WO2020139070A1 - Method of synthesizing solvent-free silver reduced graphene oxide hybrid conductive ink - Google Patents

Method of synthesizing solvent-free silver reduced graphene oxide hybrid conductive ink Download PDF

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Publication number
WO2020139070A1
WO2020139070A1 PCT/MY2019/050125 MY2019050125W WO2020139070A1 WO 2020139070 A1 WO2020139070 A1 WO 2020139070A1 MY 2019050125 W MY2019050125 W MY 2019050125W WO 2020139070 A1 WO2020139070 A1 WO 2020139070A1
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Prior art keywords
graphene oxide
conductive ink
mixture
silver
reduced graphene
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PCT/MY2019/050125
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French (fr)
Inventor
Abdul Rashid NORA'ZAH BT
Sulaiman SURAYA BINTI
Abd Aziz AIMAN SAJIDAH BINTI
Hing Wah Lee
Original Assignee
Mimos Berhad
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Publication of WO2020139070A1 publication Critical patent/WO2020139070A1/en

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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
    • C09D11/30—Inkjet printing 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
    • C09D11/52—Electrically conductive inks

Definitions

  • the present invention generally relates to conductive inks.
  • the present invention more particularly relates to a method of synthesizing a solvent-free hybrid conductive inks comprising reduced graphene oxide.
  • Conductive inks contain conductive materials that able to form films which conduct electricity.
  • Conductive components contained in conductive inks may be comprised of silver, carbon nanotubes (CNT), or other precious metal coated base material. Depending on the application, more exotic conductive fillers exist.
  • Conductive inks can be applied in several ways including screen print, flexographic or rotogravure, spray, dip, syringe dispense, and stencil print. Conductive inks are formulated for a specific method of application. Conductive inks for screen printing tend to be solvent based because water-based inks evaporate too quickly and the viscosity tends to be too low to screen effectively. Water- based inks are available for high speed printing and coating applications.
  • Graphene is a two-dimensional hexagonal lattice honeycomb structure of the two- dimensional planar film and a material of sp 2 carbon atoms. Graphene exhibits novel physical properties, a single layer of graphene having excellent transparency, absorbing only 2.3% of the light; an electron mobility at room temperature over 15000cm 2 / VS. Graphene has excellent electrical conductivity and mechanical properties, lateral (in plane) high conductivity 106 S/m, up to 130 GPa, and good thermal conductivity.
  • Graphene material is known to exhibit an excellent chemical, thermal and mechanical properties. Due to some challenges such as to up-scaling graphene production and maintaining the quality of large quantities of graphene, a derivative of graphene has become an attractive development work to produce for a low cost, high yield and more efficient graphene for mass production.
  • Graphene-based material has become a promising conductive ink to be used in electronics devices for inkjet printing technology.
  • the conductive inks have been developed with various type of fillers such as noble metal nanoparticles such as Au, Pt, Ag and Cu, carbon nanotubes (CNT) and polymer-based materials to enhance their conductivity properties.
  • One such prior art having no. CN108467629 provides a method for preparing composite type conductive ink.
  • the prior art uses natural graphite powder, potassium per sulfate and the like as a raw material, to prepare a dried powder.
  • the dry powder is then mixed with sodium nitrate, potassium permanganate and the like to obtain a dialysate, the dialysate is ultrasonically cleaned to obtain a graphite oxide suspension, the graphene oxide suspension is added into ascorbic acid and ammonia water to obtain an in-situ reaction solution, a silver crystal seed solution is added dropwise to the in-situ reaction solution under heating conditions, and finally the composite conductive ink is obtained by using E-51 type epoxy resin as an adhesion aid, and adding polyaniline particles, silver-doped reduced graphene oxide and the like.
  • a carbon powder conductive filler is used as a main filler, a silver powder conductive filler is used as a dopant.
  • Another prior art having no. CN106398397 provides a method for preparing monodisperse graphene based nano silver composite.
  • An ultrasonic dispersion of graphene oxide in water is prepared, drop-wise addition of a silver ammonia solution and a sodium citrate solution, and after even mixing, repeated ultrasonic treating and ice water cooling until the reaction is complete. After the reaction is completed, filtration by suction, washing and drying is done to obtain the monodisperse graphene based nano silver composite.
