Method for obtaining a graphene liquid dispersion

Abstract

The present invention relates to a method for obtaining a graphene liquid dispersion, to a graphene liquid dispersion and to uses thereof. In particular, the present invention relates to a method for solubilising graphite, characterised in that it comprises the following steps: 1) solubilising the graphite under an inert atmosphere so as to form a graphene solution; 2) oxidising the graphene solution obtained in step 1) so as to form an organic graphene dispersion; and 3) transferring the organic graphene dispersion obtained in step 2) into a viscous matrix so as to form a liquid graphene dispersion.

Description

[0001] PROCESS FOR OBTAINING A LIQUID DISPERSION OF GRAPHENE

[0002] Technical field

[0003] The present invention relates to the technical field of liquid graphene dispersions. The invention particularly relates to a method for obtaining a liquid graphene dispersion, a liquid graphene dispersion and its uses.

[0004] State of the art

[0005] Carbon, the basis of all organic molecules, is a fundamental constituent of all life forms known to date.

[0006] Considered one of the most abundant elements in the universe, carbon has several allotropic forms such as graphite and diamond.

[0007] Graphite is one of the crystalline forms of carbon organized according to a stack of graphene sheets presenting a hexagonal pattern.

[0008] Described in the 20th century, it was not until 2004 that graphene was isolated and considered a promising material due to its two-dimensional structure and remarkable properties.

[0009] Graphene is a versatile material with a large number of advantageous physical properties such as its electrical and thermal conductivity, mechanical strength, lightness, corrosion resistance, flexibility and transparency.

[0010] These advantages make it a material prized by industrialists for its use in very varied fields such as:

[0011] - modern electrical networks;

[0012] - energy-efficient light sources;

[0013] - semiconductors used in spintronic devices;

[0014] - more effective anti-corrosion coatings;

[0015] - water filtration for purification and desalination;

[0016] - optoelectronic communication systems;

[0017] - thermal;

[0018] - mechanics; and

[0019] - barrier materials, particularly hydrophobic ones.

[0020] Other applications less developed to date are also being considered, particularly in biomedicine and more specifically in tissue engineering.

[0021] Graphene, which does not occur naturally, can be obtained from graphite or methane. Depending on the production process, graphene sheets can come in different forms: single-layer graphene, double-layer graphene, or multi-layer graphene.

[0022] The fewer layers a graphene sheet has, the more expensive it is to produce and the higher its performance. Faced with this dilemma, manufacturers are forced to find cost / performance compromises based on the intended use.

[0023] Different techniques for isolating graphene are known, such as liquid phase mechanical exfoliation, chemical vapor deposition, graphite oxidation in acidic medium and the flash heating method.

[0024] However, several factors limit the industrialization of these processes, notably production costs requiring considerable resources for a yield and stability that are still too low.

[0025] There is therefore a need to develop alternative processes to current processes, making it possible to produce aggregate-free and stable graphene at lower cost and in larger quantities, preferably in the form of graphene dispersion.

[0026] Summary of the invention

[0027] To meet this need, the invention proposes a new method for obtaining a liquid dispersion of graphene.

[0028] This process includes the following steps:

[0029] 1) Solubilization of graphite carried out under an inert atmosphere forming a graphene solution

[0030] 2) Oxidation of the graphene solution obtained in step 1) forming the organic graphene dispersion; and

[0031] 3) Transfer of the organic graphene dispersion obtained in step 2) into a viscous matrix forming a liquid graphene dispersion.

[0032] Advantageously, the transfer into a viscous matrix makes it possible to improve stability and concentrate the liquid dispersion into graphene.

[0033] Such a method is particularly useful in the context of the invention, thus providing an alternative to the industrial production of graphene.

[0034] Preferably, the viscous matrix of step 3) has an absolute viscosity measured at 25°C using a rheometer of between 5 mPa.s and 100 Pa.s.

[0035] Advantageously, such viscosity makes it possible to obtain optimal stability, avoiding the phenomenon of reaggregation of the graphene sheets for at least 3 months.

[0036] According to a preferred object of the invention, step 1) of solubilization of graphite carried out under an inert atmosphere comprises the following steps: a) Intercalation of at least one alkali metal in graphite leading to a graphite intercalation compound; b) Chemical exfoliation combined with mechanical exfoliation of the graphite intercalation compound, characterized in that the graphite intercalation compound is mixed with a solvent in a turbulent regime having:

[0037] - a Reynolds number greater than 1000;

[0038] - a Froude number less than 1; and

[0039] - a shear rate lower than 400s-l, so as to obtain a graphene solution.

[0040] Advantageously, the combination of chemical and mechanical exfoliation of a graphite intercalation compound in a turbulent regime characterized by a particular Reynolds number, Froude number, and shear rate makes it possible to obtain an improved dissolution of the graphite intercalation compound.

[0041] More particularly, according to this embodiment the dissolution of the graphite intercalation compound in the solvent is improved by mechanical exfoliation, preferably obtained from the combination of shear, grinding and friction. The mechanical exfoliation produces a turbulent regime characterized by a Reynolds number of the system which compares the inertial effects to the viscous effects as well as the Froude number which compares the inertial effects to the effects of gravity. In other words, the Reynolds number, the Froude number and the shear rate make it possible to characterize the mechanical exfoliation of step b) for all systems. The Froude number, the Reynolds number and the shear rate therefore make it possible to characterize the mechanical exfoliation of step b) necessary to obtain an improved dissolution of the graphite intercalation compound in a solvent.

[0042] Preferably, the graphite intercalation compound is in the form of a binary compound of formula KC8.

[0043] Chemical exfoliation is preferably carried out by exposing the graphite intercalation compound to an aprotic polar solvent. Preferably, said aprotic polar solvent has a dielectric constant of between 5 and 200.

[0044] Preferably, chemical exfoliation is carried out with a graphite intercalation compound / aprotic polar solvent ratio of between 1 and 50g / L.

[0045] Advantageously, the ratio of graphite intercalation compound / polar aprotic solvent associated with mechanical exfoliation makes it possible to solubilize good quality graphene. Preferably at least one sheet, even more preferably each graphene sheet obtained according to the invention has a sheet thickness of less than 10 atomic layers, preferably less than 5 atomic layers.

[0046] According to another subject, the invention relates to a liquid dispersion of graphene without aggregates capable of being obtained by the method according to the invention. Advantageously, the liquid dispersion of graphene according to the invention does not contain any aggregates, in particular the aggregates obtained by a phenomenon of reaggregation of the graphene sheets and this for at least 3 months.

[0047] Preferably, the liquid graphene dispersion according to the invention has an absolute viscosity measured at 25°C using a rheometer of between 5 mPa.s and 100 Pa.s.

[0048] Advantageously, the viscosity of the liquid graphene dispersion makes it possible to obtain a graphene concentration that is particularly interesting for industrial use.

[0049] Thus, the liquid dispersion of graphene preferably comprises between 0.1 and 50g / L of graphene.

[0050] Finally, the invention also aims at the use of the liquid dispersion of graphene according to the invention in the manufacture of high-performance additives for improving the properties of materials and formulations such as the barrier effect, hydrophobicity, antifouling, anticorrosion, thermal management, electrical management, preservative effect as well as for electronic or microelectronic components.

[0051] Other characteristics and advantages will emerge from the detailed description of the invention and from the examples which are purely illustrative and in no way limitative of the scope of the invention.

