WO2019051382A1

WO2019051382A1 - Nanosheet and method for the manufacture thereof

Info

Publication number: WO2019051382A1
Application number: PCT/US2018/050214
Authority: WO
Inventors: Yang Zhong; Lei Liu; Jing Jiang; Li Zhang; Kexin CHEN; Zhaobo TIAN; Quanhong YANG; Wei LV
Original assignee: Rogers Corporation; Tsinghua University
Priority date: 2017-09-11
Filing date: 2018-09-10
Publication date: 2019-03-14

Abstract

In an embodiment, a method for preparing a nanosheet comprises mixing a raw material having a hexagonal crystal structure, an acid, and a salt to form the nanosheet having a hexagonal crystal structure; wherein the raw material comprises at least one of a hexagonal boron nitride, a hexagonal molybdenum disulphide, a hexagonal graphite, or a hexagonal tungsten disulphide; and isolating the nanosheet.

Description

NANOSHEET AND METHOD FOR THE MANUFACTURE THEREOF

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Chinese Patent Application Number

201710811309.2 filed September 11, 2017 and Chinese Patent Application Number

201711476954.X filed December 29, 2017. The related applications are incorporated herein in their entirety by reference.

BACKGROUND

[0001] The discovery of monolayer graphene sheets proved that two-dimensional materials with only one layer of atoms can stably exist with or without substrate support. Mono- and few-layered graphene sheets have since stimulated much excitement not only because of their excellent mechanical, electrical, and thermal properties, but also because their preparation could be industrially achieved for large-scale production. Hexagonal boron nitride (h-BN), sometimes called white graphite, is structurally analogous to graphite, with the layered sheets similarly held together by van der Waals forces. Compared to the all-carbon structure of graphene, each hexagonal boron nitride (h-BN) sheet is composed of boron and nitrogen atoms alternatively positioned in the planar hexagonal crystal structure. In contrast to graphite, h-BN has benefits such as being stable in oxygen environments at temperatures as high as 800 degrees Celsius (°C).

[0002] While some methods have been developed to produce boron nitride nanosheets, these methods are generally difficult to achieve or are not suitable for commercial production. For example, while boron nitride nanosheets can be more easily prepared by methods such as milling or ultrasonication, these methods typically greatly reduce the lateral dimensions of the boron nitride crystals. Alternatively, while high quality boron nitride nanosheets can be formed using vapor deposition, yield is low, making it difficult to achieve commercial production.

Further disadvantages with vapor deposition include the fact that the resultant two-dimensional h-BN nanostructures are supported on the metal surfaces and thus are not available in freestanding forms for applications such as for coatings and composites.

[0003] Accordingly, an improved method for successfully preparing hexagonal boron nitride nanosheets is desired.

BRIEF SUMMARY

[0004] Disclosed herein is a method of preparing a nanosheet and the nanosheet made therefrom. In an embodiment, a method for preparing a nanosheet comprises mixing a raw material having a hexagonal crystal structure, an acid, and a salt to form the nanosheet having a hexagonal crystal structure; wherein the raw material comprises at least one of a hexagonal boron nitride, a hexagonal molybdenum disulphide, a hexagonal graphite, or a hexagonal tungsten disulphide; and isolating the nanosheet.

[0005] Also disclosed herein is a composite material that comprises a polymer matrix; and the nanosheet dispersed in the polymer matrix.

[0006] Additionally described herein is a thermal management assembly comprising the composite material and an article comprising the nanosheet.

[0007] The above described and other features are exemplified by the following figures, detailed description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following Figures are exemplary embodiments, which are provided to illustrate the method of making the nanosheets and the nanosheets made therefrom. The figures are illustrative of the examples, which are not intended to limit devices made in accordance with the disclosure to the materials, conditions, or process parameters set forth herein.

[0009] FIG. 1 is a transmission electron microscopy image of the morphology of the hexagonal boron nitride nanosheet synthesized in Example 12;

[0010] FIG. 2 is a scanning electron microscopy image of the morphology of the hexagonal boron nitride nanosheet synthesized in Example 12;

[0011] FIG. 3 is an atomic force microscopy image of the morphology of the hexagonal boron nitride nanosheet synthesized in Example 12;

[0012] FIG. 4 is a transmission electron microscopy image of the morphology of the graphene nanosheet synthesized in Example 13; and

[0013] FIG. 5 is an atomic force microscopy image of the morphology of the graphene nanosheet synthesized in Example 13.

DETAILED DESCRIPTION

[0014] Prior methods of producing hexagonal boron nitride nanosheets have suffered from either complicated, expensive experimental procedures that limit commercial fabrication or from abusive fabrication processes that significantly reduce the lateral dimensions of the nanosheets. It was surprisingly discovered that a hexagonal boron nitride nanosheet could be prepared by mixing a raw material having a hexagonal crystal structure, an acid, and a salt to form the hexagonal nanosheet; and isolating the nanosheet. The present method is simple to perform and can enable the high- volume preparation of two-dimensional nanosheets. Due to the universality of the present method, it can also be applied to the formation of various other nanosheets, such as molybdenum disulphide nanosheets, graphite nanosheets (for example, graphene nanosheets), and hexagonal tungsten disulphide nanosheets. Additionally, both the acid and the salt can be recycled, increasing the suitability of the process for mass production and industrial applications.