  • Another prior art having no. W02018195170 provides a method of forming a conductive graphene ink.
  • the method comprises forming a binder solution.
  • the binder solution is formed by heating a first solvent, adding a binder to the first solvent, mixing the binder and the first solvent, and cooling the binder and the first solvent. Then, forming a reduced graphene oxide dispersion comprising a second solvent and reduced graphene oxide.
  • Forming a graphene solution comprising the binder solution, the reduced graphene oxide dispersion, a third solvent, a conductive additive, a surfactant, and a defoamer; and mixing the graphene solution to form a conductive graphene ink.
  • Another method to prepare a graphene based conductive ink is by chemical reduction of graphene oxide.
  • the drawback of these mentioned processes is that most of the oxygen groups in the graphene oxide gets removed. This leads to the production of reduced graphene oxide (rGO) which becomes less hydrophilic and low dispersity in water- based ink.
  • rGO reduced graphene oxide
  • One of the approaches to increase the dispersity of the rGO is by using organic solvent such as methanol, acetone, ethanol, N, N-dimethylformamide (DMF) and toluene.
  • organic solvent such as methanol, acetone, ethanol, N, N-dimethylformamide (DMF) and toluene.
  • DMF N-dimethylformamide
  • the primary object of the present invention is to provide a method for synthesizing Silver and Reduced Graphene Oxide (Ag/rGO) hybrid conductive ink.
  • Another object of the present invention is to provide a hybrid conductive ink comprising silver nanoparticles, reduced graphene oxide, ammonium quaternary ion and deionized water.
  • It is yet another object of the present invention is to provide a solvent-free reduced graphene oxide conductive ink having a good dispersivity and reduce agglomeration of Ag/rGO composite.
  • It is another object of the present invention is to provide a solvent-free reduced graphene oxide conductive ink having compatibility for inkjet printing method.
  • It is a further object of the present invention is to provide a solvent-free reduced graphene oxide conductive ink using water as dispersant.
  • a method of synthesizing solvent-free silver-reduced graphene oxide hybrid conductive ink is provided.
  • the method characterized in that preparing an aqueous solution of graphene oxide by mixing a predetermined amount of graphene oxide in water and sonicating the aqueous solution of graphene oxide for a predetermined time of at least 30 minutes (101). The sonicated aqueous solution of graphene oxide is stirred for at least 30 minutes (102). An aqueous solution of quaternary ammonium compound is added dropwise to the aqueous solution of graphene oxide to form a mixture and stirred for at least 60 minutes at a predetermined rpm of 1000 (103).
  • the mixture is heated in a silicon bath up to predetermined temperature of 58°C to 62°C while stirring the mixture at the predetermined rpm for at least 60 minutes (104).
  • An aqueous solution of silver nitrate is added into the mixture and stirred for at least 15 minutes at the predetermined rpm (105).
  • the mixture is kept at 60°C without stirring for at least a predetermined time period of 21 hours (106).
  • the mixture is heated up to 78°C to 80°C for at least 60 minutes while stirring at the predetermined rpm (107).
  • a reducing agent is added dropwise in the mixture and stirred for at least 4-5 hours at the predetermined rpm of 1000 to 1200 (108).
  • the mixture is centrifuged to separate out silver-reduced graphene oxide composite, wherein centrifuging is done at 10000 rpm for at least 60 minutes
  • the quaternary ammonium compound is selected from the group consisting of choline chloride, benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetalkonium chloride, cetylpyridinium chloride, cetrimonium, cetrimide, dofanium chloride, tetraethylammonium bromide, didecyldimethylammonium chloride and domiphen bromide.
  • the quaternary ammonium compound is choline chloride.
  • the quaternary ammonium compound is used in a range of 30 to 40 % v/v
  • the solution of silver nitrate is between 13 to 15 % v/v for concentration of 0.2M to 0.5M.
  • the reducing agent is sodium hydroxide in an amount of 8 to 16 % v/v for 8M.
  • the deionized water is used as a dispersant in an amount of 2.5 to 5 mL.
  • the conductivity of the conductive ink is in between 2000 to 3000 uS cm 1 .
  • the viscosity of the conductive ink is in between 1.0 to 2.0 cP at 24°C.
  • the resistivity of a printed film is 10 4 ohm. cm.
  • a solvent-free silver reduced graphene oxide hybrid conductive ink is provided.