[0052] Brief description of the Figures

[0053] Figure 1 is a graphical representation of the viscosity measurement of three liquid graphene dispersions (Condition (A): a liquid graphene dispersion comprising an aqueous matrix free of viscous agent (Outside the invention); Condition (B): a liquid graphene dispersion according to the invention comprising an aqueous viscous matrix and a viscosity agent of acrylic polymer type at 0.5% by weight of the total weight of the dispersion, said dispersion being obtained by the method according to the invention; Condition (C): a liquid graphene dispersion according to the invention comprising an aqueous viscous matrix and a viscosity agent of polyether type at 30% by weight of the total weight of the dispersion, said dispersion being obtained by the method according to the invention.)

[0054] Figure 2 is a photograph representing a macroscopic observation at D+1 of the presence of aggregates in three liquid graphene dispersions having different viscosities (Condition (A): a liquid graphene dispersion comprising an aqueous matrix free of viscous agent (Outside the invention) - 1 mPa.s; Condition (B): a liquid graphene dispersion according to the invention comprising an aqueous viscous matrix and a viscosity agent of acrylic polymer type at 0.5% by weight of the total weight of the dispersion, said dispersion being obtained by the method according to the invention - 10 mPa.s; Condition (C): a liquid graphene dispersion according to the invention comprising an aqueous viscous matrix and a viscosity agent of polyether type at 30% by weight of the total weight of the dispersion, said dispersion being obtained by the method according to the invention - 6 mPa.s.s) Figure 3 is a graphical representation of the absorbance over time of three liquid graphene dispersions having different viscosities ((Condition (A): a liquid graphene dispersion comprising an aqueous matrix free of viscous agent (Outside the invention) - 1 mPa.s; Condition (B): a liquid graphene dispersion according to the invention comprising an aqueous viscous matrix and a viscosity agent of acrylic polymer type at 0.5% by weight of the total weight of the dispersion, said dispersion being obtained by the process according to the invention - 10 mPa.s; Condition (C): a liquid graphene dispersion according to the invention comprising an aqueous viscous matrix and a viscosity agent of polyether type at 30% by weight of the total weight of the dispersion, said dispersion being obtained by the process according to the invention - 6 mPa.s).

[0055] Figure 4 is a graphical representation of the comparison of three absorption spectra of liquid graphene dispersion having different viscosities ((Condition (A): a liquid graphene dispersion comprising an aqueous matrix free of viscous agent (Outside the invention) - 1 mPa.s; Condition (B): a liquid graphene dispersion according to the invention comprising an aqueous viscous matrix and a viscosity agent of acrylic polymer type at 0.5% by weight of the total weight of the dispersion, said dispersion being obtained by the method according to the invention - 10 mPa.s; Condition (C): a liquid graphene dispersion according to the invention comprising an aqueous viscous matrix and a viscosity agent of polyether type at 30% by weight of the total weight of the dispersion, said dispersion being obtained by the method according to the invention - 6 mPa.s).

[0056] Figure 5 is a table summarizing an analysis carried out by RAMAN spectrophotometry on three liquid graphene dispersions having different viscosities ((Condition (A): a liquid graphene dispersion comprising an aqueous matrix free of viscous agent (Outside the invention) - 1 mPa.s; Condition (B): a liquid graphene dispersion according to the invention comprising an aqueous viscous matrix and a viscosity agent of acrylic polymer type at 0.5% by weight of the total weight of the dispersion, said dispersion being obtained by the method according to the invention - 10 mPa.s; Condition (C): a liquid graphene dispersion according to the invention comprising an aqueous viscous matrix and a viscosity agent of polyether type at 30% by weight of the total weight of the dispersion, said dispersion being obtained by the method according to the invention - 6 mPa.s).

[0057] Figure 6 is a graphical representation showing the characterization of the dynamic viscosity of graphene dispersions under conditions (A) and (B).

[0058] Figure 7 is a graphical representation of the absorbance over time of a graphene dispersion of condition (A).

[0059] Figure 8 is a graphical representation of the absorbance over time of a graphene dispersion of condition (B).

[0060] Figure 9 is a graphical representation showing the evolution of the dynamic viscosity of a dispersion comprising 10 g / L of graphene over time.

[0061] Detailed description of the invention

[0062] Definitions By "viscosity agent" within the meaning of the invention, we mean any polymer or mineral material whose property is to increase the viscosity of dispersions.

[0063] For the purposes of the invention, the term "aggregate" means an agglomerated structure formed from several graphene sheets in the 3 spatial directions, the size of which is large compared to the dimensions of the graphene sheet.

[0064] For the purposes of the invention, the term "inert atmosphere" means a gas or mixture of gases which does not promote the re-oxidation of reduced graphene planes into neutral graphene planes. The method according to the invention can thus be carried out under an argon or nitrogen atmosphere.

[0065] For the purposes of the invention, the term "graphite intercalation compound" means a compound comprising at least two individual negatively or positively charged graphene planes intercalated by positive or negative counterions. Graphite alkali salts are a special case of graphite intercalation compounds where the graphene planes are negatively charged and the counterions are alkali ions. They can be formed by intercalation of at least one alkali metal into graphite.

[0066] For the purposes of the invention, the term "atomic layer" means a layer composed in one direction of space of a single atom. A graphene sheet is made up of at least one atomic layer.

[0067] For the purposes of the invention, the term “liquid graphene dispersion” means a graphene dispersion having an absolute viscosity of between 5 mPa.s and 100 Pa.s, preferably between 100 mPa.s and 100 Pa.s.

[0068] For the purposes of the invention, the term “carrier gas” means a main gas in which another gas or liquid, reactive or not, will be diluted and introduced into the medium.

[0069] For the purposes of the invention, the term "viscous matrix" means the mixture of an aqueous or organic solvent with at least one viscosity agent. Preferably, the viscous matrix has an absolute viscosity of between 5 mPa.s and 100 Pa.s.

[0070] For the purposes of the invention, the term "Froude number" means the ratio between kinetic energy and gravitational potential energy. The Froude number is defined as follows:

[0071] Fr = n 2 .d / gn, d corresponds to the rotation speed (rev / sec) and the diameter of the stirring wheel (m) g: acceleration of gravity (m / s 2 )

[0072] For the purposes of the invention, the term "Reynolds number" means the ratio of inertial forces to viscous forces. The Reynolds number is defined as follows:

[0073] The calculation is performed with the parameters extracted from the process as follows:

[0074] Re = nd 2 .p / pn, d corresponds to the rotation speed (rev / sec) and the diameter of the stirring wheel (m) p, p corresponds to the density (kg / m3) and the dynamic viscosity of the fluid (Pa.s)

[0075] For the purposes of the invention, “turbulent regime” means a flow regime characterized by chaotic changes in pressure and flow velocity.

[0076] By "without aprotic polar solvent" for the purposes of the invention, it is meant that the liquid graphene dispersion contains less than 0.1% of aprotic polar solvent.

[0077] For the purposes of the invention, “RAMAN spectrophotometry” means a non-destructive vibrational spectroscopy method which makes it possible to determine the molecular composition and external structure of a material.

[0078] By "stable" in the sense of the invention, it is meant that the liquid dispersion of graphene does not contain any aggregate. Thus, destabilization phenomena such as creaming or sedimentation do not occur over time, in particular for at least 3 months.

[0079] For the purposes of the invention, "absolute viscosity" means the resistance of an incompressible fluid to laminar flow. It is measured experimentally by a rheometer.

[0080] For the purposes of the invention, “stable viscosity” means that the viscosity exhibits a variation of less than 1% over time, in particular for at least 3 months.

[0081] Process for obtaining a di

[0082] The present invention therefore relates to a method for obtaining a liquid dispersion of graphene.

[0083] The method for obtaining a liquid dispersion of graphene according to the invention comprises the following steps:

[0084] 1) Solubilization of graphite carried out under an inert atmosphere forming a graphene solution;

[0085] 2) Oxidation of the graphene solution obtained in step 1) forming the organic graphene dispersion; and

[0086] 3) Transfer of the organic graphene dispersion obtained in step 2) into a viscous matrix forming a liquid graphene dispersion.

