A graphene film with high longitudinal thermal conductivity and preparation method thereof

Abstract

The present invention relates to the field of graphene materials, and specifically provides a graphene film with high longitudinal thermal conductivity and a preparation method thereof. Graphene has very ideal thermal conductivity, and the graphene film prepared by the traditional process has a very ideal horizontal thermal conductivity, but the longitudinal thermal conductivity is very low. This is mainly attributed to the fact that no bonding-type heat conduction channel is formed in the longitudinal direction of the graphene film, and the oxygen-containing functional groups of the graphene film fall off during the thermal reduction process, resulting in the interlayer gap further hindering the longitudinal heat conduction. Although it has undergone subsequent calendering, rolling and other processing processes, the improvement effect of the longitudinal thermal conductivity is very small. The present invention provides a graphene film with high longitudinal thermal conductivity, which utilizes the different oxygen-containing functional groups carried by the graphene film itself to react with external groups, so that adjacent graphene layers between the graphene film layers form upper and lower double-bonded heat conduction channels, which effectively improves the longitudinal thermal conductivity of the graphene film, has a simple process, and is easy to use.

Description

Technical Field

[0001] The invention relates to the technical field of graphene materials, and in particular to a graphene film with high longitudinal thermal conductivity and a preparation method thereof. Background Art

[0002] Graphene has very ideal thermal properties, with a theoretical thermal conductivity of up to 5300W / mk, and has great potential for application in the field of thermal management materials. Commercially available thermally conductive graphene membranes for thermal management have been used, and conventional graphene membranes are mainly obtained by thermal reduction of graphene oxide membranes. The traditional process for preparing graphene membranes is mainly to reduce graphene oxide membranes to graphene membranes through two stages: low-temperature heat treatment and high-temperature thermal reduction. In the post-reduction treatment stage, the pore spacing between the graphene membrane layers, which is a poor thermal conductor, is adjusted by calendering or rolling, and finally a thermally conductive graphene membrane can be obtained.

[0003] At present, the horizontal thermal conductivity of graphene film has reached 1500W / mk, but its longitudinal thermal conductivity is less than one percent of the horizontal thermal conductivity. There are two main reasons for this. First, there are only simple van der Waals interactions and π-π conjugated interactions between graphene sheets in the graphene film, and no stable chemical bonding has been formed, so it is impossible to construct a longitudinal heat conduction channel. Second, the graphene film is obtained by reducing the graphene oxide film. Graphene oxide contains rich oxygen-containing functional groups. The oxygen-containing functional groups of the graphene oxide film fall off during the reduction process, which will increase the distance between the graphene layers and form pores that are poor conductors of heat, aggravating the deterioration of the longitudinal thermal conductivity, which is not conducive to the rapid transfer of heat from the lower layer to the upper layer. Summary of the invention

[0004] In view of the above problems, the present invention provides a graphene film with high longitudinal thermal conductivity and a preparation method thereof. The graphene film prepared by the present invention has a high longitudinal thermal conductivity. Combined with other excellent physical and chemical properties of the graphene film, the graphene film with optimized longitudinal thermal conductivity will shine in the field of thermal management material application.

[0005] The present invention provides a method for preparing a graphene film with high longitudinal thermal conductivity, comprising the following steps:

[0006] 1) In the film-forming stage of low-temperature heat treatment of graphene oxide, a first multifunctional medium substance containing sulfonic acid groups is introduced to bond, and a low-reduction graphene oxide film is obtained by treatment; the temperature of the low-temperature heat treatment is lower than 195° C.;

[0007] 2) subjecting a number of the low-reduction graphene oxide films and a second multifunctional dielectric substance to high-temperature heat treatment for condensation reaction and carbonization reduction, wherein the second multifunctional dielectric substance comprises a basic group bonded to a carboxyl group, and the temperature of the high-temperature heat treatment is higher than 205° C., to obtain a graphene film with a high longitudinal thermal conductivity.

[0008] Preferably, step 1) is specifically:

[0009] 11) mixing graphene oxide and a first multi-functional medium substance containing sulfonic acid groups in water to obtain graphene oxide slurry;

[0010] 12) coating the graphene oxide slurry on a substrate, and heating the coating to cure and shape the coating to obtain a graphene oxide film layer;

[0011] 13) The obtained graphene oxide film layers are heated to 150-190° C. and kept warm, preferably under pressure, to obtain a low-reduction graphene oxide film.

[0012] Preferably, in step 11), the carbon content of the graphene oxide is 35-70%; and the first multi-functional medium substance includes polystyrene sulfonate.