  • the conductive ink characterized in that silver nanoparticles, reduced graphene oxide, ammonium quaternary ion and deionized water.
  • the silver nanoparticles are embedded on the reduced graphene oxide surfaces.
  • the conductivity of the conductive ink is in a range of 2000 to 3000 uS cm 1 .
  • the viscosity of the conductive ink is in a range of 1.0 to 2.0 cP at a temperature of 24°C.
  • the resistivity of a printed film is 10 4 ohm. cm.
  • the size range of silver nanoparticles is 8 to 15 nm.
  • FIG. 1 is a flowchart showing the various steps involved in the method of synthesizing solvent-free silver-reduced graphene oxide hybrid conductive ink, according to an embodiment of the present invention.
  • FIG. 2 shows a chemical structure of the solvent-free silver-reduced graphene oxide hybrid conductive ink, according to an embodiment of the present invention.
  • FIG. 3 shows a process flow for the formation of a new graphene-based hybrid conductive ink, as an exemplary embodiment of the present invention.
  • the various embodiments of the present invention provide a solvent-free reduced graphene oxide conductive ink and a method of synthesizing the same.
  • the present invention provides a new formulation for Graphene-based conductive ink that gets disperses in a solvent-free dispersant.
  • graphene oxide (GO) and silver salt mixture is synthesize with a quaternary ammonium compound but not limited to Choline chloride [(CH 3 )3NCH 2 CH 2 0H]C1 to produce silver-reduced graphene oxide (Ag/rGO) hybrid conductive ink.
  • Choline chloride (CH 3 )3NCH 2 CH 2 0H]C1
  • the hydroxyl group present in the choline chloride modifies the characteristic of rGO from hydrophobic to hydrophilic, which enables the Ag/rGO composite to easily get dispersed in water.
  • FIG. 1 is a flowchart showing the various steps involved in the method of synthesizing solvent-free silver-reduced graphene oxide hybrid conductive ink, according to an embodiment of the present invention.
  • the method comprises preparing an aqueous solution of graphene oxide by mixing a predetermined amount of graphene oxide in water and sonicating the aqueous solution of graphene oxide for a predetermined time of at least 30 minutes 101. The sonicated aqueous solution of graphene oxide is stirred for at least 30 minutes 102.
  • a solution of quaternary ammonium compound is added dropwise to the aqueous solution of graphene oxide to form a mixture and stirred for at least 60 minutes at a predetermined rpm of 1000 103.
  • the mixture is heated in a silicon bath up to predetermined temperature of 58°C to 62°C while stirring the mixture at the predetermined rpm for at least 60 minutes 104.
  • a solution of silver nitrate is added into the mixture and stirred for at least 15 minutes at the predetermined rpm of 1000 105.
  • the mixture is kept at 60°C for at least a predetermined time period of 21 hours 106.
  • the mixture is heated up to 78°C to 80°C for at least 60 minutes while stirring at the predetermined rpm of 1000 107.
  • a reducing agent is added dropwise in the mixture and stirred for at least 4-5 hours at the predetermined rpm of 1000 to 1200 108.
  • the mixture is centrifuged to separate out silver-reduced graphene oxide composite, wherein centrifuging is done at 10000 rpm for at least 60 minutes 109.
  • the silver-reduced graphene oxide composite is rinsed with deionized water 110 and mixed with deionized water 111.
  • the predetermined amount of graphene oxide is between 1 to 1.5 mg/mL.
  • the quaternary ammonium compound is choline chloride.
  • the quaternary ammonium compound is used in a range of 30 to 40 % v/v.
  • the solution of silver nitrate is between 13 to 15 % v/v for concentration of 0.2M to 0.5M.
  • the reducing agent is sodium hydroxide in an amount of 8 to 16 % v/v for 8M.
  • the water is used as a dispersant in an amount of 2.5 to 5mL.
  • a conductivity of the conductive ink is in between 2000 to 3000 uS cm -1.
  • a viscosity of the conductive ink is in between 1.0 to 2.0 cP at 24°C.
  • a resistivity of a printed film is 10 4 ohm. cm.
  • a solvent-free silver reduced graphene oxide hybrid conductive ink comprises silver nanoparticles embedded on the reduced graphene oxide surfaces, ammonium quaternary ion which is choline chloride and deionized water.
