METHOD FOR MANUFACTURING A CONDUCTIVE COMPOSITE COMPRISING a substrate in geometric form and AT LEAST ONE SURFACE LAYER COMPRISING MULTI-LAYER GRAPHENE

Abstract

The present invention relates to the technical field of conductive composites, as well as their manufacturing processes and methods. In particular, the present invention relates to a process or method for manufacturing a conductive composite comprising at least one surface layer of multi-layered graphene and to the conductive composites obtained by said process or method. The invention also relates to a device comprising a conductive composite according to the invention, or to the use of an aqueous deposition composition comprising multi-layered graphene and at least one surfactant to form a surface layer of multi-layered graphene on a substrate in a geometric form selected from powders, films, pellets, beads, monoliths, foams, extrudates, aerosols of various sizes, and combinations thereof.

Description

Title of the invention: METHOD FOR MANUFACTURING A CONDUCTIVE COMPOSITE COMPRISING a substrate of geometric shape and AT LEAST ONE SURFACE LAYER COMPRISING MULTI-GRAPHENE LEAFLETS Technical field

[0001] The present invention belongs to the technical field of conductive composites, as well as their manufacturing processes and methods. In particular, the present invention relates to a process or method for manufacturing a conductive composite comprising at least one surface layer comprising multi-sheet graphene and to the conductive composites obtained by said process or method. The invention also relates to a device comprising a conductive composite according to the invention or even the use of an aqueous deposition composition comprising multi-sheet graphene and at least one surfactant to form a surface layer comprising multi-sheet graphene on a substrate in a geometric form chosen from powders, films, pellets, beads, monoliths, foams, extrudates, aerosols of different sizes and their combination.

[0002] In the description below, the references in brackets ([ ]) refer to the list of references presented at the end of the examples. State of the art

[0003] Conductive composites, particularly those using carbon materials as conductive filler, are attracting increasing scientific interest for many industrial applications [1-6]. Among these different carbon materials, materials close to graphene, graphite, activated carbon or carbon nanotubes / nanofibers are generally listed.

[0004] Graphene is of growing scientific and industrial interest for the production of conductive composites, particularly due to its first-rate thermoelectric properties [7-10]. Through the use of these carbon materials, the electrical conductivity of these composites can be considerably improved, thanks to the introduction of a small quantity of conductive nanofillers inside a matrix. Such composites can thus be used as lightweight heating devices for various industrial sectors such as electronics, transport, aerospace, smart buildings, or even as sensor components in various everyday applications.

[0005] However, it should be noted that for most conductive composites of the state of the art, the manufacture of these composite materials is generally based on the inclusion of carbon materials in a polymer matrix, i.e. the carbon material is mixed into the volume of the host polymer matrix; thus resulting in the formation of the conductive composite. Other conventional preparation methods consist of depositing the mixture containing the carbon material dispersed in the polymer matrix or the host resin onto a substrate, such as for example polymer, glass, ceramic or fabric, to form a composite. The carbon material can also be included in the fiber during its production before the fibers are woven into fabric. For ceramics, the carbon material can be mixed with a ceramic slip before casting and firing or with the ceramic powder before sintering depending on the nature of the ceramics and their production method.

[0006] These conventionally used manufacturing methods therefore rule out the approach which consists of simply coating a substrate with a functional layer, i.e. the deposition of multi-layer graphene (MLG) only on the surface. Most of the syntheses leading to these conductive composite materials are thus based on the inclusion of carbon-based materials, which may in particular comprise resins, within a polymer or ceramic matrix. The polymer-based conductive composite is therefore always an intimate mixture of matrix and MLG, for example polymer / resin and MLG.

[0007] These conventional synthesis methods or processes do not allow the obtaining of coatings on the surface of the conductive composite with an electrically conductive material but a dispersion of this conductive material throughout the mass of the final composite. These conventional synthesis methods or processes lead to a dispersion of this conductive material in the mass of the composite but do not allow the obtaining of a continuous coating of electrically conductive material on the surface of said composite.

[0008] In a manufacturing process using a mixture of mixtures, the mixing is done with nanofillers inserted into the polymer substrate or other insulating substrates. The main problem generated by this type of process or method is the presence of numerous conductor / insulator interfaces that significantly reduce the electrical performance of the final conductive composites. These interfaces also have local overheating points, poor conductivity between two conductive materials, which can damage the composite over time. In addition, for certain applications requiring a composite with high electrical conductivity, it is difficult or even impossible to increase the carbon material load because of the problems of final viscosity that hinders the dispersion of the conductive fillers in the mixture and also for the infiltration of this mixture into the matrix of the substrate.

[0009] For example, commercially widely available polyurethane (PU) foam is one of the foams used in many industrial applications ranging from oil absorption [11-13] to noise reduction or thermal insulation [14,15], including the production of support plates for chemical reactors

[16] or the synthesis of ceramic foams [17,18]. Due to its high elasticity under compression, foams can be effectively used as compression sensors for different applications. One of the major disadvantages of foams, and more specifically PU foam, is that they often have low electrical conductivity - an approach that would consist of improving these conduction performances could allow the consideration of new industrial devices such as piezoelectric devices or low-temperature catalyst support plates for liquid-phase reactions.Additive manufacturing of structured composites has developed significantly in recent years in various applications and industrial fields. For example, it allows the manufacture of support plates for catalysis, but also of materials for construction and transport

[19] . Additive manufacturing makes it possible to produce complex devices with shapes and sometimes properties inaccessible to traditional molding or injection methods. Indeed, it makes it possible to manufacture complex parts that can have different thicknesses and interconnection structures. The interest of “polymer” additive manufacturing also lies in its ability to accept the direct incorporation of conductive fillers into the polymer matrix [20,21].

[0010] However, the direct incorporation of conductive fillers inside the polymer matrix has two major drawbacks which are the low percolation state of the fillers inside said polymer matrix which results in poor use of electrical energy and the low heating efficiency during the on / off process due to inertia problems.

[0011] Furthermore, conventionally, in order to increase the conductivity of the final material, a relatively high concentration of filler is necessary, which can significantly modify the intrinsic properties of the virgin polymer host matrix

[22] The high concentration of the material ensuring the electrical conductivity of the final composite also causes problems of dispersion and homogeneity of the composite. It should also be noted that the presence of insulator / conductor interfaces generated by the synthesis method again poses the problems of heating power or embrittlement of said composite as discussed previously. Finally, the increase in the filler rate induces a variation in viscosity which can become incompatible with the shaping methods.

[0012] There is therefore a real need for a process or method for manufacturing conductive composites, overcoming these defects, drawbacks and obstacles of the prior art, in particular a process or method making it possible to obtain a conductive composite comprising at least one surface layer comprising multi-sheet graphene having improved conductivity and / or resistance.

[0013] In patent application WO2020079372, the applicant described a new process or method for manufacturing a composite comprising at least one surface layer made of multi-sheet graphene, partially overcoming the problems encountered with the composites of the state of the art.

