-phase capped nanoparticles as described above comprises employing the silver salt solution and the reducing agent in equi-molar amounts.
In some embodiments of the present disclosure, based on the final amount of nanoparticles required, a person skilled in the art understand the amount of capping agent that is needed to be added, to cap the nanoparticles prepared by the above method.
In some embodiments of the present disclosure, the method of preparing the mixed-phase capped nanoparticles comprises acts of: contacting silver salt solution with stabilizing or capping agent, adding a reducing agent at a rate suitable to obtain a mixture/ mixed phase of silver and silver oxide nanoparticles (mixed phase capped nanoparticles), and isolating/ separating the nanoparticles comprising a mixed phase of silver and silver oxide, by a suitable technique such as but not limited to centrifugation and optionally crushing the nanoparticles obtained.
In some embodiments of the present disclosure, the method of preparing the mixed-phase capped nanoparticles comprises acts of: contacting a silver salt solution with a stabilizing or capping agent to obtain a reaction mixture, optionally sonicating the reaction mixture, contacting the reaction mixture with a reducing agent, optionally sonicating the mixture thus obtained, to obtain the nanoparticles comprising a mixed phase of silver and silver oxide, and separating the nanoparticles formed to obtain the said nanoparticles.
In some embodiments of the present disclosure, the method of preparing the mixed-phase capped nanoparticles comprises acts of: a. contacting a silver salt solution with a stabilizing agent and optionally sonicating the mixture, b. this is followed with addition of reducing agent to the mixture and optionally sonicating the mixture thus obtained, c. centrifuging the mixture of step b) to obtain the nanoparticles comprising a mixed phase of silver and silver oxide, and d. optionally crushing the nanoparticles to obtain a fine powdery form.
In some embodiments of the present disclosure, the method of preparing the mixed-phase capped nanoparticles comprises acts of: a. subjecting silver salt solution to sonication in an ultrasonic bath; b. adding stabilizing or capping agent (such as but not limited to a polymeric agent solution like PVA or PVP) obtained by continuous stirring on a hot plate to the silver salt solution in the presence of ultrasonic waves and subjected to continuous sonication, c. adding a reducing agent solution to the reactant mixture, d. sonicating the mixture for an optimal time period such as for about 8 to about 12 hours, e. centrifuging the resultant solution at a speed ranging from about 1000 to about 20,000 rpm for about 10 to about 20 minutes and optionally washing the precipitate with a solvent and optionally drying at a temperature ranging from about 30 °C to about 50 °C for about 10 to 12 hours, to obtain the nanoparticles, and f. optionally crushing the nanoparticles to fine powdery form.
In some embodiments of the present disclosure, the silver salt is selected from a group comprising but not limiting to silver nitrate, silver acetate and silver chloride, or any combination thereof.
In some embodiments of the present disclosure, the silver salt is silver nitrate.
In some embodiments of the present disclosure, molarity of the silver nitrate may be varied in between 0.0001 M to saturated molar concentration. In some embodiments of the present disclosure, the optimal molar ratio of the silver nitrate is about 0.5 M.
In some embodiments of the present disclosure, the silver salt solution is prepared by adding the desired silver salt to a solvent selected from a group comprising but not limiting to water (preferably distilled water), alcohol and toluene, or any combination thereof.
In some embodiments of the present disclosure, the silver salt solution is prepared by adding the desired silver salt to water. In some embodiments of the present disclosure, the silver salt solution is prepared by adding the desired silver salt to alcohol.
In some embodiments of the present disclosure, the silver salt solution is prepared by adding the desired silver salt to any suitable strong solvent, as an alternative to water, alcohol and/or toluene, such as those including but not limited to acetonitrile, chloroform, methyl ethyl ketone, and chlorobenzene.
In some embodiments of the present disclosure, the alcohol used as a solvent for preparing the silver salt solution in the present disclosure is selected from a group comprising but not limited to ethanol, 2-methoxy ethanol, 2-propanol, and ethylene glycol, or any combination thereof.
In some embodiments of the present disclosure, the solvent used for preparing the silver salt solution in the present disclosure is water.
In some embodiments of the present disclosure, the reducing agent employed for preparing the mixed-phase capped nanoparticles is selected from a group comprising but not limiting to sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium borohydride, hydroxylamine, and hydrazine hydrate, or any combination thereof.
In some embodiments of the present disclosure, the reducing agent employed for preparing the mixed-phase capped nanoparticles is sodium hydroxide.
In some embodiments of the present disclosure, the reducing agent employed for preparing the mixed-phase capped nanoparticles is potassium hydroxide.
In some embodiments of the present disclosure, the reducing agent employed for preparing the mixed-phase capped nanoparticles is lithium hydroxide.
In some embodiments of the present disclosure, for preparing the mixed-phase capped nanoparticles, the reducing agent is added to the capping agent and silver salt solution at a rate ranging between 0.1 ml/min to about 90 ml/min for a batch size of 90 ml to about 180 ml of the reducing agent to be added.
In some embodiments of the present disclosure, for preparing the mixed-phase capped nanoparticles, the reducing agent is added to the capping agent and silver salt solution at a rate ranging between 0.1 ml/min to about 20 ml/min for a batch size of 90 ml to about 180 ml of the reducing agent to be added.
In some embodiments of the present disclosure, for preparing the mixed-phase capped nanoparticles, the rate of addition of reducing agent ranges from about 0.1 ml/min to about 90 ml/min for a batch size of 90 ml to about 180 ml of the reducing agent is merely illustrative and relative in nature, as the said rate at which the reducing agent is added to the capped silver salt solution can vary based on the final amount of the nanoparticles required to be prepared. The above rate of addition acts as a guidance to a person skilled in the art, who in possession of this knowledge, can easily modify the rate of the addition of the reducing agent depending on the final amount/volume of the nanoparticles and/or nano-ink composition that is desired.
In some embodiments of the present disclosure, the rate of addition of the reducing agent controls the amount of silver and silver oxide phases in the final product.
In some embodiments of the present disclosure, the method of preparing the mixed-phase capped nanoparticles is carried out under continuous sonication in an ultrasonic bath operating at a frequency ranging from about 5 kHz to about 300 kHz, at ultrasonic power ranging from about 15 W to about 150 W, and wherein the ultrasonic bath is maintained at a temperature ranging from about 5 °C to about 15 °C.
In some embodiments of the present disclosure, the sonication is carried out in an ultrasonic bath operating at a frequency ranging from about 5 kHz to about 300 kHz.
In some embodiments of the present disclosure, the sonication is carried out in an ultrasonic bath operating at a frequency ranging from about 10 kHz to about 250 kHz, from about 10 kHz to about 200 kHz, from about 10 kHz to about 150 kHz, from about 10 kHz to about 100 kHz or from about 15 kHz to about 50 kHz.
In some embodiments of the present disclosure, maintaining the ultrasonic bath temperature between temperatures ranging from about 5 °C to about 15 °C is critical to obtain the desired particle size of the nanoparticles.
In some embodiments of the present disclosure, post addition of the capping agent to the silver salt solution, the mixture is sonicated for a time period of about 1 hour; and wherein post addition of the reducing agent to the mixture, the mixture is sonicated for a time period of about 8 hours.
In some embodiments of the present disclosure, the stabilizing agent (also called as capping agent) is a surfactant/ polymer molecule used to stabilize the nanoparticles.
In some embodiments of the present disclosure, an equal and optimal weight ratio of stabilizing agent as that of the silver salt is used for the preparation of the nanoparticles.