[0013] Preferably, in step 11), the first multifunctional dielectric substance further comprises a conductive polymer that forms a π-π conjugation with the graphene carbon hexagonal ring; and the solid content of the graphene oxide slurry is 2-5%.

[0014] Preferably, in step 12), the coating thickness is 1000-8000 μm; the curing temperature is 60-100° C., and a graphene oxide film layer is obtained after separation.

[0015] Preferably, step 2) is specifically:

[0016] 21) immersing the low-reduction graphene oxide film in an aqueous solution of a second multi-functional medium substance, pumping down the pressure and letting it stand, and then drying and dehydrating;

[0017] 22) The dried and dehydrated film samples are heated to 210-280° C., kept warm for 2-4 hours, and then heated to 1000-1400° C. for carbonization reduction to obtain a graphene film with high longitudinal thermal conductivity.

[0018] Preferably, in step 21), the basic groups contained in the second multifunctional medium substance are selected from one or more of substituted or unsubstituted amino, amidine, guanidine, pyridyl, purine and pyrimidine groups.

[0019] Preferably, in step 21), the second multifunctional medium substance is polydiallyldimethylammonium halide, and the concentration of the aqueous solution is 0.01-0.5M; the temperature of the drying and dehydration is 60-100°C.

[0020] Preferably, in step 22), the dried and dehydrated membrane samples are heated to 210-280° C. in a protective atmosphere under different weight pressure conditions, with a heating rate of 1-5° C. / min.

[0021] The present invention provides a graphene film with high longitudinal thermal conductivity obtained by the preparation method as described above.

[0022] Different from the traditional graphene film preparation process, the present invention first introduces an external group sulfonic acid group (such as the sulfonic acid group in PSS, including but not limited to all dielectric substances of the sulfonic acid group that can form a bond with the hydroxyl functional group, and the medium must contain ≥2 of the functional group) in the low-temperature heat treatment film-forming stage, which forms a bond with the hydroxyl functional group in the graphene film; then in the high-temperature heat treatment stage, introduces a basic group that forms a bond with the carboxyl functional group in the graphene (such as the amino group in PDDA, including but not limited to all dielectric substances of the amino group that can form a bond with the carboxyl functional group, and the medium must contain ≥2 of the functional group), thereby forming an upper and lower "double bond lock" between adjacent graphene layers in the graphene film, constructing a longitudinal heat conduction channel, and optimizing the longitudinal heat conduction performance of the graphene film.

[0023] Compared with traditional graphene films, the high longitudinal thermal conductivity graphene film provided by the present invention has the characteristics of higher longitudinal thermal conductivity, smaller micro-nano gap spacing, etc., which provides important reference and reference for the practical application of graphene and similar research. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a SEM image of the cross section of the graphene film obtained in Example 1 of the present invention;

[0025] Figure 2 This is a cross-sectional SEM image of a graphene film prepared using a conventional process;

[0026] Figure 3 This is a cohesion test curve of the graphene film sample obtained in Example 1 of the present invention;

[0027] Figure 4 This is a graph of the cohesion test curve of the graphene film prepared by traditional technology. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0029] The primary purpose of the present invention is to provide a graphene film with high longitudinal thermal conductivity, and another purpose is to provide a method for preparing the same. At present, in order to obtain higher thermal conductivity, the main strategies are: continuously increasing the thickness of the graphene film, obtaining better thermal conductivity by increasing the heat capacity, regulating the interlayer spacing of the graphene film by means of calendering and rolling, reducing the pores of poor thermal conductors and constructing longitudinal thermal conduction channels to improve the longitudinal thermal conductivity of the graphene film.

[0030] To achieve the above object, the present invention provides a method for preparing a graphene film with high longitudinal thermal conductivity, comprising the following steps:

[0031] 1) In the film-forming stage of low-temperature heat treatment of graphene oxide, a first multifunctional medium substance containing sulfonic acid groups is introduced to bond, and a low-reduction graphene oxide film is obtained by treatment; the temperature of the low-temperature heat treatment is lower than 195° C.;

[0032] 2) subjecting a number of the low-reduction graphene oxide films and a second multifunctional dielectric substance to high-temperature heat treatment for condensation reaction and carbonization reduction, wherein the second multifunctional dielectric substance comprises a basic group bonded to a carboxyl group, and the temperature of the high-temperature heat treatment is higher than 205° C., to obtain a graphene film with a high longitudinal thermal conductivity.