[0015] The raw material can comprise at least one of a hexagonal boron nitride, a hexagonal molybdenum disulphide, a hexagonal graphite, or a hexagonal tungsten disulphide. As used herein, the term "raw material" refers to the material as received from a supplier and could also be referred to as an "as received material". The raw material can comprise a hexagonal boron nitride. The raw material can have a layered structure comprising multiple layers of a hexagonal lattice material. The respective layers can be held together by van der Waals forces. The raw material can comprise particles having an average of greater than or equal to 150 layers, or greater than or equal to 250 layers, or 150 to 1,000 layers. The raw material can comprise particles having a D50 value by weight of greater than or greater than or equal to 2 micrometers, or 2 to 10 micrometers. The particle size can be determined using dynamic light scattering.

[0016] The acid can have a pKa of less than or equal to 8, or less than or equal to 4, or less than or equal to 2, or less than or equal to 0, or -10 to 0. The acid can comprise a strong acid, for example, that completely dissociates in an aqueous solution. The acid can comprise at least one of carbonic acid, chloric acid, chloro sulfuric acid, hydrobromic acid, hydrochloric acid, hypochlorous acid, hydrofluoric acid, hydroiodic acid, perchloric acid, nitric acid, or sulfuric acid. The acid can comprise at least one of sulfuric acid, nitric acid, perchloric acid,

hypochlorous acid, hydrochloric acid, carbonic acid, or hydrofluoric acid.

[0017] The salt can comprise at least one of ammonium chloride, ammonium fluoride, potassium chloride, potassium permanganate, potassium sulfate, sodium chloride, sodium fluoride, or sodium sulfate.

[0018] The mixture can have a pH of 2 to 5, or 3 to 4. The mixture can comprise 0.05 to 5 moles (mol), or 0.2 to 2.5 mol, or 0.5 to 1.5 mol of the acid per liter of the mixture. The mixture can comprise 0.05 to 5 mol, or 0.2 to 2.5 mol, or 0.5 to 1.5 mol of the salt per liter of the mixture. The mixture can have a weight ratio of the salt to the raw material, for example, to the boron nitride of 0.1 : 1 to 5: 1, or 0.5: 1 to 1 :0.5, or 0.9: 1 to 1 :0.9. The mixture can comprise less than or equal to 1 weight percent (wt%), or 0.0001 to 1 wt% of water based on the total weight of the mixture.

[0019] The mixture can further comprise a dispersant to improve dispersion of the raw material. The type of dispersant can depend on the type of raw material. The dispersant can be a surfactant. The surfactant can be anionic, nonionic, cationic, or zwitterionic. The surfactant can be anionic.

[0020] Among the anionic surfactants that can be used are the alkali metal, alkaline earth metal, ammonium and amine salts of organic sulfuric reaction products having in their molecular structure a C_8-36 or C_8-22 alkyl or acyl group and a sulfonic acid or sulfuric acid ester group. In an embodiment, the dispersant comprises at least one of sodium dodecyl sulfate, sodium lauryl sulfate, sodium laureth sulfate, sodium dioctyl sulfosuccinate, sodium dihexyl sulfosuccinate, perfluorooctane sulfonate, perfluorooctanoic acid, or sodium

dodecylbenzenesulfonate. In an embodiment, the dispersant comprises sodium dodecyl sulfate.

[0021] Nonionic surfactants can be used and can include a C_8-22 aliphatic alcohol ethoxylate having about 1 to about 25 moles of ethylene oxide and having have a narrow homolog distribution of the ethylene oxide ("narrow range ethoxylates") or a broad homolog distribution of the ethylene oxide ("broad range ethoxylates"); and for example, Cio-20 aliphatic alcohol ethoxylates having about 2 to about 18 moles of ethylene oxide. Examples of commercially available nonionic surfactants of this type are TERGITOL 15-S-9 (a condensation product of Ci i-15 linear secondary alcohol with 9 moles ethylene oxide), TERGITOL 24-L- NMW (a condensation product of C12-14 linear primary alcohol with 6 moles of ethylene oxide) with a narrow molecular weight distribution, from Dow. Other nonionic surfactants that can be used include polyethylene, polypropylene, or polybutylene oxide condensates of G5-12 alkyl phenols, for example, compounds having 4 to 25 moles of ethylene oxide per mole of C₆-i2 alkylphenol, for example, 5 to 18 moles of ethylene oxide per mole of C₆-i2 alkylphenol.

Commercially available surfactants of this type include Igepal CO-630, TRITON X-45, X-l 14, X-100 and X102, TERGITOL™ N- 10, TERGITOL™ N-100X, and TERGITOL™ N-6 (all polyethoxylated 2,6,8-trimethyl-nonylphenols or mixtures thereof) from Dow.

[0022] The mixture can comprise 0.01 to 10 wt%, or 0.1 to 5wt % of the dispersant, based on the total weight of the mixture.