In an some embodiments of the present disclosure, the method for preparation of the mixed- phase capped nanoparticles employs about 0.1 g to about 10 g, preferably about 1.53 g of silver salt in about 90 ml of DI water.
In some embodiments of the present disclosure, the method for preparation of the mixed- phase capped nanoparticles employs about 0.01 g to about 10 g, preferably about 0.153 g to about 1.53 g of stabilizing agent in about 90 ml of DI water.
In some embodiments of the present disclosure, the method for preparation of the mixed- phase capped nanoparticles employs about 0.05 g to about 5 g, preferably about 0.36 g of reducing agent in about 90 ml of DI water.
In some embodiments of the present disclosure, the stabilizing or the capping agent is selected from a group comprising but not limiting to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1- hexadecylamine and octadecyl-p-vinylbenzyldimethyl ammonium chloride, or any combination thereof.
In some embodiments of the present disclosure, the stabilizing or the capping agent is poly vinyl alcohol (PVA).
In some embodiments of the present disclosure, the surfactant poly vinyl alcohol (PVA) having an average molecular weight of about 2000 to 1 million Da, is used as a capping agent for the nanoparticles. In some embodiments, the average molecular weight of the PVA is ranging from about 13,000 to about 23,000 Da.
In some embodiments of the present disclosure, the stabilizing or the capping agent is polyvinyl pyrrolidone (PVP). In some embodiments of the present disclosure, the stabilizing agent is prepared by continuous stirring on a hot plate at temperature ranging from about 100 °C to about 120 °C for about 1 hour to about 2 hour.
The method of preparation of the mixed-phase capped nanoparticles comprises addition of the stabilizing agent (such as but not limited to PVA or PVP) before the reducing agent to aid in formation of a mixed phase of silver and silver oxide. This also prevents the formed nanoparticles to agglomerate and thus controls their size.
In some embodiments of the present disclosure, the method of preparing the mixed-phase capped nanoparticles as described above comprises employing the silver salt solution such as the AgNO3 solution and the reducing agent such as NaOH, KOH or the Li OH, in equimolar amounts.
In some embodiments of the present disclosure, addition of the stabilizing agent towards the end of the process, fails to give a mixed phase of silver and silver oxide nanoparticles.
In some embodiments of the present disclosure, the continuous ultrasonication during the addition and/or mixing of reactants in the method of preparation of nanoparticles is critical for obtaining the desired size and constituent of nanoparticles.
In some embodiments of the present disclosure, post its preparation, the mixed-phase capped nanoparticle is isolated or separated from the solution by centrifugation, and wherein the centrifugation is carried out at a speed ranging from about 1000 rpm to about 20000 rpm for about 1 to about 60 minutes.
In some embodiments of the present disclosure, the centrifugation results in formation of a precipitate and wherein the precipitate obtained is washed and dried for removal of unreacted agents.
In some embodiments of the present disclosure, the washing and/or drying is done gently so as to not cause dislodging of the nanoparticle capping.
In some embodiments, centrifugation is carried out at a speed ranging from about 1000 rpm to about 20000 rpm for about 10 to about 20 minutes. The precipitate obtained may be washed by any suitable solvent such as but not limited to distilled water, alcohol (e.g. ethanol) etc. and optionally dried in an oven at temperature ranging from about 35 °C to about 40 °C for about 10 to about 12 hours. In some embodiments of the present disclosure, the method of sonochemistry was employed to develop a mixture of silver and silver oxide nanoparticles capped by a polymeric agent such as PVA or PVP. In an exemplary embodiment, about 90 ml to about 180 ml of 0.1 M aqueous silver salt solution (such as AgNO3 solution) was taken in a glass beaker and subjected to sonication in an ultrasonic bath operating at a frequency of about 5 kHz to about 300 kHz and ultrasonic power of about 80 W to about 150 W. About 90 ml to about 180 ml of stabilizing agent (such as PVA solution) was obtained by continuous stirring on a hot plate at about 100 °C to about 120 °C for about 1 hour to about 2 hour, which was then added to the silver salt solution in the presence of ultrasonic waves. After about 1 to about 2 hour of continuous sonication, about 90 ml to about 180 ml of 0.1 M aqueous reducing agent (such as NaOH solution) was added to the reactant mixture, which turned the reactant mixture into a dark grey colour. The mixture was henceforth sonicated for an optimal time of about 8 hours to about 12 hours during which no colour change was observed. The resulting solution was then centrifuged at an optimum speed of about 1000 rpm to about 20000 rpm for about 10 to about 20 minutes and the precipitate was washed with a suitable solvent (such as but not limited to water (preferably distilled water) and alcohol (e.g. ethanol)) and dried in an oven at temperature ranging from about 35 °C to about 40 °C for about 10 to about 12 hours. The nanoparticles thus obtained by centrifugation were protected from direct light exposure to avoid the decomposition/ transformation of the Ag2O phase to metallic Ag.
In some embodiments of the present disclosure, the precipitated nanoparticles are washed with excess amount of de-ionized water or alcohol or a mixture thereof in order to remove any unreacted silver salt, reducing agent or capping agent present. After several rounds of washing, the precipitated nanoparticles are dried carefully either at room temperature or at temperature ranging from about 35 °C to about 40 °C or in a vacuum desiccator to obtain dry mixed phase nanoparticles. The temperature during the drying process must not exceed 40 °C in order to avoid any unwanted conversion of silver oxide to silver. The mixed phase nanoparticles are then stored in dark and cool place in order to avoid light and temperature assisted conversion of Ag2O to Ag.
The present disclosure also pertains to a kit comprising the mixed-phase capped nanoparticles of the present disclosure, and a method of preparation thereof. In some embodiments of the present disclosure, the kit comprises:
- the mixed-phase capped nanoparticles comprising a mixed phase of silver and silver oxide, wherein the nanoparticles are capped by one or more stabilizing agent, at least one solvent, at least one excipient, and optionally along with user instructions for obtaining the said composition.
In some embodiments of the present disclosure, the user instructions provide direction to obtain the nano-ink composition of the present disclosure by employing the mixed-phase capped nanoparticles of the present disclosure.
In some embodiments, the present disclosure also provides a method of manufacturing the kit that comprises combining/assembling:
- the mixed-phase capped nanoparticles of the present disclosure comprising a mixed phase of silver and silver oxide, wherein the nanoparticles are capped by one or more stabilizing agent, at least one solvent, at least one industrially acceptable excipient, and optionally user instructions for obtaining the said composition.
In some embodiments of the present disclosure, each of the mixed-phase capped nanoparticle within the kit comprises of about 5 vol.% to about 95 vol.% silver phase, and of about 5 vol.% to about 95 vol.% silver oxide phase.
In some embodiments of the present disclosure, the silver nano-ink composition obtained as a result of using the kit comprises about 1 wt.% to about 55 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
In some embodiments of the present disclosure, the silver nano-ink composition obtained as a result of using the kit comprises about 45 wt.% to about 99 wt.% of the solvent.
In some embodiments of the present disclosure, the solvent employed as part of the kit is a polar or non-polar solvent.
In some embodiments of the present disclosure, the solvent employed as part of the kit is selected from a group comprising but not limited N-Methyl-2-Pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile, ethyl acetate, dichloromethane, hexamethylphosphoric triamide, cyclohexyl-pyrrolidinone, chlorobenzene, dimethylformamide, N-vinyl- pyrrolidinone, N-methyl formamide and cyclohexanone, or any combination thereof.
