DE102011109457A1 - Preparing a dispersion, useful e.g. to prepare a composite and coat a surface, comprises applying a mixture comprising graphene and a liquid under pressure and passing the pressurized mixture via an opening - Google Patents

Abstract

Preparing a dispersion comprises (a) applying a mixture comprising graphene and a liquid under pressure and (b) passing the pressurized mixture through an opening. Independent claims are included for: (1) the dispersion obtained by the above process, provided that graphene does not contain nitrogen and the liquid is not propylene carbonate, where the graphene comprises carboxy group and/or phenolic hydroxy group in deprotonated form and liquid is water, isopropanol or acetone; (2) producing a composite comprising contacting a substrate with the dispersion; and (3) the composite obtained by the above method.

Description

The invention relates to a method for producing a stable dispersion of graphene in a liquid without the addition of binders or stabilizers such as surfactants. Furthermore, the invention relates to the dispersion, composites containing graphene, processes for the preparation of composites by means of the dispersion and the use of the dispersion for coating surfaces and for producing films and objects which conduct the electric current and heat.

Graphene is known to have high mechanical strength and excellent electrical conductivity. Therefore, it can be advantageously used in electrical engineering, electronics and materials technology.

It is often necessary for graphene to be in dispersed form for these applications, for example as an aqueous dispersion. For the preparation of these dispersions, starting from graphite, the latter can first be oxidized in a known manner to give graphite oxide (GO) which, if appropriate after exfoliation to graphene oxide, is in turn converted into graphene and dispersed in, for example, water.

Graphite oxide has various oxygen functionalities, namely epoxide, hydroxyl, carbonyl and carboxyl groups. It is known that this oxygen present in the graphite oxide can be removed by at least partial reduction. As a result, the electrically non-conductive graphite oxide is converted into electrically conductive graphene. Such graphene is also referred to in the art as chemically modified graphene (CMG).

The reduction can be carried out with reducing agents such as hydrazine. It is known that a CMG produced in this way after the reduction contains considerable amounts of nitrogen, ie has nitrogen functionalities ( X. Gao, J. Jang and S. Nagase, J. Phys. Chem. C 2010, 114, 832-842 ; H.-P. Boehm, A. Clauss, GO Fischer, U. Hofmann, Z. Naturforschg. 1962, 17b, 150 ).

Furthermore, the reduction with dimethylhydrazine, hydroquinone and sodium borohydride is known ( Y. Zhu, MD Stoller, W. Cai, A. Velamakanni, RD Piner, D. Chen, and RS Ruoff, ACSNano, Vol. 4, 2, 1227-1223 (2010) ). The use of vitamin C as a reducing agent is also possible ( MJ Fernández-Merino, L. Guardia, JI Paredes, S. Villar-Radil, P. Solis-Fernández, A. Martinez-Alonso, JMD Tascón, J. Phys. Chem. C. 2010, 114, 6426 (doi: 10.1021 / jp100603h) ).

For reduction, graphene oxide can also be subjected to a heat treatment, wherein likewise the oxygen functionality is reduced and graphene or CMG is formed. In addition to the terms "graphene" and "CMG", the term "thermally reduced graphite oxide (TRGO)" is also used to describe the resulting graphene in this form of reduction. This heat treatment can take place at temperatures above 700 ° C ( X. Gao, J. Jang and S. Nagase, J. Phys. Chem. C 2010, 114, 832-842 ; HC Schniepp, J.-L. Li, MJ McAllister, H. Sai, M. Herrera-Alonso, DH Adamson, RK Prud'homme, R. Car, DA Saville, IA Aksay, J. Phys. Chem. B 2006, 110, 8535 ; MJ McAllister, J.-L. Li, DH Adamson, HC Schniepp, AA Abdala, J. Liu, M. Herrera-Alonso, DL Milius, R. Car, RK Prud'homme, IA Aksay, Chem. Mater. 2007, 19, 4396 ).

It is also known that the carbon layers (graphene) prepared by the above known processes, for example in water, can agglomerate and flocculate with each other. They then precipitate undesirably from the dispersion as a solid precipitate, i. H. the dispersion is not stable. In order to avoid agglomeration or flocculation, compounds which are capable of stabilizing the dispersion must generally be added to the mixture of graphene oxide and, for example, water and / or the graphene or chemically modified graphene formed in water. Preferably, for stabilization binders or surface-active compounds such as surfactants are used. However, it is known that these stabilizers can interfere with applications of graphene dispersions, for example aqueous graphene dispersions, which in particular require electrical conductivity.

An aqueous suspension of graphene oxide can be reduced with hydrazine to form an aqueous dispersion of graphene that is stable even without the addition of stabilizers, provided that the dispersion contains neither salts and acids nor excess hydrazine and CMG's containing carboxyl groups with ammonia be neutralized ( D. Li, MB Müller, S. Gilje, RB Kaner and GG Wallace, nature nanotechnology, Vol 3, February 2008, pages 101-105 (doi: 10.1038 / nnano.2007.451) ).

Also known are aqueous dispersions of graphene which are stable without the addition of binders or stabilizers such as surfactants, if in a separate reaction step, a functionalization of the graphene oxide is carried out, for example with sulfonic acid or sulfonate. For this purpose, the graphene oxide is first prereduced with sodium borohydride and then by reaction with a diazonium salt of sulfanilic acid the Sulfonic acid groups are introduced. Only after a further reduction with hydrazine a sulfonated graphene was obtained in this way, which forms stable suspension, for example in water ( Y. Si, ET Samulski, Nano Lett. 2008, 8, 1679 (doi: 10.1021 / nl080604h) ).

Colloidal suspensions of graphene oxide obtained by exfoliation of graphite oxide can be reduced with hydrazine to give dispersions of graphene which may be stable even without the addition of stabilizers such as surfactants or binders. The solvent used is a mixture of dimethylformamide and water. It is also possible to add further solvents, for example acetone, to this dispersion without impairing the stability thereof ( Park, J.An, I. Jung, RD Piner, SJ An, X. Li, A. Velamakanni, RS Ruoff, Nano Letters 2009, 9, 1593-1597 (doi: 10.1021 / nl803798y) ).

An electrostatic stabilization of graphene suspensions obtained by reduction with hydrazine is also known. By treating an aqueous graphene oxide dispersion with KOH and subsequent reduction with hydrazine, stable, aqueous graphene suspensions were obtained ( S. Park, J. An, RD Piner, I. Jung, D. Yang, A. Velamakanni, ST Nguyen, RS Ruoff, Chem. Mater. 2008, 20, 6592. (doi: 10.1021 / cm801932u) ).