[0087] Advantageously, the process for obtaining a liquid dispersion of graphene makes it possible to obtain a liquid dispersion of graphene without aggregate, stable, and comprising up to 50g / L of graphene.

[0088] Preferably, step 1) of graphite solubilization carried out under an inert atmosphere comprises the implementation of the following steps: a) Intercalation of at least one alkali metal in graphite leading to a graphite intercalation compound; and b) Chemical exfoliation and / or mechanical exfoliation of the graphite intercalation compound. According to a preferred embodiment, the graphite solubilization process carried out under an inert atmosphere of step 1) comprises the following steps, carried out under an inert atmosphere: a) Intercalation of at least one alkali metal in graphite leading to a graphite intercalation compound; b) Chemical exfoliation combined with mechanical exfoliation of the graphite intercalation compound, characterized in that the graphite intercalation compound is mixed with a solvent in a turbulent regime having:

[0089] - a Reynolds number greater than 1000;

[0090] - a Froude number less than 1; and

[0091] - a shear rate lower than 400s-l, so as to obtain a graphene solution.

[0092] According to another embodiment, the graphite solubilization process carried out under an inert atmosphere in step 1) comprises the following steps: a) Intercalation of at least one alkali metal in graphite leading to a graphite intercalation compound; b) Chemical exfoliation of the graphite intercalation compound using a solvent, preferably using an aprotic polar solvent, preferably THF, so as to obtain a graphenide solution.

[0093] According to another embodiment, the process for solubilizing graphite carried out under an inert atmosphere in step 1) comprises the following steps: a) Intercalation of at least one alkali metal by graphite leading to a graphite intercalation compound; b) Mechanical exfoliation of the graphite intercalation compound characterized in that the graphite intercalation compound is mixed in a turbulent regime having:

[0094] - a Reynolds number greater than 1000;

[0095] - a Froude number less than 1; and

[0096] - a shear rate lower than 400s-l, so as to obtain a graphene solution.

[0097] Advantageously, the graphite solubilization method according to the invention makes it possible to effectively solubilize the graphite in order to produce a graphene solution comprising a sufficient concentration of good quality graphene to provide for industrial use.

[0098] The graphite used in step a) may be natural or synthetic graphite. Preferably, the graphite from step a) has a carbon proportion of at least 99%. Preferably, the graphite from step a) has a particle size of between 100 μm and 5 mm, in particular between 300 and 800 μm.

[0099] According to a preferred embodiment, at least one alkali metal intercalated in graphite from step a) is chosen from potassium, sodium, lithium, rubidium and cesium. Preferably, at least one alkali metal intercalated in graphite in step a) is potassium.

[0100] In another embodiment, the intercalation in step a) is carried out in the presence of an alkali metal salt obtained from an alkali metal. For example, the intercalation may be carried out in the presence of an alkali polyaryl salt of formula A+B-, in which A+ represents a cation of an alkali ion, and B- represents an anion of a polyaromatic compound.

[0101] Such alkaline polyaryl salts and their manufacturing process are described for example in (C. Stein, J. Poulenard, L. Bonnetain, J. Golé, CR Acad. Sci. Paris 260, 4503 (1965); “Synthesis of graphite intercalation compounds”, A. Hérold in Chemical physics of intercalation, AP Legrand and S. Flandrois Eds, NATO ASI Series, series B, Vol. 172, pp. 3-45 (1987); F. Béguin and R. Setton New ternary lamellar compounds of graphite, Carbon 13, 293-)295 (1975).

[0102] According to one embodiment, the polyaromatic compound is selected from the group comprising naphthalene, benzophenone, fluorenone, benzoquinone and anthraquinone.

[0103] In a particular embodiment, the polyaromatic compound is naphthalene.

[0104] In another particular embodiment, the alkali polyaryl salt is a potassium polyaryl salt (i.e., a salt of formula A+B-, wherein A+ represents K+).

[0105] Advantageously, the alkali polyaryl salt of formula A+B-, is a potassium salt of naphthalene (Naph- K+).

[0106] Thus, following the intercalation of at least one alkali metal into graphite, the graphene sheets constituting the graphite intercalation compound are negatively charged, and are then referred to as grapheneide. These negative charges contribute to improving the solubility of the graphene sheets.

[0107] Preferably, the graphite intercalation compound of step a) is in the form of a binary compound of formula KC8.

[0108] According to a particular embodiment of the invention, the graphite intercalation compound obtained in step a) has an inter-graphene sheet distance of at least 5 Angstroms.

[0109] The measurement of the inter-graphene sheet distance can be carried out under an inert atmosphere by methods well known to those skilled in the art such as X-ray diffraction.

[0110] Advantageously, when step b) includes chemical exfoliation, this allows the interlayer Van der Waals interactions of the graphite to be replaced by electrostatic interactions. Thus, when exposed to a suitable solvent, the entropy of the counterions of the electrostatic bonds allows for a negative free energy of dissolution. In other words, exposing the intercalation compound to a suitable solvent facilitates its solubilization.

[0111] According to a preferred embodiment, the chemical exfoliation of step b) is carried out by exposing the graphite intercalation compound to an aprotic polar solvent. Preferably, said aprotic polar solvent has a dielectric constant of between 5 and 200.

[0112] Preferably, the aprotic polar solvent is chosen from: tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), 2-Methyltetrahydrofuran (Me-THF) and cyclopentylmethylether.

[0113] According to a particularly preferred embodiment, the aprotic polar solvent is THF.

[0114] Preferably, the chemical exfoliation of step b) is carried out with a graphite intercalation compound / solvent ratio, preferably aprotic polar solvent, of between 1 and 50g / L.

[0115] When step b) includes the combination of chemical and mechanical exfoliation, modulation of the graphite intercalation compound / solvent ratio, preferably aprotic polar solvent, is important to maximize the energy transfer related to the turbulent regime generated by mechanical exfoliation to the graphite intercalation compound.

[0116] Initially, the concentration of graphite intercalation compound is high relative to the volume of solvent, preferably aprotic polar. This initial concentration allows for improved exfoliation by combining the effect of shear but also friction between the graphite intercalation compounds and the grinding medium (blade mixer, ball mill, magnetic bar, stirred attritor or detritor or an "Ultra-Turrax").

[0117] The combination of the shear / friction / grinding effect can be measured in the mixture comprising the graphite intercalation compound and the solvent, preferably a polar aprotic solvent, by measuring the velocity and then calculating the Reynolds number and the Froude number.

[0118] Step b) of chemical exfoliation, when combined with mechanical exfoliation, is carried out in a mixture comprising the graphite intercalation compound and a solvent in a turbulent regime having a Reynolds number greater than 1000 and a Froude number less than 1 and a shear rate less than 400s-l.

[0119] Unexpectedly, the combination of chemical and mechanical exfoliation of the graphite intercalation compound in a turbulent regime with a Reynolds number greater than 1000, a Froude number less than 1, and a shear rate less than 400s-l allows for the enhanced dissolution of the graphite intercalation compound, especially in the solvent, preferentially an aprotic polar solvent.

[0120] Preferably, shearing is carried out for 24 to 200 hours.

[0121] Said shear rate can be measured by torque measurement or evaluated by correlation. The mechanical exfoliation of step b) can be carried out by any means, in particular any means making it possible to obtain a Reynolds number greater than 1000, a Froude number less than 1, and a shear rate less than 400s-l.

[0122] The Reynolds number, Froude number and shear rate required for mechanical exfoliation can be obtained using a device chosen from a paddle mixer, a ball mill, a magnetic stirrer, an attritor or detritor in stirred media or an "Ultra-Turrax".