[0023] The mixture can be stirred at a temperature of 0 to 200 degrees Celsius (°C), or 20 to 100°C, or 50 to 200°C. The mixture can be stirred for 10 minutes (min) to 72 hours (h), or 1 to 72 hours, or 12 to 72 hours, or 20 to 36 hours. When reduced mixing times are used, for example, 10 minutes to 10 hours, the mixture can be mixed at an increased temperature, for example, of 50 to 200°C, or 80 to 200°C. The mixing can comprise wet ball mixing. The mixing can comprise stirring, for example, with a magnetic stir bar. The mixing can comprise ultrasonically vibrating the mixture. The mixture can be ultrasonically vibrated for 1 to 5 hours, or 1 to 3 hours. [0024] The nanosheet can be isolated from the mixture by a variety of methods. For example, the nanosheet can be isolated by at least one of evaporation, heating, suction filtration, or centrifugation. The nanosheet can be rinsed one or more times with a solvent to remove or reduce the amount of at least one of residual salt, acid, or impurities. The solvent can comprise at least one of an organic solvent, chloroform, or water. The organic solvent can comprise at least one of a Ci-6 alkanol (for example, ethanol, methanol, propanol (e.g. n-propanol or isopropanol), butanol, pentanol, or hexanol), a polyol (for example, glycerin, pentaerythritol, ethylene glycol, or sucrose), a polyether (for example, polyethylene glycol or polypropylene glycol), or tetrahydrofuran. The solvent can comprise at least one of ethanol, methanol, or water.

[0025] The nanosheets can have an average number of layers of 1 to 100 layers, or 1 to 30 layers, or 1 to 5 layers. The nanosheets can have an average thickness of less than or equal to 50 nanometers (nm), or less than or equal to 15 nm, 0.2 to 10 nm, or 0.3 to 2 nm. The nanosheets can have a surface area of 50 nanometers squared (nm²) to 500 micrometers squared, or 0.2 to 100 micrometers squared, or 0.5 to 50 micrometers squared. The number of layers and the surface area of the nanosheets can be determined by various methods including scanning electron microscopy (SEM), regular or high resolution transmission electron microscopy (TEM or HR-TEM), or atomic force microscopy (AFM).

[0026] The nanosheets can have a specific surface area of 20 to 100 meters squared per gram (m²/g), or 70 to 100 m²/g, or 20 to 90 m²/g as determined using the Brunauer-Emmett- Teller (BET) method.

[0027] The nanosheets can have a hexagonal lattice structure. The nanosheets can comprise hexagonal boron nitride nanosheets. The hexagonal boron nitride nanosheets can have a high peak intensity ratio as determined by X-ray diffractometry of 7 to 70, or 15 to 66, or 20 to 66. As used herein, the peak intensity ratio is the ratio of I002/I100, where I002 is the intensity of the (002) diffraction line and I100 is the intensity of the (100) diffraction line. The high peak intensity ratio is indicative of a highly crystalline material and reflects the increase in the relative amount of boron nitride surface exposed in the Z-axis direction.

[0028] The nanosheets can comprise hexagonal boron nitride nanosheets. The hexagonal boron nitride nanosheets can have a thermal conductivity, according to ASTM

E1225-13, of 1 to 2,000 watts per meter-Kelvin (W/m K) or more, or 1 to 2,000 W/m K, or 10 to 1,800 W/m K, or 100 to 1,600 W/m K, or 1,500 to 2,000 W/m K. The hexagonal boron nitride nanosheets can also have an electrical resistivity of 5 to 15 ohm-centimeters (Ω-cm) at room temperature (for example, at 25°C), or 8 to 12 Ω-cm, a dielectric constant of 3 to 4, for example 3.01 to 3.36 at room temperature at 5.75 x 10⁹ hertz (Hz), and a loss tangent of 0.0001 to 0.001, or 0.0003 to 0.0008 at room temperature at 5.75 x 10⁹ Hz, or 0.0003 to 0.0008.

[0029] The present method can result in an efficient, low-cost preparation of nanosheets to open up a new shortcut for further improvement of the quality and output of two-dimensional nanosheets that can lay a strong foundation for the manufacture of an improved, insulating composite material with high thermal conductivity. The composite material can comprise the nanosheets and a polymer. The polymer can comprise a thermoset polymer or a thermoplastic polymer. The composite material can be free of void spaces. Conversely, the composition material (i.e. the polymer) can be a foam comprising a plurality of void spaces.