It is also known to convert graphite oxide into propylene carbonate by exfoliation in graphene oxide, which in turn is then converted by a thermal treatment at a temperature of 150 ° C in graphene. The resulting dispersion is stable without the addition of stabilizers ( Y. Zhu, MD Stoller, W. Cai, A. Velamakanni, RD Piner, D. Chen, and RS Ruoff, ACSNano, Vol. 4, 2, 1227-1223 (2010) ).

An object of the present invention was to provide a graphene dispersion which may or may not be stable without the addition of binders or stabilizers such as surfactants, and which graphene preferably does not contain any nitrogen functionalities, ie contains no nitrogen and otherwise no by-products from a chemical reduction contains, since such in applications, which in particular require the electrical conductivity of the graphene, can interfere.

This object has been achieved by a method as defined in claim 1, which provides for the pressure release of a mixture comprising graphene and a liquid or consisting of graphene and a liquid.

• (i) Beaufschlagen eines Gemischs umfassend Graphen und eine Flüssigkeit mit Druck;
• (ii) Führen des unter Druck stehenden Gemischs der Stufe (i) durch eine Öffnung.

A first aspect of the invention relates to the preparation of the dispersion according to the invention. Accordingly, the object is achieved by a process for the preparation of a dispersion comprising graphene and a liquid which is characterized in that it comprises stages (i) and (ii):

• (i) applying a mixture comprising graphene and a liquid under pressure;
• (ii) passing the pressurized mixture of step (i) through an orifice.

• (iiia) Reduzieren von Graphitoxid oder Graphenoxid zu Graphen.

In one embodiment, the method according to the invention is characterized in that before step (i) it comprises the step (iiia):

• (iiia) reducing graphite oxide or graphene oxide to graphene.

The graphite oxide required for step (iiia) can be prepared by oxidation of graphite by known methods. As the oxidizing agent sulfuric acid, sodium nitrate and / or permanganates such as potassium or sodium permanganate can be used. Graphene oxide can be obtained by exfoliation of graphite oxide.

In one embodiment, in step (iiia) graphite or graphene oxide is not thermally reduced by a chemical reduction, in particular not by reduction with hydrazine, but preferably thermally.

• (iiib) thermisches Reduzieren von Graphitoxid oder Graphenoxid zu Graphen.

In one embodiment, the method according to the invention is characterized in that before step (i) it comprises the step (iiib):

• (iiib) thermally reducing graphite oxide or graphene oxide to graphene.

In one embodiment, the graph formed in step (iiia) or (iiib) contains no nitrogen. Accordingly, in this embodiment, reduction by hydrazine is excluded.

In a further embodiment, the reduction is also excluded with dimethylhydrazine or by reduction with sodium borohydride or with vitamin C.

In a further embodiment, the use of a reducing agent in the reduction of graphite oxide or graphene oxide to graphene is excluded.

In a further embodiment, it is excluded that the liquid consists of propylene carbonate. In a further embodiment, it is also excluded that the liquid comprises propylene carbonate. In a further embodiment, it is excluded that the dispersion formed comprises propylene carbonate.

In another embodiment, the graphene contains no nitrogen and the dispersion does not contain propylene carbonate or does not contain propylene carbonate.

In a further embodiment, the graphene formed in step (iiia) or (iiib) contains no sulfonic acid or sulfonate groups and / or no potassium.

In another embodiment, the graphene formed in step (iiia) or (iiib) contains neither nitrogen nor sulfonic acid or sulfonate groups and / or potassium.

In a further embodiment, the graphene formed in step (iiia) or (iiib) contains neither nitrogen nor a sulfonic acid or sulfonate group and / or potassium and the liquid does not consist of propylene carborate or does not comprise propylene carbonate.

The term "dispersion" means that graphene is distributed as a solid phase in the liquid phase. Synonymous with this term, the terms "suspension", "nanosuspension" or "colloid" are used. These and all subsequent definitions refer to definitions as used in the context of the invention.

The term "stable dispersion" means that when the dispersion is allowed to stand still after 5 hours, more preferably 10 hours, more preferably 15 hours, no precipitation is detectable in the dispersion by the naked eye.

The term "graphene" means a monolayer of carbon atoms which are tightly packed in a two-dimensional honeycomb lattice.

In one embodiment, the term "graphene" means that oxygen groups are attached to carbon atoms of that layer. Oxygen groups may be present for example in the form of hydroxyl groups and / or epoxide groups and / or bound via carboxyl groups and / or via carbonyl groups. The term "graphene" thus also encompasses the terms "chemically modified graphene (CMG)" and "thermally reduced graphite oxide (TRGO)", in which embodiment the graphene preferably has no nitrogen functionalities, ie contains no nitrogen.

The graphene used in step (i) is produced by reduction, preferably by thermal reduction of graphite oxide or graphene oxide. Suitable methods are known from the prior art, for example from the prior art as cited above. For example, graphite oxide can be used as the starting material, which can be converted into graphene oxide before the reduction by exfoliation, preferably by treatment with ultrasound.

The term "reduction" in step (iiia) means that the oxygen content in the graphite oxide or graphene oxide is lowered or reduced.

The term "thermal reduction" in step (iiib) means that graphite oxide or graphene oxide is subjected to a heat treatment, preferably exposed to a temperature of more than 100 ° C in order to lower the oxygen content in graphene oxide, which is said to produce graphene. This graph may also be in the form of CMG or in admixture with CMG.

In one embodiment, the heat treatment of the graphite oxide or graphene oxide takes place at temperatures greater than 120 ° C, preferably at a temperature greater than 200 ° C, more preferably greater than 300 ° C, especially at temperatures greater than 400 ° C.

The upper limit of the thermal treatment is generally 2,000 ° C, more preferably 1,500 ° C, even more preferably 1,000 ° C, further preferably 500 ° C.

In one embodiment, the thermal reduction takes place at a temperature of 150 to 1000 ° C, preferably at a temperature of 200 to 900 ° C, more preferably at a temperature of 300 to 800 ° C, more preferably at a temperature of 350 to 700 ° C, or 350 to 600 ° C, or 350 to 500 ° C, or 350 to 450 ° C.

The structure of the graphene produced by thermal reduction may be temperature dependent. This means that graphene made by thermal deoxidization at relatively low temperatures may or may not have a structure other than graphene made at higher temperatures. Consequently, graph types produced in this way can also differ from each other in their properties.

If aqueous dispersions are to be prepared, a reduction temperature in the range of 350 to 800 ° C is preferred, more preferably 350 to 700 ° C, more preferably 350 to 600 ° C, and more preferably 350 to 500 ° C or 350 to 450 ° C.

The term "mixture" in step (i) means that graphene and the liquid are present as a dispersion, the term "dispersion" having the abovementioned meaning. Such a mixture is not yet a stable suspension. It can be prepared by known methods by combining the components graphene and Liquid, wherein the mixing can be assisted by stirring or shaking. The suspension formation can also take place under the action of ultrasound.

