CN115141487B - Graphene heat conduction foam, graphene heat conduction gasket and preparation method - Google Patents
Graphene heat conduction foam, graphene heat conduction gasket and preparation method Download PDFInfo
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- CN115141487B CN115141487B CN202210815989.6A CN202210815989A CN115141487B CN 115141487 B CN115141487 B CN 115141487B CN 202210815989 A CN202210815989 A CN 202210815989A CN 115141487 B CN115141487 B CN 115141487B
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 397
- 229910021389 graphene Inorganic materials 0.000 title claims abstract description 397
- 239000006260 foam Substances 0.000 title claims abstract description 138
- 238000002360 preparation method Methods 0.000 title claims abstract description 44
- 238000001035 drying Methods 0.000 claims abstract description 107
- 239000011248 coating agent Substances 0.000 claims abstract description 85
- 238000000576 coating method Methods 0.000 claims abstract description 85
- 238000004108 freeze drying Methods 0.000 claims abstract description 57
- 238000010438 heat treatment Methods 0.000 claims abstract description 51
- 238000011282 treatment Methods 0.000 claims abstract description 35
- 239000000758 substrate Substances 0.000 claims abstract description 5
- 229920000642 polymer Polymers 0.000 claims description 73
- 239000007787 solid Substances 0.000 claims description 48
- 239000002002 slurry Substances 0.000 claims description 45
- 238000000034 method Methods 0.000 claims description 35
- 239000002904 solvent Substances 0.000 claims description 35
- 238000005470 impregnation Methods 0.000 claims description 20
- 238000003825 pressing Methods 0.000 claims description 12
- 238000005520 cutting process Methods 0.000 claims description 11
- -1 polydimethylsiloxane Polymers 0.000 claims description 9
- 238000009826 distribution Methods 0.000 claims description 7
- 239000004205 dimethyl polysiloxane Substances 0.000 claims description 6
- 229920000435 poly(dimethylsiloxane) Polymers 0.000 claims description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 4
- 238000007710 freezing Methods 0.000 claims description 4
- 238000007654 immersion Methods 0.000 claims description 4
- 229920001296 polysiloxane Polymers 0.000 claims description 4
- 239000000741 silica gel Substances 0.000 claims description 4
- 229910002027 silica gel Inorganic materials 0.000 claims description 4
- 229920001083 polybutene Polymers 0.000 claims description 2
- 229920002635 polyurethane Polymers 0.000 claims description 2
- 239000004814 polyurethane Substances 0.000 claims description 2
- HYBBIBNJHNGZAN-UHFFFAOYSA-N furfural Chemical compound O=CC1=CC=CO1 HYBBIBNJHNGZAN-UHFFFAOYSA-N 0.000 claims 2
- 239000004593 Epoxy Substances 0.000 claims 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N acrylic acid group Chemical group C(C=C)(=O)O NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 claims 1
- 238000004519 manufacturing process Methods 0.000 claims 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N phenol group Chemical group C1(=CC=CC=C1)O ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 claims 1
- 239000011148 porous material Substances 0.000 abstract description 24
- 239000002131 composite material Substances 0.000 abstract description 9
- 230000002787 reinforcement Effects 0.000 abstract description 3
- 238000012360 testing method Methods 0.000 description 30
- 239000012065 filter cake Substances 0.000 description 26
- 239000010410 layer Substances 0.000 description 25
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 19
- 230000000052 comparative effect Effects 0.000 description 17
- 230000001276 controlling effect Effects 0.000 description 15
- 239000000463 material Substances 0.000 description 14
- 230000000694 effects Effects 0.000 description 10
- 238000005516 engineering process Methods 0.000 description 10
- 239000011247 coating layer Substances 0.000 description 9
- 238000005087 graphitization Methods 0.000 description 9
- 238000001338 self-assembly Methods 0.000 description 7
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 6
- 238000010586 diagram Methods 0.000 description 5
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 4
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 4
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 4
- 238000002408 directed self-assembly Methods 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- 235000010290 biphenyl Nutrition 0.000 description 3
- 239000004305 biphenyl Substances 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
- ZUOUZKKEUPVFJK-UHFFFAOYSA-N phenylbenzene Natural products C1=CC=CC=C1C1=CC=CC=C1 ZUOUZKKEUPVFJK-UHFFFAOYSA-N 0.000 description 3
- 238000010998 test method Methods 0.000 description 3
- 239000011800 void material Substances 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000003153 chemical reaction reagent Substances 0.000 description 2