  • the size range of silver nanoparticles is 8 to 15 nm.
  • FIG. 2 shows a chemical structure of the solvent-free silver-reduced graphene oxide hybrid conductive ink, according to an embodiment of the present invention. With respect to FIG. 2, the reduced graphene oxide can be seen which gets reduced by adding sodium hydroxide and is functionalized with choline chloride.
  • the silver nanoparticles are embedded on the reduced graphene oxide surfaces.
  • FIG. 3 shows a process flow for the formation of a new graphene-based hybrid conductive ink, as an exemplary embodiment of the present invention.
  • the process is started (301) and a 1 mg/ml aqueous solution of graphene oxide is sonicated and stirred for atleast 30 minutes (302).
  • An optimum amount of choline chloride is added (303) to form a mixture.
  • the mixture is stirred at 60°C for 1 hour (304). Further, 0.2M silver nitrate solution is added to the mixture and the mixture is stirred for 15 minutes (305).
  • the reaction is made to carry out by keeping the mixture without agitation at 60°C for at least 21 hours (306).
  • the mixture is heated while stirring up to a temperature of 80°C for at least 1 hour (307). Further, 2 ml of 8M solution of sodium hydroxide is dropwise added to the mixture and the mixture is stirred for at least 4 hours (308).
  • the composite/precipitates of silver-reduced graphene oxide (Ag/rGO) is formed and separated by centrifugation at an rpm of 10000 for at least 1 hour (309).
  • the composite of silver-reduced graphene oxide (Ag/rGO) is rinsed with deionised water (310).
  • the composite of silver-reduced graphene oxide (Ag/rGO) is dispersed in deionized water (311) and sonicated for at least 48 hours (312).
  • the process end and the conductive ink is synthesized (313).
  • the graphene oxide (GO) solution is mixed with Choline Chloride (ChCl) to functionalize the graphene oxide.
  • Silver nitrate (AgNOs) aqueous is added in the GO mixture which is used as a source of silver nanoparticles (Ag NPs) for the improvement of the conductivity of the GO.
  • Sodium hydroxide (NaOH) functions as a reducing agent to form Ag NPs and reduced graphene oxide (rGO). The process is done at temperature 80°C.
  • the mixture of the Ag-rGO hybrid mixture is centrifuged at 10000 rpm for 60 min to separate the composite.
  • the Ag/rGO hybrid composite is dispersed in deionized water and sonicated for 48h. Once completed it is ready to be function as solvent-free Ag/rGO hybrid conductive ink.
  • the conductive ink has a good dispersity in water and reduced agglomeration of Ag/rGO composite.
  • the conductive ink is compatible for inkjet printing method.

Abstract

The present invention relates to a method of synthesizing solvent free silver with reduced graphene oxide hybrid conductive ink. The conductive ink has improved properties of water dispersity and less agglomeration. The conductive ink is graphene oxide with a quaternary ammonium salt. The conductive ink uses silver nanoparticles as metal base.

Description

METHOD OF SYNTHESIZING SOLVENT-FREE SILVER REDUCED GRAPHENE OXIDE HYBRID CONDUCTIVE INK
FIELD OF INVENTION
The present invention generally relates to conductive inks. The present invention more particularly relates to a method of synthesizing a solvent-free hybrid conductive inks comprising reduced graphene oxide.
BACKGROUND OF THE INVENTION
Conductive inks contain conductive materials that able to form films which conduct electricity. Conductive components contained in conductive inks may be comprised of silver, carbon nanotubes (CNT), or other precious metal coated base material. Depending on the application, more exotic conductive fillers exist.
Conductive inks can be applied in several ways including screen print, flexographic or rotogravure, spray, dip, syringe dispense, and stencil print. Conductive inks are formulated for a specific method of application. Conductive inks for screen printing tend to be solvent based because water-based inks evaporate too quickly and the viscosity tends to be too low to screen effectively. Water- based inks are available for high speed printing and coating applications.
Graphene is a two-dimensional hexagonal lattice honeycomb structure of the two- dimensional planar film and a material of sp2 carbon atoms. Graphene exhibits novel physical properties, a single layer of graphene having excellent transparency, absorbing only 2.3% of the light; an electron mobility at room temperature over 15000cm2 / VS. Graphene has excellent electrical conductivity and mechanical properties, lateral (in plane) high conductivity 106 S/m, up to 130 GPa, and good thermal conductivity.