The concentration of graphene in the liquid in step (i) can vary within wide limits. Preferred is a concentration range of 0.001 wt .-% to 50 wt .-% graphene in the liquid based on the total amount of graphene and liquid.

In a further embodiment, the concentration range of graphene in the liquid in step (i) is from 0.001% to 10%, more preferably from 0.001% to 5%, even more preferably 0.001% by weight. % to 1% by weight.

In a further embodiment, the concentration range of graphene in the liquid in step (ii) is from 0.001% to 0.1%, more preferably from 0.001% to 0.05% by weight.

In a further embodiment, the concentration range of graphene in the liquid in step (ii) is from 0.01% to 0.1% by weight, more preferably from 0.01% to 0.05% by weight. ,

The term "liquid" includes protic as well as aprotic liquids or solvents.

In one embodiment, the boiling point of the liquid used or the liquids used at normal pressure in a temperature range of 20 to 300 ° C.

In a further embodiment, a liquid can be used whose boiling point at normal pressure is 300 ° C and more. In one embodiment, the boiling point of the liquid used or of the liquids used at normal pressure in a temperature range of 300 to 400 ° C.

In one embodiment, in particular for printing inks, liquids are used which have a relatively low boiling point and can therefore be relatively easily removed from them in applications of the dispersion, preferably by heating or by evaporation.

In one embodiment, the boiling point of the liquid at atmospheric pressure in a temperature range of 20 to 210 ° C, preferably 30 to 180 ° C. Such liquids have a lower boiling point than, for example, propylene carbonate having a relatively high boiling point of 242 ° C. They are easier to remove from the dispersion in applications, preferably by heating. This improves their suitability in applications, for example in the application for coatings, since such a liquid is easier to remove from the coating than, for example, propylene carbonate.

Preferred protic liquids are water and aliphatic alcohols such as methanol, ethanol, propanol, isopropanol or butanol such as 1-butanol, 2-butanol or t-butanol.

Particularly preferred is water.

Preferred aprotic liquids are ketones such as acetone, methyl ethyl ketone, diethyl ketone, diisopropyl ketone; Amides such as dimethylformamide; Nitriles such as acetonitrile or benzonitrile; Sulfoxides such as dimethylsulfoxide; Carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate; Plasticizer z. In the form of phthalic esters such as diisononyl phthalate or fats and oils.

In one embodiment, relatively high boiling liquids such as ethylene carbonate, sulfolane, N-methylpyrrolidone or propylene carbonate may also be used.

A particularly preferred aprotic liquid is acetone.

In another embodiment, propylene carbonate is excluded as aprotic liquid. In another embodiment, the liquid is not propylene carbonate.

It is also possible to use two or more of the liquids mentioned.

Concentration levels of graphene in the dispersion obtained after step (iii) correspond to the contents of the mixture of step (ii) used.

The temperature of the mixture of step (i) as used in step (ii) may vary within wide limits. In one embodiment, step (ii) is carried out at a temperature of 10 to 100 ° C, preferably 10 to 90 ° C or at a temperature of 15 to 40 ° C, or 20 to 30 ° C.

In one embodiment of the process according to the invention, the mixture of stage (i) is depressurized in stage (ii). The term "depressurized" means that the pressure on the outlet side of the opening is smaller than on the supply side of the opening. Preferably, a pressure of preferably 1 to 10 bar is set or formed on the outlet side of the opening.

In one embodiment of the method according to the invention, the mixture of stage (i) in step (ii) is passed through the opening such that a pressure gradient is formed between the feed side of the mixture to the opening and the outlet side of the opening, the pressure on the outlet side being lower is as on the feed side.

In one embodiment, the method is characterized in that the mixture in step (i) is subjected to a pressure of more than 100 bar, or that the pressure difference between the supply side of the opening and the outlet side of the opening is greater than 100 bar.

In another embodiment, the pressure is greater than 500 bar, or greater than 700 bar, or greater than 900 bar, or greater than 1,100 bar, or greater than 1,300 bar, or is the pressure difference between the feed side of the opening and the outlet side of the opening greater than 500 bar, or greater than 700 bar, or greater than 900 bar, or greater than 1,100 bar, or greater than 1,300 bar.

The upper limit of the pressure is preferably 3,000 bar, more preferably 2,000 bar, in particular 1,500 bar.

The application of pressure to the mixture in step (i) can be effected by pressing on a gas, preferably an inert gas. Inert gases are preferably nitrogen and noble gases such as helium or argon.

In another embodiment, pressurization may be by mechanical means such as pumps or pistons.

In one embodiment, the mixture is continuously pressed through the opening in step (ii) of the method according to the invention with a pump. In another embodiment, the mixture is forced under high pressure by a piston discontinuously through the opening.

Accordingly, in one embodiment, stages (i) and (ii) are performed in parallel, while in another embodiment, stage (ii) is performed after stage (i).

In both embodiments, the sudden release of the mixture causes high shear forces and gravitational effects on the mixture. Without wishing to be bound by theory, it is believed that these cause the dispersion of graphene in the solvent or liquid.

Devices with which a pressure difference between the supply side of the opening and the outlet side of the opening can be generated, are known from the prior art. For example, commercial high-pressure homogenizers can be used.

In one embodiment, the opening in step (ii) is formed as an opening of a nozzle.

In a further embodiment, the opening is formed as a gap or as an annular gap.

By suitable dimensioning of the opening in step (ii) or the gap width, the pressure differences between the feed side and export side can be adjusted according to the invention. These pressure differences as a function of the dimensioning can be determined by routine tests.

In one embodiment, the diameter of the opening or the width of the gap is 0.1 to 2 mm, or 0.1 to 0.5 mm.

If the liquid is water or comprises water, in one embodiment of the process the pH of the mixture of step (i) or of the dispersion obtained after step (ii) is adjusted to a value greater than 7, preferably greater than 8, more preferably greater than 9. In one embodiment, the pH is 9 to 10. In another embodiment, a pH of greater than 10 may also be adjusted.

A pH greater than 7 is preferably adjusted when protic liquids, preferably water, are used as the liquid in the dispersion.

For this purpose, the mixture can be mixed with basic substances. It is preferred to use bases which do not interfere with subsequent applications of the dispersion since they can evaporate from the dispersion or are volatile.

In one embodiment, nitrogen bases are used which are already volatile at room temperature, or which are volatile when heated to temperatures up to 100 ° C, preferably up to 80 ° C, more preferably up to 50 ° C. Suitable compounds are preferably ammonia or volatile organic amines. Volatile organic amines are preferably C1-C5-alkyl-substituted ammonia, preferably diethyl and triethylamine. Heterocyclic amines such as morpholine or piperidine can also be used.

Ammonia is particularly preferred. It can be used in gaseous form or also in the form of ammonia water.