- 238000013329 compounding Methods 0.000 description 2
- 238000012937 correction Methods 0.000 description 2
- 238000001938 differential scanning calorimetry curve Methods 0.000 description 2
- 238000010790 dilution Methods 0.000 description 2
- 239000012895 dilution Substances 0.000 description 2
- 239000003814 drug Substances 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910052594 sapphire Inorganic materials 0.000 description 2
- 239000010980 sapphire Substances 0.000 description 2
- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical compound [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 description 1
- 239000004925 Acrylic resin Substances 0.000 description 1
- 229920000178 Acrylic resin Polymers 0.000 description 1
- JVTAAEKCZFNVCJ-UHFFFAOYSA-M Lactate Chemical compound CC(O)C([O-])=O JVTAAEKCZFNVCJ-UHFFFAOYSA-M 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- KPUWHANPEXNPJT-UHFFFAOYSA-N disiloxane Chemical class [SiH3]O[SiH3] KPUWHANPEXNPJT-UHFFFAOYSA-N 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 229940079593 drug Drugs 0.000 description 1
- 239000003822 epoxy resin Substances 0.000 description 1
- 239000006261 foam material Substances 0.000 description 1
- 229920005546 furfural resin Polymers 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229920006158 high molecular weight polymer Polymers 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000010907 mechanical stirring Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 229920001568 phenolic resin Polymers 0.000 description 1
- 239000005011 phenolic resin Substances 0.000 description 1
- 229920000647 polyepoxide Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000007581 slurry coating method Methods 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/02—Elements
- C08K3/04—Carbon
- C08K3/042—Graphene or derivatives, e.g. graphene oxides
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
- C09K5/08—Materials not undergoing a change of physical state when used
- C09K5/14—Solid materials, e.g. powdery or granular
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Health & Medical Sciences (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Physics & Mathematics (AREA)
- Combustion & Propulsion (AREA)
- Thermal Sciences (AREA)
- Materials Engineering (AREA)
- Carbon And Carbon Compounds (AREA)
Abstract
The invention provides graphene heat-conducting foam, a preparation method thereof, a graphene heat-conducting gasket and a preparation method thereof, wherein the preparation method of the graphene heat-conducting foam comprises the following steps: coating a graphene oxide coating on a substrate; drying the graphene oxide coating to ensure that the graphene oxide coating is not completely dried, wherein the drying treatment comprises normal-temperature drying or/and heating drying; freeze-drying the incompletely dried graphene oxide coating to obtain graphene oxide heat-conducting foam; and carrying out heat treatment on the graphene oxide heat conduction foam to obtain the graphene oxide heat conduction foam. The invention can realize the regulation and control of the pore structure of the graphene foam, can regulate and control the directional arrangement of the graphene, and can realize good directional arrangement of the graphene when the graphene foam is used as a high-heat-conductivity composite material reinforcement, thereby realizing the directional high-heat-conductivity performance of the composite material.
Description
Technical Field
The invention relates to the technical field of graphene heat conduction interface materials, in particular to graphene heat conduction foam, graphene heat conduction gaskets and a preparation method.
Background
The graphene heat-conducting foam material can be obtained by assembling, regulating and controlling graphene oxide and performing heat treatment. In order to obtain graphene heat-conducting foam with good heat-conducting performance, the graphene inside the foam needs to be arranged in a directional mode, so that sufficient self-assembly of graphene oxide is required, and a good self-assembly effect can be achieved by adopting a coating film-forming mode. However, the graphene heat-conducting foam formed by the direct coating and drying method has randomness of internal void structures, shapes and the like, and has small size. When the foam is combined with other materials such as high molecular polymers, the high molecular polymers are difficult to fully fill, the distribution of the high molecular polymers is also not uniform, the formed composite material is often poor in internal consistency and stability, and the mechanical properties such as tensile strength and tensile elongation at break are low (such as patent document CN113183544A, CN113290958A, CN 113556925A).