[0033] In an embodiment of the present invention, an aqueous solution of a first multifunctional dielectric substance containing sulfonic acid groups can be prepared, and then mixed with graphene oxide cake, preferably configured into a graphene oxide slurry with a solid content of 2-5%. Wherein, the first multifunctional dielectric substance is a dielectric substance containing one or more sulfonic acid groups, preferably including polystyrene sulfonate, such as sodium polystyrene sulfonate (PSS), whose average molecular weight is less than 1000000; sodium polystyrene sulfonate can be directly purchased from reagent websites such as Aladdin and McLean without synthesis. Further preferably, the first multifunctional dielectric substance also includes a conductive polymer that forms a π-π conjugated effect with the graphene carbon hexagonal ring, preferably poly 3,4-ethylenedioxythiophene (PEDOT).

[0034] The graphene oxide raw material described in the embodiment of the present invention can be a commercially available product. The number of graphene oxide layers after oxidation is ≤10 layers, the thickness is about <4nm, and there is no special requirement for the functional group. The graphene oxide prepared by the conventional oxidation process has functional groups such as hydroxyl, carboxyl, epoxy, and carbonyl; its carbon content can be 35-70%. Carbon content refers to the C element content in graphene oxide, that is, the carbon content before oxidation is 99.99%, and the carbon content after oxidation is 35-70%. The rest is non-carbon elements such as oxygen and hydrogen. Since the weight of hydrogen is relatively light, the carbon content value of this description is approximately equal to the carbon-oxygen ratio. Specifically, an aqueous solution containing 0.01-0.5M PEDOT:PSS (poly 3,4-ethylenedioxythiophene / polystyrene sulfonate) can be configured, and the configured PEDOT / PSS aqueous solution and the graphene oxide cake (carbon content 35-70%) purchased from Yuntian Mo Rui are used to configure a graphene oxide slurry with a solid content of 2-5%.

[0035] In the embodiment of the present invention, the graphene oxide slurry configured in the above steps is coated on a substrate, such as a polyethylene terephthalate (PET) filter cloth; the coating thickness is preferably 1000-8000 μm, more preferably 1500-5000 μm, and can be coated once or multiple times. In addition, the temperature of the coating plate is preferably set to 60-100°C, further 80-90°C, and the coating plate is turned on for heating after coating. After the coating plate is heated until the coating is fixed, it can be transferred to a 60-100°C forced air oven for 10-48 hours. During the curing and shaping process of the coating of the embodiment of the present invention, as the water content of the coating slurry continues to evaporate, the hydroxyl functional groups and carboxyl functional groups on the edges of the graphene oxide sheets self-assemble into a layer film. The surface and edges of the graphene oxide film formed by self-assembly and densely stacking layers still retain a large number of hydroxyl, carboxyl, epoxy and other functional groups, among which carboxyl and hydroxyl groups account for the vast majority of the oxygen-containing functional groups in the graphene oxide film.

[0036] In addition, the first multifunctional dielectric material such as PEDOT:PSS is evenly distributed between the sheets of the graphene oxide film. In the embodiment of the present invention, the dried graphene oxide / PET filter cloth can be taken out, and anhydrous ethanol can be sprayed on the surface of the PET filter cloth to completely remove and separate the graphene oxide film to obtain a graphene oxide film layer.

[0037] In some specific embodiments of the present invention, 10-50 graphene oxide films of comparable size are obtained and stacked with graphite paper at intervals, placed in a rectangular mold, and transferred to a forced air oven, slowly heated (e.g., a heating rate of 1-5°C / min) to 150-190°C and kept warm for 2-10h, preferably heated to 160-180°C and kept warm for reaction, to obtain a low-reduction graphene oxide film.

[0038] The specific structure of the rectangular mold described therein is composed of two punched steel plates with the same length and width and four steel pillars with the same length. The four pillars are fixed to one of the steel plates by threaded connection as a base, and the other steel plate is directly punched at the corresponding positions of the four corner pillars; the membrane sample is placed between the two steel plates, and preferably different pressures are applied to the sample by different weights for reaction, and the weight range can be 10-100kg, such as 40-80kg.

[0039] Under the low temperature treatment condition of less than 195°C in the above embodiment, the sulfonic acid groups on the PSS uniformly distributed in the graphene oxide film layer (taking this as an example) undergo condensation reaction with the hydroxyl groups on the graphene oxide film (removing one water) to form a stably bonded sulfonate bond. Since the PSS polymer long chain contains abundant sulfonic acid groups, it can form multi-site bonding with the hydroxyl groups on the surface of the upper and lower layers of graphene oxide, thereby enhancing the bonding strength of the upper and lower graphene sheets in the graphene oxide film, and at the same time, constructing a heat conduction channel to the upper and lower layers through chemical bonding. In addition, PEDOT and PSS are similar to a "polymer zipper", and the PEDOT thiophene molecular structure can form a strong π-π conjugated interaction with the graphene carbon hexagonal ring. In addition, the PEDOT polymer chain has an ideal conductivity, and the heat conduction relying on the movement of phonons and electrons can be assisted by the PEDOT molecule, further enhancing the heat conduction effect constructed by the PSS molecular weight, thereby obtaining a low-reduction graphene oxide film that "bonds" to construct a heat conduction channel for the first time.