In some embodiments of the present disclosure, the solvent employed as part of the kit is N- Methyl-2-Pyrrolidone (NMP).
In some embodiments of the present disclosure, the solvent employed as part of the kit is dimethyl sulfoxide (DMSO).
In some embodiments of the present disclosure, the kit comprises about 0. 1 wt.% to about 20 wt.% of the excipient with respect to weight of the nanoparticles.
In some embodiments of the present disclosure, the excipient employed as part of the kit is selected from a group comprising but not limited to capping agent, viscosity modifier, wetting/de-wetting agent, curing agent, adhesion promoter, anti-foaming agent and humectant, or a combination thereof.
In some embodiments of the present disclosure, the excipient employed as part of the kit is selected from a group comprising but not limited to terpineol, glycol, glycerol, glycol ether and cellulose ether, tripropylene glycol mono methyl ether, diethylene glycol mono butyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, hydroxypropyl methylcellulose, ethyl cellulose, hydroxy ethyl cellulose, methyl cellulose, sodium carboxy methyl cellulose and benzyl cellulose, or any combination thereof.
In some embodiments of the present disclosure, the excipient employed as part of the kit is terpineol.
In some embodiments of the present disclosure, the excipient employed as part of the kit is a capping agent selected from a group comprising but not limited to poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1- hexadecylamine and octadecyl-p-vinylbenzyldimethyl ammonium chloride, or any combination thereof.
Thus, in some embodiments, the kit of the present disclosure comprises mixed-phase capped nanoparticles, poly vinyl alcohol (PVA) and terpineol. Similarly, in some embodiments, the kit of the present disclosure comprises mixed-phase capped nanoparticles, polyvinyl pyrrolidone (PVP) and terpineol.
The present disclosure also pertains to use of the silver nano-ink composition of the present disclosure for preparing a substrate comprising a conductive silver pattern.
In some embodiments of the present disclosure, the silver nano-ink composition of the present disclosure is used for making a conductive silver pattern on a substrate.
In some embodiments of the present disclosure, the silver nano-ink composition of the present disclosure is used for making a conductive silver pattern on a substrate, by applying the silver nano-ink composition of the present disclosure on the substrate followed by curing the substrate to obtain the conductive silver pattern.
Accordingly, the present disclosure also relates to a method of making a conductive silver pattern on a substrate, said method comprising applying the silver nano-ink composition of the present disclosure on the substrate followed by curing the substrate to obtain the conductive silver pattern.
In some embodiments of the present disclosure, the silver nano-ink composition is applied onto the substrate using commercially or industrially known solution processing or printing technology.
In some embodiments of the present disclosure, the pattern formed by curing of the silver nano-ink of the present disclosure could be of any given geometry and size, depending on the respective end use/application; and each such pattern is formed on a substrate as a whole or any part thereof. All permutation-combinations with respect to size and geometry of the pattern and the size and geometry of the substrate are envisaged within the purview of the present disclosure.
In some embodiments of the present disclosure, the silver nano-ink composition is applied onto the substrate using inkjet printing.
In some embodiments of the present disclosure, the thickness of the silver conductive pattern printed using inkjet printing ranges from about 0.05 μm to about 5 μm.
In some embodiments of the present disclosure, the nano-ink composition of the present disclosure is thus suitable for use in printers selected from a group comprising but not limited to R&D printers, inkjet printers, gravure printers, offset printers, flexo printers and any commercial functional ink printer.
In some embodiments, the silver nano-ink of the present disclosure suitable for use in any printer with nozzle diameter 20 μm. In some embodiments, the silver nano-ink of the present disclosure suitable for use in any printer with nozzle diameter lower than 20 μm.
After printing of silver nano-ink of the present disclosure, a curing process has to be performed in order to form a conductive printed pattern. In view of the constitution of the silver nano-ink of the present disclosure, the curing temperature or energy required in the present disclosure is relatively low. In some embodiments of the present disclosure, the thermal curing can be performed at 150 °C or less, for example, at a temperature ranging from about 80 °C to about 120 °C for about 1 hour to about 2 hours. Heating at a said low temperature converts the remaining oxide phase in the ink/particles into pure silver phase, and in that process the stabilizer molecules get removed to obtain interparticle contact. As a result, a silver conductive layer/film/lines having high conductivity and low resistance is formed.
In some embodiments of the present disclosure, the curing is carried out through thermal curing or photonic curing.
In some embodiments of the present disclosure, the thermal curing is a low temperature thermal curing.
In some embodiments of the present disclosure, the thermal curing is a low temperature thermal curing, carried out at a temperature ranging from about 40 °C to about 150 °C, for time period ranging from about 10 minutes to about 120 minutes.
In some embodiments of the present disclosure, the thermal curing is carried out at a temperature lower than or equal to 150 °C. In some embodiments, the heating is carried out at a temperature lower to or equal to about 150 °C, 140 °C, 130 °C, 120 °C, 110 °C, 100 °C, 90 °C, 85 °C, 80 °C, 75 °C, 70 °C, 65 °C, 60 °C, 55 °C, 50 °C, 45 °C, or about 40 °C.
In some embodiments of the present disclosure, the photonic curing is carried out at room temperature or slightly elevated temperature thereof. As photonic curing is a well-known technique, a person skilled in the art will readily know and understand how it is to be applied in the context of the present disclosure, to obtain a conductive silver layer from the nano-ink of the present disclosure.
In some embodiments of the present disclosure, curing results in phase change of silver oxide to silver in the mixed-phase capped nanoparticles causing a volume change driven removal of the capping agent from the nanoparticles and facilitating formation of the conductive silver pattern.
In some embodiments of the present disclosure, thickness of the conductive silver pattern applied through inkjet printing ranges from about 0.05 μm to about 5 μm.
In some embodiments of the present disclosure, thickness of the conductive silver pattern applied through processes or technologies other than inkjet printing could deviate from the abovementioned range of 0.05 μm to 5 μm, and a person skilled in the art would be aware of the same. Thus, depending on the end use or application, and the manner/technique by which the silver nano-ink is applied onto a substrate, the thickness of the conductive silver pattern formed after curing could vary accordingly, and all such variations are meant to be included and incorporated as part of the present disclosure. Further, the present disclosure also envisages and encompasses all variations possible with respect to thickness or no. of patterns or no. of layers of patterns formed through the curing of the silver nano-ink of the present disclosure. All such permutation-combinations are also within the ambit of the present disclosure.
In some embodiments of the present disclosure, the substrate on which the conductive silver pattern can be formed by use of the silver nano-ink herein, is selected from a group comprising but not limited to photopaper, cellulose, polyethylene terephthalate (PET), textile and glass, or any combination thereof. Here again, a person skilled in the art is fully aware of the kind of substrates that can be employed for forming a conductive silver pattern. Thus, the list of substrates described herein is not exhaustive and only provides a very small representation for the purposes of understanding. Any such substrate capable of being used for forming a conductive silver pattern, but not listed explicitly herein, also falls under the purview of the present disclosure.
In some embodiments of the present disclosure, the substrate on which the conductive silver pattern can be formed by use of the silver nano-ink herein, is employed in applications selected from a group comprising but not limited to printed circuit boards, RFID tags, thin film transistors, memristors, flexible e-readers, reflective displays, capacitive displays, sensors, conductive tracers, capacitor and resistor elements, resistive tracers on windshield defrosters, automotive sensors, touch screens, and thin film photovoltaic solar cells. Here again, a person skilled in the art is fully aware of the applications of substrates that carry a conductive silver pattern. Thus, the list of applications or uses described herein is not exhaustive and only provides a very small representation for the purposes of understanding. Any such application or use of a substrate having conductive silver pattern known to a person skilled in the art, but not listed explicitly herein, also falls under the purview of the present disclosure.