Graphene material is known to exhibit an excellent chemical, thermal and mechanical properties. Due to some challenges such as to up-scaling graphene production and maintaining the quality of large quantities of graphene, a derivative of graphene has become an attractive development work to produce for a low cost, high yield and more efficient graphene for mass production. Graphene-based material has become a promising conductive ink to be used in electronics devices for inkjet printing technology. The conductive inks have been developed with various type of fillers such as noble metal nanoparticles such as Au, Pt, Ag and Cu, carbon nanotubes (CNT) and polymer-based materials to enhance their conductivity properties.
One such prior art having no. CN108467629 provides a method for preparing composite type conductive ink. The prior art uses natural graphite powder, potassium per sulfate and the like as a raw material, to prepare a dried powder. The dry powder is then mixed with sodium nitrate, potassium permanganate and the like to obtain a dialysate, the dialysate is ultrasonically cleaned to obtain a graphite oxide suspension, the graphene oxide suspension is added into ascorbic acid and ammonia water to obtain an in-situ reaction solution, a silver crystal seed solution is added dropwise to the in-situ reaction solution under heating conditions, and finally the composite conductive ink is obtained by using E-51 type epoxy resin as an adhesion aid, and adding polyaniline particles, silver-doped reduced graphene oxide and the like. A carbon powder conductive filler is used as a main filler, a silver powder conductive filler is used as a dopant.
Another prior art having no. CN106398397 provides a method for preparing monodisperse graphene based nano silver composite. An ultrasonic dispersion of graphene oxide in water is prepared, drop-wise addition of a silver ammonia solution and a sodium citrate solution, and after even mixing, repeated ultrasonic treating and ice water cooling until the reaction is complete. After the reaction is completed, filtration by suction, washing and drying is done to obtain the monodisperse graphene based nano silver composite.
Another prior art having no. W02018195170 provides a method of forming a conductive graphene ink. The method comprises forming a binder solution. The binder solution is formed by heating a first solvent, adding a binder to the first solvent, mixing the binder and the first solvent, and cooling the binder and the first solvent. Then, forming a reduced graphene oxide dispersion comprising a second solvent and reduced graphene oxide. Forming a graphene solution comprising the binder solution, the reduced graphene oxide dispersion, a third solvent, a conductive additive, a surfactant, and a defoamer; and mixing the graphene solution to form a conductive graphene ink.
Another method to prepare a graphene based conductive ink is by chemical reduction of graphene oxide. The drawback of these mentioned processes is that most of the oxygen groups in the graphene oxide gets removed. This leads to the production of reduced graphene oxide (rGO) which becomes less hydrophilic and low dispersity in water- based ink. There is increased aggregation due to the strong p - p stacking and Van der Waals interactions, which limits the application of graphene-based conductive ink for inkjet printing technology due to nozzle jam during printing.
One of the approaches to increase the dispersity of the rGO is by using organic solvent such as methanol, acetone, ethanol, N, N-dimethylformamide (DMF) and toluene. The drawback is some of the solvent can be carcinogenic and toxic which is harmful to human.
In view of the foregoing, there is a need to develop a solvent-free hybrid conductive inks which are having enhanced properties of conductivity and dispersity.
SUMMARY OF THE INVENTION
Thus, the primary object of the present invention is to provide a method for synthesizing Silver and Reduced Graphene Oxide (Ag/rGO) hybrid conductive ink.
Another object of the present invention is to provide a hybrid conductive ink comprising silver nanoparticles, reduced graphene oxide, ammonium quaternary ion and deionized water.
It is yet another object of the present invention is to provide a solvent-free reduced graphene oxide conductive ink having a good dispersivity and reduce agglomeration of Ag/rGO composite.
It is another object of the present invention is to provide a solvent-free reduced graphene oxide conductive ink having compatibility for inkjet printing method.
It is a further object of the present invention is to provide a solvent-free reduced graphene oxide conductive ink using water as dispersant.