[0123] Thus, the graphite solubilization process according to the invention makes it possible to obtain graphene sheets of large lateral size, preferably greater than 300nm, in particular greater than 600nm, even more preferably greater than 900nm.

[0124] The measurement of the lateral size of the sheets according to the invention can be carried out by transmission electron microscopy, by atomic force microscopy or by measurement of light scattering.

[0125] Preferably, the graphite solubilization process comprises a step b') of removing the aggregates, occurring after step b).

[0126] Step b') of removing the aggregates advantageously makes it possible to remove any aggregates comprising the non-exfoliated graphite intercalation compounds.

[0127] Preferably, step b') comprises the following steps:

[0128] - Sedimentation and rejection of aggregates located in the lower part of the graphene solution and / or

[0129] - Centrifugation and rejection of aggregates located in the lower part of the graphene solution.

[0130] Advantageously, step b') of eliminating the aggregates makes it possible to obtain a graphene solution without aggregates.

[0131] The presence of aggregates in the graphene solution can be verified by different methods, including:

[0132] -By optical microscopy; A sample of the graphene solution can be taken at different intervals in the centrifugation or sedimentation step to determine when this has resulted in a solution free of aggregates. Examination under an optical microscope makes it possible to detect possible aggregates having a minimum size of the order of a micron. In a particular embodiment, the sample of the solution can be analyzed under an optical microscope with a magnification of times 50 to times 100.

[0133] - By correlation between microscopy and observation of the Tyndal effect; passing a laser through the graphene solution makes it possible to ensure that it contains particles in solution at a scale small enough for them not to be visible under microscopy. - By correlation between microscopy and Raman spectroscopy; observing a specific wavelength of carbon, preferably 1064nm, makes it possible to ensure the presence of carbon not visible under microscopy.

[0134] - Conductivity measurement; Since the graphene sheets are loaded into the graphene solution, it is possible to measure the conductivity of the graphene solution through the contribution of graphene and counterions to it.

[0135] According to one embodiment, step 1) of solubilization of graphite carried out under an inert atmosphere comprises the following steps: a) Intercalation of at least one alkali metal in graphite leading to a graphite intercalation compound; b) Chemical exfoliation and / or mechanical exfoliation of the graphite intercalation compound, so as to obtain a graphenide solution b') Removal of aggregates from the graphenide solution obtained in step b), preferably by sedimentation and / or centrifugation.

[0136] Preferably, step 1) of solubilization of graphite carried out under an inert atmosphere comprises the following steps: a) Intercalation of at least one alkali metal in graphite leading to a graphite intercalation compound; b) Chemical exfoliation combined with mechanical exfoliation of the graphite intercalation compound, characterized in that the graphite intercalation compound is mixed with a solvent in a turbulent regime having:

[0137] - a Reynolds number greater than 1000;

[0138] - a Froude number less than 1; and

[0139] - a shear rate of less than 400s-l, so as to obtain a graphene solution; b') Removal of aggregates from the graphene solution obtained in step b), preferably by sedimentation and / or centrifugation

[0140] The oxidation of the graphene solution of step 2) can be carried out using a gas mixture comprising oxygen and at least one carrier gas. Preferably, the carrier gas is chosen from neutral gases, in particular nitrogen or argon.

[0141] Preferably, the gas mixture comprises a mixture of oxygen and nitrogen.

[0142] Advantageously, the gas composition and humidity are controlled to oxidize the graphene solution.

[0143] The oxidation of the graphene solution neutralizes the negative charges of the graphene sheets, making them dispersible in aqueous solvents. Preferably, the oxidation of the graphene solution in step 2) is carried out using a gas mixture comprising between 70 and 85% oxygen and 30 to 15% nitrogen.

[0144] Advantageously, the gas mixture ensures stability and repeatability of the process without depending on the quality of the ambient air.

[0145] According to one variant, the invention relates to a process for obtaining a liquid dispersion of graphene comprising a step of oxidation in synthetic air.

[0146] Step 3) of transferring the organic graphene dispersion is preferably carried out in a viscous matrix having an absolute viscosity measured at 25°C using a rheometer of between 5mPa.s and 100Pa.s, preferably between 100mPa.s and 100Pa.s.

[0147] Advantageously, the viscous matrix makes it possible to avoid the phenomenon of reaggregation of the graphene sheets.

[0148] According to a variant of the invention, the viscous matrix of step 3) consists of a viscosity agent.

[0149] The viscous matrix of step 3) can be chosen from an aqueous viscous matrix or an organic viscous matrix.

[0150] When the viscous matrix of step 3) is an aqueous viscous matrix, it preferably comprises a mixture of water and at least one viscosity agent. Preferably, the aqueous viscous matrix comprises between 0.1 and 30% of viscosity agent.

[0151] According to one variant, the aqueous viscous matrix consists of a viscosity agent, preferably a polyether. In other words, according to one variant, the aqueous viscous matrix does not comprise water.

[0152] Preferably, the viscosity agent present in the aqueous viscous matrix can be chosen from the family of acrylic polymers, polyethers, alginates, clays or cellulose derivatives.

[0153] According to a particular embodiment, the viscosity agent present in the aqueous viscous matrix is ​​a copolymer, preferably a copolymer comprising at least one acrylic block and at least one isopropyl acrylate block.

[0154] According to another embodiment, the viscosity agent present in the aqueous viscous matrix is ​​a polyether, preferably a polyether glycol, even more preferably a polyether glycol having a molar mass of 60 g / mol.

[0155] When the viscous matrix of step 3) is an organic viscous matrix, it preferably comprises a mixture of organic solvent and at least one viscosity agent. Preferably, the organic viscous matrix comprises at least 10% viscosity agent, in particular at least 30%. According to one variant, the organic viscous matrix consists of a viscosity agent, preferably an epoxy. In other words, according to one variant, the organic viscous matrix does not comprise an organic solvent.

[0156] Preferably, the viscosity agent present in the organic viscous matrix can be chosen from the family of epoxies, elastomers, polyurethanes, polyethylenes, polypropylenes, polyamides, polyetherketones, inorganic, metallic and carbon particles.

[0157] The organic solvent present in the organic viscous matrix may be any organic solvent miscible with the matrix. Preferably, said organic solvent is chosen from:

[0158] - aliphatic or aromatic hydrocarbon solvents, in particular toluene, xylene, pentane, decane, dodecane; and / or

[0159] - solvents comprising at least one oxygen atom, in particular ketones, acids, esters, ethers, preferably acetone, ethyl acetate or glycol ethers.

[0160] Preferably, the transfer of the organic dispersion of graphene into a viscous matrix does not include a degassing step.

[0161] In a particular embodiment of the invention, the method for obtaining a liquid dispersion of graphene comprises an additional step 4) of evaporation and / or distillation of the aprotic polar solvent.

[0162] The liquid graphene dispersion obtained in step 4) comprises a portion of aprotic polar solvent. To remove the remaining proportion of aprotic polar solvent, step 4) comprises at least one evaporation and / or one distillation.

[0163] Preferably, step 4) includes at least:

[0164] - evaporation for a period of between 6 and 10 days, preferably 7 days; and / or

[0165] - distillation at an evaporation rate of between 100mL / h and 2L / h, preferably 500mL / h.

[0166] Advantageously, step 4) makes it possible to obtain a liquid dispersion of graphene without aprotic polar solvent.