[0030] Thermoset polymers are derived from thermosetting monomers or prepolymers (resins) that can irreversibly harden and become insoluble with polymerization or cure, which can be induced by heat or exposure to radiation (e.g., ultraviolet light, visible light, infrared light, or electron beam (e-beam) radiation). Thermoset polymers include alkyds, bismaleimide polymers, bismaleimide triazine polymers, cyanate ester polymers, benzocyclobutene polymers, benzoxazine polymers, diallyl phthalate polymers, epoxies, hydroxymethylfuran polymers, melamine-formaldehyde polymers, phenolics (including phenol-formaldehyde polymers such as novolacs and resoles), benzoxazines, polydienes such as polybutadienes (including

homopolymers and copolymers thereof, e.g. poly(butadiene-isoprene)), polyisocyanates, polyureas, polyurethanes, triallyl cyanurate polymers, triallyl isocyanurate polymers, certain silicone polymers, and polymerizable prepolymers (e.g., prepolymers having ethylenic unsaturation, such as unsaturated polyesters, polyimides), or the like. The prepolymers can be polymerized, copolymerized, or crosslinked, e.g., with a reactive monomer such as styrene, alpha-methylstyrene, vinyltoluene, chloro styrene, acrylic acid, (meth)acrylic acid, a (Ci-6 alkyl)acrylate, a (Ci-6 alkyl) methacrylate, acrylonitrile, vinyl acetate, allyl acetate, triallyl cyanurate, triallyl isocyanurate, or acrylamide. The weight average molecular weight of the prepolymers can be 400 to 10,000 Daltons based on polystyrene standards.

[0031] As used herein, the term "thermoplastic" refers to a material that is plastic or deformable, melts to a liquid when heated, and freezes to a brittle, glassy state when cooled sufficiently. Examples of thermoplastic polymers that can be used include cyclic olefin polymers (including polynorbornenes and copolymers containing norbornenyl units, for example, copolymers of a cyclic polymer such as norbornene and an acyclic olefin such as ethylene or propylene), fluoropolymers (e.g., polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), fluorinated ethylene-propylene (FEP), polytetrafluoroethylene (PTFE), poly(ethylene- tetrafluoroethylene (PETFE), perfluoroalkoxy (PFA)), polyacetals (e.g., polyoxyethylene and polyoxymethylene), poly(Ci-6 alkyl)acrylates, polyacrylamides (including unsubstituted and mono-N- and di-N-(C_1-8 alkyl)acrylamides), polyacrylonitriles, polyamides (e.g., aliphatic polyamides, polyphthalamides, and polyaramides), polyamideimides, polyanhydrides, polyarylene ethers (e.g., polyphenylene ethers), polyarylene ether ketones (e.g., polyether ether ketones (PEEK) and polyether ketone ketones (PEKK), polyarylene ketones, polyarylene sulfides (e.g., polyphenylene sulfides (PPS)), polyarylene sulfones (e.g., polyethersulfones (PES), polyphenylene sulfones (PPS), and the like), polybenzothiazoles, polybenzoxazoles, polybenzimidazoles, polycarbonates (including homopolycarbonates and polycarbonate copolymers such as polycarbonate-siloxanes, polycarbonate-esters, and polycarbonate-ester- siloxanes), polyesters (e.g., polyethylene terephthalates, polybutylene terephthalates, polyarylates, and polyester copolymers such as polyester-ethers), polyetherimides (including copolymers such as polyetherimide-siloxane copolymers), polyimides (including copolymers such as polyimide-siloxane copolymers), poly(Ci-6 alkyl)methacrylates, polymethacrylamides (including unsubstituted and mono-N- and di-N-(C_1-8 alkyl)acrylamides), polyolefins (e.g., polyethylenes, such as high density polyethylene (HDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE), polypropylenes, and their halogenated derivatives (such as polytetrafluoroethylenes), and their copolymers, for example ethylene-alpha-olefin copolymers, polyoxadiazoles, polyoxymethylenes, polyphthalides, polysilazanes, polysiloxanes (silicones), polystyrenes (including copolymers such as acrylonitrile-butadiene-styrene (ABS) and methyl methacrylate-butadiene-styrene (MBS)), polysulfides, polysulfonamides, polysulfonates, polysulfones, polythioesters, polytriazines, polyureas, polyurethanes, vinyl polymers (including polyvinyl alcohols, polyvinyl esters, polyvinyl ethers, polyvinyl halides (e.g., polyvinyl fluoride), polyvinyl ketones, polyvinyl nitriles, polyvinyl thioethers, and polyvinylidene fluorides), or the like. A mixture comprising at least one of the foregoing thermoplastic polymers can be used.

[0032] The nanosheets can be contained in the composite in an amount sufficient to provide the composite suitable thermal conductivity, dielectric constant, and mechanical properties. The nanosheets can be present in the composite in an amount of 1 to 90 wt%, or 1 to 85 wt%, or 5 to 80 wt%, or 1 to 20 wt% based on a total weight of the composite. The composite can have a thermal conductivity of 1 W/m K or more, or of 2 W/m K or more, or 4 W/m K or more, or 1 to 50 W/m K measured according to ASTM D5470-12. The composite can have a dielectric constant of 1.5 to 15, or 3 to 12, or 4 to 10, measured, for example, at room temperature at 5.75 x 10⁹ Hz. The composite can have a coefficient of thermal expansion of 1 to 50 parts per million per degree Celsius (ppm/°C), or 2 to 40 ppm/°C, or 4 to 30 ppm/°C.