[0040] After the low-temperature heat treatment step is completed, the low-reduction graphene oxide film is taken out in the embodiment of the present invention. At this time, the hydroxyl functional groups in the internal groups of the low-reduction graphene oxide film have basically completed the reaction or fallen off, and the remaining functional groups are mostly carboxyl functional groups that are difficult to fall off. In addition, the water reactants generated by the reaction or falling off of the hydroxyl groups form certain micro-nano pores due to gasification.

[0041] The embodiment of the present invention configures an aqueous solution of a second multifunctional dielectric substance: preferably, a 0.01-0.5M PDDA (polydiallyldimethylammonium chloride) aqueous solution is configured. Then the removed low-reduction graphene oxide membrane is immersed in the PDDA aqueous solution and transferred to a vacuum degassing machine, and the low pressure (lower than the normal atmospheric pressure is sufficient, and the pressure needs to be pumped slowly, and too fast will easily cause the air in the micro-nano pores inside the graphene membrane to swell due to too fast negative pressure) is allowed to stand for 0.1-2 hours, so as to promote the PDDA aqueous solution to enter the low-reduction graphene oxide membrane through the micro-nano pores obtained in the above steps.

[0042] The second multifunctional medium substance contains a basic group, which mainly reacts with the carboxyl group. The basic group can be selected from one or more of substituted or unsubstituted amino, amidine, guanidine, pyridyl, purine and pyrimidine groups. All organic substances containing the above basic groups can react with carboxyl groups, such as carboxyl groups and amino groups can react to form peptide bonds. In addition, carboxyl groups can react with organic substances containing hydroxyl groups to produce ester groups, react with carbonyl chloride and thionyl chloride to produce acyl chlorides, and react with halogenated alkyls to produce esters. In a specific embodiment of the present invention, the second multifunctional medium substance is preferably polydiallyl dimethyl ammonium halide, and more preferably PDDA, which can react with carboxyl groups at a relatively low temperature. The number of functional groups of the second multifunctional medium substance is ≥2, and the optional substances can also be amino acids containing amino groups (such as glutamic acid, alanine, phenylalanine, etc.), fatty diamines (such as ethylenediamine, hexamethylenediamine, etc.).

[0043] After the preferred embodiment of the present invention is immersed, pressurized and left to stand, the carboxyl groups remaining on the graphene sheet at this time are hydrolyzed in water, showing negative charge, and form electrostatic field adsorption with the amino groups of PDDA that are ionized and positively charged. The amino groups on the PDDA polymer chain are precisely adsorbed with the carboxyl groups remaining in the graphene membrane layer to form a pre-"bonding" site. Since the long chain of PDDA contains abundant amino functional groups, it can form multi-point pre-"bonding" adsorption between adjacent sheets in the graphene membrane. Afterwards, it can be taken out and transferred to a blast oven or a vacuum oven, preferably dried at 60-100°C, until the moisture inside the graphene membrane is completely removed. Since the long chain molecules of PDDA and the carboxyl groups remaining on the graphene are adsorbed by electrostatic fields, only moisture is removed during the drying process, and the second multifunctional dielectric material such as PDDA remains on the load site.

[0044] In an embodiment of the present invention, 10-20 membrane samples obtained in the above steps can be stacked with graphite paper at intervals, transferred to the mold used in the above-mentioned low-temperature heat treatment step, the steel plate is weighted with 10-100kg, and transferred to an atmosphere furnace, preferably using nitrogen for atmosphere protection, and / or, preferably under different weight pressure conditions, slowly heating to 210-280°C (such as a heating rate of 1-5°C / min) and keeping warm for 2-4h, and then slowly heating to 1000-1400°C (preferably 1100-1350°C), keeping warm for 2-10h, and naturally cooling to room temperature after the insulation is completed, and taking out the prepared graphene film.

[0045] In a preferred embodiment of the present invention, in the temperature range of 210-280°C, the amino groups on PDDA react with the carboxyl functional groups remaining on the low-reduced graphene oxide sheets by condensation dehydration reaction to form a second stable chemical bond. Since the carboxyl groups and PDDA are adsorbed by the electrostatic field during pretreatment, a multi-point pre-"bonding" precise adsorption is formed, and a condensation reaction occurs under subsequent temperature conditions, and a water is shed at the same time. Then, the embodiment of the present invention can achieve the final carbonization reduction in the temperature range of 1000-1400°C. The graphene membrane preparation method provided by the present invention realizes two "bonding locks" of adjacent graphene sheets in the graphene membrane in two temperature ranges, builds a stable upward heat conduction channel, and at the same time, the product water shed during the reduction process of the graphene membrane is regulated by weight to cause the micro-nano pore spacing to be regulated, so as to obtain the target product, a graphene membrane with a high longitudinal thermal conductivity.