[0014] The process or method described in patent application WO2020079372 makes it possible to produce a homogeneous and continuous layer of conductive material on a substrate, greatly reducing the problems linked to the presence of insulator / conductor interfaces in the composite. Said process is easy to implement to meet market demand. Said process also has the advantage of being able to be implemented on host substrates from a solution comprising multi-layer graphene. Said process thus allows the use of non-harmful materials to replace potentially toxic or dangerous chemical compounds (resins, polymers) which can pose problems of waste recovery and tedious post-synthesis treatment.The surface coating further significantly reduces the loss of electrical conductivity typically encountered with composites constructed from a blend of graphene and polymer where the graphene is embedded in an insulating polymer layer.

[0015] In certain cases, it is desired to apply the graphene multi-sheets to an object whose complex or large shape does not allow the method as described in patent application WO2020079372 to be applied while perfectly matching the shape of the object.

[0016] In certain cases it is also desirable not to make said object excessively heavy. This is particularly important if the object is a vehicle, in particular an aircraft for which the concept of weight is crucial.

[0017] There is therefore a real need for a process or method for manufacturing conductive composites, overcoming this obstacle of the prior art, in particular a process or method making it possible to obtain a conductive composite comprising at least one surface layer comprising multi-sheet graphene having improved conductivity and / or resistance and which can be applied to any type of object, even one of complex shape. Statement of the invention

[0018] It is to the applicant's credit that he has developed a new process or method for manufacturing a composite comprising at least one surface layer consisting of multi-sheet graphene which totally or partially overcomes the problems encountered in the prior art by applying the graphene multi-sheets to a substrate whose particular geometric shape makes it possible to address the problem posed. Thus, the substrate according to the present invention is in a geometric shape chosen from powders, films, pellets, beads, monoliths, foams, extrudates, aerosols of different sizes and their combination, preferably in the form of beads. The graphene fillers used to coat the substrates can be modulated according to the intended application to achieve specific levels of thermal or electrical conductivity according to the intended application.

[0019] The geometric shapes cited, and in particular the ball shape of the substrate, allow its application over the entire surface of the object on which it is desired to be applied, by fitting it perfectly, in particular by adjusting the size of the balls according to the angles with cavities to be filled. It makes it possible to avoid the problems of rigidity or folding encountered with substrates in the form of textiles which do not allow uniformity of coverage.

[0020] Furthermore, a substrate comprising polystyrene, in particular polystyrene beads, addresses the problem of weight because polystyrene has a density of between 15 and 40 kg / m3.

[0021] It is also a cheap and easy-to-obtain material because it has already been used for many years for its insulation applications, and can therefore be used in complete safety.

[0022] The invention thus relates to a process or method for manufacturing a conductive composite comprising at least one surface layer comprising multi-sheet graphene, comprising the steps of: a. bringing into contact a substrate, preferably non-metallic, and an aqueous deposition composition comprising: i. multi-layer graphene at a concentration greater than or equal to 0.2 g / l, and ii. at least one surfactant; b) heat treatment of the substrate obtained in step a) at a temperature ranging from 60 to 300°C, preferably 100 to 250°C; and obtaining the composite;

[0023] characterized in that the substrate is in a geometric form chosen from powders, films, pellets, beads, monoliths, foams, extrudates, aerosols of different sizes and their combination.

[0024] Advantageously, the substrate is in the form of beads.

[0025] Advantageously, the substrate is in the form of beads and comprises polystyrene.

[0026] Advantageously, the substrate is made of polystyrene beads, that is to say not comprising only polystyrene.

[0027] Advantageously, the polystyrene beads have a size between 0.5 and 10 mm in diameter, preferably 1 to 6 mm in diameter. The polystyrene beads have variable densities. Advantageously, the polystyrene beads can be 1 mm, 2 mm, 3 mm, 4 mm, or 6 mm in diameter with respective densities of 28 kg / m3, 19 kg / m3, 16 kg / m3, 11 kg / m3 and 6 kg / m3.

[0028] According to another embodiment of the invention, the substrate is a polystyrene foam or a polyester foam (such as for example aerosleep™) which will be coated with multi-layer graphene.

[0029] According to one embodiment of the invention, the coating rates of the substrates are adjusted according to the geometry and composition of the chosen substrate in order to obtain the desired electrical conductivity characteristics and percolation rate. A person skilled in the art will adapt this coating rate to obtain the desired result using his general knowledge.

[0030] Advantageously, the heat treatment of step b) is carried out at a temperature of between 60 and 300°C, preferably from 100 to 300°C, preferably from 90 to 300°C, preferably from 80 to 280°C and even more preferably from 100 to 250°C. The duration of the heat treatment of step b) may be in an interval ranging from 1 minute to 5 hours, preferably from 5 minutes to 2 hours, or from 30 minutes to 1 hour. The heat treatment of step b) may be carried out by means of different heating modes such as for example in a Joule effect, infrared (IR) or halogen oven, electromagnetic induction and microwave.

[0031] Advantageously, the process or method according to the invention may further comprise a step c) of low-temperature treatment of the composite obtained in step b). The duration of the low-temperature treatment may be in an interval ranging from 1 minute to 5 hours, preferably from 5 minutes to 2 hours, or from 30 minutes to 1 hour. The low-temperature treatment may be carried out by the same heating systems described previously used at low operating temperatures.

[0032] Low temperature means a temperature in the range from 40°C to 80°C, preferably between 50°C and 70°C.

[0033] The process or method according to the invention also has the advantage of being able to be implemented successively to obtain a composite with variable thicknesses of conductive layers. This makes it possible in particular to precisely refine the electrical conductivity of the composite obtained and therefore the properties of the final object such as the quantity of heat that it can emit. Step c) of low-temperature treatment can be carried out between each deposition cycle a), b) and can in certain cases make it possible to further increase the adhesion of the graphene layer to the substrate.

[0034] Advantageously, steps a), b) and optionally c) of the process or method can be repeated at least once, preferably from 1 to 30 times (1 to 30 iterations of the sequence a), b) and optionally c)), even more preferably from 1 to 20 times or even from 1 to 10 times or even 1 to 5 times.

[0035] Advantageously, step a) of bringing the substrate, preferably non-metallic, into contact with the aqueous deposition composition can be carried out by any method of direct application of the aqueous composition (for example with a brush, a sprayer), impregnation of the aqueous composition onto the substrate, immersion of the substrate in the aqueous composition, screen printing. When the contacting requires immersion or an excess supply of aqueous composition onto the substrate, the process or method further comprises an intermediate step a') of emitting the substrate from the aqueous composition or of removing the excess aqueous composition from the surface of the substrate. Step a') is optional and generally depends on the type of contacting. A person skilled in the art, by virtue of his general knowledge, is capable of applying the appropriate step a') when it is required.