In a further embodiment, the hydroxides of the alkali metals or the alkaline earth metals can be used as basic substances. Suitable compounds are preferably sodium hydroxide or potassium hydroxide.

This basic treatment also causes existing in the graphene carboxyl groups and / or phenolic hydroxyl groups are either completely or partially deprotonated, ie present as carboxylate or phenate groups.

On the other hand, in one embodiment, when aprotic solvents are used as the liquid, it is also possible to set a pH which is 7 or less.

It has surprisingly been found that agglomeration and / or flocculation of the graphene or of the carbon layers can be prevented in a dispersion of graphene in the liquid prepared according to the invention without the addition of stabilizers, ie without the addition of binders and / or surfactants. Thus, the dispersion prepared according to the invention is stable even without the addition of a stabilizer, for example a binder and / or surfactant.

In one embodiment, the method is characterized in that it is carried out in the absence of substances which prevent agglomeration or flocculation of the graphene. Thus, the dispersion contains no stabilizer for the dispersion, so for example, neither a binder nor a surfactant.

The terms "agglomeration" and "flocculation" are used synonymously. They mean the aggregation of graphene layers such that they precipitate out of the dispersion, for example in the form of a precipitate.

The term "binder" encompasses polymers, preferably water-soluble or water-dispersible polymers such as cellulose derivatives, polyvinyl alcohol, phenolic resins, polyvinylpyrrolidone, and similar substances.

The term "surfactants" encompasses substances which reduce the surface tension of a liquid or the interfacial tension between the solid graphene phase and the water and enable or assist the formation of the dispersion or act as solubilizers.

Binders and surfactants commonly used to stabilize dispersions are known to those skilled in the art. The suitability or unsuitability thereof as a stabilizer for an aqueous graphite dispersion can also be determined by routine experiments.

The term "binders and / or surfactants" is thus also defined as meaning "amphiphiles" which reduce the interfacial tension between two phases and / or an average molecular weight Mw of 500-5,000,000 g / mol, preferably from 600 to 3,000 .000 g / mol, more preferably from 1,000 to 1,000,000 g / mol ". The term "amphiphile" means that the molecule has hydrophilic (eg, polar hydroxyl groups or ionic carboxylate groups) and hydrophobic groups. The Mw values can be determined, for example, by gel permeation chromatography.

A second aspect of the invention relates to a dispersion consisting of or comprising graphene and a liquid.

In one embodiment, the invention relates to a dispersion consisting of or comprising graphene and a liquid which is characterized in that it is prepared by the process according to the invention.

In one embodiment, the invention relates to a dispersion consisting of graphene and a liquid or a dispersion comprising graphene and a liquid which is characterized in that it is produced by the process according to the invention, with the proviso that the graphene contains no nitrogen and the liquid not made of propylene carbonate.

In one embodiment, the dispersion obtained according to step (ii) comprising graphene and a liquid or consisting of graphene and a liquid, characterized in that it is prepared by the process according to the invention, wherein it contains no substances that agglomeration or flocculation of graphene prevent.

In one embodiment, the dispersion of graphene in the liquid obtained according to step (ii) consists of graphene and the liquid, wherein carboxyl groups present in the graphene and / or the phenolic hydroxyl groups may be present in neutralized or deprotonated form.

In one embodiment, the dispersion obtained after step (ii) consists of graphene and the liquid, wherein carboxyl groups contained in the graphene may be in neutralized form, and wherein the graphene contains no nitrogen.

In one embodiment, the invention relates to a dispersion consisting of graphene and a liquid or a dispersion comprising graphene and a liquid, wherein in the graph contained carboxyl groups or phenolic OH groups may be present in neutralized or deprotonated form, with the proviso that the graph contains no nitrogen and the liquid does not consist of propylene carbonate.

In one embodiment, the liquid is water or contains water.

In one embodiment, the liquid is isopropanol or contains isopropanol.

In another embodiment, the liquid is acetone or contains acetone.

In one embodiment, the invention relates to a dispersion consisting of graphene and a liquid consisting of water or comprising water, or a dispersion comprising graphene and a liquid consisting of water or comprising water, wherein carboxyl groups present in the graphene may be present in neutralized form, with the proviso in that the graph contains no nitrogen.

In a further embodiment, the invention relates to a dispersion consisting of graphene and a liquid consisting of acetone or comprising acetone, or a dispersion comprising graphene and a liquid consisting of acetone or comprising acetone, with the proviso that the graph contains no nitrogen.

The absence of substances such as binders or surfactants in the dispersion according to the invention renders them valuable, in particular for electronic or electrical applications, since there are no foreign substances in the dispersion which could adversely affect this application.

In one embodiment, substances may be added to the dispersion for applications, preferably for applications as described below, which enhance the conductivity thereof. Such substances are preferably metallic nanoparticles or Kohlenstoffnanotubes. The addition of metal salts, preferably for catalytic applications, is also possible.

A third aspect of the invention relates to the preparation of composites comprising or comprising graphene.

The term "composite" means a composite of at least one substrate associated with graphene or comprising or having graphene.

The preparation of a composite comprising a substrate and graphene can be carried out in a simple manner by contacting the substrate with the inventive graphite dispersion. After evaporation of the solvent, graphene remains on the surface of the article. Optionally, if the substrate has pores, graphene may also be incorporated in the interior of the substrate. The evaporation of the solvent may optionally be accelerated by the action of heat.

• (i) Kontaktieren des Substrats mit der erfindungsgemäßen Dispersion.

In an embodiment, the method for producing a composite comprising a substrate and graphene is characterized in that it comprises the step (i):

• (i) contacting the substrate with the dispersion of the invention.

The term "substrate" means any material. It can have any shape.

Depending on the intended application, the substrate may be a solid or even a fluid.

In one embodiment, the solid is selected from the group: paper, plastic, metal, wood, ceramics, glass.

Paper as a substrate is particularly preferred. The term "paper" includes all products based on cellulose, which are suitable for writing or packaging, including cardboard.

The term "plastic" includes organic polymers such as polyethylene, polyethylene terephthalate, polyesters, polystyrene, phenolic resins, polyamide, and / or glass fibers.

The term "ceramic" includes both artificial ceramics and stone.

In one embodiment, the solid is in film form. Films may preferably be formed from plastics or ceramics.

In another embodiment, the solid is present as a fiber. The fibers may also be in the form of a nonwoven.

The application of the dispersion of the invention to the solid can be accomplished by methods known in the art.

Suitable methods are preferably printing methods, ie methods by which the dispersion is preferably applied to the surface of the article by means of a printing plate. Preferably, as the printing process, the Offset printing, gravure or flexographic printing can be used.

In one embodiment, as the printing method, an ink-jet printing method can be used.