[0033] The composite can further comprise an additional filler, for example, a filler to adjust the dielectric properties of the composite. A low coefficient of expansion filler, for example, at least one of glass beads, silica, or ground micro-glass fibers, can be used. A thermally stable fiber, for example, an aromatic polyamide, or a polyacrylonitrile, can be used. Representative fillers include at least one of titanium dioxide (rutile and anatase), barium titanate (BaTiC ), aiT Ow, strontium titanate, fused amorphous silica, corundum, wollastonite, aramide fibers (for example KEVLAR™ from DuPont), fiberglass, quartz, aluminum nitride, silicon carbide, beryllia, alumina, magnesia, mica, talcs, nanoclays, aluminosilicates (natural and synthetic), or fumed silicon dioxide (for example Cab-O-Sil, available from Cabot Corporation). The composite can comprise the raw material.

[0034] The nanosheets, for example, the hexagonal boron nitride nanosheets can be used in thermal management applications, for example, in a thermal management assembly. The thermal management assembly can comprise the composite material, wherein the composite material is in contact with at least one external heat transfer surface to conduct heat away from the at least one external heat transfer surface. The composite material can be disposed between an external surface of a heat-generating member and an external surface of a heat-dissipative member to provide a thermally conductive transfer there between. The heat-generating member can be an electronic component or circuit board, and the heat dissipative member can be a heat sink or circuit board.

[0035] An article can comprise the nanosheets. The article can be for use, for example, in a sewage treatment application, a military application, or an aviation application.

[0036] The following examples are provided to illustrate the method of preparing the nanosheets. The examples are merely illustrative and are not intended to limit devices made in accordance with the disclosure to the materials, conditions, or process parameters set forth therein. Obviously, the examples described are merely some, not all, of the examples of the present disclosure. All other examples obtained by those skilled in the art on the basis of the examples in the present disclosure, without making any inventive effort, are included in the scope of protection of the present disclosure. The following examples, and features therein, can be combined with each other where no conflict arises.

EXAMPLES

[0037] In the examples, x-ray diffraction (XRD) was used to analyze the boron nitride nanosheets by determining the ratio of I002 to I100, where I002 is the intensity of the (002) diffraction line and I100 is the intensity of the (100) diffraction line.

[0038] Transmission electron microscopy images were obtained using a JEOL 2100 transmission electron microscope. [0039] Scanning electron microscopy images were obtained using a ZEISSV018 scanning electron microscope.

[0040] Atomic force microscopy images were obtained using a Nanoscope MultiMode V instrument (Digital Instruments/Bruker Systems), operated in the air tapping mode.

Examples 1-3: Effect of adding salt in the formation of a hexagonal boron nitride sheet

[0041] Three mixtures were prepared by mixing 1 gram (g) of raw hexagonal boron nitride (having a D50 particle size by weight of 20 micrometers, obtained from Merck

Performance Materials), 20 milliliters (mL) of 0.368 molar sulfuric acid, and in the case of Example 3, 1 g of sodium fluoride. The mixtures were stirred for the amount of times shown in Table 1 at a temperature of 0°C. After mixing, the mixtures were subjected to suction filtration and rinsed with ethanol. The boron nitride powders were centrifuged to further remove impurities such as sulfuric acid and sodium fluoride. The samples were then freeze-dried and subjected to an XRD analysis. The I002/I100 ratios of the XRD patterns were then compared to characterize intercalation efficacy.

[0042] Table 1 shows that the peak intensity ratio of the boron nitride nanosheets of Example 3, is almost three times that of Examples 1 and 2.

Examples 3-6: Effect of changing the stirring temperature

[0043] Three more mixtures (Examples 4-6) were prepared by mixing 1 g of raw hexagonal boron nitride, 20 milliliters (mL) of 0.368 molar sulfuric acid, and 1 g of sodium fluoride. The mixtures were stirred for 24 hours at the temperatures indicated in Table 2. After mixing, the mixtures were subjected to suction filtration and rinsed with ethanol. The boron nitride powders were centrifuged to further remove impurities such as sulfuric acid and sodium fluoride. The samples were then freeze-dried and subjected to an XRD analysis. The I002/I100 ratios of the XRD patterns were then compared to characterize intercalation efficacy. [0044] Table 2 shows that the peak intensity ratio of the boron nitride nanosheets increases with increasing stirring temperature to obtain a peak intensity ratio of more than 32 as shown in Example 6.

Examples 4, 7, and 8: Effect of changing the stirring time

[0045] Two more mixtures (Examples 7 and 8) were prepared by mixing 1 g of raw hexagonal boron nitride, 20 mL of 0.368 molar sulfuric acid, and 1 g of sodium fluoride. The mixtures were stirred at 25°C for the times indicated in Table 3. After mixing, the mixtures were subjected to suction filtration and rinsed with ethanol. The boron nitride powders were centrifuged to further remove impurities such as sulfuric acid and sodium fluoride. The samples were then freeze-dried and subjected to an XRD analysis. The I002/I100 ratios of the XRD patterns were then compared to characterize intercalation efficacy.

[0046] Table 3 shows that the peak intensity ratio of the boron nitride nanosheets increases with increasing stirring time to obtain a peak intensity ratio.