[0036] Advantageously, the duration of step a) depends essentially on the contacting method but may be in the range from 1 second to several minutes, preferably from 30 seconds to 30 minutes, even more preferably from 1 to 10 minutes. For example, in the case of immersion, the duration of step a) may be in the range from 10 seconds to 10 minutes, preferably from 20 seconds to 5 minutes, even more preferably from 30 seconds to 2 minutes. In the case of application by means of a brush or a brush, the duration of step a) may be in the range from 10 seconds to 60 minutes, preferably from 2 to 30 minutes, even more preferably from 5 to 20 minutes. In the case of spraying, the duration of step a) may be within a range from 10 seconds to 60 minutes, preferably from 2 to 30 minutes, even more preferably from 5 to 20 minutes.It should be noted that the application time also depends on the total surface area of ​​the substrate to be covered. At the end of step a), a substrate is obtained which can be described as a substrate impregnated or soaked with aqueous deposition composition.

[0037] Advantageously, the process or method according to the invention may further comprise a step d) of applying a finishing polymer layer. Step d) may be carried out after step b) or step c) of the process or method according to the invention. When the implementation of the process according to the invention involves one or more iterations of steps a), b) and optionally c), step d) is carried out only once, when all steps a), b) and c) have been carried out. Step d) may be carried out by any technique known to those skilled in the art for applying a polymer layer to a composite. The finishing polymer may be Among the known polymers, we can cite for example polyurethane, PDMS, polystyrene, or other compounds such as glycerol paints or high temperature paints available commercially.

[0038] Advantageously, the aqueous deposition composition of step a) comprises multi-layer graphene (FLG) and at least one surfactant. Typically, the FLG concentration in the aqueous deposition composition may be greater than or equal to 0.2 g / l, preferably greater than or equal to 1 g / l or even more preferably greater than or equal to 2 g / l. The FLG concentration in the aqueous deposition composition generally does not exceed 50, 60 or 70 g / l. It may for example be in a range from 0.2 to 50 g / l, preferably from 1 to 20 g / l and even more preferably from 2 to 10 g / l.

[0039] In the present text, the term "multi-sheet graphene", "few-layer graphene", "GMF" or "FLG" means graphene containing more than one sheet. Generally, in the context of the invention, the FLG has between 3 and 200 sheets and the sheets have lateral dimensions of between 0.5 and 10 μm, preferably between 1 and 5 μm or even more preferably 1 and 3 μm. The FLG has a thickness of between 1 and 640 nm, preferably between 5 and 320 nm or even more preferably between 20 and 200 nm. Compared with GO (graphene oxide) and rGO (reduced graphene oxide), FLG has significantly superior properties in terms of conductivity due to the absence of oxygenated groups on the surface and also a lower density in terms of defects.

[0040] Advantageously, the aqueous deposition composition of step a) comprises at least one surfactant. The surfactant may be one or more surfactants chosen from the group comprising anionic, cationic, non-ionic and amphoteric (or zwitterionic) surfactants and mixtures thereof. Any type of surfactant, natural or synthetic, may be used within the scope of the invention.

[0041] The term "anionic surfactant" means a surfactant which releases a negative charge (anion) in aqueous solution. An anionic surfactant generally has a relatively high hydrophilic / lipophilic balance (FILB) (which may be between 8 and 18). Examples include soaps, which are salts of fatty acids, of general formula RCOOM (for example R is generally a hydrophobic aliphatic chain and M a metal, an alkali metal or an organic base). Examples include alkaline soaps (such as Na+, K+, NH4+ salts), metal soaps (such as calcium salts) and organic soaps (such as triethanolamine salts, for example, including triethanolamine stearate). There are also sulfated derivatives (examples: sodium laureth sulfate, sodium lauryl sulfate and triethanolamine lauryl sulfate) and sulfonated derivatives (example: sodium dioctylsufosuccinate). There are also lipoamino acids.

[0042] The term "canionic surfactant" means a surfactant that releases a positive charge (cation) in aqueous solution. These are generally nitrogenous products (with a positively charged nitrogen atom). Examples include quaternary ammonium salts such as alkyltrimethylammonium salts (e.g., alkyltrimethylammonium bromide), alkylbenzyldimethylammonium salts (e.g., benzalkonium chloride).

[0043] The term "non-nionic surfactant" means a surfactant that has no net charge and does not ionize in water. Three main categories of non-ionic surfactant are identified:

[0044] ester-linked surfactants (RC(O)-O-R', R and R' being, for example, hydrophobic aliphatic chains) among which mention may be made of glycol esters (for example: ethylene glycol stearate), glycerol esters (for example glycerol stearate), polyoxyethylene glycol esters (obtained by the action of ethylene oxide on a fatty acid or a mixture of fatty acids), sorbitan esters, polyoxyethylene sorbitan esters (more commonly called Tweens 20, 60, 80, etc. or polysorbates), sucrose esters (consisting of a hydrophilic osidic group and a hydrophobic fatty chain);

[0045] ether-linked surfactants (RO-R1, R and R' being, for example, hydrophobic aliphatic chains) among which we can cite ethers of fatty alcohols and polyoxyethylene glycol for example;

[0046] surfactants with an amide bond (RC(O)-NH-R', R and R' being, for example, hydrophobic aliphatic chains).

[0047] The term "amphoteric surfactant" or "zwitterionic surfactant" means a surfactant which comprises both acid and basic functions. Depending on the pH of the medium in which it is found, it releases either a positive ion or a negative ion. Amphoteric surfactants generally have a high HLB. Examples include cocamidopropyl betaine (comprising a quaternary ammonium group and a carboxylic acid group), rimidazoline derivatives or polypeptides.

[0048] Advantageously, the anionic surfactant may be chosen from the group comprising carboxylates, sulfonates or sulfates such as, for example, sulfosuccinates, alpha olefin sulfonates, alkyl glyceryl ether sulfonates and sodium cocoyl monoglyceride sulfates, alkylbenzene sulfonates and mixtures thereof. Advantageously, the cationic surfactant may be chosen from the group comprising quaternary ammonium salts such as, for example, alkylamidodimethyl propylamine or methyl triethanolammonium and mixtures thereof.

[0049] Advantageously, the non-ionic surfactant may be chosen from the group comprising esters, amides or ethers with a hydrophobic aliphatic chain such as, for example, polyglycerol alkyl ethers, glucosyl dialkyl ethers, sorbitan esters, polysorbates, polyglyceryl-3-diisostearates and their mixtures.

[0050] Advantageously, the amphoteric surfactant may be chosen from the group comprising, for example, cocoamidopropyl betaine, cocoamidopropyl sultaine, lauroamphoglycinate, dihydroxyethyl tallow glycinate, disodium cocoamphoacetate, isostearoamphopropionate and mixtures thereof.

[0051] Advantageously, the aqueous deposition composition, for example when it is a commercial solution of surfactants in which the FLG is added, may further comprise and without limitation: preservatives, antimicrobials, stabilizers, humectants, chelators, viscosity regulators or any other additive, and mixtures thereof.

[0052] Advantageously, the mass concentration of surfactant(s) in the aqueous deposition composition of step a) is within a range from 0.1 to 50%, preferably from 0.5 to 10% and even more preferably from 0.5 to 3%. The mass concentration of surfactant(s) in the aqueous deposition composition of step a) may also be within a range from 1 to 50%.