Thus, the present disclosure also pertains to a printed substrate having the conductive silver pattern formed by the silver nano-ink composition of the present disclosure.
In some embodiments of the present disclosure, sheet resistance of printed substrate is assessed using the four-probe van der Pauw method. In an exemplary' embodiment, the sheet resistance of the film is obtained as per the equation,
Figure imgf000032_0001
where π /ln2, ΔV and I are the van der Pauw constant, voltage difference measured between two contact points and current injected between two other contact points, respectively .
The resistivity of the printed silver films was calculated using the following equation,
Figure imgf000032_0002
where, R and t are the sheet resistance and thickness of the films (measured by optical profilometry), respectively .
In some embodiments of the present disclosure, the printed nanoparticulate silver film has a resistivity of ≤ about 4.5 x 10- 5Ωcm.
In some embodiments of the present disclosure, tire printed nanoparticulate silver film has a resistivity of ≤ about 3x 10- 5Ωcm . In some embodiments of the present disclosure, the mechanical flexibility of the printed nanoparticulate silver film is also high, and printed films can endure different strain conditions (compressive stress, tensile stress etc.) even after 10,000 cycles.
As mentioned above, since the curing is performed at a low temperature, the present disclosure allows usage of wide variety of substrate including heat-resistant substrates. In an exemplary and non-limiting embodiment the substrate include photopaper, cellulose, polyethylene terephthalate (PET), textile, glass etc.
In some embodiments, advantages of the present disclosure include but are not limited to:
Unlike pure silver metal based nanoparticles, the capped nanoparticles (mixed phase of silver and silver oxide) of the present disclosure can be stored at cold, dry and dark place for very long time ranging from months to years and they can be easily converted to functional printable nano-ink in a short time. While silver nanoparticles have a tendency to sinter (when not heavily capped) and agglomerate at room temperature, the nanoparticles of the present disclosure comprising a mixed phase of silver oxide and silver have a lower tendency of agglomeration as each particle is capped by a capping agent.
The present disclosure allows a user to customise the nano-ink composition by employing solvents or other industrially acceptable excipient suitable for the intended application.
The nano-ink composition of the present disclosure is a particle based ink having a long shelf life, low temperature thermal curing, and high conductivity.
The nano-ink is suitable for use in printers which require very low agglomerate size to avoid clogging.
The cost of ink will be significantly lower than commercial inks.
The silver inks of the present disclosure require low annealing/curing temperatures. A high conducting silver pattern can be achieved upon heating the silver nano-ink compositions of the present disclosure at a very low temperature (as low as 80-85 °C or even lower) or by a small energy photonic curing that would not damage/ physically alter even a low temperature stable substrate. The nano-ink composition of the present application can thus be employed on various substrates (including temperature sensitive substrates) such as photopaper, cellulose, polyethylene terephthalate (PET) etc.
The silver nano-ink of the present disclosure forms conductive layer having high conductivity and low resistance.
Additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based on the description provided herein. The embodiments herein provide various features and advantageous details thereof in the description. Descriptions of well-known/conventional methods and techniques are omitted so as to not unnecessarily obscure the embodiments herein.
Any possible combination of two or more of the embodiments described herein is comprised within the scope of the present disclosure.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments in this disclosure have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
Further, while the instant disclosure is susceptible to various modifications and alternative forms, specific aspects thereof has been shown by way of examples and drawings and are described in detail below. However, it should be understood that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and the scope of the invention.
EXAMPLES:
The present disclosure is further described with reference to the following examples, which are only illustrative in nature and should not be construed to limit the scope of the present disclosure in any manner.
All the solutions used during the synthesis of silver nanoparticles were prepared in de- ionized/distilled water.
The molar concentration of the reagents for synthesis of nanoparticles is: 0.1 M each of analytical grade aqueous silver nitrate ( AgNO3) (S D Fine-Chem Ltd.) and aqueous sodium hydroxide (NaOH) (S D Fine-Chem Ltd.) solution and an equal weight ratio (as that of AgNO3) of a surfactant poly(vinyl alcohol) (PVA) (average molecular weight~ 13,000- 23,000); Sigma-Aldrich Chemie GmbH).
Nomenclature Used in The Examples:
Batch A represents the nanoparticles and nano-ink containing a mixed phase of silver and silver oxide nanoparticles that are produced using a reducing agent flow rate of 14 ml/min and can be cured and converted to complete silver at a temperature as low as 80 °C.
Batch B represents the nanoparticles and nano-ink containing mixed phase of silver and silver oxide nanoparticles that are produced using a reducing agent flow rate of 8 ml/min and can be cured and converted to complete silver at a temperature as low as 120 °C.
Batch C represents the nanoparticles and nano-ink containing mixed phase of silver and silver oxide nanoparticles that are produced using an extremely slow reducing agent addition rate of 0.4 ml/min and it partially converts to silver at a temperature as low as 120 °C. Example 1A: Synthesis of nanoparticles with NaOH as reducing agent
The method of sonochemistry was employed to develop a mixed phase of silver and silver oxide nanoparticles capped by a polymeric agent PVA. 90 ml of 0.1 M aqueous AgNO3 solution was taken in a glass beaker and was subjected to sonication in an ultrasonic bath operating at a frequency of 40 kHz and ultrasonic power of 100 W. 90 ml of PVA solution was obtained by continuous stirring on a hot plate at 100 °C for 1 hour on a hot plate with magnetic stirrer, which was then added to the AgNO3 solution in the presence of ultrasonic waves. After 1 hour of continuous sonication, 90 ml of 0.1 M aqueous NaOH solution (a reducing agent) was added to the reactant mixture, which turned the reactant mixture into a dark grey colour. The mixture was henceforth sonicated for an optimal time of 8 hours during which no colour change was observed. The resulting solution was then centrifuged at an optimum speed of 8000 rpm for 10 minutes and the precipitate was washed with ethanol and distilled water and dried in an oven at 40 °C for overnight. The nanoparticles thus obtained were protected from direct light exposure to avoid the decomposition/ transformation of the Ag2O phase to metallic Ag. Figure 2(a) depicts the as-synthesised Ag+Ag2O nanoparticles capped by PVA.
The flow rate during the addition of PVA and NaOH to the reactant mixture is controlled and varied as 14 ml/min (Batch A), 8 ml/min (Batch B) and 0.4 ml/min (Batch C), which thereby result in a mixture of Ag2O and Ag in the final resulting precipitate. The addition rate of PVA and NaOH mixture to the silver salt controls the relative composition of silver and silver oxide in the final product [see Figure 1(a)].