The graphene oxide slurry is subjected to freeze drying treatment, so that the regulation and control of the internal pore structure of the graphene heat-conducting foam can be realized. However, the graphene heat-conducting foam obtained by directly performing freeze drying treatment has no orientation in the arrangement of the graphene, completely belongs to random distribution, has the characteristic of isotropy, has poor heat-conducting property, and is difficult to become a reinforcement of the high-heat-conducting composite material.
Disclosure of Invention
Aiming at one or more of the problems in the prior art, the invention provides a preparation method of graphene heat-conducting foam, which comprises the following steps:
coating graphene oxide slurry on a substrate to obtain a graphene oxide coating;
drying the graphene oxide coating to ensure that the graphene oxide coating is not completely dried, wherein the drying treatment comprises normal-temperature drying or/and heating drying;
freeze-drying the incompletely dried graphene oxide coating to obtain graphene oxide heat-conducting foam;
and carrying out heat treatment on the graphene oxide heat conduction foam to obtain the graphene oxide heat conduction foam.
In the step of drying the graphene oxide coating, since the graphene oxide is subjected to directional self-assembly during drying, the directional self-assembly degree is controlled by controlling the drying degree, and finally the control of the graphene orientation degree is realized, wherein the orientation degree refers to the included angle between the graphene and the transverse direction, but the included angles between all the graphene sheets and the transverse direction are impossible to be the same, and the graphene distributed along a certain angle reaches a set proportion; in the step of freeze-drying the incompletely dried graphene oxide coating, the solvent in the incompletely dried graphene oxide coating occupies a certain volume content, the volume of the graphene oxide coating is almost unchanged during freeze-drying, the solvent is volatilized during the freeze-drying process, and the volume occupied by the original solvent becomes a pore structure. Thus, the degree of drying, i.e., the pore structure, can be controlled. The pore structure can be quantified as pore size range and porosity in the entire graphene thermal foam.
According to one aspect of the invention, the graphene oxide slurry has a solid content of 0.5wt.% to 9.5wt.%, is too thin to be coated, can be severely cast, cannot control the coating thickness, cannot control the thickness uniformity, and can flow away directly; above 9.5wt.% it is too thick and likewise not coatable.
Preferably, the graphene oxide slurry has a solids content of 4wt.% to 6wt.%.
According to one aspect of the present invention, the step of drying the graphene oxide coating layer such that the graphene oxide coating layer is not completely dried includes:
the drying degree is controlled by controlling the solid content of the graphene oxide coating, and the higher the solid content is, the higher the drying degree is.
According to one aspect of the present invention, in the drying treatment, the solid content of the graphene oxide coating is controlled to be 40wt.% to 75wt.%, less than 40wt.%, and the orientation is not yet formed; above 75wt.%, the internal solvent content, the pore size formed after freeze-drying is too small, which is detrimental to the impregnation of the polymer in the later stages.
Preferably, the solid content of the graphene oxide coating is controlled to be 50wt.% to 70wt.%.
The orientation degree can be realized by controlling the drying degree of the graphene oxide coating, the drying degree can be realized by controlling the solid content of the graphene oxide coating, the solid content is improved, the orientation self-assembly degree of the graphene oxide is improved, the orientation degree is improved, and vice versa; if the drying is complete, the directional self-assembly is completed, and the full orientation is realized.
The orientation degree is controlled by controlling the solid content of the graphene oxide coating in the drying process, the graphene oxide coating performs orientation self-assembly in the drying process, and the drying degree, namely the solid content, can be controlled.