[0053] Advantageously, the aqueous deposition composition can be obtained by ultrasonication of graphite, preferably expanded, in an aqueous solution comprising one or more surfactants, for example, in micellar water (liquid composed of water and micelles). The aqueous deposition solution can further comprise other compounds such as preservatives, antimicrobials, stabilizers, humectants, chelators, viscosity regulators or any other additive, and mixtures thereof.

[0054] The substrate (or host substrate) is in a geometric form chosen from powders, films, pellets, beads, monolith, foams, extrudates, aerosols of different sizes and their combination, preferably in the form of beads and comprises polystyrene and may further comprise any type of material, preferably non-metallic, not having intrinsic electrical conductivity, such as polymers, fabrics, ceramics or glasses.For example, the substrate in the form of beads which comprises polystyrene may also comprise a material chosen from the group comprising thermoplastic polymers (such as poly(methyl)alkyl methacrylate), polystyrene, polyethylene, polypropylene, polyamides, polycarbonate, polydimethylsiloxane), in particular bio-sourced thermoplastic polymers (such as, for example, castor oil, cellulose, lignin), thermosetting polymers (such as epoxies, polyimides, polyurethane), fabrics based on natural fibers (such as, for example, cotton, linen, bamboo, silk, hemp, jute), fabrics based on synthetic fibers (such as, for example, polyamides or polyesters, aramids, acrylics, carbon fibers, glass fibers or ceramic fibers), ceramics (such as SiC, AI203), glasses and their mixtures (for example, a mixture of several polymers or a fabric based on natural fibers and synthetic).

[0055] Preferably, the substrate is a polystyrene bead.

[0056] The invention also relates to conductive composites obtained according to the process or method of the invention. The conductive composites according to the invention have high or improved percolation performances and / or a lower charge concentration in comparison with the conductive composites known from the state of the art.

[0057] Advantageously, the conductive composites according to the invention comprise at least one surface layer comprising multi-sheet graphene (on the surface of the substrate which is in a geometric form chosen from powders, films, pellets, beads, monoliths, foams, extrudates, aerosols of different sizes and their combination, preferably in the form of beads comprising polystyrene, preferably polystyrene beads). The heat treatment step makes it possible to permanently anchor the graphene layer on the surface of the substrate.

[0058] Advantageously, the surface layer comprising multi-sheet graphene has a thickness in a range from 1 to 1000 nm, preferably from 5 to 800 nm and even more preferably from 10 to 500 nm. These ranges refer to the individual layers because the final layer (resulting from one or more iterations of the process or method according to the invention) has a thickness that can be up to a few micrometers or more. The thickness of the final layer can be between 1 and 100 μm, preferably between 3 and 50 μm, and preferably between 4 and 30 μm. Of course, those skilled in the art will adapt the total thickness of the at least one surface layer comprising graphene depending on the intended application.

[0059] The invention thus also relates to a conductive composite comprising a substrate in a geometric form chosen from powders, films, pellets, beads, monoliths, foams, extrudates, aerosols of different sizes and their combination, preferably in the form of beads comprising polystyrene, preferably polystyrene beads as defined above, said substrate comprising at least one surface layer comprising multi-sheet graphene, preferably each of the at least one surface layer has a thickness ranging from 1 to 1000 nm, preferably from 5 to 800 nm and even more preferably from 10 to 500 nm.

[0060] The synthesized composites can be used in various fields of application such as: heating systems for domestic uses where rapid exchanges between the surface heating element and the ambient air are improved, frost-free systems for pipes carrying fluids, defrosting systems for polymer-based materials in various fields, stress detection systems or for controlled closures / openings, metal-free thermal signaling systems, flexible systems for applications in the field of electronics, systems for protecting against electromagnetic radiation.

[0061] Advantageously, the surface layer comprising multi-sheet graphene may have a thickness varying from one part of the composite to another, and consequently a different local electrical conductivity. For example, on two determined areas of the substrate, the implementation of the process or method according to the invention may be different in number of iterations or in concentration in the deposition solution. The number of iterations and / or the charge concentration of the initial solution (step a)) of the process or method may vary from one area of ​​the substrate to another to thus obtain a composite having a surface layer comprising multi-sheet graphene with variable thickness and / or properties.

[0062] Advantageously, the composite according to the invention can have a variable local electrical conductivity. The difference in terms of thickness of the surface layer comprising multi-layer graphene on the substrate thus generates differences in terms of electrical conductivity which can be used for certain applications such as defrosting or in keeping pipes carrying different fluids frost-free, for example, at the junction of a fluid mixer with different inlet temperatures.

[0063] Advantageously, the surface layer comprising multi-sheet graphene is essentially free of surfactant(s), or other elements initially present in the aqueous deposition composition. Preferably, the surface layer consists of multi-sheet graphene and optionally traces of surfactant(s) or other elements initially present in the aqueous deposition composition. The surface layer generally comprises less than 1%, preferably less than 0.1%, of surfactant(s), or other elements initially present in the aqueous deposition composition.

[0064] Advantageously, the surface layer comprising multi-layer graphene does not comprise polymer or resin.

[0065] Advantageously, the surface layer may be made of multi-sheet graphene or made of multi-sheet graphene and the substrate itself, when the latter mixes at the interface, superficially, with the multi-sheet graphene, during the implementation of the method or process according to the invention. In this embodiment, the surface layer comprises a so-called lower part, in contact with the substrate, slightly intermingled at the interface with the latter and a so-called upper part continuous with multi-sheet graphene. This is not a mixture as observed in the prior art where the graphene is mixed in the mass of the substrate, nor a coating made of a mixture of multi-sheet graphene and polymer or resin subsequently applied to the surface of the substrate as described in the prior art. Indeed, in such cases the carbon material (the filler), minority in mass and volume, is then dispersed more or less homogeneously in the polymer / resin matrix.

[0066] Advantageously, the electrical conductivity of the surface layer comprising multi-sheet graphene, measured by the four-point method, may be greater than 200 S / m, preferably greater than 2000 S / m and even more preferably greater than 5000 S / m.

[0067] Advantageously, the structure of the FLG sheets is not altered during the implementation of the process or method. The FLG sheets contained in the surface layer of the composite, generally parallel to the surface of the substrate, according to the invention have a structure similar to that which they have in the aqueous deposition solution.

[0068] Advantageously, the surface layer comprising multi-sheet graphene has a resistance in a range from 1W to 2 kΩ, preferably from 10W to 1000W, and more preferably from 80W to 500W. This resistance value can be measured by applying two copper bars on either side of the surface of the composite, the resistance then being measured by ohmmeter between these two terminals.

[0069] Advantageously, the surface layer of multi-sheet graphene can act as a protective layer to reduce the formation of scratches in the device. The surface layer of multi-sheet graphene, after implementation of the method, can be treated by additional heating (step c')), preferably by laser pulse, in order to eliminate the oxygen residues attached to its surface and which results in an increase in its hydrophobic character. The hydrophobic character makes it possible to reduce the deposition of other substances on the surface of the composite. An example that can be cited is the reduction of hydrate germs in gas or fluid transport pipes that can gradually block the pipe.