[0167] According to one embodiment, the method for obtaining a liquid dispersion of graphene comprises the following steps:

[0168] 1) Solubilization of graphite carried out under an inert atmosphere so as to obtain a graphenide solution by implementing the following steps: a) Intercalation of at least one alkali metal in graphite carried out under an inert atmosphere leading to a graphite intercalation compound; b) Chemical exfoliation or mechanical exfoliation carried out under an inert atmosphere of the graphite intercalation compound, so as to obtain a graphenide solution: b') Removal of aggregates from the graphenide solution obtained in step b) from the graphenide solution obtained in step b), preferably by sedimentation and / or centrifugation. More particularly, step b') may comprise the following steps:

[0169] - Sedimentation and rejection of aggregates located in the lower part of the graphene solution and / or

[0170] - Centrifugation and rejection of aggregates located in the lower part of the graphene solution.

[0171] 2) Oxidation of the aggregate-free graphene solution obtained in step b') to obtain an organic graphene dispersion;

[0172] 3) Transfer of the organic graphene dispersion into a viscous matrix forming a liquid graphene dispersion; and

[0173] 4) Evaporation and / or distillation of the aprotic polar solvent.

[0174] According to one embodiment, the liquid dispersion of graphene obtained at the end of step 3) and / or 4) has an absolute viscosity measured at 25°C using a rheometer of between 5 mPa.s and 100 Pa.s, preferably between 100 mPa.s and 100 Pa.s.

[0175] According to a preferred embodiment, the method for obtaining a liquid dispersion of graphene comprises the following steps:

[0176] 1) Solubilization of graphite carried out under an inert atmosphere so as to obtain a graphene solution by implementing the following steps: a) Intercalation of at least one alkali metal by graphite carried out under an inert atmosphere leading to a graphite intercalation compound; b) Chemical exfoliation combined with mechanical exfoliation carried out under an inert atmosphere of the graphite intercalation compound characterized in that the graphite intercalation compound is mixed with a solvent in a turbulent regime having:

[0177] - a Reynolds number greater than 1000;

[0178] - a Froude number less than 1; and

[0179] - a shear rate of less than 400s-l, so as to obtain a graphenide solution; b') Removal of aggregates from the graphenide solution obtained in step b), preferably by sedimentation and / or centrifugation. More particularly, step b') may comprise the following steps:

[0180] - Sedimentation and rejection of aggregates located in the lower part of the graphene solution and / or

[0181] - Centrifugation and rejection of aggregates located in the lower part of the graphene solution.

[0182] 2) Oxidation of the aggregate-free graphene solution obtained in step b') to obtain an organic graphene dispersion; 3) Transfer of the organic graphene dispersion into a viscous matrix forming a liquid graphene dispersion; and

[0183] 4) Evaporation and / or distillation of the aprotic polar solvent

[0184] According to a variant, when the process for obtaining a liquid dispersion of graphene comprises step 4), said process may comprise an optional step 5) of recycling the aprotic polar solvent.

[0185] Step 5) of recycling the aprotic polar solvent may include the following steps:

[0186] Recovery of vapors from the solvent evaporated or distilled during step 4);

[0187] - Purification by membrane separation or extractive distillation;

[0188] - possibly reuse in the process by injection of the aprotic polar solvent recycled in step b).

[0189] Advantageously, step 5) makes it possible to reduce solvent losses and to reduce the production costs of the liquid graphene dispersion.

[0190] According to another variant of the invention, the method for obtaining a liquid dispersion of graphene comprises the following steps:

[0191] 1) Solubilization of graphite carried out under an inert atmosphere so as to obtain a graphene solution by implementing the following steps: a) Intercalation of at least one alkali metal by graphite carried out under an inert atmosphere leading to a graphite intercalation compound; b) Chemical exfoliation combined with mechanical exfoliation carried out under an inert atmosphere of the graphite intercalation compound in a viscous matrix characterized in that the graphite intercalation compound is mixed with a solvent in a turbulent regime having:

[0192] - a Reynolds number greater than 1000;

[0193] - a Froude number less than 1; and

[0194] - a shear rate of less than 400s-l, so as to obtain a graphenide solution; b') Removal of aggregates from the graphenide solution obtained in step b), preferably by sedimentation and / or centrifugation. More particularly, step b') may comprise the following steps:

[0195] - Sedimentation and rejection of aggregates located in the lower part of the graphene solution and / or

[0196] - Centrifugation and rejection of aggregates located in the lower part of the graphene solution.

[0197] 2) Oxidation of the aggregate-free graphene solution obtained in step b') to obtain an organic dispersion of graphene. Thus, according to a variant, step b) of chemical and / or mechanical exfoliation is carried out on a graphite intercalation compound in a viscous matrix. Step 3) of the process is then carried out in step b) simultaneously. ene

[0198] Also, according to another aspect, the invention relates to a liquid dispersion of graphene comprising between 0.1 and 50 g / L of graphene and having an absolute viscosity measured at 25°C using a rheometer of between 5 mPa.s and 100 Pa.s.

[0199] Preferably, the liquid dispersion of graphene comprises between 1 and 50 g / L of graphene, in particular between 1 and 20 g / L, even more preferably between 5 and 50 g / L.

[0200] Graphene occurs as sheets in the liquid graphene dispersion.

[0201] Preferably, the graphene sheets present in the liquid graphene dispersion have a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers. According to one embodiment, at least one graphene sheet present in the liquid graphene dispersion has a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers. Preferably, each sheet present in the liquid graphene dispersion has a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers.

[0202] According to one variant, at least one graphene sheet has less than 4 atomic layers, preferably less than 3 atomic layers, less than two atomic layers. According to one embodiment, at least one graphene sheet is single-layer, preferably at least two, and according to one variant, all the graphene sheets are single-layer.

[0203] According to one embodiment, the graphene sheets present in the liquid dispersion have:

[0204] - an average thickness of 1 to 8 nm, preferably 2 to 3 nm, and / or

[0205] - an average lateral size greater than 300nm, preferably between 300nm and 1pm, in particular between 500 and 700nm.

[0206] Advantageously, the liquid graphene dispersion according to the invention has good quality graphene sheets.

[0207] The liquid graphene dispersion according to the invention is stable, preferably for a period of at least 3 months. Thus, for at least 3 months, the liquid graphene dispersion according to the invention does not have any aggregates, in particular no aggregates resulting from the reaggregation of the graphene sheets. In the context of the invention, it is possible to verify the stability of the liquid dispersion over time by monitoring the viscosity. Indeed, if the viscosity increases over time, this means that there is a reaggregation of the graphene. Thus, according to a preferred embodiment of the invention, the liquid graphene dispersion has a stable viscosity, preferably for a period of at least 3 months.

[0208] Preferably, the liquid graphene dispersion has an absolute viscosity measured at 25°C using a rheometer of between 100 mPa.s and 100 Pa.s.

[0209] Advantageously, the particular viscosity of the liquid graphene dispersion according to the invention allows it to guarantee stability and a particularly high graphene concentration.

[0210] According to one embodiment, the liquid graphene dispersion according to the invention comprises an aqueous viscous matrix or an organic viscous matrix.

[0211] According to one embodiment, the liquid graphene dispersion according to the invention comprises an aqueous viscous matrix and at least one viscosity agent, in which the viscosity agent has a concentration of between 0.1 and 30% by weight of the total weight of the dispersion.

[0212] According to one variant, the aqueous viscous matrix consists of a viscosity agent, preferably a polyether. In other words, according to one variant, the aqueous viscous matrix does not comprise water.

[0213] Preferably, the viscosity agent present in the aqueous viscous matrix can be chosen from the family of acrylic polymers, polyethers, alginates, clays or cellulose derivatives.

[0214] According to another embodiment, the liquid graphene dispersion according to the invention comprises an organic matrix and a viscosity agent, in which the viscosity agent has a concentration of at least 10% by weight of the total weight of the dispersion. Preferably, when the liquid graphene dispersion according to the invention comprises an organic matrix and a viscosity agent, said viscosity agent has a concentration of at least 20%, in particular at least 50%, even more preferably at least 75% by weight of the total weight of the dispersion.