According to one aspect of the present invention, the step of drying the graphene oxide coating layer such that the graphene oxide coating layer is not completely dried includes:
the method comprises the steps of drying a graphene oxide coating, and reserving a set amount of solvent, wherein the smaller the set amount is, the larger the drying degree is, the solvent is used in graphene oxide slurry, and the drying treatment is to reduce the content of the solvent because the solid content of graphene oxide is lower and the solvent is mostly reserved; the solvent used in the present invention is water or other solvents including a mixture of one or more of ethanol, methanol, DMF or NMP, but water is preferably selected as the solvent in view of economy, environmental protection, ease of use, and operability of the post-lyophilization.
According to one aspect of the present invention, the step of drying the graphene oxide coating layer such that the graphene oxide coating layer is not completely dried includes: and controlling the drying degree of the graphene oxide coating by controlling the proportion of the transverse heat conductivity coefficient and the longitudinal heat conductivity coefficient of the graphene oxide coating, wherein the larger the proportion is, the larger the drying degree is.
The orientation degree can be judged by the transverse and longitudinal heat conduction properties of the prepared graphene heat conduction foam, and specifically comprises the following steps: the graphene of the completely dried graphene heat conduction foam without freeze drying is almost completely arranged along the transverse direction, so that the transverse heat conduction effect is optimal, the longitudinal heat conduction is worst, and the ratio of the transverse heat conduction coefficient to the longitudinal heat conduction coefficient reaches the maximum ratio; the graphene heat-conducting foam subjected to freeze drying is directly adopted without coating and drying treatment, and the corresponding ratio of the transverse heat conductivity coefficient to the longitudinal heat conductivity coefficient is the smallest ratio (close to 1:1) due to isotropy, and the ratio of the transverse heat conductivity coefficient to the longitudinal heat conductivity coefficient of the graphene oxide coating is between the largest ratio and the smallest ratio, and is preferably larger than the intermediate value of the largest ratio and the smallest ratio.
According to one aspect of the invention, the vacuum level of freeze drying is: the air pressure is 50-300mTorr, the air pressure is lower than 50mTorr, the air pressure is too low, the equipment requirement is too high, and the vacuumizing time is too long, so that the sample preparation is not facilitated; if the pressure is higher than 300mTorr, the vacuum degree is insufficient, the preparation of the sample is affected, and the sample may shrink, so that the internal structure is deformed.
Preferably, the range is 100-200mTorr.
Preferably, the freeze drying time is 12-72h, and the time is less than 12h, and the drying is incomplete.
According to one aspect of the invention, in the heat treatment, the heat treatment temperature is not less than 2400 ℃, preferably not less than 2800 ℃; the heat treatment time is more than or equal to 2 hours, preferably more than or equal to 5 hours. The temperature is lower than 2400 ℃ or the time is lower than 2 hours, so that the heat treatment is incomplete, and the heat conduction performance of the sample is poor.
According to a second aspect of the invention, there is provided a graphene thermal conductive foam obtained by the above-described preparation method.
Preferably, the graphene in the graphene heat-conducting foam is in orientation distribution, and the orientation distribution refers to orientation arrangement along a certain direction.
Preferably, the graphene heat conduction foam is internally and horizontally arranged in a-45 degree orientation mode to reach a set proportion, and further preferably, the graphene heat conduction foam is internally and horizontally arranged in a-30 degree orientation mode to reach a set proportion; further preferably, the set proportion is not less than 60%. The proportion of the graphenes arranged within the angle range of-45 degrees to 45 degrees is less than 60 percent, which is not beneficial to the later-stage pressing orientation, and the more the graphenes are arranged in the range, the more the graphenes are beneficial to being arranged along the transverse direction during the later-stage pressing; if the ratio is less than 60%, it may occur that some of the graphene is aligned in other directions, even in the longitudinal direction, and the orientation effect is deteriorated in the post-pressing, and at the same time, a cracking phenomenon may be caused because a considerable amount of the graphene is aligned in other directions, resulting in a non-uniform degree of graphene porosity, occurrence of internal stress, and deformation cracking.