[0046] It is not feasible to introduce a single external group, and the effect will vary greatly. This is attributed to the fact that GO generally has the characteristics of shedding functional groups (mainly hydroxyl groups) at low temperatures (<250°C) and shedding functional groups (mainly carboxyl groups) at high temperatures (>500°C). The most oxygen-containing functional group in GO is hydroxyl groups, which are mainly distributed in the surface and edges of the graphene oxide sheets. During the GO film formation process, a small part of the hydroxyl groups will be consumed due to the self-assembly characteristics of GO. If there is no other consumption, the hydroxyl groups will all fall off and form water in the low-temperature stage of carbonization. There is a certain amount of gasification of water to form a large volume of water vapor, which causes a large amount of internal stress between graphene sheets. The graphene sheets are in a micro-peeling state without bond connection, which is also the key node for the loss of graphene longitudinal thermal conductivity.

[0047] The inventors have found that the sulfonic acid group is a rare functional group that can combine with the hydroxyl functional group at a very low temperature to form a stable bond. Although water is also formed, because its reaction temperature is lower than the hydroxyl shedding temperature, the shedding water vaporizes weakly and forms a stable bond between the upper and lower graphene layers, greatly reducing the possibility of forming a large amount of internal stress between the graphene layers. Although there are certain micro-nano pores, the stable bond formed by the upper and lower layers will ensure that the upper and lower layers of graphene will not have large internal stress, large pores, and peeling.

[0048] In the embodiments of the present invention, due to the highest hydroxyl content, a large number of bonds will be formed in the low-temperature heat treatment film-forming stage, and serve as the first heat conduction channel for the upper and lower sheets. The second largest oxygen-containing functional group in GO is the carboxyl group. Because the carbonization and shedding temperature of the carboxyl group is relatively high, the shedding functional group is more seriously gasified, which will further cause the graphene sheets to peel off in the second stage; if a stable bond is first constructed between the upper and lower graphene sheets in the low-temperature stage, it will greatly offset the internal stress impact and peeling under the high-temperature gasification in the second stage. Of course, if the carboxyl functional group is directly shed by high temperature in the second stage, it will also greatly impact the stability of the bond formed in the low-temperature stage.

[0049] The inventors further discovered that if the carboxyl group can be directly eliminated in the second stage of carbonization, the adverse effects caused by the shedding and gasification of the functional group will be greatly avoided; the amino group is a functional group that can undergo a condensation reaction with the carboxyl group at a temperature far below the shedding temperature of the carboxyl group. The carboxyl shedding temperature is greater than 500°C, and the reaction temperature of the amino group and the carboxyl group can be 200-280°C, which is far lower than the shedding temperature of the carboxyl group. Although the condensation reaction also produces water, the volume expansion caused by its gasification is far less than the volume expansion formed by the shedding of the carboxyl group to produce water and carbon monoxide or carbon dioxide, and the degree of peeling is also minimal. In addition, the carboxyl group and the amino group are precisely matched in the liquid phase through mutual attraction of charges. There is no uneven reaction caused by the absence of individual carboxyl groups. The condensation reaction also constructs a second heat conduction channel for the upper and lower layers of graphene.

[0050] The main functional groups hydroxyl and carboxyl on GO in the embodiment of the present invention complete the reaction under the condition far below the carbonization and shedding temperature, and evenly form stable chemical bonds on the graphene sheets in the membrane, which, as a heat conduction channel, greatly eliminate the adverse effects of hydroxyl and carboxyl groups caused by internal stress during the shedding process; although there are still functional groups such as epoxy and carbonyl on GO, their content is very small, and epoxy groups are converted into carboxyl groups under alkaline conditions, so the introduced external functional group dielectric material is indispensable, otherwise it will greatly affect the construction of the heat conduction channel of the upper and lower graphene sheets. Moreover, the order of introducing functional groups in the two heat treatment stages cannot be interchanged, because the reaction temperature of hydroxyl and sulfonic acid groups is less than 200°C, and the reaction temperature of carboxyl and amino groups is about 200-280°C. If interchanged, the hydroxyl groups will all fall off before the amino and carboxyl groups react, and a large amount of internal stress will be formed, which may result in the inability to form upper and lower graphene sheets to form bonds, and may cause bonds to be formed on a single graphene sheet, which cannot construct upper and lower heat conduction channels, and cannot fundamentally improve the longitudinal thermal conductivity.