According to the embodiments of the present invention, a method of synthesizing solvent-free silver-reduced graphene oxide hybrid conductive ink is provided. The method characterized in that preparing an aqueous solution of graphene oxide by mixing a predetermined amount of graphene oxide in water and sonicating the aqueous solution of graphene oxide for a predetermined time of at least 30 minutes (101). The sonicated aqueous solution of graphene oxide is stirred for at least 30 minutes (102). An aqueous solution of quaternary ammonium compound is added dropwise to the aqueous solution of graphene oxide to form a mixture and stirred for at least 60 minutes at a predetermined rpm of 1000 (103). The mixture is heated in a silicon bath up to predetermined temperature of 58°C to 62°C while stirring the mixture at the predetermined rpm for at least 60 minutes (104). An aqueous solution of silver nitrate is added into the mixture and stirred for at least 15 minutes at the predetermined rpm (105). The mixture is kept at 60°C without stirring for at least a predetermined time period of 21 hours (106). The mixture is heated up to 78°C to 80°C for at least 60 minutes while stirring at the predetermined rpm (107). A reducing agent is added dropwise in the mixture and stirred for at least 4-5 hours at the predetermined rpm of 1000 to 1200 (108). The mixture is centrifuged to separate out silver-reduced graphene oxide composite, wherein centrifuging is done at 10000 rpm for at least 60 minutes
(109). The silver-reduced graphene oxide composite is rinsed with deionized water
(110) and mixed with deionized water (111). The predetermined amount of graphene oxide is between 1 to 1.5 mg/mL. The quaternary ammonium compound is selected from the group consisting of choline chloride, benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetalkonium chloride, cetylpyridinium chloride, cetrimonium, cetrimide, dofanium chloride, tetraethylammonium bromide, didecyldimethylammonium chloride and domiphen bromide. The quaternary ammonium compound is choline chloride. The quaternary ammonium compound is used in a range of 30 to 40 % v/v The solution of silver nitrate is between 13 to 15 % v/v for concentration of 0.2M to 0.5M. The reducing agent is sodium hydroxide in an amount of 8 to 16 % v/v for 8M. The deionized water is used as a dispersant in an amount of 2.5 to 5 mL.
According to an embodiment of the present invention, the conductivity of the conductive ink is in between 2000 to 3000 uS cm 1.
According to an embodiment of the present invention, the viscosity of the conductive ink is in between 1.0 to 2.0 cP at 24°C. According to an embodiment of the present invention, the resistivity of a printed film is 10 4 ohm. cm.
According to another embodiment of the present invention, a solvent-free silver reduced graphene oxide hybrid conductive ink is provided. The conductive ink characterized in that silver nanoparticles, reduced graphene oxide, ammonium quaternary ion and deionized water. The silver nanoparticles are embedded on the reduced graphene oxide surfaces. The conductivity of the conductive ink is in a range of 2000 to 3000 uS cm 1. The viscosity of the conductive ink is in a range of 1.0 to 2.0 cP at a temperature of 24°C. The resistivity of a printed film is 10 4 ohm. cm. In the preferred embodiment, the size range of silver nanoparticles is 8 to 15 nm.
These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features, and advantages of the invention will be apparent from the following description when read with reference to the accompanying drawings. In the drawings, wherein like reference numerals denote corresponding parts throughout the several views:
FIG. 1 is a flowchart showing the various steps involved in the method of synthesizing solvent-free silver-reduced graphene oxide hybrid conductive ink, according to an embodiment of the present invention.
FIG. 2 shows a chemical structure of the solvent-free silver-reduced graphene oxide hybrid conductive ink, according to an embodiment of the present invention. FIG. 3 shows a process flow for the formation of a new graphene-based hybrid conductive ink, as an exemplary embodiment of the present invention.
DETAILED DESCRPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in detail with reference to the accompanying drawings.
The various embodiments of the present invention provide a solvent-free reduced graphene oxide conductive ink and a method of synthesizing the same. The present invention provides a new formulation for Graphene-based conductive ink that gets disperses in a solvent-free dispersant.
According to an embodiment of the present invention, graphene oxide (GO) and silver salt mixture is synthesize with a quaternary ammonium compound but not limited to Choline chloride [(CH3)3NCH2CH20H]C1 to produce silver-reduced graphene oxide (Ag/rGO) hybrid conductive ink. The hydroxyl group present in the choline chloride modifies the characteristic of rGO from hydrophobic to hydrophilic, which enables the Ag/rGO composite to easily get dispersed in water.