Preferably, the thickness of the graphene heat-conducting foam is 0.3-5mm, the thickness is lower than 0.3mm, the internal gap is difficult to control due to over-thinness, and the size is small; the thickness is higher than 5mm, so that uniformity of drying rate between the upper and lower parts is difficult to ensure, and the upper and lower structures are different, and further preferably, the thickness of the graphene heat-conducting foam is 1-3mm.
According to a third aspect of the present invention, there is provided a method for preparing a graphene thermal pad, comprising:
immersing a high molecular polymer into the graphene heat-conducting foam obtained by the preparation method of the graphene heat-conducting foam;
stacking a plurality of impregnated graphene heat-conducting foams layer by layer, pressing, bonding and forming along the stacking direction, and curing to obtain a graphene heat-conducting block, preferably, applying pressure to the bonded and formed multi-layer graphene heat-conducting foam before curing, so as to improve the orientation effect, for example, the included angle between graphene of the graphene heat-conducting foam and the transverse direction is mostly in the range of-30 degrees to 30 degrees, and the orientation of the graphene can be controlled to be in the range of-10 degrees to 10 degrees by applying pressure to the bonded and formed multi-layer graphene heat-conducting foam;
and cutting the graphene heat conduction blocks into pieces along the stacking direction to obtain the graphene heat conduction gasket.
The graphene heat-conducting foam obtained by direct heat treatment has a pure carbon system with a rich pore structure, has poor mechanical properties, particularly poor compression properties, and is easy to fall off powder; the defects can be improved by compounding the high molecular polymer with the high molecular polymer, and the heat-conducting gasket suitable for a heat-conducting interface can be obtained by the high molecular polymer.
According to a third aspect of the invention, further comprising:
at least one of vacuum impregnation, normal pressure impregnation and high pressure impregnation is adopted to enable graphene heat conduction foam to enter a high polymer.
Among them, the higher the vacuum degree used for vacuum impregnation, the better the impregnation effect, and preferably, the vacuum degree for vacuum impregnation is 0.095 to 0.099MPa, which has been very close to the vacuum degree of absolute vacuum (0.101325 MPa).
Preferably, the pressure of high-pressure impregnation is 0.5-10 MPa, and the pressure is lower than 0.5MPa, so that the pressure is too small to achieve the effect of high-pressure impregnation, and compared with normal-pressure impregnation, the pressure is not obviously improved; the pressure is higher than 10Mpa, and the pressure is too high, so that the internal structure of the graphene heat-conducting foam can be changed, and further the graphene heat-conducting foam can be damaged.
Preferably, the curing temperature is 60-200 ℃, the curing temperature is higher than 200 ℃, the reaction is too severe, and stress concentration can occur in the sample, so that the sample is cracked and damaged.
Preferably, after being immersed in the high molecular polymer, the content of the high molecular polymer is 20wt.% to 60wt.%, less than 20wt.%, the content of the high molecular polymer is too small, the internal pores cannot be sufficiently impregnated, and the prepared sample is easily cracked; above 60wt.%, the heat conducting properties are severely affected.
Further preferably, the high molecular polymer is present in an amount of 30wt.% to 50wt.%.
According to a fourth aspect of the present invention, there is provided a graphene heat conduction gasket, comprising a plurality of layers of graphene heat conduction foam stacked in a thickness direction, and a high molecular polymer, wherein graphene inside the graphene heat conduction foam is in orientation distribution, and the high molecular polymer is immersed in the graphene;
preferably, the high molecular polymer is at least one of epoxy resin, phenolic resin, furfural resin, polyurethane, acrylic resin, polybutene and organic silica gel;
preferably, the high molecular polymer is organic silica gel;
preferably, the high molecular polymer is at least one of polydimethylsiloxane, alpha, omega-dihydroxypolydimethylsiloxane, alpha, omega-dihydroxypolymethyl3, 3-trifluoropropyl siloxane, dimethyl diphenyl polysiloxane, cyanoalkoxysilane and alpha, omega-divinyl polydimethylsiloxane, and the high molecular polymer is organic silica gel existing in the market, and manufacturers such as national medicine reagent net, dakangnin and the like.