[0070] Advantageously, the composite according to the invention may further comprise a finishing polymer layer. In this variant of the invention, the layer comprising multi-layer graphene is covered totally or in part by the finishing polymer layer. In such a compound, the scratches generated on the surface of the polymer layer can be eliminated by heating the graphene / substrate composite below to the required temperature in order to slightly soften the surface polymer layer and thus make the scratches disappear by flattening the surface. This application is of interest in particular in anti-scratch devices.

[0071] The conductive composites according to the invention can find applications in many fields. In particular, the conductive composites in heating, and can in particular allow better management of heat dissipation thus significantly reducing the charge concentration and increasing the heating efficiency. Indeed, the surface layer comprising the multi-layer graphene providing the heating has the advantage of being continuous. This can thus allow a better reaction to the applied current with a significantly lower thermal inertia than that of the composites of the state of the art, where the conductive material is dispersed discontinuously throughout the matrix.

[0072] The composites according to the invention may find application, without limitation, in fields such as low temperature heaters (domestic or fluid conduits in aircraft or other devices), force or medium detectors (via a change in conductivity or resistance when a force is exerted or in the presence of compounds which adsorb on the surface), deicing of polymer-based composites, repulsive surfaces (for example to accelerate the evacuation of vapors), flexible electrical circuits or even temperature detectors by changing the overall resistance as a function of the temperature of the exposed medium, the reduction of deposits originating from solids which may be present in fluids, on the surface in contact with gas or oil in transport pipes, and which, by progressive growth,can block the tubing (for example, hydrate deposits in the gas or oil exploitation area).

[0073] Advantageously, the applied current / emitted energy efficiencies, for the same type of substrate are within a range from 50 W / m2 to 5000 W / m2, preferably between 500 W / m2 and 3000 W / m2, and more preferably from 1000 W / m2 to 3000 W / m2. These efficiencies are generally observed for applied voltages of less than 40 V. Higher powers can be obtained by applying higher voltages, for example for an applied voltage of 20 V a power of 2000 W / m2 is obtained whereas for an applied voltage of 220 V the generated power will be of the order of 22000 W / m2.

[0074] The conductive composites according to the invention comprise a surface layer comprising multi-sheet graphene. Advantageously, said surface layer comprising multi-sheet graphene is uniformly distributed and comprises a thin surface layer of graphene. This results in the use of a small quantity of graphene and a low heating voltage, thus allowing a higher switching frequency (start / stop) than with known composites.

[0075] These characteristics and performances allow in particular the use of these conductive composites according to the invention in intelligent heating devices or in mechanical sensors to control stress and deformation phenomena.

[0076] Advantageously, the conductive composite according to the invention has a frequency switching to very high heating between 30 seconds and 60 minutes, preferably between 60 seconds and 30 minutes, and preferably between 120 seconds and 15 minutes, depending on the voltage applied.

[0077] The invention further relates to a device, for example a heating device or a mechanical sensor, comprising a conductive composite according to the invention. The invention also relates to the use of an aqueous deposition composition as defined above, for forming a surface layer comprising multi-layer graphene on a substrate in a geometric form chosen from powders, films, pellets, beads, monoliths, foams, extrudates, aerosols of different sizes and their combination, preferably in the form of beads comprising polystyrene, preferably polystyrene beads. Brief description of the figures

[0078] [Fig-1] represents (A) digital photos of a polymer-based structure ABS (acrylonitrile butadiene styrene) produced by 3D printing before and after four coating cycles by brushing a paint based on an aqueous solution of multi-layer graphene (10 g / l) followed each time by a heat treatment at 110°C (composite no. 1), (B) the result of an ultrasonication process of composite no. 1 highlighting the mechanical resistance of the composite according to the invention and the strong adhesion of GMF on the surface of the polymer: left image: composite no. 1 before ultrasonication, right image: the composite after ultrasonication showing the total absence of residue in the solution thus confirming the strong adhesion of the graphene layer on the surface of the substrate.

[0079] [Fig.2] represents SEM (scanning electron microscopy) micrographs of the polymer (ABS) as printed (A) and this one after four coating cycles (B) (composite no. 1), showing a highly homogeneous surface coating of the polymer host matrix with a layer of FLG and a high-resolution SEM micrograph showing the smooth coating layer covering the polymer surface after heat treatment at 110 °C (C).

[0080] [Fig.3] represents (A) optical images of a PMMA (Polymethacrylate) plate of methyl) before and after coating with a layer of FLG with a weight loading of approximately 0.8% by weight, (B) SEM micrographs with a cross-sectional view of the composite no. 7 FLG@PMMA showing the thickness of the FLG layer of the order of 4 pm and (C) a measurement of electrical conductivity (S. nrrl ) as a function of the weight loading of FLG (%) recorded on a series of FLG @ PMMA composites (no. 2 to 7).

[0081] [Fig.4] represents (Al ) an optical image of the FLG@PMMA composite (composite n°8) with a weight loading of FLG of 0.23%. (B1 is the thermal image showing the temperature collected at the surface of the composite after applying a voltage of 20 V. (A2 and B2) represent the same composite (A) coated with a polyurethane topcoat and its corresponding thermal properties. (A3 and B3) represent the same composite (A2) coated with a glycerol-based white paint topcoat and its corresponding thermal properties.

[0082] [Fig.5] represents (A, B): photos of an ABS airplane manufactured by 3D printing covered with a surface layer of FLG (composite no. 9) and the corresponding resistance values. (C, D) The digital and thermal images of the ABS aircraft were generated with a 24V power supply and acquired using an IR thermal camera.

[0083] [Fig.6] represents (A) a deposit of FLG on an aircraft manufactured by 3D printing in ABS (composite no. 10). The aircraft rests on a container containing liquid nitrogen in order to create a thin layer of ice on its surface. (B to D) Thermal images show the different surface temperatures of the aircraft as a function of time with a 24V supply. The highest temperature reached after 120s of supply is above 40°C - in the presence of liquid nitrogen under the aircraft. These results illustrate the effectiveness of the FLG layer deposited for deicing applications in cold environments.

[0084] [Fig.7] represents (A, D) the optical and thermal images of an aircraft in coated ABS of an FLG layer (composite no. 1 1 ) after spending 30 min in the freezer so as to produce a thick layer of ice over the entire surface. (B, E, C, F) Optical and thermal photographs show the melting of the ice layer and the temperatures recorded on the aircraft with an applied voltage of 24 V - as a function of the heating time.

[0085] [Fig.8] represents (A, B) SEM images of the cotton-based fabric with different magnifications. (C, D) SEM images of the cotton-based fabric covered with a multi-layer graphene layer (composite no. 12), after heat treatment in air at 130 °C in an oven, with different magnifications.