The silver content is relatively the highest in the case of Batch A, thereby can transform to complete silver and a high conducting film at a temperature of 80-85 °C or lower. In the case of Batch B, a highly conductive printed silver pattern has been achieved at 120 °C or lower. However, in case of Batch C, a very low content of silver was obtained, which gave rise to a very high sheet resistance at a curing temperature of 120 °C (above which the paper substrate starts to degrade). Hence, with decreasing the addition rate of the reactants, a significant decrease in the amount of silver was evident which inherently affects the curing temperature and the sheet resistance. Example IB: Synthesis of nanoparticles with KOH as the reducing agent
The method of sonochemistry was employed to develop a mixed phase of silver and silver oxide nanoparticles capped by a polymeric agent PVA. 135 ml of 0.1 M aqueous AgNO3 solution was taken in a glass beaker and was subjected to sonication in an ultrasonic bath operating at a frequency of 100 kHz and ultrasonic power of 100 W. 135 ml of PVA solution was obtained by continuous stirring on a hot plate at 100 °C for 1.5 hours on a hot plate with magnetic stirrer, which was then added to the AgNO3 solution in the presence of ultrasonic waves. After 1.5 hours of continuous sonication, 135 ml of 0.1 M aqueous KOH solution (a reducing agent) was added to the reactant mixture, which turned the reactant mixture into a dark grey colour. The mixture was henceforth sonicated for an optimal time of 10 hours during which no colour change was observed. The resulting solution was then centrifuged at an optimum speed of 10000 rpm for 15 minutes and the precipitate was washed with ethanol and distilled water and dried in an oven at 40 °C for overnight. The nanoparticles thus obtained were protected from direct light exposure to avoid the decomposition/ transformation of the Ag2O phase to metallic Ag. Figure 7(a) depicts the XRD patterns of the as-synthesised nanoparticles (using KOH as reducing agent) showing a mixture/mixed phase of both Ag and Ag2O phases.
Example 1C: Synthesis of nanoparticles with LiOH as the reducing agent
The method of sonochemistry was employed to develop a mixed phase of silver and silver oxide nanoparticles capped by a polymeric agent PVA. 180 ml of 0.1 M aqueous AgNO3 solution was taken in a glass beaker and was subjected to sonication in an ultrasonic bath operating at a frequency of 300 kHz and ultrasonic power of 100 W. 180 ml of PVA solution was obtained by continuous stirring on a hot plate at 100 °C for 2 hours on a hot plate with magnetic stirrer, which was then added to the AgNO3 solution in the presence of ultrasonic waves. After 2 hours of continuous sonication, 180 ml of 0.1 M aqueous LiOH solution (a reducing agent) was added to the reactant mixture, which turned the reactant mixture into a dark grey colour. The mixture was henceforth sonicated for an optimal time of 12 hours during which no colour change was observed. The resulting solution was then centrifuged at an optimum speed of 5000 rpm for 20 minutes and the precipitate was washed with ethanol and distilled water and dried in an oven at 40 °C for overnight. The nanoparticles thus obtained were protected from direct light exposure to avoid the decomposition/ transformation of the Ag2O phase to metallic Ag. Figure 8(a) depicts the XRD patterns of the as-synthesised nanoparticles (using LiOH as reducing agent) showing a mixture/mixed phase of both Ag and Ag2O phases.
Example ID: Synthesis of nanoparticles with polyvinyl pyrrolidone (PVP) as the capping agent
The method of sonochemistry was employed to develop a mixed phase of silver and silver oxide nanoparticles capped by a polymeric agent polyvinyl pyrrolidone (PVP). 90 ml of 0.1 M aqueous AgNO3 solution was taken in a glass beaker and was subjected to sonication in an ultrasonic bath operating at a frequency of 40 kHz and ultrasonic power of 100 W. 90 ml of PVA solution was obtained by continuous stirring on a hot plate at 100 °C for 1 hour on a hot plate with magnetic stirrer, which was then added to the AgNO3 solution in the presence of ultrasonic waves. After 1 hour of continuous sonication, 90 ml of 0.1 M aqueous NaOH solution (a reducing agent) was added to the reactant mixture, which turned the reactant mixture into a dark grey colour. The mixture was henceforth sonicated for an optimal time of 8 hours during which no colour change was observed. The resulting solution was then centrifuged at an optimum speed of 8000 rpm for 10 minutes and the precipitate was washed with ethanol and distilled water and dried in an oven at 40 °C for overnight. The nanoparticles thus obtained were protected from direct light exposure to avoid the decomposition/ transformation of the Ag2O phase to metallic Ag. Figure 9(a) depicts the XRD patterns of the as-synthesised nanoparticles (using PVP as surfactant/stabilizing agent) showing a mixture/mixed phase of both Ag and Ag2O phases.
Example 2A: Preparation of the nano-ink composition
The silver and silver oxide mixed phase nanoparticles synthesized as per Example 1A were crushed to a fine powder with a mortar and pestle prior to ink preparation. The solvent of the ink was N-Methyl-2-Pyrrolidone (NMP) (Sigma-Aldrich Chemie GmbH). 5 wt% of PVA (with respect to the weight of nanoparticles) is dissolved in NMP by heating at 100 °C for 1 hour on a hot plate with magnetic stirrer, prior to the addition of silver nanoparticles. About 20 wt.% of the crushed nanoparticles was dispersed in the mixture of NMP and PVA to obtain superior dispersion quality, and sonicated for 30 minutes in an ultrasonic bath to break the agglomerates and obtain a fine dispersion. 10 vol.% of terpineol (with respect to NMP) was then added to the ink which enables better flowability of the ink and better printing, and then sonicated for more 30 minutes. Figure 2(b) depicts the stable nano-ink of the Ag+Ag2O mixed-phase nanoparticles dispersed in NMP.
Conductive Ink
The inks were converted to pure metallic silver by heating/sintering at about 80 °C or about 120 °C on a hot plate for about 1 hour.
It was found that for the Batch A, that is when the phase mixture is dominated by the silver as the major phase, it can transform to complete silver and a high conducting film at a temperature of about 80-85 °C or lower. In the Batch B, a highly conductive printed silver pattern has been achieved at 120 °C or lower. The phase mixture has been characterized as a mixture of silver and silver oxide following the JCPDS database for Ag (JCPDS 04-0783) and Ag2O (JCPDS 75-1532), respectively (Figure 1).
XRD Analysis
XRD analysis is carried out for the nanoparticles of Example 1 [Figure 1(a)] and nano-ink comprising the same post subjecting it to the heating process [Figure 1(b)]. Figure 1 depicts (a) XRD patterns of the as-synthesised Batch C, Batch B and Batch A nanoparticles showing a mixture of both Ag and Ag2O phases and (b) their annealed counterparts (Batch A at 80 °C and Batches B & C at 120 °C for 1 hour) showing pure Ag phase in case of Batch A and B, whereas Batch C contains minor traces of silver oxide still present after annealing at 120 °C for 1 hour. The standard Ag and Ag2O patterns are also shown at the bottom for reference.
Dynamic light scattering (DLS) measurement
DLS measurement was carried out for the dispersed ink to obtain particle/agglomerate size distribution immediately after ink preparation and post 3 months as well (Figure 2c). Further, Figure 2© depicts the comparison of DLS measurement of both Batch A and Batch B nano- inks soon after ink preparation and after 3 months. It was found that sonication for 15 mins makes the ink ready for printing through narrow nozzle (down to 20 μm or lower) inkjet printer even after 3 months of preparation. Therefore, the synthesized nano-ink also shows a long shelf life.
Scanning Electron (SEM) Microscopy
SEM microscopy was conducted to analyse the surface topography of the nanoparticles of Example 1 and the nano-ink of Example 2. Figure 3 depicts SEM micrographs of (a) as- prepared Batch A nanoparticles and its (b) inkjet-printed nano-ink layer. Figure 4 depicts SEM micrographs of (a) as-prepared Batch B nanoparticles and its (b-d) inkjet-printed nano- ink layer. It is observed that the nanoparticles exhibit almost a spherical shape with a narrow size range. The clear boundary between the nanoparticles reveals that the particles are barely accumulated, instead they are fairly separated, which means the nanoparticles are covered by the capping agent PVA, and hence the particles cannot interact with each other. This makes tire nanoparticles to be extremely stable for longer period and also prevents any decomposition of the unstable phase Ag2O. These nanosized particles allow the formation of a highly packed dense particulate film. The SEM micrographs of the printed silver films reveal the presence of well-connected and homogeneous network of silver nanoparticles. After annealing, the morphology of the printed patterns reveals a uniform film with agglomerates of particles, and percolation networks due to the necking between lire nanoparticles and indeed will be a driving factor to attain high conductivity values.