FIG. 1 is a flowchart showing the various steps involved in the method of synthesizing solvent-free silver-reduced graphene oxide hybrid conductive ink, according to an embodiment of the present invention. With respect to FIG. 1, the method comprises preparing an aqueous solution of graphene oxide by mixing a predetermined amount of graphene oxide in water and sonicating the aqueous solution of graphene oxide for a predetermined time of at least 30 minutes 101. The sonicated aqueous solution of graphene oxide is stirred for at least 30 minutes 102. A solution of quaternary ammonium compound is added dropwise to the aqueous solution of graphene oxide to form a mixture and stirred for at least 60 minutes at a predetermined rpm of 1000 103. The mixture is heated in a silicon bath up to predetermined temperature of 58°C to 62°C while stirring the mixture at the predetermined rpm for at least 60 minutes 104. A solution of silver nitrate is added into the mixture and stirred for at least 15 minutes at the predetermined rpm of 1000 105. The mixture is kept at 60°C for at least a predetermined time period of 21 hours 106. The mixture is heated up to 78°C to 80°C for at least 60 minutes while stirring at the predetermined rpm of 1000 107. A reducing agent is added dropwise in the mixture and stirred for at least 4-5 hours at the predetermined rpm of 1000 to 1200 108. The mixture is centrifuged to separate out silver-reduced graphene oxide composite, wherein centrifuging is done at 10000 rpm for at least 60 minutes 109. The silver-reduced graphene oxide composite is rinsed with deionized water 110 and mixed with deionized water 111. The predetermined amount of graphene oxide is between 1 to 1.5 mg/mL. The quaternary ammonium compound is choline chloride. The quaternary ammonium compound is used in a range of 30 to 40 % v/v. The solution of silver nitrate is between 13 to 15 % v/v for concentration of 0.2M to 0.5M. The reducing agent is sodium hydroxide in an amount of 8 to 16 % v/v for 8M. The water is used as a dispersant in an amount of 2.5 to 5mL.
According to an embodiment of the present invention, a conductivity of the conductive ink is in between 2000 to 3000 uS cm -1.
According to an embodiment of the present invention, a viscosity of the conductive ink is in between 1.0 to 2.0 cP at 24°C.
According to an embodiment of the present invention, a resistivity of a printed film is 10 4 ohm. cm.
According to another embodiment of the present invention, a solvent-free silver reduced graphene oxide hybrid conductive ink is provided. The conductive ink comprises silver nanoparticles embedded on the reduced graphene oxide surfaces, ammonium quaternary ion which is choline chloride and deionized water. The size range of silver nanoparticles is 8 to 15 nm. FIG. 2 shows a chemical structure of the solvent-free silver-reduced graphene oxide hybrid conductive ink, according to an embodiment of the present invention. With respect to FIG. 2, the reduced graphene oxide can be seen which gets reduced by adding sodium hydroxide and is functionalized with choline chloride. The silver nanoparticles are embedded on the reduced graphene oxide surfaces. EXAMPLE 1
FIG. 3 shows a process flow for the formation of a new graphene-based hybrid conductive ink, as an exemplary embodiment of the present invention. With respect to FIG. 3, the process is started (301) and a 1 mg/ml aqueous solution of graphene oxide is sonicated and stirred for atleast 30 minutes (302). An optimum amount of choline chloride is added (303) to form a mixture. The mixture is stirred at 60°C for 1 hour (304). Further, 0.2M silver nitrate solution is added to the mixture and the mixture is stirred for 15 minutes (305). The reaction is made to carry out by keeping the mixture without agitation at 60°C for at least 21 hours (306). The mixture is heated while stirring up to a temperature of 80°C for at least 1 hour (307). Further, 2 ml of 8M solution of sodium hydroxide is dropwise added to the mixture and the mixture is stirred for at least 4 hours (308). The composite/precipitates of silver-reduced graphene oxide (Ag/rGO) is formed and separated by centrifugation at an rpm of 10000 for at least 1 hour (309). The composite of silver-reduced graphene oxide (Ag/rGO) is rinsed with deionised water (310). The composite of silver-reduced graphene oxide (Ag/rGO) is dispersed in deionized water (311) and sonicated for at least 48 hours (312). The process end and the conductive ink is synthesized (313).