[0215] According to one variant, the organic viscous matrix consists of a viscosity agent, preferably an epoxy. In other words, according to one variant, the organic viscous matrix does not comprise an organic solvent.

[0216] Preferably, the viscosity agent present in the organic viscous matrix can be chosen from the family of epoxies, elastomers, polyurethanes, polyethylenes, polypropylenes, polyamides, polyetherketones, inorganic, metallic and carbon particles.

[0217] Thus, depending on its production process, the liquid graphene dispersion according to the invention may comprise an aqueous viscous matrix or an organic viscous matrix.

[0218] When the liquid graphene dispersion comprises an organic matrix, the absence of aggregates can be verified using one of the techniques previously mentioned, namely by optical microscopy, by correlation between microscopy and observation of the Tyndal effect, by measurement of conductivity or by monitoring of viscosity. When the liquid graphene dispersion comprises an aqueous matrix, the absence of aggregates is preferably measured by spectrophotometry.

[0219] According to a preferred embodiment of the invention, the liquid graphene dispersion comprising an aqueous matrix has an absorption spectrum comprising a peak at 269 nm.

[0220] Absorbance can be measured using a UV spectrophotometer. UV spectroscopy is one of the techniques used according to the invention to ensure the absence of aggregates.

[0221] Advantageously, the presence of a peak at 269nm is a parameter describing the presence of graphene. It is thus an indicator of the quality of the dispersion demonstrating that the solution contains graphene and not graphite or oxidized graphene. Thus the presence of a peak at 269nm is an indirect indicator of the stability of the liquid graphene dispersion.

[0222] According to another embodiment, the liquid graphene dispersion according to the invention comprising an aqueous matrix has an absorption spectrum not comprising a peak at 230nm.

[0223] When the liquid graphene dispersion comprising an aqueous matrix includes a peak at 230nm in its absorption spectrum, this means the presence of graphene oxide, an undesirable element at this stage of the process.

[0224] The liquid graphene dispersion according to the invention comprising an aqueous matrix can be characterized using 3 vibrational bands observed by RAMAN spectrophotometry, namely:

[0225] - 1350 cm-1 (peak D);

[0226] - 1580 cm-1 (peak G); and

[0227] - between 2680 and 2700 cm-1 (2D peak).

[0228] These three peaks are characteristic of a graphitic signature.

[0229] Thus, according to a particularly preferred embodiment, the liquid dispersion of graphene comprising an aqueous matrix, comprises 3 vibrational bands observed by RAMAN spectrophotometry:

[0230] - 1350 cm-1 (peak D);

[0231] - 1580 cm-1 (peak G); and

[0232] - between 2680 and 2700 cm-1 (2D peak).

[0233] The presence of the D peak is representative of a disorder or defect (sp3) in the graphene dispersion. The presence of the G peak is representative of the presence of graphene (sp2 vibration in the plane). Finally, the presence of the 2D peak is representative of the number of layers. When the 2D peak is thin, symmetrical and intense, it is a single-layered material. When the 2D peak is broad, with a shoulder and of low intensity, it is graphite.

[0234] Thus, the intensity of the vibrational bands of the liquid graphene dispersion can be used to define the stability of said dispersion. According to one embodiment, the liquid graphene dispersion comprising an aqueous matrix comprises:

[0235] - a peak intensity ratio D / peak intensity G less than 1.5; and

[0236] - a 2D peak intensity / G intensity ratio greater than 1.

[0237] According to another embodiment, the liquid graphene dispersion comprising an aqueous matrix comprises:

[0238] - a peak D with a width at half-height of less than 33 cm-1; and / or

[0239] - a 2D peak with a width at mid-height less than 55cm-l, preferably less than 50cm-l.

[0240] Advantageously, the intensity and the half-height width of the vibrational bands make it possible to demonstrate the quality of the graphene present in the dispersion.

[0241] UV spectroscopy and RAMAN spectrophotometry are parameters that can be measured over time to show the stability and / or quality of the liquid graphene dispersion according to the invention.

[0242] According to a preferred embodiment of the invention, the liquid dispersion of graphene is capable of being obtained by the method for obtaining a liquid dispersion described or any of the embodiments.

[0243] Thus, the liquid dispersion of graphene is likely to be obtained by implementing the following steps:

[0244] 1) Solubilization of graphite carried out under an inert atmosphere so as to obtain a graphene solution by implementing the following steps: a) Intercalation of at least one alkali metal in graphite carried out under an inert atmosphere leading to a graphite intercalation compound; and

[0245] ) Chemical exfoliation and / or mechanical exfoliation carried out under an inert atmosphere of the graphite intercalation compound, so as to obtain a graphene solution;

[0246] 2) Oxidation of the graphene solution obtained in step b) to obtain an organic dispersion of graphene; and

[0247] 3) Transfer of the organic graphene dispersion into a viscous matrix forming a liquid graphene dispersion.

[0248] Preferably, the liquid dispersion of graphene is likely to be obtained by implementing the following steps:

[0249] 1) Solubilization of graphite carried out under an inert atmosphere so as to obtain a graphenide solution by implementing the following steps: a) Intercalation of at least one alkali metal in graphite carried out under an inert atmosphere leading to a graphite intercalation compound; b) Chemical exfoliation and / or mechanical exfoliation carried out under an inert atmosphere of the graphite intercalation compound, so as to obtain a graphenide solution; b') Removal of aggregates from the graphenide solution obtained in step b), preferably by sedimentation and / or centrifugation. More particularly, step b') may comprise the following steps:

[0250] - Sedimentation and rejection of aggregates located in the lower part of the graphene solution and / or

[0251] - Centrifugation and rejection of aggregates located in the lower part of the graphene solution.

[0252] 2) Oxidation of the aggregate-free graphene solution obtained in step b') to obtain an organic graphene dispersion; and

[0253] 3) Transfer of the organic graphene dispersion into a viscous matrix forming a liquid graphene dispersion; and

[0254] 4) Evaporation and / or distillation of the aprotic polar solvent.

[0255] According to a particularly preferred embodiment, the liquid dispersion of graphene can be obtained by implementing the following steps:

[0256] 1) Solubilization of graphite carried out under an inert atmosphere so as to obtain a graphene solution by implementing the following steps: a) Intercalation of at least one alkali metal in graphite carried out under an inert atmosphere leading to a graphite intercalation compound; b) Chemical exfoliation combined with mechanical exfoliation carried out under an inert atmosphere of the graphite intercalation compound characterized in that the graphite intercalation compound is mixed with a solvent in a turbulent regime having:

[0257] - a Reynolds number greater than 1000;

[0258] - a Froude number less than 1; and

[0259] - a shear rate of less than 400s-l, so as to obtain a graphenide solution; b') Removal of aggregates from the graphenide solution obtained in step b), preferably by sedimentation and / or centrifugation. More particularly, step b') may comprise the following steps:

[0260] - Sedimentation and rejection of aggregates located in the lower part of the graphene solution and / or

[0261] - Centrifugation and rejection of the aggregates located in the lower part of the graphene solution. 2) Oxidation of the aggregate-free graphene solution obtained in step b') to obtain an organic dispersion of graphene;

[0262] 3) Transfer of the organic graphene dispersion into a viscous matrix forming a liquid graphene dispersion; and

[0263] 4) Evaporation and / or distillation of the aprotic polar solvent.

[0264] Uses

[0265] According to another aspect, the invention relates to the use of a liquid dispersion of graphene capable of being obtained by the method according to the invention for the manufacture of electronic or microelectronic components, such as capacitors or transistors.