Shelf Life Analysis
Comparison of shelf life of the mixed-phase nanoparticles was carried out by measuring the XRD pattern of the Batch A nanoparticles just after their preparation, and after storing them for 6 months. As can be seen from Figure 11, the two sets showed very similar XRD patterns, confirming that the nanoparticles of the present disclosure have high shelflife.
Example 2B: Preparation of the nano-ink composition
The silver and silver oxide mixed phase nanoparticles synthesized as per Example IB were crushed to a fine powder with a mortar and pestle prior to ink preparation. The solvent of the ink was N-Methyl-2-Pyrrolidone (NMP) (Sigma-Aldrich Chemie GmbH). 5 wt.% of PVA (with respect to the weight of nanoparticles) is dissolved in NMP by heating at 100 °C for 1 hour on a hot plate with magnetic stirrer, prior to the addition of silver nanoparticles. About 20 wt.% of the crushed nanoparticles was dispersed in the mixture of NMP and PVA to obtain superior dispersion quality, and sonicated for 30 minutes in an ultrasonic bath to break the agglomerates and obtain a fine dispersion. 10 vol.% of terpineol (with respect to NMP) was then added to the ink which enables better flowability of the ink and better printing, and then sonicated for more 30 minutes. The nano-ink so prepared was converted to pure metallic silver by heating/ sintering at about 110 °C on a hot plate for about 1 hour. Figure 7(b) depicts the XRD patterns of the annealed ink showing a pure Ag phase.
Example 2C: Preparation of the nano-ink composition
The silver and silver oxide mixed phase nanoparticles synthesized as per Example 1C were crushed to a fine powder with a mortar and pestle prior to ink preparation. The solvent of the ink was N-Methyl-2-Pyrrolidone (NMP) (Sigma-Aldrich Chemie GmbH). 5 wt% of PVA (with respect to the weight of nanoparticles) is dissolved in NMP by heating at 100 °C for 1 hour on a hot plate with magnetic stirrer, prior to the addition of silver nanoparticles. About 20 wt.% of the crushed nanoparticles was dispersed in the mixture of NMP and PV to obtain superior dispersion quality, and sonicated for 30 minutes in an ultrasonic bath to break the agglomerates and obtain a fine dispersion. 10 vol.% of terpineol (with respect to NMp) was then added to the ink which enables better flowability of the ink and better printing, and then sonicated for more 30 minutes. The nano-ink so prepared was converted to pure metallic silver by heating/ sintering at about 120 °C on a hot plate for about 1 hour. Figure 8(b) depicts the XRD patterns of the annealed ink showing a pure Ag phase.
Example 2D: Preparation of the nano-ink composition
The silver and silver oxide mixed phase nanoparticles synthesized as per Example ID were crushed to a fine powder with a mortar and pestle prior to ink preparation. The solvent of the ink was N-Methyl-2-Pyrrolidone (NMP) (Sigma-Aldrich Chemie GmbH). 5 wt.% of PVA (with respect to the weight of nanoparticles) is dissolved in NMP by heating at 100 °C for 1 hour on a hot plate with magnetic stirrer, prior to the addition of silver nanoparticles. About 20 wt.% of the crushed nanoparticles was dispersed in the mixture of NMP and PVA to obtain superior dispersion quality, and sonicated for 30 minutes in an ultrasonic bath to break the agglomerates and obtain a fine dispersion. 10 vol.% of terpineol (with respect to NMP) was then added to the ink which enables better flowability of the ink and better printing, and then sonicated for more 30 minutes. The nano-ink so prepared was converted to pure metallic silver by heating/sintering at about 150 °C on a hot plate for about 1 hour. Figure 9(b) depicts the XRD patterns of the annealed ink showing a pure Ag phase.
Example 2E: Preparation of nano-ink and conductive ink
The silver and silver oxide mixed phase nanoparticles synthesized as per Example 1A were crushed to a fine powder with a mortar and pestle prior to ink preparation. The solvent of the ink was Dimethyl sulfoxide (DMSO) (Sigma-Aldrich Chemie GmbH). 5 wt% of PVA (with respect to the weight of nanoparticles) is dissolved in DMSO by heating at 100 °C for 1 hour on a hot plate with magnetic stirrer, prior to the addition of silver nanoparticles. About 20 wt.% of the crushed nanoparticles was dispersed in the mixture of DMSO and PVA to obtain superior dispersion quality, and sonicated for 30 minutes in an ultrasonic bath to break the agglomerates and obtain a fine dispersion. 10 vol.% of terpineol (with respect to DMSO) was then added to the ink which enables better flowability of the ink and better printing, and then sonicated for more 30 minutes. Figure 10(a) depicts the stable nano-ink of the Ag+Ag2O mixed-phase nanoparticles dispersed in DMSO. Further, Figure 10(b) provides a comparison of DLS measurements of the as-prepared nano-ink synthesised using NMP (example 2A) and DMSO (this example) as the solvents.
Example 3: A comparative study
The nanoparticles were obtained as per Example 1, wherein the flow rate during the addition of PVA and NaOH to the reactant mixture is controlled and varied as 14 ml/min (Batch A), 8 ml/min (Batch B), and 0.4 ml/min (Batch C), which thereby helped to control the amounts of Ag2O and Ag in the final resulting precipitate. The obtained nanoparticles were protected from direct light exposure to avoid their degradation.
XRD patterns of the as-synthesised Batch A, Batch B and Batch C nanoparticles showing a mixture of both Ag and Ag2O phases was assessed and the results are depicted in Figure 1(a). The nanoparticles of Batches A-C were formulated into inks as per Example 2, and the inks were converted to pure metallic silver by heating/ sintering at about 80 °C or about 120 °C on a hot plate for about 1 hour. Their XRD patterns are depicted in Figure 1(b).
In particular, Figure 1 depicts (a) XRD patterns of the as-synthesised Batch C, Batch B and Batch A nanoparticles showing a mixture of both Ag and Ag2O phases and (b) their annealed counterparts (Batch A at 80 °C and Batches B & C at 120 °C for 1 hour) showing pure Ag phase in case of Batch A and B, whereas Batch C contains minor traces of silver oxide still present after annealing at 120 °C for 1 hour. The standard Ag and Ag2O patterns are also shown at the bottom for reference.
The silver content is relatively the highest in the case of Batch A, which thereby can transform to complete silver and a high conducting film at a temperature of 80-85 °C or lower. In the case of Batch B, a highly conductive printed silver pattern has been achieved at 120 °C or lower. However, in case of Batch C, a very low content of silver was obtained, which gave rise to a very high sheet resistance at a curing temperature of 120 °C (above which the Epson photographic paper substrate starts to degrade). Hence, with decreasing the addition rate of the reactants, a significant decrease in the amount of silver was evident which inherently affects the curing temperature and the sheet resistance.