[0051] That is, the present invention provides a graphene film with high longitudinal thermal conductivity obtained by the preparation method as described above. Compared with traditional graphene films, the graphene film with high longitudinal thermal conductivity has higher longitudinal thermal conductivity and smaller micro-nano pore spacing. Among them, the present invention realizes stable bonding by introducing external groups to react with graphene's own functional groups, and realizes the construction of longitudinal heat conduction channels by constructing stable "bonding locks" twice. The construction of the two "bonding locks" not only enhances the longitudinal thermal conductivity of the graphene film, but also enhances the cohesion of the graphene film.

[0052] Specifically, the present invention realizes the reaction of externally introduced groups with the hydroxyl and carboxyl groups of graphene under low temperature conditions, which is conducive to the shedding of oxygen-containing groups under relatively low temperature conditions, and will not cause large interlayer peeling and large pores due to the violent vaporization of product water under high temperature conditions. When the first "bonding lock" is constructed, the strong π-π interaction and conductivity of PEDOT can be used to enhance the first "bonding lock" to build a heat conduction channel; the interlayer peeling and excessive micro-nano pore spacing caused by the vaporization of product water during the bonding reaction are also suppressed by counterweights. Compared with traditional graphene membranes, most of the oxygen-containing functional groups of the high longitudinal thermal conductivity graphene membrane described in the present invention are relatively gently shed in a lower temperature range, which is conducive to ensuring the integrity of the graphene membrane, and is more conducive to applications in the fields of thermal management materials.

[0053] The content of the present invention is further described below in conjunction with specific examples, but it should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0054] Among them, the monomer molecular weight of PEDOT / PSS is 326.4, the CAS number is 155090-83-8, it is an aqueous solution with a solute content of 1.5% by mass, and can be purchased directly from the reagent website.

[0055] Example 1

[0056] This embodiment provides a graphene film with high longitudinal thermal conductivity, and the specific preparation process steps are as follows:

[0057] S1. Prepare an aqueous solution containing 0.2M PEDOT:PSS (poly 3,4-ethylenedioxythiophene / polystyrene sulfonate), and use the prepared PEDOT / PSS aqueous solution and graphene oxide cake purchased from Yuntian Mo Rui (carbon content 55%, graphene oxide layer number ≤10 layers after oxidation, thickness about <4nm) to prepare a graphene oxide slurry with a solid content of 3%;

[0058] S2. The graphene oxide slurry prepared in step S1 is coated on a PET filter cloth, the coating thickness is 2000 μm, the coating is applied once, the coating plate temperature is set to 85° C. After coating, the coating plate is heated again. After the coating plate is heated until the coating is fixed, it is transferred to an 80° C. forced air oven for drying and kept warm for 24 hours.

[0059] S3. Take out the graphene oxide coating / PET filter cloth dried in step S2, spray anhydrous ethanol on the surface of the PET filter cloth to make the graphene oxide film fall off completely, and obtain a graphene oxide film.

[0060] The obtained 30 pieces of graphene oxide membranes of equal size were stacked with graphite paper in a rectangular mold (the mold consists of two punched steel plates of the same length and width and four steel pillars of the same length. The four pillars are fixed to one of the steel plates by screws as a base, and the other steel plate is directly punched at the corresponding positions of the four corner pillars. The sample is placed between the two steel plates, and pressure is applied to the sample by a 50kg counterweight). After that, it was transferred to a blast oven and slowly heated to 160°C at a heating rate of 2°C / min, and kept warm for 4 hours to obtain a low-reduction graphene oxide membrane that was "bonded" for the first time to construct a heat conduction channel, and had certain micro-nano pores;

[0061] After the completion of steps S4 and S3, the low-reduction graphene oxide film is taken out. A 0.2M PDDA (polydiallyldimethylammonium chloride) aqueous solution is prepared, and the removed low-reduction graphene oxide film is immersed in the PDDA aqueous solution and transferred to a vacuum degassing machine, and the low pressure (lower than the normal atmospheric pressure can be used, and the pressure needs to be pumped slowly) is pumped for 0.5 hours to promote the PDDA aqueous solution to enter the low-reduction graphene oxide film through the micro-nano pores obtained in S3.

[0062] After vacuuming and letting it stand, take it out and transfer it to a blast oven, and dry it at 80°C until all the moisture inside the graphene film is removed.