In a further embodiment, the dispersion can also be contacted to the substrate by means of a device with which the production of three-dimensional objects is possible. The technology of a 3D plotter and the production of three-dimensional objects via 3D plotting are described, for example, in US Pat WO 01/78968 and from R. Landers, U. Hübner, R. Schmelzeisen, R. Mülhaupt, Biomaterials 23 (2002) 4437-4447 , This method provides that a material from a three-dimensionally movable dispenser is applied to another material or introduced into this.

Compared to ink-jet printing, which preferably works with dispersions of relatively low viscosity of about 25 mPa · s, graphite dispersions of both high and low viscosity can be printed with this method. For example, pastes having a viscosity of up to 1,000 Pa · s can be processed. The printed layers may already have a thickness of about 10 μm after a printing step, while in the inkjet process generally only layer thicknesses in the range of 300 nm are achieved. The resolution of the 3D plot is i. A. in the range of 100 microns to 2,000 microns.

The applied by contacting or printed layers have i. A. a specific conductivity in the range of 10 S / cm, which is retained even with repeated bending of the composite, preferably a composite, which preferably comprises paper or film as a substrate.

In a further embodiment, substances which improve the electrical conductivity can be added to the dispersion according to the invention or to the dispersion prepared by a process according to the invention.

In one embodiment, metal nanoparticles are added. Suitable metal nanoparticles are, for example, nanoparticles of gold or silver or iron. Such nanoparticles are known from the prior art.

In a further embodiment, carbon particles in the form of nanotubes, also referred to as carbon nanotubes, can be added, which can likewise increase the electrical conductivity. Such particles are known in the art.

In a further embodiment, metal salts can be added to the dispersion or the dispersion according to the invention prepared by the process according to the invention. In this way, it is possible to produce catalytically active metal particles after contacting on the substrate, preferably by chemical or thermal reduction. In one embodiment, the contacted substrate is heated above the decomposition point of the metal salt. In one embodiment, fixed-bed supported catalysts can be prepared in this manner by contacting, preferably by printing on the substrate. In a further embodiment, it is possible to apply a plurality of different graphite dispersions according to the invention side by side or one above the other onto a substrate, preferably by printing, preferably by 3D technology, whereby multicenter catalysts are formed.

In one embodiment, one or more iron salts, preferably selected from iron nitrate or iron acetate, are added to the dispersion according to the invention or to the dispersion prepared by the process according to the invention.

In one embodiment, the substrate is a ceramic which is contacted with the dispersion according to the invention or the dispersion prepared by the process according to the invention which contains an iron salt or iron salts. After heating the composite, reducing the iron salts to iron particles, such a composite can be used as a catalyst, for example for the catalytic polymerization of ethylene.

In one embodiment, it is possible to encapsulate the printed and / or graphene layers or graphene layers of the composites produced by the contacting directly after drying with a suitable polymer, preferably with silicone. In this way it is possible to produce so-called encapsulated electronics. These preferably have a high mechanical strength.

• (ii) Verkapseln des mit der Dispersion kontaktierten Substrats mit Silikon.

In an embodiment, the method for producing a composite is characterized in that after step (i) it comprises step (ii):

• (ii) Encapsulating the substrate contacted with the dispersion with silicone.

In a further embodiment, cells can be applied to the composite according to the invention or to the composite prepared by the process according to the invention, for example animal or plant cells. Such a cell-populated composite can be used as a nerve tract.

• (iii) Besiedeln des mit der Dispersion kontaktierten Substrats mit menschlichen, tierischen oder pflanzlichen Zellen.

In an embodiment, the method for producing a composite is characterized in that after step (i) it comprises step (iii):

• (iii) colonizing the substrate contacted with the dispersion with human, animal or plant cells.

Other suitable contacting methods other than printing methods are preferably the known spraying, dipping or rolling methods. Accordingly, the dispersion can be sprayed onto the surface of the substrate to be contacted, the substrate to be contacted dipped into the dispersion or applied by means of a roller to the surface of the substrate. Brushing, so the application by means of a brush or a brush, are also possible.

The application of graphene from the dispersion according to the invention to paper can also be carried out by the known method of vacuum filtration.

In one embodiment, the application may be repeated several times, i. H. several layers of graphene can be applied to the substrate or applied side by side.

In addition to solid substrates and fluids can be contacted with the dispersion of the invention, d. H. be mixed. In one embodiment, the fluid is a dispersion of a substance or a solution of the substance, preferably a dispersion of a substance in water or a solution of the substance in water. Suitable dispersions are preferably aqueous plastic dispersions or aqueous plastic solutions. Examples of suitable plastics are organic polymers such as, for example, acrylates, polyesters, polyvinyl alcohol.

In a preferred embodiment, the method for producing a composite is characterized in that the dispersion according to the invention or the dispersion prepared by the process according to the invention is contacted with the substrate by metering from a three-dimensionally movable dispenser. In this case, extrusion or spraying can be used.

The term "dispenser" means a dispenser for the dispersion.

In one embodiment, the contacting takes place via the above-defined 3D technology, preferably with a 3D plotter. In another embodiment, also by spraying, z. As "paint-jet" or "airbrush" method.

The composites produced by the process according to the invention are electrically conductive. In one embodiment, they are also thermally conductive.

A fourth aspect of the invention relates to a composite comprising a substrate and graphene. This composite is characterized in that it is produced by a process which provides for contacting the substrate with the dispersion according to the invention or with a dispersion prepared by the process according to the invention.

In one embodiment, the invention relates to a composite comprising a substrate and graphene, characterized in that it is produced by contacting the substrate with the dispersion according to the invention.

In one embodiment, the invention relates to a composite comprising a substrate and graphene, characterized in that it is produced by contacting the substrate with the dispersion according to the invention. As a result, a graphene layer forms on the substrate. In one embodiment, the substrate is paper or comprises paper. An advantage of the method according to the invention is that thermal and / or chemical aftertreatment of the printed layers can be dispensed with. As a result, especially thermally and / or chemically sensitive substrates, for. As paper to be printed.

In one embodiment, the invention relates to a composite constructed as a multilayer system in which graphene layers formed from the dispersion according to the invention alternate continuously with identical or different substrates.

Furthermore, it is also possible within the scope of the invention to produce such a graphene layer without the finished graphene layer being bound to a substrate as defined above, e.g. B. in the form of a graphene sheet. In this embodiment, graphene is also the substrate at the same time.

The dispersion according to the invention or the composites produced therefrom allow a multiplicity of possible uses and applications.

A fifth aspect of the invention relates to possible uses and applications of the dispersion or composites made therefrom.

In one use, the dispersion of the invention is used to coat surfaces of a substrate.

The dispersion of the invention can be printed, resulting in flexible, electrically conductive layers on a variety of substrates, including on paper. This opens in a further embodiment, the possibility of use as a printing ink or for the production of an ink.

Accordingly, the dispersion can be used to make composites that conduct the electrical current.

Conductive composites can be prepared analogous to composites known in the art.