[0086] [Fig.9] represents (A, B) the electrical conductivity (in Siemens / m) of the composites graphene@tissue (no. 13-22), after synthesis and after heat treatment at 200°C in air in an oven, depending on the graphene load and the number of deposits.

[0087] [Fig. 10] represents (A) Digital photos of an electric radiator and a graphene®fabric composite (n°22) of dimension 16 x 16 cm2 covered by a layer of resin to insulate the conductive surface. (B) Thermal image of the temperature taken at the center of the radiator supplied with a voltage of 230V. (C) (Top left) Digital image of the composite with the electrical connections. (Top center and right and bottom left to right) Thermal images of the graphene®fabric composite with applied voltages ranging from 5 V to 24 V showing the increase in temperature with applied voltage.

[0088] [Fig. 11] represents (A) the optical images illustrating the process of synthesis of graphene and multi-layer graphene by sonication from a solution based on water and Garnier micellar water (surfactant: Dissodium cocoamphodiacetate). (B 1 ) micro-Raman image of the analyzed area, (B2) the Raman spectra corresponding to each dilution (B3) high resolution spectra of the 2D band.

[0089] [Fig. 12] represents the scanning and transmission electron microscopy images of graphene and multi-layer graphene synthesized by sonication using Garnier micellar water as exfoliating agent (surfactant: Dissodium cocoamphodiacetate).

[0090] [Fig. 13] shows (A) an uncoated PEEK tube with the following dimensions: external diameter, 24 mm, internal diameter, 22 mm, length 61 mm, (B) the same PEEK tube covered by a film of FLG, (C) surface temperature measured on the PEEK tube covered by the film of FLG without any voltage applied and (D) the surface temperature of the PEEK-FLG tube measured after applying a voltage of 14 V for two minutes. EXAMPLES

[0091] Example 1: METHOD FOR MANUFACTURING CONDUCTIVE COMPOSITES FLG ©SUBSTRAT

[0092] Composites according to the invention were obtained from different substrates such as ABS, PMMA and were synthesized according to the method described according to the invention.

[0093] The following method was implemented:

[0094] a) an aqueous deposition composition comprising a concentration of 10 g / l of FLG and 0.25% (vol.%) of disodium cocoamphodiacetate (micellar water type) was deposited on the host substrate (ABS grid obtained by 3D printing) by a brush coating technique.

[0095] b) the soaked substrate from step a) thus formed was then dried in an oven at a temperature of 110°C for a period of 30 minutes.

[0096] Sequence a), b) was repeated four times. The FLG@ABS composite was obtained. Figure 1A represents the FLG@ABS composite. In the same way the following composites were prepared: [Tables 1] Composition aqueuse de dépôt Composite N° composite Type de substrat Tensioactif (concentration vol.%) Concentration flg (g / 1) Nombre de couche(s) N°1 FLG@ABS ABS Disodium cocoampho-diacetate (0,25) 10 4 N°2 FLG@PMMA PMMA Disodium cocoampho-diacetate (0,25) 10 1 N°3 FLG@PMMA PMMA Disodium cocoampho-diacetate (0,25) 10 2 N°4 FLG@PMMA PMMA Disodium cocoampho-diacetate (0,25) 10 3 N°5 FLG@PMMA PMMA Disodium cocoampho-diacetate (0,25) 10 4 N°6 FLG@PMMA PMMA Disodium cocoampho-diacetate (0,25) 10 5 N°7 FLG@PMMA PMMA Disodium cocoampho-diacetate (0,25) 10 6 N°8 FLG@PMMA PMMA Disodium cocoampho-diacetate (0,25) 10 2 N°9 FLG@ ABS ABS Disodium cocoampho-diacetate (0,1) 5 4 N°10 FLG@ ABS ABS Disodium cocoampho-diacetate (0,1) 5 4 N°ll ABS Disodium cocoampho- 5 4 FLG@ ABS diacetate (0,1) N° 23 FLG @ PEEK PEEK Disodium cocoampho-diacetate (0,1) 3 4 N° 24 FLG @ PEEK PEEK Disodium cocoampho-diacetate (0,5) 10 6

[0097] Table 1: composites nos. 1 to 11 and 23 to 24 according to the invention. Example 2: FLG @ ABS STABILITY TEST

[0098] The mechanical stability of the surface layer of composite No. 1 FLG@ABS is evaluated by subjecting the composite to ultrasound in an aqueous medium for 30 min.

[0099] The surrounding liquid medium remains colorless, which confirms the very high stability of the coating because if graphene has been released into the liquid, the latter should have a grayish coloring ([Fig.l] B).

[0100] The corresponding micrographs taken with a microscope

[0101] Scanning Electron Micrograph (SEM) of the FLG@ABS composite are shown in Figures 2A to C. The SEM micrograph in Figure 2A highlights the native roughness of the ABS polymer surface, which was 3D printed layer by layer. The same surface after deposition of the FLG layer followed by heat treatment at 110°C has a smooth appearance due to the formation of a continuous and percolated graphene layer (Fig. 2b and c).

[0102] The extremely smooth appearance of the FLG layer (Figure 2C) makes it possible to account for its continuity. Example 3: CONDUCTIVITY OF FLG@ABS

[0103] The optical images corresponding to composite No. 7 FLG@PMMA are presented in Fig. 3A.

[0104] The surface of the composite (right) has a dark gray color characteristic of the formation of an FLG surface layer.

[0105] Fig. 3B shows the SEM images of composite No. 7. The images show good percolation and continuity of the FLG layer with a thickness of about 4 miti. The electrical conductivity (S. nrrl ) as a function of FLG loading and as a function of the deposition number was measured on a series of FLG@PMMA composites No. 2 to No. 7, and are presented in Fig. 3C. It is demonstrated here that the electrical conductivity increases gradually as a function of the coating cycles, i.e. of the FLG concentration, and an electrical conductivity of approximately 1.3-105 S. nrrl was recorded for a mass loading of FLG 0.8% relative to the mass of PMMA.

[0106] Composite No. 8 was made from a PMMA plate (18 x 30 x 0.1 cm) coated with a layer of FLG of approximately 0.23% by weight relative to the weight of the PMMA plate.

[0107] An external voltage of 24 V was applied to the device. The optical and thermal images recorded on the sample as a function of time are presented in [Fig.4] Al and Bl. According to the results obtained, a rapid increase in temperature at the surface of the composite is observed, ranging from ambient to approximately 70°C in less than 10 minutes and which stabilizes under electrical voltage.

[0108] No apparent degradation, i.e., crack formation or debonding of the interface and device components was observed throughout the heating process.

[0109] The same device was coated with a polyurethane-based protective resin to insulate the top FLG layer ([Fig.4] A2) and a voltage of 24V was again applied. The optical and thermal images collected under the same heating conditions used previously are shown in [Fig.4] A2 and B2. According to the results obtained, the polyurethane film does not change the heat properties of the device in any way.