[0063] S5, stack 20 film samples obtained in step S4 with graphite paper at intervals, transfer to the mold of S3, weight the steel plate with 50kg, transfer to the atmosphere furnace, use nitrogen for atmosphere protection, slowly heat to 250℃ (heating rate is 2℃ / min) and keep warm for 2h under different weight pressure conditions, then slowly heat to 1300℃ and keep warm for 6h. After the insulation is completed, naturally cool to room temperature and take out the target product high longitudinal thermal conductivity graphene film.

[0064] The control sample is a graphene film prepared by traditional process. The specific preparation process is as follows:

[0065] S1. Stirring graphene oxide cake (carbon content 55%) purchased from Yuntian Mo Rui with deionized water to prepare graphene oxide slurry with a solid content of 3%;

[0066] S2. The graphene oxide slurry prepared in step S1 is coated on a PET filter cloth, the coating thickness is 2000 μm, the coating is applied once, the coating plate temperature is set to 85° C. After coating, the coating plate is heated again. After the coating plate is heated until the coating is fixed, it is transferred to an 80° C. forced air oven for drying and kept warm for 24 hours.

[0067] S3. Take out the graphene oxide coating / PET filter cloth dried in step S2, spray anhydrous ethanol on the surface of the PET filter cloth to make the graphene oxide film fall off completely, and obtain a graphene oxide film.

[0068] The obtained 30 pieces of graphene oxide membranes of equal size were stacked with graphite paper in a rectangular mold (the mold consists of two punched steel plates of the same length and width and four steel pillars of the same length. The four pillars are fixed to one of the steel plates by screws as a base, and the other steel plate is directly punched at the corresponding positions of the four corner pillars. The sample is placed between the two steel plates, and pressure is applied to the sample by a counterweight of 50 kg). After that, it was transferred to a blast oven, and the temperature was slowly raised to 160°C at a heating rate of 2°C / min, and kept warm for 4 hours to obtain a low-reduction graphene oxide membrane;

[0069] S4, stack 20 film samples obtained in step S3 with graphite paper at intervals, transfer to the mold of S3, weight the steel plate with 50 kg, transfer to the atmosphere furnace, use nitrogen for atmosphere protection, slowly heat to 250 ° C (heating rate is 2 ° C / min) and keep warm for 2 hours under different weight pressure conditions, then slowly heat to 1300 ° C and keep warm for 6 hours. After the insulation is completed, naturally cool to room temperature to obtain a control group graphene film.

[0070] The cross-sectional SEM (scanning electron microscope) image of the high longitudinal thermal conductivity graphene film obtained in Example 1 is as follows: Figure 1 As shown, its cross section shows that it remains relatively compact, uniform and complete after carbonization.

[0071] Figure 2 The cross-sectional SEM image of the graphene film (control sample) prepared by the conventional process shows that the graphene film prepared by the conventional process has large peeling and gaps due to the shedding of oxygen-containing functional groups after carbonization. The SEM image can directly distinguish the sample of Example 1 from the control sample, and the difference between the two is obvious.

[0072] A 180° peel test was performed using a universal testing machine at a peeling speed of 300 mm / min. Figure 3 This is the cohesion test curve of the sample in Example 1. Figure 4 The graph of the cohesion test of the graphene film prepared by the traditional process (control sample) is shown in the following figure. The test results show that the cohesion of the graphene film prepared by the traditional process is 0.3727N, and the cohesion of the graphene film after optimization and improvement in Example 1 is 1.4819N.

[0073] The longitudinal thermal conductivity of the graphene film prepared by the traditional process is 3.52 W / mK, and the longitudinal thermal conductivity of the improved graphene film in Example 1 is 8.86 W / mK.

[0074] The test of graphene thermal conductive film is basically carried out using LFA467 equipment. The thermal conductivity test of this experiment is carried out using LFA467 equipment (the thermal conductivity test method is well known in the industry, and the following embodiments are the same).

[0075] Example 2

[0076] This embodiment is a high longitudinal thermal conductivity graphene film provided by the present invention. The difference between this embodiment and Example 1 is that mold pressurization is not used in step S3. Its purpose is to explore the influence of pressurization on the performance of the graphene film in the first "bonding" stage.

[0077] The results show that the cohesive force of the graphene film is 1.3213N and the longitudinal thermal conductivity is 6.11W / mK.

[0078] Example 3

[0079] This embodiment is a high longitudinal thermal conductivity graphene film provided by the present invention. The difference between this embodiment and Embodiment 1 is that mold pressurization is not used in steps S3 and S5. The purpose is to explore the influence of pressurization on the performance of the graphene film during the "bonding" stage.

[0080] The results show that the cohesive force of the graphene film is 0.8577N and the longitudinal thermal conductivity is 4.45W / mK.