In one embodiment, the composite is an electrode, preferably an electrode for fuel cells, lithium-ion batteries, capacitors, and / or double-layer capacitors. The latter can preferably be produced by printing on a film or paper with the dispersion according to the invention, wherein a thin polymer film is applied to the graphene layer produced, preferably by printing, onto which in turn a further graphene layer is applied, preferably by printing with the dispersion according to the invention.

Preferably, the electrode can be made of films. Suitable films are preferably plastic films and / or ceramic films to which a graphite dispersion according to the invention or a graphite dispersion prepared by the process according to the invention is applied.

The films or electrodes can also be processed with separators or other electrodes in film form by known methods to batteries, such as lithium-ion batteries.

By coating or laminating films coated with graphene with suitable materials, it is possible to produce capacitors by methods which are also known in principle.

In one embodiment, the dispersion is used: to make a printing ink or as an ink; for the production of printed electronics; for the production of encapsulated electronics, for the production of printed catalyst systems and for the production of printed three-dimensional objects.

The term "printed electronics" is used synonymously with the term "printed circuit". For the preparation, preferably an electrically insulating substrate, preferably paper or a fiber-reinforced plastic, preferably glass fiber plates or phenolic resin, with the dispersion of the invention or with a dispersion prepared by the process according to the invention, contacted in a suitable manner and coated, preferably by printing, so in that electrically conductive areas are formed on the insulating material. These areas can then be populated with other electronic components such as transistors, capacitors or resistors.

Similarly, printed catalyst systems comprising graphene can be prepared by printing a suitable material, preferably by methods as described above.

The composites can also be used for power, for example to power a pacemaker.

The dispersion according to the invention or the dispersion prepared by the process according to the invention can furthermore be applied to a suitable substrate, preferably by printing, that a film in the form of a bar code; an advertising space; and / or a touchpad.

Since graphene or CMG has hydrophobic and thus water-repellent properties, the dispersion can be used in a further use to produce composites which are water-repellent.

Since graphene or CMG has good mechanical properties such as strength, in another embodiment the dispersion can be used to mechanically stabilize substrates.

1 shows TEM (transmission electron microscopy) images of the graphus suspension according to the invention prepared according to example 1. In a) a sample is shown, which was dispersed by means of ultrasound without high-pressure homogenization. An agglomerate of several graphene flakes with dimensions of> 10 μm can be seen. Dark areas in the image are assigned to thick graphene structures that can be created, for example, by folding or stacking individual graphene layers. In b) the same sample is shown after it was treated analogously to Example 1C at 1,500 bar in the high-pressure homogenizer. After homogenization, the graphene structures appear significantly thinner in the TEM and large agglomerates are no longer present.

Figure 2 shows a specific conductivity analysis with repeated bending of binderless printed graphene films on paper and film. The rectangles indicate the use of the binder-containing dispersion of Example 5 which Circle the use of the inventive dispersion of Example 3. On the ordinate, the specific conductivity in S / cm is plotted on the abscissa, the number of bending cycles.

Examples

example 1

Step A) Preparation of graphite oxide

60 g of graphite were with 1.4 l 95 percent. Sulfuric acid and 30 g of sodium nitrate for a period of 20 h at room temperature. Subsequently, the mixture was cooled to 0 ° C and slowly added to 180 g of potassium permanganate. The mixture was then stirred for 2.5 h without cooling. The resulting reaction mixture was poured into 2 ice-water and slowly with 200 ml 3 percent. Hydrogen peroxide added. The precipitated solid was filtered off and washed several times with 5 percent strength. Hydrochloric acid. The residue was washed with demineralized water until the effluent water was neutral. The resulting solid was then dried at a temperature of 40 ° C for a period of 4 days in a vacuum oven. The dried product was ground, dried again for a period of 4 days and then used for thermal reduction according to Example 2.

Step B) Preparation of graphene in the form of a chemically modified graphene by thermal reduction

The dried graphite oxide obtained according to Example 1A was fed in countercurrent of nitrogen into an electrically heated oven which had been preheated to the desired reduction temperature, for example to 400.degree. The formed graphene was collected and used without further purification.

Step C) Preparation of an aqueous graphite dispersion according to the invention

800 ml of deionized water was brought to pH 10 with sodium hydroxide. 200 mg of graphene obtained by reduction (thermal reduction) of graphite oxide at 400 ° C. according to Example 1B was predispersed in the alkaline solution by means of an ultrasonic bath. The predispersed product was transferred to a high pressure homogenizer (GEA Niro Soavi, Model Panda NS 1001L 2K). The pressure was gradually increased to 1,400 bar and the product conveyed in a circle until the final pressure was reached. After reaching 1,400 bar, the dispersion was collected and used for further experiments. The 0.025% by weight dispersion had a water-like consistency.

Example 2: Preparation of an aqueous graphite dispersion according to the invention

The procedure was as in Example 1 with the difference that in step C, a 1.5 wt .-% dispersion was prepared. The consistency of the dispersion was pasty. This dispersion could be printed and could therefore be used as printing ink.

Example 3: Preparation of an aqueous graphite dispersion according to the invention

The procedure was as in Example 1 with the difference that in step B, a reduction at 500 ° C was performed and in step C, a 1.25 wt .-% dispersion was prepared. The consistency of the dispersion was pasty. This dispersion was printable and could therefore be used in Example 6 as an ink.

Example 4: Preparation of a non-aqueous graphite dispersion according to the invention

200 mg of graphene, which was obtained by reduction of graphite oxide at 600 ° C analogously to Example 16, was predispersed by means of an ultrasonic bath in 800 ml of acetone. The predispersed product was transferred to a high pressure homogenizer (GEA Niro Soavi, Model Panda NS 1001L 2K). The pressure was gradually increased to 1,400 bar and the product conveyed in a circle until the final pressure was reached. After reaching 1,400 bar, the dispersion was collected. It was used for experiments, eg. As applications used.

Example 5 (Comparative Example): Preparation of a binder-containing graphite dispersion

200 ml of water were brought to a pH of 9-10 with NaOH and admixed with 4 g of graphene (obtained by thermal reduction of graphite oxide). To the mixture was added 0.8 ml of a 30 wt% aqueous solution of polyvinylpyrrolidone PVP (Mw 360,000 g / mol, Sigma, St. Louis, USA). The pasty substance was predispersed by stirring and then treated at 500 bar in a high-pressure homogenizer.