Further, a comparison of sheet resistance of the nano-inks formulated using nanoparticles of Batches A-C was carried out at a heating/ sintering temperature of about 120 °C on a hot plate for about 1 hour, employing Epson photographic paper substrate. The sheet resistance was measured using the four-probe van der Pauw method. The results are tabulated in Table 1 below.
Table 1: Comparison of sheet resistance of nano-inks of Batch A, Batch B and Batch C
Figure imgf000043_0001
Figure imgf000044_0003
Hence, with decreasing the addition rate of the reactants, a significant decrease in the amount of silver was evident which inherently affects the curing temperature and the sheet resistance.
Example 4: Inkjet Printing
A square of 3 layers was inkjet-printed on the paper substrate by employing the nano-inks obtained from Example 2, which was further used to measure the sheet resistance using the four-probe van der Pauw method. Hie sheet resistance of the film is obtained as per the equation,
Figure imgf000044_0001
where, π /ln2, ΔV and I are the van der Pauw constant, voltage difference measured between inner contact points and current injected between two outer contact points, respectively.
Tire resistivity of the printed silver films was calculated using the following equation,
Figure imgf000044_0002
where, R and t are the sheet resistance and thickness of the films (measured by optical profilometry), respectively.
An optical microscope image of a printed silver square (obtained on using the Batch A nano- ink) which is used for the four-probe measurement is depicted in Figure 5(a).
The printed silver films thus obtained showed a resistivity of about <4.5x 10- 4Ωcm or lower (see Table 2 below). Table 2:
Figure imgf000045_0001
The mechanical flexibility of the printed nanoparticulate film was also investigated. Inkjet- printed silver films were subjected to different bending fatigue tests under compressive and tensile stress. The bending diameters has been varied as 25 mm, 12.5 mm and 6.25 mm to achieve a strain of 1%, 2% and 4%, respectively for both the conditions of compression and tension and for both the nano-inks (Batch A and Batch B). The number of bending cycles were also varied as 10, 100, 1000 and 10,000 in each of the strain conditions and the sheet resistance values were compared with the as-printed sample. Figure 5(b) depicts the variability of sheet resistance with the number of bending cycles, where the solid and dashed lines represent tension and compression conditions and the hollow circle, triangle, and square represent the 1%, 2% and 4% strain conditions of Batch A ink, whereas the solid shapes represent Batch B ink, respectively. It is observed that the films subjected to different strain conditions have shown more or less no change in their sheet resistance even after 10,000 cycles. Example 5: Effect of capping the precipitated nanoparticles by addition of capping agent post addition of the reducing agent
The nanoparticles were synthesized as per Example 1 with the exception that the reducing agent NaOH was first added to the silver nitrate solution, which was followed by the addition of the polymeric agent PVA solution. Adding the reducing agent to the silver salt solution resulted in phase pure silver oxide nanoparticles, which were then capped by a stabilizing agent by the addition of PVA solution. Figure 6(a) represents the XRD of the as-synthesised nanoparticles showing phase pure silver oxide phase. The nanoparticles were further used in the preparation of nano-ink in the presence of the solvent NMP, and SEM micrograph of the printed film is shown in Figure 6(b). This nano-ink on storage for 72 hours results in the formation of a shell around the nanoparticles as shown in Figure 6(c) of the printed film. This shell thereby deteriorates the conductivity of the film. It is due to the formation of σ-bond by the lone pairs of electrons on oxygen or nitrogen atoms of the solvent NMP with the silver species. Also, oxygen atom can act as a π-donor, and both the σ- and π- bond, along with the donation of electrons to the d-orbitals of silver lowers its energy and hence increases its catalytic reactivity. (X. Y. Toy et al., Royal Society of Chemistry, 2014, 4, 516). This leads to the formation of a shell, which thus hinders the conductivity of the silver layer.
Additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based on the description provided herein. The embodiments herein provide various features and advantageous details thereof in the description. Descriptions of well-known/conventional methods and techniques are omitted so as to not unnecessarily obscure the embodiments herein.
The foregoing description of the specific embodiments fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments in this disclosure have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” wherever used, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Similarly, terms such as “include” or “have” or “contain” and all their variations are inclusive and will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The terms "about" or “approximately” are used herein to mean approximately, in the region of, roughly, or around. When the term "about" is used in conjunction with a numerical value/range, it modifies that value/range by extending the boundaries above and below the numerical value(s) set forth. In general, the term "about" is used herein to modify a numerical value(s) or a measurable value(s) such as a parameter, an amount, a temporal duration, and the like, above and below the stated value(s) by a variance of +/-20% or less, +/-10% or less, +/-5% or less, +/-1% or less, and +/-0. 1% or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention, and achieves the desired results and/or advantages as disclosed in the present disclosure. It is to be understood that the value to which the modifier “about” or “approximately” refers is itself also specifically, and preferably, disclosed.
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. As used in this specification and the appended claims, the singular forms “a,” “an” and “the” includes both singular and plural references unless the content clearly dictates otherwise. The use of the expression ‘at least’ or ‘at least one’ suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. As such, the terms “a” (or “an”), “one or more”, and “at least one” can be used interchangeably herein. Numerical ranges stated in the form ‘from x to y’ include the values mentioned and those values that he within the range of the respective measurement accuracy as known to the skilled person. If several preferred numerical ranges are stated in this form, of course, all the ranges formed by a combination of the different end points are also included.
As regards the embodiments characterized in this specification, it is intended that each embodiment be read independently as well as in combination with another embodiment. For example, in case of an embodiment 1 reciting 3 alternatives A, B and C, an embodiment 2 reciting 3 alternatives D, E and F and an embodiment 3 reciting 3 alternatives G, H and I, it is to be understood that the specification unambiguously discloses embodiments corresponding to combinations A, D, G; A, D, H; A, D, I; A, E, G; A, E, H; A, E, I; A, F, G; A, F, H; A, F, I; B, D, G; B, D, H; B, D, I; B, E, G; B, E, H; B, E, I; B, F, G; B, F, H; B, F, I; C, D, G; C, D, H; C, D, I; C, E, G; C, E, H; C, E, I; C, F, G; C, F, H; C, F, I, unless specifically mentioned otherwise.
Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other modifications in the nature of the disclosure or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
All references, articles, publications, general disclosures etc. cited herein are incorporated by reference in their entireties for all purposes. However, mention of any reference, article, publication etc. cited herein is not, and should not be taken as, an acknowledgment or any form of suggestion that they constitute valid prior art or form part of the common general knowledge in any country in the world.

Claims

48 We claim:
1. A silver nano-ink composition comprising plurality of mixed-phase capped nanoparticles, at least one solvent and at least one excipient; wherein the mixed-phase capped nanoparticle comprises of about 5 vol.% to about 95 vol.% silver phase, and of about 5 vol.% to about 95 vol.% silver oxide phase.
2. The silver nano-ink composition as claimed in claim 1, comprising about 1 wt.% to about 55 wt.% of the mixed-phase nanoparticles with respect to weight of the solvent used.
3. The silver nano-ink composition as claimed in claim 1, comprising about 45 wt.% to about 99 wt.% of the solvent.
4. The silver nano-ink composition as claimed in claim 1, comprising about 0.1 wt.% to about 20 wt.% of the excipient with respect to weight of the nanoparticles.
5. The silver nano-ink composition as claimed in any one of the preceding claims, wherein the mixed-phase capped nanoparticle comprises of about 15 vol.% to about 85 vol.% silver phase, and of about 15 vol.% to about 85 vol.% silver oxide phase.
6. The silver nano-ink composition as claimed in any one of the preceding claims, wherein the nanoparticle has a size ranging from about 3 nm to about 200 nm.