According to an embodiment of the present invention, the graphene oxide (GO) solution is mixed with Choline Chloride (ChCl) to functionalize the graphene oxide. Silver nitrate (AgNOs) aqueous is added in the GO mixture which is used as a source of silver nanoparticles (Ag NPs) for the improvement of the conductivity of the GO. Sodium hydroxide (NaOH) functions as a reducing agent to form Ag NPs and reduced graphene oxide (rGO). The process is done at temperature 80°C. The mixture of the Ag-rGO hybrid mixture is centrifuged at 10000 rpm for 60 min to separate the composite. Once centrifugation is completed, the unwanted liquid is removed, followed by rinsing the composite with deionized water. The Ag/rGO hybrid composite is dispersed in deionized water and sonicated for 48h. Once completed it is ready to be function as solvent-free Ag/rGO hybrid conductive ink.
The conductive ink has a good dispersity in water and reduced agglomeration of Ag/rGO composite. The conductive ink is compatible for inkjet printing method. As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its essential characteristics. The present embodiments is, therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and all changes which come within therefore intended to be embraced therein.

Claims

1. A method of synthesizing solvent-free silver reduced graphene oxide hybrid conductive ink, is characterized by the step of:
(a) preparing an aqueous solution of graphene oxide by mixing a predetermined amount of graphene oxide in water and sonicating the aqueous solution of graphene oxide for a predetermined time of at least 30 minutes;
(b) stirring the sonicated aqueous solution of graphene oxide for at least 30 minutes;
(c) dropwise adding a solution of a quaternary ammonium compound to the aqueous solution of graphene oxide to form a mixture and stirring the mixture for at least 60 minutes at a predetermined rpm;
(d) heating the mixture in a silicon bath up to predetermined temperature of 58°C to 62°C while stirring the mixture at the predetermined rpm for at least 60 minutes;
(e) adding a solution of silver nitrate into the mixture and stirring the mixture for at least 15 minutes at the predetermined rpm;
(f) keeping the mixture without stirring at 60°C for at least a predetermined time period of 21 hours;
(g) heating the mixture up to 78°C to 80°C for at least 60 minutes while stirring the mixture at the predetermined rpm;
(h) dropwise adding a reducing agent in the mixture and stirring the mixture for at least 4-5 hours at the predetermined rpm of 1000 to 1200;
(i) centrifuging the mixture to separate out silver-reduced graphene oxide composite, wherein centrifuging is done at 10000 rpm for at least 60 minutes;
(j) rinsing the silver-reduced graphene oxide composite with deionized water; and
(k) mixing the rinsed silver-reduced graphene oxide composite with deionized water.
2. The method as claimed in claim 1, wherein the predetermined amount of graphene oxide is between 1 to 1.5 mg/mL.
3. The method as claimed in claim 1, wherein the quaternary ammonium compound is choline chloride.
4. The method as claimed in claim 1, wherein the quaternary ammonium compound is used in a range of 30 to 40 % v/v.
5. The method as claimed in claim 1, wherein the solution of silver nitrate is between 13 to 15 % v/v for concentration of 0.2M to 0.5M.
6. The method as claimed in claim 1, wherein the reducing agent is sodium hydroxide, wherein the solution of sodium hydroxide is added in an amount of 8 to 16 % v/v for 8M.
7. The method as claimed in claim 1, wherein the water is used as a dispersant, wherein the water is added in an amount of 2.5 to 5mL.
8. The method as claimed in claim 1, wherein the predetermined rpm is 1000.
9. A solvent-free silver reduced graphene oxide hybrid conductive ink, characterized in that the conductive ink comprises of:
silver nanoparticles;
reduced graphene oxide, wherein the silver nanoparticles are embedded on the reduced graphene oxide surfaces;
ammonium quaternary ion; and
deionized water.
10. The conductive ink as claimed in claim 12, wherein a conductivity of the conductive ink is in a range of 2000 to 3000 uS cm 1.
11. The conductive ink as claimed in claim 12, wherein a viscosity of the conductive ink is in a range of 1.0 to 2.0 cP at a temperature of 24°C.
12. The conductive ink as claimed in claim 12, wherein a resistivity of a printed film obtained by using the conductive ink is 10 4 ohm. cm.
PCT/MY2019/050125 2018-12-28 2019-12-23 Method of synthesizing solvent-free silver reduced graphene oxide hybrid conductive ink WO2020139070A1 (en)

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