Example 6: Printing of aqueous graphene dispersions

The graphite ink was printed on a substrate in the form of an aqueous dispersion and dried at room temperature. In all printing processes, films (30 × 10 mm) were printed using a 3D plotter (3D Bioplotter ^™ , 3rd generation, Envisontec, Germany). All further analyzes were performed on these printed films. The layer thickness of the printed films was measured with a micrometer screw (Micromaster, Tesa, Switzerland) certainly. Depending on the viscosity of the material, the pressure used and the number of repetitions, layer thicknesses between 5 ± 3 μm and 20 ± 3 μm were obtained. Each printing step was performed twice by default. The conductivity of the resulting films was determined by 4-point measurement and calculated by a correction factor according to known methods ( SM Sze, Physics of Semiconductor Devices, 2nd Edition ). For the statistical evaluation, a sum of three samples was examined in each case.

conductivity measurement

The specific conductivity of all listed samples was determined using a 4-point measurement method. For this purpose, four precision contacts (Bürklin, Germany) were arranged at a uniform distance of 2.5 mm and placed with constant pressure on the sample to be measured. An electrical current was applied to the outer poles via a multimeter (Keithley 617 Programmable Electrometer, Keithley, USA) and to the inner poles with a second multimeter (Fluke 8846A 6-1 / 2 Digit Precision Multimeter, Fluke Deutschland GmbH, Germany) respective voltage tapped. Several measurements were taken around the center of the sample. The layer thickness of the printed films was determined by means of a micrometer screw (Micromaster, Tesa, Switzerland). The sample geometry was determined by a correction factor ( SM Sze, Physics of Semiconductor Devices, 2nd Edition ) considered. For the statistical evaluation, a sum of three samples was examined in each case.

Variant A: on paper with binder

The background was standardized paper (80 g / m ² , m-real) using the dispersion of Example 5. The resulting layer had an average thickness of 17 ± 2 μm and had a conductivity of 0.5 ± 0.2 S / cm.

Variant B: on foil with binder

The background was standardized photocopy film (Soennecken, Overath, Germany). The dispersion from Example 5 was used. The resulting layer had an average thickness of 6 ± 2 μm and a handsability of 0.3 ± 0.1 S / cm.

Variant C: on paper without binder

The background was standardized printing paper (80 g / m ² , m-real). The dispersion from example 3 was used. The resulting layer had an average thickness of 14 ± 2 μm and had a conductivity of 8.3 ± 2.1 S / cm.

Variant D: on film without binder

The background was standardized photocopy film (Soennecken, Overath, Germany). The dispersion from example 3 was used. The resulting layer had an average thickness of 5 ± 2 μm and had a conductivity of 10.2 ± 3.6 S / cm.

bending tests

Bending tests were performed to check the stability of the printed films on the substrate. For this purpose, the sample to be examined was bent by hand on the concave and convex side. A bending cycle was correspondingly bent once as a concave and counted once convexly curved. After every 100 bending cycles, the specific conductivity was determined by means of a 4-point measurement. A total of 1,000 bending cycles per sample was performed. For the statistical evaluation, a sum of three samples was examined in each case.

Example 7: Preparation of Graphene Papers:

By vacuum filtration of 26 ml of the suspension of Example 1C graphs the graphene flakes (0.2 micron pore, 47 mm diameter, Whatman Cyclopore ^® track-etched,) were used as paper-like film deposited on a membrane filter. After drying overnight, the film could be released from the filter. A free-standing, flexible, electrically conductive graphene paper was obtained. Analogously to Example 6, the thickness was determined by means of micrometer screw and the conductivity by means of four-point measurement. At a thickness of 11 ± 1 μm, the paper had a conductivity of 12 ± 1 S / cm.

Example 8: Biocompatibility test

To verify the biocompatibility of the graphene produced according to the invention, cell culture experiments were carried out. Graphene papers were prepared by vacuum filtration as described in Example 7. Pressed tablets of graphite were pressed with a standard tablet press and served as a reference substance. All samples were washed several times to remove impurities with Dulbecco's PBS (without Ca ²⁺ , Mg ²⁺ , PAA Laboratories GmbH, Pasching, Austria) and then sterilized in an autoclave (Tuttnauer, New York, USA, Model 3870 ELV) (120 ° C, 5 bar, 30 min). Sterilized TRGO papers and graphite tablets (3 samples each) were placed in 24 well plates (TCPS, Greiner, Frickenhausen, Germany) and probed with CAL 72 cells (Human Osteosarcoma Cell Line, ACC 439, German Collection for Microorganisms and Cell Cultures GmbH , DSMZ, Braunschweig, Germany) populated. For each well, a concentration of 1 × 10 ⁵ cells was chosen. The samples were taken in Dulbecco's Modified Eagle Medium (DMEM, Biowhittaker, Verviers, Belgium) with 10% fetal calf serum (FCS, PAA Laboratories GmbH, Linz, Austria), 1% penicillin / streptomycin (Biochrom, Berlin, Germany) and insulin transferrin ( 1 vial / 5 l medium) for 48 h in an incubator (Kendro-Heraeus, Osterode, Germany). The vitality of the cells was checked by a staining experiment with fluorescein diacetate (FDA) and propidium iodide (PI) as specific fluorophores. In fluorescence micrographs, live cells appear in green, whereas dead cells are displayed in red. Images were obtained with a microscope (Axiover 135, Zeiss, Oberkochen, Germany) with camera (AE 1, Canon, Amstelveen, The Netherlands). The graphene papers used had no negative effect on cell growth.

Example 9: Preparation of epoxy resin / graphene nanocomposites

Epoxy resin / graphene nanocomposites based on bisphenol A diglycidyl ether (BADGE) with dicyandiamide (DICY) as hardener were prepared.

Variant A: with known dispersion methods

171 g of epoxy resin (CY 225, Huntsman) were dissolved in acetone and 1.5 g of graph (obtained from the thermal reduction of graphite oxide at 750 ° C) is by treatment by means of Ultra-Turrax ^® (T25, IKA) dispersed. The acetone was removed in vacuo and the reaction mixture transferred to an aluminum can. There was added 7.9 g of the reactive diluent (Cardolite Lite ^® HP 2513, Cardolite) and stirred for 1 h at 90 ° C in Platenrührer. 19 g of the hardener (Dyhard 100 SH, Alz Chem) and 0.6 g of the accelerator (Dyhard UR 300 AB, Alz Chem) were stirred in by spatula and 0.5 h at 90 ° C under reduced pressure (40-70 mbar) in the planetary stirrer touched. The casting took place in a tempered steel mold (140 ° C). It was cured for 1 h at 140 ° C followed by 1 h at 180 ° C.

The ends of a cuboid test piece (1 × 0.4 × 0.2 cm) were contacted with conductive silver and the electrical resistance was measured using a multimeter (Keithley 617 Programmable Electrometer, Keithley, USA). From this measurement and the length and cross-sectional area of the specimen, the electrical conductivity of this composite was determined to be 0.75 wt% graphene at 5 × 10 ^-20 S / cm.