[0110] The last experiment was carried out by applying a layer of white glycerol paint to the surface of the polyurethane film ([Fig.4] A3) and the same heating protocol was repeated. The results presented in [Fig.4] B3 clearly show that the heat capacity of the latter is significantly higher than that of the systems either uncoated or coated only with the polyurethane resin, with a temperature around 95°C instead of 72°C for the same heating times. This can be explained by the fact that the glycerol paint-based film acts as a thermal confinement limiting excessive heat exchange with the ambient atmosphere and thus allowing the confinement of the heat produced by the conductive FLG layer.

[0111] The electrical conductivity measurements of FLG@polymer composites as a function of graphene concentration are presented in Table 2, and compared to the values ​​reported in the literature. [Tables 2] Matrix Conductive filler Filler / matrix mass ratio (%) Process Conductivity of the composite (S / m) Ref. Insulating Conductive Epoxy wrGO 15 In-situ 10 PS foam CNT 7 In-situ 0.5 PMMA foam Graphene 5 In-situ 3 PDMS Graphene 0.8 In-situ 108 PEDOT Graphene 35 In-situ 5008 PANI Graphene 30 In-situ 3900 PANI SWCNT 41 In-situ 120000 PMMA Nano EG 10 In-situ 78 PS Graphene 2 In-situ 1.102 Nylon FG 0.75 In-situ 1.105 HDPE UG 5 Fusion 1.10 10 PANI Graphene 1.5 In-situ 5 PET FGS 0.47 Fusion 7.4.10-2 Poly-carb onate FGS 2 Fusion 1.109 PDMS GF 5 In-situ 10 PS Graphene 0.1 In-situ 0.1 PMMA GMF 0.05 Surface coating 8896 Comp. (No. 2) PMMA GMF 0.2 Surface coating 14000 Comp. (No. 3) PMMA GMF 0.4 Surface coating 43000 Comp. (No. 4) PMMA GMF 0.5 Surface coating 65000 Comp. (No. 5) PMMA GMF 0.6 Surface coating 100000 Comp. (No. 6) PMMA GMF 0.8 Surface coating 130000 Comp. (No. 7)

[0112] Table 2: comparison of conductivity of composites according to the invention No. 2 to 7 and composites according to the prior art.

[0113] Example 4: DEFROSTING OF ABS-BASED POLYMER STRUCTURES

[0114] An ABS structure in the shape of an airplane was manufactured by 3D printing and coated with an FLG layer according to the method of the invention.

[0115] [Fig.5] represents the results obtained.

[0116] To conduct the experiment, two configurations were used in order to evaluate the resistance values ​​at different points ([Fig.5] A and B):

[0117] 1. In the first case, the surface of the aircraft was completely coated with a layer surface of FLG with a concentration of 0.23 wt.%

[0118] 2. In the second case, only the wings were coated with a surface layer of FLG with a concentration of 0.15 wt.%

[0119] The surface temperature observed by infrared camera at different applied voltages and for various configurations is presented in Figure 5C and D - confirms the high efficiency of the deposited layer giving the surface both heating and homogeneous resistance values.

[0120] The temperature at the surface of the composite is homogeneous at the locations where the FLG deposition was carried out, i.e. on the wings or on the entire surface - thus confirming the high efficiency of the composites according to the invention for applications or heating elements.

[0121] In further tests, the aircraft was held on a container containing liquid nitrogen (Fig. 6A) and an electrical voltage of 24V was applied to the wings of the aircraft (Fig. 6B to D). Using the IR images, it was noted that the temperature quickly reached 40°C after only 120 seconds of power supply - making it possible to highlight a de-icing effect on the surface of the aircraft, despite the presence of a cold environment below.

[0122] Finally, the aircraft was placed in a freezer for 2 hours in order to generate a thick layer of ice on its surface. Temperatures recorded by IR camera show values ​​below 4°C ([Fig.7] A and D). Electrical voltage was applied to the wings and temperature readings by thermal photography were taken as a function of time in order to demonstrate the effectiveness of such a system for deicing (Fig. 7B to F). The results show that the ice formed on the surface of the aircraft is completely melted after 240s of 24V voltage applied.

[0123] Example 5: HEATING ON GRAPHENE@FABRIC COMPOSITES

[0124] FLG@tissue composites are prepared according to the following method.

[0125] A cotton-based substrate (Fig. 8A and B) is coated with a multi-layer graphene layer (Figure 8C and D). The composition of the aqueous solution is 10 g / l. The deposition was carried out four times and the composite after each deposition is treated at 130°C in an oven for 15 minutes. The SEM images in Figures 8A and C (as well as the inserts in the figures) indicate that the morphology of the fibers constituting the fabric is preserved after the graphene deposition and the heat treatment. The images in Figures 8C and D confirm the presence of a graphene layer covering the entire surface of the fiber.

[0126] Similar experiments were carried out with the cotton fabric as a function of successive depositions and the results are shown in Table 3. After each deposition of the graphene layer, the soaked substrate is heat treated at 200°C for a period of 30 minutes. The corresponding electrical conductivities are shown in [Fig.9] as a function of either the graphene loading or the number of depositions. The following composites are obtained: [Tables 3] Composite No. Substrate type Surfactant (vol.%) concentration FLG concentration (g / D) Number of layers No. 12 FLG@ fabric Fabric Disodium cocoampho-diacetate (0.25) 10 4 No. 13 FLG@ fabric Fabric Disodium cocoampho-diacetate (0.1) 5 1 No. 14 FLG@ fabric Fabric Disodium cocoampho-diacetate (0.1) 5 2 No. 15 FLG@ fabric Fabric Disodium cocoampho-diacetate (0.1) 5 3 No. 16 FLG@ fabric Fabric Disodium cocoampho-diacetate (0.1) 5 4 No. 17 FLG@ fabric Fabric Disodium cocoampho-diacetate (0.1) 5 5 No. 18 FLG@ fabric Fabric Disodium cocoampho-diacetate (0.1) 5 6 No. 19 FLG@ fabric Fabric Disodium cocoampho-diacetate (0.1) 5 7 No. 20 FLG@ fabric fabric Disodium cocoampho-diacetate (0.1) 5 8 No. 21 FLG@ fabric fabric Disodium cocoampho-diacetate (0.1) 5 9 No. 22 fabric Disodium cocoampho- 5 10 FLG @ diacetate fabric (0.1)

[0127] Table 3: composites n°12 to 22 according to the invention

[0128] Depending on the measured electrical conductivity the deposition can be repeated in order to increase the graphene load in the composite ([Fig.9]).

[0129] FLG@tissue composites No. 13 to 22 were prepared with different graphene loadings (number of process implementations ranging from 1 to 10 iterations). As shown by the results in Figures 9A and B, the increase in the number of deposits, and consequently, the increase in the graphene loading, contributes to a strong increase in the electrical conductivity of the composite.

[0130] The FLG composite @ fabric n°22 (dimension 16x16 cm2) is covered by a transparent polyurethane resin topcoat to electrically insulate it for heating applications (Figure 10A).