[0266] Preferably, the liquid dispersion of graphene capable of being obtained by the process according to the invention is particularly suitable for its use as an additive, in particular in compositions such as coatings such as paints, inks or polymers.

[0267] According to a particularly preferred embodiment, the liquid dispersion of graphene can be used as a coating, preferably as a surface coating.

[0268] According to another embodiment, the liquid dispersion of graphene can be used to improve at least one property of a material chosen from:

[0269] - waterproofness

[0270] - the water-repellent effect

[0271] -thermal management

[0272] - thermal conductivity

[0273] - electrical conductivity

[0274] - the antistatic effect

[0275] - mechanical resistance and

[0276] - surface hardness.

[0277] According to a final aspect, the invention relates to hydrophobic, lubricating, anti-scratch, electromagnetic shielding, anti-corrosion compositions comprising the liquid dispersion of graphene according to the invention.

[0278] Examples of phene in various matrices and measurement of

[0279] In this example, the stability of three types of dispersions are compared as a function of the viscosity of the matrix used. The three dispersions used in this example are as follows: - Condition (A): a liquid dispersion of graphene comprising an aqueous matrix free of viscous agent (Outside the invention);

[0280] - Condition (B): a liquid dispersion of graphene comprising an aqueous viscous matrix and an acrylic viscosity agent at 0.5% by weight of the total weight of the dispersion, said dispersion being obtained by the process according to the invention, and

[0281] - Condition (C): a liquid dispersion of graphene comprising an aqueous viscous matrix and a polyether-type viscosity agent at 30% by weight of the total weight of the dispersion, said dispersion being obtained by the process according to the invention.

[0282] The viscosity agent used in condition (B) is a copolymer comprising an acrylic block and an isopropyl acrylate block, the trade name of this agent is AcrysolTT-935.

[0283] The viscosity agent used in condition (C) is a polyether glycol with a molecular weight of 60 g / mol, the trade name of this agent is PEG600.

[0284] Process for obtaining liquid graphene dispersions:

[0285] The liquid graphene dispersions described in this example are obtained by implementing a method according to the invention comprising the following steps under an inert atmosphere:

[0286] - Mixture of 1.77 g of graphite with 0.73 g of potassium at 150°C for 5 hours;

[0287] - The obtained KC8 salt is placed in a glass reactor with 500mL of THF and stirred at a shear rate of 50s-l for 140h;

[0288] - The unexfoliated salt is removed by sedimentation then centrifugation.

[0289] - The obtained graphene solution free of aggregate is oxidized in synthetic air at a flow rate of 0.1L / min then immediately mixed with the corresponding matrix in a ratio of 4:1;

[0290] - THF is removed by evaporation to obtain a liquid dispersion of graphene.

[0291] The dispersions thus obtained include a concentration of lg / L in graphene.

[0292] Viscosity study:

[0293] Figure 1 shows the dynamic viscosity of graphene liquid dispersions. The matrices containing a viscous agent have a viscosity of 1 mPa.s, 6 mPa.s and 10 mPa.s for the dispersion containing only water, containing 0.5% by mass of an acrylic viscous agent and containing 30% by mass of a polyether viscous agent respectively. Furthermore, this viscosity is stable over time, especially after 7 days.

[0294] Macroscopic observation on D+1 and D+7:

[0295] Visually, the dispersions produced are gray in color (Figure 2), the dispersion at lmPa.s corresponding to condition (A) presents graphene aggregates visible to the eye while the other dispersions are homogeneous, without visible aggregates. The results observed at D+7 are identical. ie UV-visible: The UV-visible spectroscopy analysis shown in Figure 3 confirms this observation with a constant absorbance for the dispersions at 6 and lOmPa.s while the absorbance decreases over time for the dispersion at lmPa.s, proof of the destabilization of the sample. In other words, the dispersion of condition (A) is not stable over time. Figure 3 thus illustrates the appearance of aggregates over time in condition (A). Figure 4 shows that all the dispersions have a peak at 269 nm and an absence of a peak at 230 nm, which confirms the presence of graphene in dispersion and not graphene oxide.

[0296] Raman spectroscopy:

[0297] Raman spectroscopy confirms the presence of quality graphene with:

[0298] - a peak intensity ratio D / peak intensity G less than 1.5; and

[0299] - a 2D peak intensity / G intensity ratio greater than 1.

[0300] - a peak D with a width at mid-height less than 33 cm-1

[0301] - a 2D peak with a width at mid-height less than 55cm-l, preferably less than 50cm-l.

[0302] Raman spectroscopy (Figure 5) confirms the presence of quality graphene in all 3 conditions. Indeed, after subtracting the water signal, we can see the characteristic bands of a graphitic signature: the G band (at 1580 cm-1), the 2D band (2685 cm-1) and the D band (1350 cm-1) for graphene.

[0303] The evaluation of the 2D band width and the 2D / G and D / G band intensity ratios allow the characterization of the number of graphene layers and the level of disorder and defects within the sheets. : Dispersions of in various matrices vi niques and measurement of control

[0304] In this example, the stability of two types of dispersions are compared as a function of the viscosity of the matrix used. The two dispersions used in this example are:

[0305] - Condition (A): a liquid dispersion of graphene comprising an organic viscous matrix of epoxy type containing 30 to 50% of 1,4-Butanediol diglycidyl ether and 50 to 70% of Poly[(phenyl glycidyl ether)]-co-formaldehyde

[0306] - Condition (B): a liquid dispersion of graphene comprising an organic viscous epoxy-type matrix containing 100% 2,2-bis[p-(2,3-epoxypropoxy)phenyl]propane.

[0307] Process for obtaining the di graphene niques:

[0308] The organic graphene dispersions described in this example are obtained by implementing a process according to the invention comprising the following steps under an inert atmosphere:

[0309] - Mixture of 1.77 g of graphite with 0.73 g of potassium at 150°C for 5h; - The KC8 salt obtained is placed in a glass reactor with 500mL of THF and stirred at a shear rate of 50s-l for 140h;

[0310] - The unexfoliated salt is removed by sedimentation then centrifugation.

[0311] - The obtained graphene solution free of aggregate is oxidized in synthetic air at a flow rate of 0.1L / min then immediately mixed with the corresponding matrix in a ratio of 4:1;

[0312] - THF is removed by evaporation to obtain a liquid dispersion of graphene.

[0313] The liquid graphene dispersions thus obtained are then mixed with an organic viscous matrix as defined in conditions (A) and (B).

[0314] Viscosity study:

[0315] Figure 6 shows the dynamic viscosity of conditions (A) and (B). Furthermore, this viscosity is stable over time, especially after 60 days.

[0316] After rheology analysis at 25°C, for a shear of 0.1 to 100s-l, a viscosity of 1 Pa.s with Newtonian behavior characterizes the dispersion corresponding to condition A. After rheology analysis at 25°C, for a shear of 0.1 to 100s-l, a viscosity of 23 Pa.s with Newtonian behavior characterizes the dispersion corresponding to condition B. i.e. UV-visible:

[0317] The UV-visible spectroscopy analysis shown in Figures 7 and 8 demonstrates that the produced dispersions contain graphene that absorbs in the UV-visible spectrum. The absorbance is constant for both conditions for 60 days. In other words, the dispersions of conditions (A) and (B) are stable over time, thus avoiding the formation of aggregates.

[0318] Example 3: Graphene dispersions in an organic viscous matrix and measurement of quality control parameters

[0319] The objective of this example is to demonstrate the stability of a graphene dispersion with a graphene concentration of 10g / L.

[0320] For this, this example uses a liquid dispersion of graphene comprising an organic viscous matrix of epoxy type containing 100% of 2,2-bis[p-(2,3-epoxypropoxy)phenyl]propane.