Examples 4 and 9-12: Effect of changing the sodium fluoride concentration

[0047] Four more mixtures (Examples 9-12) were prepared by mixing 1 g of raw hexagonal boron nitride, 20 mL of 0.368 molar sulfuric acid, and an amount of sodium fluoride as indicated in Table 4. The mixtures were stirred at 25°C for 24 h. After mixing, the mixtures were subjected to suction filtration and rinsed with ethanol. The boron nitride powders were centrifuged to further remove impurities such as sulfuric acid and sodium fluoride. The samples were then freeze-dried and subjected to an XRD analysis. The I002/I100 ratios of the XRD patterns were then compared to characterize intercalation efficacy. Table 4

Example 9 10 4 11 12

Stirring Temperature (°C) 25 25 25 25 25

Stirring Time (h) 24 24 24 24 24

Sodium Fluoride Added (g) 0.1 0.5 1 1.5 5

Peak Intensity Ratio 13.4 19.5 28.5 50.3 65.7

[0048] Table 4 shows that the peak intensity ratio of the boron nitride nanosheets increases with increasing amount of sodium fluoride added to obtain a peak intensity ratio of more than 65 as shown in Example 12.

[0049] It is clear from the examples that different boron nitride intercalation and delamination effects can be obtained by adjusting three different experimental conditions: the stirring temperature, stirring time, and amount of sodium fluoride added. XRD analysis showed that the intensity of the (002) peak relative to (100) peak in the boron nitride can be increased by adjusting the experimental conditions of the intercalation and delamination, thereby modifying the relative amount of boron nitride surface exposed in the Z-axis direction.

[0050] FIG. 1, FIG. 2, and FIG. 3, respectively, are transmission electron microscopy, scanning electron microscopy, and an atomic force microscopy images of the hexagonal boron nitride nanosheets synthesized in Example 12.

Example 13 : Effect of adding salt in the formation of a graphene sheet

[0051] A mixture was prepared by mixing 1 g of raw graphite (having a D50 particle size by weight of 0.28 micrometers, obtained from Tianheda. Co.) and 20 mL of 0.368 molar sulfuric acid. The mixture was stirred for 24 hours at a temperature of 25°C. After mixing, the mixture were subjected to suction filtration and rinsed with ethanol. The powder was centrifuged to further remove impurities such as sulfuric acid.

[0052] FIG. 4 and FIG. 5, respectively, are atomic force microscopy and transmission electron microscopy images of the graphene synthesized in Example 13.

[0053] Set forth below are various non-limiting aspects of the present disclosure.

[0054] Aspect 1 : A method for preparing a nanosheet, the method comprising: mixing a raw material having a hexagonal crystal structure, an acid, and a salt to form the nanosheet having a hexagonal crystal structure; wherein the raw material comprises at least one of a hexagonal boron nitride, a hexagonal molybdenum disulphide, a hexagonal graphite, or a hexagonal tungsten disulphide; and isolating the nanosheet.

[0055] Aspect 2: The method of Aspect 1, wherein the isolating comprises filtering the mixture via suction filtration. [0056] Aspect 3 : The method of Aspect 2, wherein the filtering comprises rinsing with at least one of ethanol or water.

[0057] Aspect 4: The method of any one or more of the preceding aspects, wherein the isolating comprises centrifuging the mixture.

[0058] Aspect 5: The method of any one or more of the preceding aspects, wherein the raw material comprises a hexagonal boron nitride.

[0059] Aspect 6: The method of any one or more of the preceding aspects, wherein the acid has a pKa of less than or equal to 8, or less than or equal to 4, or less than or equal to 2, or less than or equal to 0.

[0060] Aspect 7: The method of any one or more of the preceding aspects, wherein the acid comprises at least one of carbonic acid, chloric acid, chloro sulfuric acid, hydrobromic acid, hydrochloric acid, hypochlorous acid, hydrofluoric acid, hydroiodic acid, perchloric acid, nitric acid, or sulfuric acid.

[0061] Aspect 8: The method of any one or more of the preceding aspects, wherein the mixture comprises a weight ratio of the salt to the raw material of 0.1 : 1 to 5 : 1.

[0062] Aspect 9: The method of any one or more of the preceding aspects, wherein the mixture has a pH of 2 to 5.

[0063] Aspect 10: The method of any one or more of the preceding aspects, wherein the mixture comprises 0.05 to 5 moles of the salt per liter of the mixture.

[0064] Aspect 11 : The method of any one or more of the preceding aspects, wherein the salt comprises at least one of ammonium chloride, ammonium fluoride, potassium chloride, potassium permanganate, potassium sulfate, sodium chloride, sodium fluoride, or sodium sulfate.

[0065] Aspect 12: The method of any one or more of the preceding aspects, wherein the mixture comprises less than or equal to 1 wt%, or 0.0001 to 1 wt% of water based on the total weight of the mixture.

[0066] Aspect 13 : The method of any one or more of the preceding aspects, wherein the mixing occurs for 10 minutes to 72 hours, or 1 to 72 hours, or 12 to 72 hours, or 20 to 36 hours.

[0067] Aspect 14: The method of any one or more of the preceding aspects, wherein the mixing occurs at a temperature of 0 to 200°C, or 20 to 100°C, or 50 to 200°C.