Variant B: Dispersing by means of high-pressure homogenizer

200 ml of acetone were mixed with 0.75 g of graphene (obtained from thermal reduction of graphite oxide at 750 ° C.) and predispersed in an ultrasonic bath for 15 minutes. The suspension obtained was treated by means of high-pressure homogenizer at 900 bar and then 85 g of the epoxy resin (CY 225, Huntsman) dissolved therein. According to a further dispersion by means of Ultra-Turrax ^® (T25, IKA), the acetone was removed in vacuo and transferred to the reaction mixture in an aluminum can. There were added and stirred for 1 h at 90 ° C in a planetary mixer 4.0 g of the reactive diluent (Cardolite Lite ^® HP 2513, Cardolite). 9.6 g of the hardener (Dyhard 100 SH, Alz Chem) and 0.3 g of the accelerator (Dyhard UR 300 AB, Alz Chem) were stirred in by spatula and 0.5 h at 90 ° C under reduced pressure (40-70 mbar) in Stirred planetary stirrer. The casting was carried out in a tempered steel mold (140 ° C) and it was cured for 1 h at 140 ° C followed by 1 h at 180 ° C.

The ends of a cuboid test piece (1 × 0.4 × 0.2 cm) were contacted with conductive silver and the electrical resistance was measured using a multimeter (Keithley 617 Programmable Electrometer, Keithley, USA). For this measurement, as well as the length and the cross-sectional area of the specimen, the electric conductivity of this graph composites to 1 × 10 ^-8 S / cm was determined to 0.75 wt .-%.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 01/78968 [0119]

Cited non-patent literature

• X. Gao, J. Jang and S. Nagase, J. Phys. Chem. C 2010, 114, 832-842 [0005]
• H.-P. Boehm, A. Clauss, GO Fischer, U. Hofmann, Z. Naturforschg. 1962, 17b, 150 [0005]
• Y. Zhu, MD Stoller, W. Cai, A. Velamakanni, RD Piner, D. Chen and RS Ruoff, ACSNano, Vol. 4, 2, 1227-1223 (2010) [0006]
• MJ Fernández-Merino, L. Guardia, JI Paredes, S. Villar-Radil, P. Solis-Fernández, A. Martinez-Alonso, JMD Tascón, J. Phys. Chem. C. 2010, 114, 6426 (doi: 10.1021 / jp100603h) [0006]
• X. Gao, J. Jang and S. Nagase, J. Phys. Chem. C 2010, 114, 832-842 [0007]
• HC Schniepp, J.-L. Li, MJ McAllister, H. Sai, M. Herrera-Alonso, DH Adamson, RK Prud'homme, R. Car, DA Saville, IA Aksay, J. Phys. Chem. B 2006, 110, 8535 [0007]
• MJ McAllister, J.-L. Li, DH Adamson, HC Schniepp, AA Abdala, J. Liu, M. Herrera-Alonso, DL Milius, R. Car, RK Prud'homme, IA Aksay, Chem. Mater. 2007, 19, 4396 [0007]
• D. Li, MB Müller, S. Gilje, RB Kaner and GG Wallace, nature nanotechnology, Vol 3, February 2008, pages 101-105 (doi: 10.1038 / nnano.2007.451) [0009]
• Y. Si, ET Samulski, Nano Lett. 2008, 8, 1679 (doi: 10.1021 / nl080604h) [0010]
• Park, J.A., I. Jung, RD Piner, SJ An, X. Li, A. Velamakanni, RS Ruoff, Nano Letters 2009, 9, 1593-1597 (doi: 10.1021 / nl803798y) [0011]
• S. Park, J. An, RD Piner, I. Jung, D. Yang, A. Velamakanni, ST Nguyen, RS Ruoff, Chem. Mater. 2008, 20, 6592. (doi: 10.1021 / cm801932u) [0012]
• Y. Zhu, MD Stoller, W. Cai, A. Velamakanni, RD Piner, D. Chen and RS Ruoff, ACSNano, Vol. 4, 2, 1227-1223 (2010) [0013]
• R. Landers, U. Hübner, R. Schmelzeisen, R. Mülhaupt, Biomaterials 23 (2002) 4437-4447 [0119]
• SM Sze, Physics of Semiconductor Devices, 2nd Edition [0171]
• SM Sze, Physics of Semiconductor Devices, 2nd Edition [0172]

Claims (10)

A process for the preparation of a dispersion comprising graphene and a liquid, characterized in that it comprises steps (i) and (ii): (i) applying a mixture comprising graphene and a liquid under pressure; (ii) passing the pressurized mixture of step (i) through an orifice. A method according to claim 1, characterized in that prior to step (i) it comprises the step (iiib): (iiib) Thermal reduction of graphite oxide or graphene oxide. Method according to one of the preceding claims, characterized in that the pressure is greater than 100 bar, or 500 bar, or 900 bar, or 1,100 bar, or 1,300 bar. Method according to one of the preceding claims, characterized in that the liquid is selected from the group consisting of: water; Methanol, ethanol, n-propanol, i-propanol, butanol; Acetonitrile, benzonitrile; Acetone, methyl ethyl ketone, diethyl ketone, diisopropyl ketone; Dimethylformamide, N-methylformamide, N-methylpyrrolidone; Dimethyl sulfoxide, sulfolane; Dimethycarbonate, diethyl carbonate, ethylene carbonate, propylene carbonate; or two or more of these liquids. Method according to one of the preceding claims, characterized in that it is carried out in the absence of binders and / or surfactants. Dispersion consisting of graphene and a liquid, or dispersion comprising graphene and a liquid, characterized in that it is prepared by a process as defined in any one of claims 1 to 5, with the proviso that the graphene contains no nitrogen and the liquid does not consists of propylene carbonate. Dispersion, characterized in that it consists of graphene and a liquid, or comprises graphene and a liquid, wherein in the graph contained carboxyl groups and / or phenolic OH groups can be present in deprotonated form, with the proviso that the graph contains no nitrogen and the liquid does not consist of propylene carbonate, the liquid preferably consisting of water, isopropanol or acetone or comprising water, isopropanol or acetone. Process for the preparation of a composite comprising a substrate and graphene, characterized in that it comprises the step (i): (i) contacting the substrate with a dispersion as defined in claim 6 or 7. Composite comprising a substrate and graphene, characterized in that it is produced by a process as defined in claim 8. Use of a dispersion as defined in claim 6 or 7 for coating surfaces; for producing a printing ink or as an ink; for producing a composite that conducts electrical current and / or heat; for preparing a composite which is water repellent; for the mechanical stabilization of a composite, wherein preferably the coated surface or the composite are: a printed product; an electronics; an encapsulated electronics (encapsulated electronics); a catalyst or a catalyst system; an electrode; a capacitor; a double-layer capacitor; a lithium-ion battery; a graphene paper; a bar code; an advertising space; a touchpad; a cell-populated composite; and / or a printed three-dimensional object, e.g. B. comprising a polymer.

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