[0321] Process for obtaining graphene dispersion

[0322] The organic graphene dispersions described in this example are obtained by implementing a process according to the invention comprising the following steps under an inert atmosphere:

[0323] - Mixture of 1.77 g of graphite with 0.73 g of potassium at 150°C for 5 hours;

[0324] - The obtained KC8 salt is placed in a glass reactor with 500mL of THF and stirred at a shear rate of 50s-l for 140h; - The non-exfoliated salt is removed by sedimentation then centrifugation.

[0325] - The obtained graphene solution free of aggregate is oxidized in synthetic air at a flow rate of 0.1L / min then immediately mixed with the corresponding matrix in a ratio of 4:1;

[0326] - The THF is removed by evaporation to obtain a liquid dispersion of graphene. Viscosity study:

[0327] Figure 9 shows the dynamic viscosity of graphene dispersion over time.

[0328] In the same way as UV-visible analysis, viscosity analysis over time confirms the stability of the liquid dispersion containing graphene described in this example. Indeed, when graphene is not stable and forms aggregates, the aggregates formed oppose the shear, thus increasing the measured viscosity. Here over the measurement time of 22 days, with storage of the dispersion at 25°C, the measured viscosity is constant, proof of the stability of the dispersion comprising 10g / L of graphene is stable over time.

Claims

CLAIMS

1. Liquid dispersion of graphene, characterized in that it comprises between 0.1 and 50 g / L of graphene and an absolute viscosity measured at 25°C using a rheometer of between 5 mPa.s and 100 Pa.s.

2. Liquid dispersion of graphene according to the preceding claim, characterized in that the graphene is in the form of sheets and in that at least one sheet has a thickness of less than 10 atomic layers.

3. Liquid dispersion of graphene according to the preceding claim, characterized in that at least one sheet has a sheet thickness of less than 5 atomic layers.

4. Liquid dispersion of graphene according to one of claims 2 or 3, characterized in that each sheet has a thickness of less than 10 atomic layers, preferably less than 5 atomic layers.

5. Liquid dispersion of graphene according to one of the preceding claims, characterized in that it does not comprise an aggregate.

6. Liquid dispersion of graphene according to one of the preceding claims, characterized in that it comprises an aqueous viscous matrix comprising a mixture of water and at least one viscosity agent, the viscosity agent being present at a concentration of between 0.1 and 30% by weight of the total weight of the dispersion.

7. Liquid dispersion of graphene according to the preceding claim, characterized in that the viscosity agent is chosen from the family of acrylic polymers, polyethers, alginates, clays or cellulose derivatives.

8. Liquid dispersion of graphene according to one of claims 1 to 5, characterized in that it comprises an organic viscous matrix and at least one viscosity agent, the viscosity agent being present at a concentration of at least 10% by weight of the total weight of the dispersion.

9. Liquid dispersion of graphene according to the preceding claim, characterized in that the viscosity agent is chosen from the family of epoxies, elastomers, polyurethanes, polyethylenes, polypropylenes, polyamides, polyetherketones, inorganic, metallic and carbon particles.

10. Liquid graphene dispersion according to one of claims 1 to 7, characterized in that the dispersion has an absorption spectrum having a peak at 269nm.

11. Liquid dispersion of graphene according to one of claims 1 to 7 or according to claim 10, characterized in that it comprises 3 vibrational bands observed by RAMAN spectrophotometry: - 1350 cm-1 (peak D); - 1580 cm-1 (peak G); and - between 2680 and 2700 cm-1 (2D peak).

12. Liquid dispersion of graphene according to the preceding claim, characterized in that it has: - a peak intensity ratio D / peak intensity G less than 1.5; and - a 2D peak intensity / G intensity ratio greater than 1.

13. Liquid dispersion of graphene according to one of claims 11 or 12, characterized in that it comprises: - a peak D with a width at half-height of less than 33 cm-1; and / or - a 2D peak with a width at half-height less than 55cm-l.

14. Liquid dispersion of graphene according to one of the preceding claims, obtained by a process comprising the implementation of the following steps: 1) Solubilization of graphite carried out under an inert atmosphere forming a graphene solution; 2) Oxidation of the graphene solution obtained in step 1) to obtain an organic graphene dispersion; and 3) Transfer of the organic graphene dispersion obtained in step 2) into a viscous matrix forming a liquid graphene dispersion.

15. Liquid dispersion of graphene according to the preceding claim, characterized in that step 1) of solubilization carried out under an inert atmosphere of the graphite of the process comprises the following steps: a) Intercalation of at least one alkali metal in graphite leading to a graphite intercalation compound; and b) Chemical exfoliation combined with mechanical exfoliation of the graphite intercalation compound, characterized in that the graphite intercalation compound is mixed with a solvent in a turbulent regime having: - a Reynolds number greater than 1000; - a Froude number less than 1; and - a shear rate lower than 400s-1, in order to obtain a graphene solution.

16. Method for obtaining a liquid dispersion of graphene characterized in that it comprises the following steps: 1) Solubilization of graphite carried out under an inert atmosphere forming a graphene solution; 2) Oxidation of the graphene solution obtained in step 1) to obtain an organic graphene dispersion; and 3) Transfer of the organic graphene dispersion obtained in step 2) into a viscous matrix forming a liquid graphene dispersion.

17. Method according to the preceding claim, characterized in that the viscous matrix of step 3) has an absolute viscosity measured at 25°C using a rheometer of between 5 mPa.s and 100 Pa.s.

18. Method according to one of claims 16 or 17, characterized in that the viscous matrix of step 3) is chosen from an aqueous viscous matrix or an organic viscous matrix.

19. Method according to the preceding claim, characterized in that the aqueous viscous matrix comprises a mixture of water and at least one viscosity agent, said at least one viscosity agent being chosen from the family of acrylic polymers, polyethers, alginates, clays, or cellulose derivatives.

20. Method according to claim 19, characterized in that the organic viscous matrix comprises a mixture of organic solvent and at least one viscosity agent, said at least one viscosity agent being chosen from the family of epoxies, elastomers, polyurethanes, polyethylenes, polypropylenes, polyamides, polyetherketones, inorganic, metallic and carbon particles.

21. Method according to one of claims 16 to 20, characterized in that the solubilization step carried out under an inert atmosphere of the graphite comprises the following steps: a) Intercalation of at least one alkali metal in graphite leading to a graphite intercalation compound; and b) Chemical exfoliation combined with mechanical exfoliation of the graphite intercalation compound, characterized in that the graphite intercalation compound is mixed with a solvent in a turbulent regime having: - a Reynolds number greater than 1000; - a Froude number less than 1; and - a shear rate lower than 400s-1, in order to obtain a graphene solution.

22. Method according to the preceding claim, characterized in that the chemical exfoliation of step b) is carried out by exposing the graphite intercalation compound to an aprotic polar solvent, said aprotic polar solvent having a dielectric constant of between 5 and 200.

23. Process according to the preceding claim, characterized in that the aprotic polar solvent is chosen from tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), 2-Methyltetrahydrofuran (Me-THF) and cyclopentylmethylether.

24. Method according to one of claims 21 to 23, characterized in that the graphite intercalation compound is in the form of a binary compound of formula KC8.

25. Method according to one of claims 21 to 24, characterized in that the chemical exfoliation is carried out with a graphite intercalation compound / aprotic polar solvent ratio of between 1 and 50g / L.

26. Use of a liquid graphene dispersion according to one of claims 1 to 15 as an additive.

27. ​​Use of a liquid graphene dispersion according to one of claims 1 to 15 for the manufacture of electronic or microelectronic components, such as capacitors or transistors.

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