[0131] The chosen dimensions allow to have the same heating surface as an electric radiator (Figure 10A) which serves as a reference. The temperature of the radiator, supplied by a voltage of 230 V, measured by a thermal camera is approximately 46°C in the center and with a maximum around 87°C (Figure 10B).

[0132] The graphene®fabric composite is powered with different voltages ranging from 5 to 24V and the thermal images are shown in Figure 10C. With an applied voltage of 24V the graphene®fabric composite generates a more homogeneous temperature of around 83°C in the center and with a maximum around 86°C.

[0133] These results can be explained by the difference in the heating systems: in the radiator the heating is carried out by wire resistors embedded in a block whereas the composite according to the invention has a continuous conductive layer. This results in better temperature homogeneity while the low thickness of the composite also allows the system to be heated up quickly.

[0134] Example 6: Preparation of an aqueous deposition composition, by sonication of expanded graphite in an aqueous solution comprising a surfactant (disodium cocoamphodiacetate).

[0135] 5.4 g of expanded graphite is added to a 1 liter beaker, then 540 ml (540 g) of a mixture composed of water (450 ml) and micellar water (90 ml) is added to the beaker and subjected to the sonication process (40 watts) assisted by stirring for 2 hours ( [Fig. 11] ). The volume of the surfactant (disodium cocoamphodiacetate) is 1.35 ml and corresponds to 0.25% of the total volume, and the graphene concentration is 10 g / l or in other words 1% of the solution. The dispersion obtained can be directly filtered, dried and / or redispersed in an aqueous solution.

[0136] The FLG dispersion thus obtained can be separated into two phases by a sedimentation process ([Fig. 11] A). The first part (A) consists of the remaining exfoliating solution (400 ml) and can be reused to carry out an additional exfoliation process. Part B consisting of 38.5 g / l (3.85%) of graphene and multi-layer graphene can be directly used. According to the results of Raman analysis, the obtained graphene solution exhibits a 2D band characteristic of FLG-based materials with a number of layers less than 20 ([Fig.l 1]. B1, B2, B3).

[0137] The morphology and microstructures of the synthesized FLG were studied by scanning electron microscopy (SEM) and the observations revealed the lateral size between 5 nm and 25 pm (Figures 12A and B).

[0138] Example 7: METHOD FOR PRODUCING FLG@PEEK CONDUCTIVE POLYMER COMPOSITES. Production of a 3g / L concentration solution of multi-layer graphene (500 ml H2O, 1 ml (1.1 g) of disodium cocoamphodiacetate and 1.5 g of graphite) according to the method described in Example 6.

[0139] Contacting by spraying method using an airbrush of the FLG solution to the surface of a polyetheretherketone (PEEK) tube. The tube has the following dimensions: external diameter, 24 mm, internal diameter, 22 mm, length 61 mm)., Drying is then applied in an oven at 80 °C to remove the excess aqueous composition from the surface of the substrate and evaporate the water (optionally). The drying is followed by a heat treatment at 250 °C for 15 minutes in a tubular electric furnace. The operation is repeated four times in order to achieve a deposition of 0.1% by weight of FLG on the PEEK tube.

[0140] The PEEK@FLG composites are obtained (composites no. 23 and 24, see table no. 1).

[0141] FLG load: 6.2 mg (-0.1% of the mass of the PEEK support)

[0142] Longitudinal resistance ~9.6 W.

[0143] Temperature measured by IR camera > 180 °C with an applied voltage of 14 V.

[0144] The PEEK@FLG composite was heated and cooled (by applying alternately a voltage of 0 V and 14 V) six times and the maximum temperature is always above 180°C for the same applied voltage of 14 V, thus indicating excellent stability regarding the adhesion of the FLG film on the polymer surface. List of references

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Claims

Claims

1. Method for manufacturing a conductive composite comprising at least one surface layer comprising multi-sheet graphene, comprising the steps of: a. bringing into contact a substrate, preferably non-metallic, and an aqueous deposition composition comprising: i. multi-sheet graphene at a concentration greater than or equal to 0.2 g / l, preferably greater than or equal to 1 g / l or even more preferably greater than or equal to 2 g / L and ii. at least one surfactant; b. heat treatment of the substrate obtained in step a) at a temperature ranging from 60 to 300°C, preferably 100 to 250°C; and obtaining the composite; characterized in that the substrate is in a geometric form chosen from powders, films, pellets, beads, monoliths, foams, extrudates, aerosols of different sizes and their combination.

2. Method according to the preceding claim, characterized in that the substrate is in the form of beads.

3. Method according to the preceding claim, characterized in that the substrate is in the form of beads and comprises polystyrene.

4. Method according to the preceding claim, characterized in that the substrate consists of polystyrene beads.

5. Method according to the preceding claim, characterized in that the polystyrene beads have a size between 0.5 and 10 mm in diameter.

6. Method according to the preceding claim, further comprising a step c) of low temperature treatment of the composite obtained in step b), preferably for a period of time in the range from 5 minutes to 5 hours.

7. Method according to any one of the preceding claims, wherein steps a), b) and optionally c) are repeated at least once, preferably from 1 to 30 iterations.

8. A method according to any preceding claim, wherein step a), of contacting the substrate and the composition aqueous deposition, is carried out by direct application of the aqueous composition with a brush, a brush or a sprayer, by impregnation of the aqueous composition on the substrate, by immersion of the substrate in the aqueous composition or by screen printing.

9. A method according to any preceding claim, wherein the duration of the heat treatment of step b) is in the range from 1 minute to 5 hours.

10. A method according to any preceding claim, wherein the at least one surfactant is selected from the group comprising anionic, cationic, amphoteric, non-ionic surfactants and mixtures thereof.

11. Method according to any one of the preceding claims, in which the mass concentration of surfactant(s) in the aqueous deposition composition is in a range from 0.1 to 50%.

12. Method according to any one of the preceding claims, in which the substrate comprises a material chosen from the group comprising thermoplastic polymers, in particular bio-sourced polymers, thermosetting polymers, fabrics based on natural and / or synthetic fibers, ceramics, glasses and their mixtures.

13. Conductive composite comprising at least one surface layer consisting of multi-sheet graphene obtained according to the method of any one of the preceding claims.

14. Conductive composite comprising at least one surface layer consisting of multi-sheet graphene on a substrate consisting of polystyrene beads, obtained according to the method of claim 3, 4 or 5.

15. Composite according to the preceding claim in which the at least one surface layer consisting of multi-sheet graphene has a thickness in a range from 1 to 1000 nm.

16. A composite according to any one of claims 13 to 15 having an electrical conductivity greater than 200 S / m.

17. A device comprising a composite according to any one of claims 13 to 16.

18. Use of an aqueous deposition composition comprising multi-sheet graphene at a concentration greater than or equal to 0.2 g / l, preferably greater than or equal to 1 g / l or even more preferably greater than or equal to 2 g / l, and at least one surfactant, to form a surface layer consisting of multi-sheet graphene on a substrate in a geometric form chosen from powders, films, pellets, beads, monolith, foams, extrudates, aerosols of various sizes and their combination, preferably a substrate made of polystyrene beads.

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