[0068] Aspect 15: The method of any one or more of the preceding aspects, wherein if the mixing occurs for a mixing time of 10 minutes to 10 hours, then the mixing occurs at a temperature of 50 to 200°C. [0069] Aspect 16: The method of any one or more of the preceding aspects, wherein the nanosheet has an average thickness of less than or equal to 50 nm, or less than or equal to 15 nanometers, 0.2 to 10 nm, or 0.3 to 2 nm.

[0070] Aspect 17: The method of any one or more of the preceding aspects, wherein the nanosheet comprises an average of 1 to 100 layers, or 1 to 30 layers, or 1 to 5 layers.

[0071] Aspect 18: The method of any one or more of the preceding aspects, wherein the nanosheet has a surface area of 50 nm² to 500 micrometers squared, or 0.2 to 100 micrometers squared, or 0.5 to 50 micrometers squared.

[0072] Aspect 19: The method of any one or more of the preceding aspects, wherein the nanosheet has a peak intensity ratio of 7 to 70, or 15 to 66, or 20 to 66, where the peak intensity ratio is the ratio of I002/I100, where I002 is the intensity of the (002) diffraction line and I100 is the intensity of the (100) diffraction line.

[0073] Aspect 20: The method of any one or more of the preceding aspects, further comprising mixing the nanosheet with a polymer to form a polymer composite material.

[0074] Aspect 21 : A composite material comprising: a polymer matrix; and the nanosheet of any one or more of the preceding aspects dispersed in the polymer matrix.

[0075] Aspect 22: The composite material of at least Aspect 21, wherein the composite material has a first and a second heat transfer surface.

[0076] Aspect 23 : The composite material of at least any one or more of Aspects 21 to

22, comprising 1 to 90 weight percent, or 5 to 80 weight percent, or 1 to 20 weight percent of the nanosheet, based on the total weight of the composite material.

[0077] Aspect 24: The composite material of at least any one or more of Aspects 21 to

23, wherein the composite material has an average thickness of 0.1 to 25 millimeters.

[0078] Aspect 25: The composite material of at least any one or more of Aspects 21 to

24, wherein the polymer matrix comprises at least one of a polyurethane, a silicone polymer, a polyolefin, a polyester, a polyamide, a fluorinated polymer, a polyalkylene oxide, polyvinyl alcohol, an ionomer, cellulose acetate, or a polystyrene.

[0079] Aspect 26: The composite material of at least any one or more of Aspects 21 to

25, wherein the polymer matrix is a compressible foam.

[0080] Aspect 27: The composite material of at least any one or more of Aspects 21 to

26, wherein the composite has one or more of a thermal conductivity of 1 W/m K or more, or of 2 W/m K or more, or 4 W/m K or more, or 1 to 50 W/m K measured according to ASTM D5470-12; a dielectric constant of 1.5 to 15, or 3 to 12, or 4 to 10, measured, for example, at 23°C at 5.75 x 10⁹ Hz; and a coefficient of thermal expansion of 1 to 50 ppm/°C, or 2 to 40 ppm/°C, or 4 to 30 ppm/°C. [0081] Aspect 28: A thermal management assembly comprising the composite material of at least one or more of Aspects 21 to 27, wherein the composite material is in contact with at least one external heat transfer surface to conduct heat away from the at least one external heat transfer surface.

[0082] Aspect 29: The thermal management assembly of at least Aspect 28, wherein the composite material is disposed between an external surface of a heat-generating member and an external surface of a heat-dissipative member to provide a thermally conductive transfer there between.

[0083] Aspect 30: The thermal management assembly of at least Aspect 29, wherein the heat-generating member is an electronic component or circuit board, and the heat dissipative member is a heat sink or circuit board.

[0084] Aspect 31 : An article comprising the nanosheet of any one or more of the preceding aspects.

[0085] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any appropriate materials, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any materials (or species), steps, or components, that are otherwise not necessary to the achievement of the function or objectives of the compositions, methods, and articles.

[0086] The terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The term "or" means "and/or" unless clearly indicated otherwise by context. Reference throughout the specification to "an aspect", "an embodiment", "another embodiment", "some embodiments", and so forth, means that a particular element (e.g., feature, structure, step, or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.

[0087] In general, the compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any ingredients, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated, conducted, or manufactured so as to be devoid, or substantially free, of any ingredients, steps, or components not necessary to the achievement of the function or objectives of the present claims.

[0088] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears. [0089] The endpoints of all ranges directed to the same component or property are inclusive of the endpoints, are independently combinable, and include all intermediate points and ranges. For example, ranges of "up to 25 wt%, or 5 to 20 wt%" is inclusive of the endpoints and all intermediate values of the ranges of "5 to 25 wt%," such as 10 to 23 wt%, etc.

[0090] The term "mixing" is inclusive of any method of combining, including dissolving, reacting, alloying, and the like; and the term "mixture" is inclusive of any combination, including blends, mixtures, alloys, reaction products, and the like. Also,

"combination comprising at least one of the foregoing" or "at least one of means that the list is inclusive of each element individually, as well as mixtures of two or more elements of the list, and mixtures of at least one element of the list with like elements not named.

[0091] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this disclosure belongs.

[0092] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0093] While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.