7. A method of preparing the silver nano-ink composition as claimed in claim 1, said method comprising act of mixing plurality of mixed-phase capped nanoparticles with at least one solvent and at least one excipient.
8. The method as claimed in claim 7, wherein the mixing is carried out by sonication or vigorous mixing of the mixed-phase capped nanoparticle dispersed in at least one solvent and at least one excipient. 49 The method as claimed in claim 8, wherein the sonication is carried out at a frequency ranging from about 5 kHz to about 300 kHz; and wherein the sonication or the vigorous mixing is carried out for a time period ranging from about 2 minutes to about 120 minutes. The method as claimed in any one of claims 7 to 9, comprising: a) preparing a reaction mixture by dissolving a capping agent in a solvent at a temperature ranging between 100 °C to about 200 °C for about 1 hour to about 2 hours, followed by adding mixed-phase capped nanoparticles to the reaction mixture; and b) subjecting the mixture comprising the nanoparticles to sonication or vigorous mixing, followed by addition of an excipient to obtain the silver nano-ink composition. The method as claimed in any one of claims 7 to 10, wherein the mixed-phase capped nanoparticle is prepared by method comprising acts of: a) contacting a silver salt solution with a capping agent to obtain a mixture; and b) adding a reducing agent at a rate suitable to obtain the mixed-phase nanoparticle comprising the silver and silver oxide phases. The method as claimed in claim 11, wherein the silver salt solution is prepared by adding a silver salt to a solvent selected from a group comprising water, alcohol and toluene or any combination thereof; and wherein the silver salt is selected from a group comprising silver nitrate, silver acetate and silver chloride, or any combination thereof. The method as claimed in claim 12, wherein the alcohol is selected from a group comprising ethanol, 2-methoxy ethanol, 2-propanol and ethylene glycol, or any combination thereof. The method as claimed in claim 11, wherein the rate of addition of the reducing agent ranges from about 0.1 ml/min to about 90 ml/min for a batch size of 90 ml to about
Figure imgf000050_0001
50 The method as claimed in claim 11, wherein the method is carried out under continuous sonication in an ultrasonic bath operating at a frequency ranging from about 5 kHz to about 300 kHz; and wherein post addition of the capping agent to the silver salt solution, the mixture is sonicated for a time period of about 1 hour; and wherein post addition of the reducing agent to the mixture, the mixture is sonicated for a time period of about 8 hours. The method as claimed in claim 11, wherein post its preparation, the nanoparticle is isolated or separated from the solution by centrifugation, and wherein the centrifugation is carried out at a speed ranging from about 1000 rpm to about 20000 rpm for about 1 to about 60 minutes. The method as claimed in claim 16, wherein the centrifugation results in formation of a precipitate and wherein the precipitate obtained is washed and dried for removal of unreacted agents. The silver nano-ink composition as claimed in claim 1, or the method as claimed in claim 7, wherein the solvent is a polar or non-polar solvent; and wherein the solvent is selected from a group comprising N-Methyl-2-Pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile, ethyl acetate, dichloromethane, hexamethylphosphoric triamide, cyclohexyl-pyrrolidinone, chlorobenzene, dimethylformamide, N-vinyl-pyrrolidinone, N-methyl formamide and cyclohexanone, or any combination thereof. The silver nano-ink composition as claimed in claim 1, or the method as claimed in claim 7, wherein the excipient is selected from a group comprising capping agent, viscosity modifier, wetting/de-wetting agent, curing agent, adhesion promoter, antifoaming agent and humectant, or a combination thereof; and wherein the capping agent, viscosity modifier, wetting/de-wetting agent, curing agent, adhesion promoter, anti-foaming agent or humectant is selected from a group comprising terpineol, glycol, glycerol, glycol ether and cellulose ether, tripropylene glycol mono methyl ether, diethylene glycol mono butyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, hydroxypropyl methylcellulose, ethyl cellulose, 51 hydroxy ethyl cellulose, methyl cellulose, sodium carboxy methyl cellulose and benzyl cellulose, or any combination thereof. The method as claimed in claim 11, or claim 19, wherein the reducing agent is selected from a group comprising sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium borohydride, hydroxylamine and hydrazine hydrate, or any combination thereof. The silver nano-ink composition as claimed in claim 1, or the method as claimed in claim 7 or claim 19, wherein the nanoparticle is capped by at least one capping agent; wherein the capping agent is a surfactant or a polymer molecule; and wherein the capping agent is selected from a group comprising poly vinyl alcohol (PVA), polyvinyl chloride, polyvinyl pyrrolidone (PVP), poly(methyl methacrylate) (PMMA), 1 -hexadecylamine and octadecyl-p-vinylbenzyldimethyl ammonium chloride, or any combination thereof. A kit for obtaining the silver nano-ink composition of claim 1, said kit comprising plurality of mixed-phase capped nanoparticles, at least one solvent and at least one excipient, optionally along with user instructions for obtaining the said composition. Use of the silver nano-ink composition of claim 1, for preparing a substrate comprising a conductive silver pattern. A method of making a conductive silver pattern on a substrate, said method comprising applying the silver nano-ink composition of claim 1 on the substrate followed by curing the substrate to obtain the conductive silver pattern. The method as claimed in claim 24, wherein the silver nano-ink composition is applied onto the substrate using commercially or industrially known solution processing or printing technology; or wherein the silver nano-ink composition is applied onto the substrate through inkjet printing. The method as claimed in claim 24, wherein the curing is carried out through thermal curing at a temperature ranging from about 40 °C to about 150 °C, for time period ranging from about 10 minutes to about 120 minutes; or wherein the curing is carried out through photonic curing. The method as claimed in any one of claims 24 to 26, wherein the thermal or photonic curing results in phase change of silver oxide to silver in the mixed-phase capped nanoparticles causing a volume change driven removal of the capping agent from the nanoparticles and facilitating formation of the conductive silver pattern. The method as claimed in any one of claims 24 to 27, wherein thickness of the conductive silver pattern applied through inkjet printing ranges from about 0.05 μm to about 5 μm. The use as claimed in claim 23 and the method as claimed in claim 24, wherein the substrate is selected from a group comprising photopaper, cellulose, polyethylene terephthalate (PET), textile and glass, or any combination thereof. The use and the method as claimed in claim 29, wherein the substrate comprising the conductive silver pattern is employed in applications selected from a group comprising printed circuit boards, RFID tags, thin film transistors, memristors, flexible e-readers, reflective displays, capacitive displays, sensors, conductive tracers, capacitor and resistor elements, resistive tracers on windshield defrosters, automotive sensors, touch screens, and thin film photovoltaic solar cells.
PCT/IB2022/050582 2021-01-22 2022-01-24 Silver nano-ink composition comprising mixed-phase capped nanoparticles, methods of preparation, kit and applications thereof WO2022157725A1 (en)

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KR20080013787A (en) * 2006-08-07 2008-02-13 주식회사 잉크테크 Process for preparing silver nanoparticles or silver nanocolloid, and the compositions of silver ink containing the silver nanoparticles
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KR20080013787A (en) * 2006-08-07 2008-02-13 주식회사 잉크테크 Process for preparing silver nanoparticles or silver nanocolloid, and the compositions of silver ink containing the silver nanoparticles
KR20140120953A (en) * 2013-02-28 2014-10-15 (주) 파루 Composition for aqueous conductive ink using silver nano gel, manufacturing composition using silver nano gel and manufacturing method thereof

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