[0081] Example 4

[0082] This embodiment is a high longitudinal thermal conductivity graphene film provided by the present invention. The difference between this embodiment and Example 1 is that PSSA is used instead of PEDOT:PSS in step S1, and the other steps remain the same as Example 1 and are not repeated here.

[0083] The purpose is to explore the effect of the externally introduced groups on the properties of the graphene film in the first "bonding" stage. The results show that the cohesive force of the graphene film is 1.1794N and the longitudinal thermal conductivity is 6.49W / mk.

[0084] As can be seen from the above embodiments, the high longitudinal thermal conductivity graphene film and the corresponding preparation method provided by the present invention mainly utilize the different oxygen-containing functional groups carried by the graphene film itself to react with certain external groups, so that the adjacent graphene layers between the graphene film layers form a double-bonded heat conduction channel, which effectively improves the longitudinal thermal conductivity of the graphene film. Combined with other excellent physical and chemical properties such as the cohesion of the graphene film, the graphene film with optimized longitudinal thermal conductivity is conducive to practical application in the fields of thermal management.

[0085] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. The above is only a preferred implementation of the present invention. It should be pointed out that due to the limitations of textual expression and the objective existence of infinite specific structures, ordinary technicians in this technical field can make several improvements, modifications or changes without departing from the principles of the present invention, and can also combine the above technical features in an appropriate manner; these improvements, modifications, changes or combinations, or the direct application of the inventive concept and technical solution to other occasions without improvement, should be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a graphene film with high longitudinal thermal conductivity, characterized in that: The following steps are involved: 1) In the film-forming stage of low-temperature heat treatment of graphene oxide, a first multifunctional medium substance containing sulfonic acid groups is introduced to bond, and a low-reduction graphene oxide film is obtained by treatment; the temperature of the low-temperature heat treatment is lower than 195° C.; 2) subjecting a plurality of the low-reduction graphene oxide films and a second multifunctional dielectric substance to high-temperature heat treatment to condensation reaction and carbonization reduction, wherein the second multifunctional dielectric substance comprises a basic group bonded to a carboxyl group, and the temperature of the high-temperature heat treatment is higher than 205° C., to obtain a graphene film with a high longitudinal thermal conductivity.

2. The preparation method according to claim 1, characterized in that: Step 1) is as follows: 11) mixing graphene oxide and a first multi-functional medium substance containing a sulfonic acid group in water to obtain a graphene oxide slurry; 12) coating the graphene oxide slurry on a substrate, and heating the coating to solidify and shape the coating to obtain a graphene oxide film layer; 13) The obtained graphene oxide film layers are heated to 150-190° C. and kept warm, and reacted under pressure to obtain low-reduction graphene oxide films.

3. The preparation method according to claim 2, characterized in that: In step 11), the carbon content of the graphene oxide is 35-70%; and the first multi-functional medium substance includes polystyrene sulfonate.

4. The preparation method according to claim 3, characterized in that: In step 11), the first multifunctional dielectric substance also includes a conductive polymer that forms a π-π conjugated effect with the graphene carbon hexagonal ring; and the solid content of the graphene oxide slurry is 2-5%.

5. The preparation method according to claim 4, characterized in that: In step 12), the coating thickness is 1000-8000 μm; the curing temperature is 60-100° C., and a graphene oxide film layer is obtained after separation.

6. The preparation method according to any one of claims 1 to 5, characterized in that: Step 2) is as follows: 21) immersing the low-reduction graphene oxide film in an aqueous solution of a second multi-functional medium substance, pumping down the pressure and allowing it to stand, and then drying and dehydrating; 22) The dried and dehydrated film samples are heated to 210-280° C., kept warm for 2-4 hours, and then heated to 1000-1400° C. for carbonization reduction to obtain a graphene film with high longitudinal thermal conductivity.

7. The preparation method according to claim 6, characterized in that: In step 21), the basic groups contained in the second multifunctional medium substance are selected from one or more of substituted or unsubstituted amino, amidine, guanidine, pyridyl, purine and pyrimidine groups.

8. The preparation method according to claim 7, characterized in that: In step 21), the second multifunctional medium substance is polydiallyldimethylammonium halide, and the concentration of the aqueous solution is 0.01-0.5M; the temperature of the drying and dehydration is 60-100°C.

9. The preparation method according to claim 7, characterized in that: In step 22), the dried and dehydrated membrane samples are heated to 210-280° C. in a protective atmosphere under different weight pressure conditions, with a heating rate of 1-5° C. / min.

10. A graphene film with high longitudinal thermal conductivity obtained by the preparation method according to any one of claims 1 to 9.

Images