Claims

CLAIMS What is claimed is:

1. A method for preparing a nanosheet, the method comprising:

mixing a raw material having a hexagonal crystal structure, an acid, and a salt to form the nanosheet having a hexagonal crystal structure, wherein the raw material comprises at least one of a hexagonal boron nitride, a hexagonal molybdenum disulphide, a hexagonal graphite, or a hexagonal tungsten disulphide; and

isolating the nanosheet.

2. The method of Claim 1, wherein the isolating comprises filtering the mixture via suction filtration.

3. The method of Claim 2, wherein the filtering comprises rinsing, preferably rinsing with at least one of ethanol or water.

4. The method of any one or more of the preceding claims, wherein the isolating comprises centrifuging the mixture.

5. The method of any one or more of the preceding claims, wherein the raw material comprises a hexagonal boron nitride.

6. The method of any one or more of the preceding claims, wherein the acid has a pKa of less than or equal to 8, or less than or equal to 4, or less than or equal to 2, or less than or equal to 0.

7. The method of any one or more of the preceding claims, wherein the acid comprises at least one of carbonic acid, chloric acid, chloro sulfuric acid, hydrobromic acid, hydrochloric acid, hypochlorous acid, hydrofluoric acid, hydroiodic acid, perchloric acid, nitric acid, or sulfuric acid.

8. The method of any one or more of the preceding claims, wherein the mixture comprises a weight ratio of the salt to the raw material of 0.1 : 1 to 5 : 1.

9. The method of any one or more of the preceding claims, wherein the mixture comprises 0.05 to 5 moles of the salt per liter of the mixture.

10. The method of any one or more of the preceding claims, wherein the salt comprises at least one of ammonium chloride, ammonium fluoride, potassium chloride, potassium permanganate, potassium sulfate, sodium chloride, sodium fluoride, or sodium sulfate.

11. The method of any one or more of the preceding claims, wherein the mixture comprises less than or equal to 1 wt%, or 0.0001 to 1 wt% of water based on the total weight of the mixture.

12. The method of any one or more of the preceding claims, wherein the mixing occurs for 10 minutes to 72 hours, or 1 to 72 hours, or 12 to 72 hours, or 20 to 36 hours.

13. The method of any one or more of the preceding claims, wherein the mixing occurs at a temperature of 0 to 200°C, or 20 to 100°C, or 50 to 200°C.

14. The method of any one or more of the preceding claims, wherein if the mixing occurs for a mixing time of 10 minutes to 10 hours, then the mixing occurs at a temperature of 50 to 200°C.

15. The method of any one or more of the preceding claims, wherein the nanosheet has an average thickness of less than or equal to 50 nm, or less than or equal to 15 nanometers, 0.2 to 10 nm, or 0.3 to 2 nm.

16. The method of any one or more of the preceding claims, wherein the nanosheet comprises an average of 1 to 100 layers, or 1 to 30 layers, or 1 to 5 layers.

17. The method of any one or more of the preceding claims, wherein the nanosheet has a surface area of 50 nm² to 500 micrometers squared, or 0.2 to 100 micrometers squared, or 0.5 to 50 micrometers squared.

18. The method of any one or more of the preceding claims, wherein the nanosheet has a peak intensity ratio of 7 to 70, or 15 to 66, or 20 to 66, where the peak intensity ratio is the ratio of I002/I100, where I002 is the intensity of the (002) diffraction line and I100 is the intensity of the (100) diffraction line.

19. The method of any one or more of the preceding claims, further comprising mixing the nanosheet with a polymer to form a polymer composite material.

20. A composite material comprising:

a polymer matrix; and

the nanosheet of any one or more of the preceding claims dispersed in the polymer matrix.

21. The composite material of Claim 20, wherein the composite material has a first and a second heat transfer surface.

22. The composite material of any one or more of Claims 20 to 21, comprising 1 to 90 weight percent, or 5 to 80 weight percent, or 1 to 20 weight percent of the nanosheet, based on the total weight of the composite material.

23. The composite material of any one or more of Claims 20 to 22, wherein the composite material has an average thickness of 0.1 to 25 millimeters.

24. The composite material of any one or more of Claims 20 to 23, wherein the polymer matrix comprises at least one of a polyurethane, a silicone, a polyolefin, a polyester, a polyamide, a fluorinated polymer, a polyalkylene oxide, polyvinyl alcohol, an ionomer, cellulose acetate, or a polystyrene.

25. The composite material of any one or more of Claims 20 to 24, wherein the polymer matrix is a compressible foam.

26. A thermal management assembly comprising the composite material of one or more of Claims 20 to 25, wherein the composite material is in contact with at least one external heat transfer surface to conduct heat away from the at least one external heat transfer surface.

27. The thermal management assembly of Claim 26, wherein the composite material is disposed between an external surface of a heat-generating member and an external surface of a heat-dissipative member to provide a thermally conductive transfer there between.

28. The thermal management assembly of Claim 27, wherein the heat-generating member is an electronic component or circuit board, and the heat dissipative member is a heat sink or circuit board.

29. An article comprising the nanosheet of any one or more of the preceding claims.