The preparation method adopts a semi-drying and semi-freezing preparation method to prepare the graphene heat-conducting foam, wherein the semi-drying refers to that the graphene oxide is coated and then is subjected to partial drying treatment, and the graphene oxide coating is not completely dried but a certain solvent is reserved; by semi-frozen is meant that the freeze-drying has been preceded by a semi-drying but still contains a part of the solvent, in which case the freeze-drying process is performed.
After the graphene oxide slurry is coated, a mode of not completely drying but keeping a certain solvent is adopted, so that the oriented self-assembly degree of the graphene oxide is controlled, and the semi-orientation of the graphene oxide is realized; the semi-oriented graphene oxide coating realizes the maintenance of the semi-oriented structure by a freeze-drying mode, and meanwhile, as the graphene oxide coating is not completely dried before being immersed in freeze-drying equipment, a large number of open holes with controllable structures can be formed in the freeze-drying process, the size of the open holes is larger than that of the completely dried pores, and the graphene oxide is converted into graphene after heat treatment, so that the semi-oriented and porous structures of the graphene oxide coating are also maintained.
According to the invention, a mode of combining coating drying and semi-freeze drying is adopted to realize semi-directional arrangement of graphene in the graphene heat-conducting foam; semi-freeze drying can realize control of the internal void structure of the graphene heat-conducting foam, and the void structure suitable for the composite material can be obtained. The invention can realize the regulation and control of the pore structure of the graphene heat conduction foam, and can also meet the requirement that the graphene can realize good directional arrangement when the graphene heat conduction foam is used as a high heat conduction composite material reinforcement, thereby realizing the directional high heat conduction performance of the composite material.
According to the preparation method of the graphene heat-conducting gasket, after the graphene is immersed in the high-molecular polymer, the semi-oriented graphene can be pressed in the normal direction, and the semi-oriented graphene is further oriented along the transverse direction, so that the heat-conducting performance in the transverse direction can be improved, and the possibility of heat conduction in the longitudinal direction can be improved.
According to the graphene heat-conducting foam, the pore structure is increased while the graphene in the graphene heat-conducting foam is semi-oriented through semi-drying and semi-freezing, so that not only can the graphene heat-conducting foam be impregnated with low-viscosity high polymers, but also high-viscosity high-molecular polymers can be impregnated, and the graphene heat-conducting foam has the advantages that certain high-viscosity high-molecular polymers can be impregnated without being diluted by solvents, so that steps of dissolution, volatilization and the like are omitted, and the problem of performance reduction of the high-molecular polymers caused by easy volatilization and the environmental problem possibly caused by volatilization of organic solvents can be avoided; in addition, the method is also suitable for certain high molecular polymers with higher viscosity and no dilution by a proper solvent; after the high-molecular polymer is impregnated, the orientation of the graphene can be further improved through a simple pressing process; due to the combination effect of the graphene thermal conductive foam and the high molecular polymer, cracking and other phenomena cannot occur in the pressing process, and the high molecular polymer can improve the mechanical property of the graphene thermal conductive foam.
Drawings
Other objects and results of the present invention will become more apparent and readily appreciated by reference to the following detailed description taken in conjunction with the accompanying drawings. In the drawings:
FIG. 1 is a schematic diagram of one embodiment of a flow chart of a method of preparing graphene thermal foam according to the present invention;
FIG. 2 is a schematic diagram of a preferred embodiment of a flow chart of a method of preparing graphene thermal foam according to the present invention;
FIG. 3 is a schematic diagram of one embodiment of a flow chart of a method of preparing a graphene thermal pad according to the present invention;
fig. 4 is an SEM image of the graphene heat-conducting foam impregnated with a high molecular polymer according to the present invention.
Detailed Description
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) may be practiced without these specific details.
Various embodiments according to the present invention will be described in detail below with reference to the accompanying drawings.
Fig. 1 is a schematic diagram of an embodiment of a flowchart of a preparation method of a graphene heat-conducting foam according to the present invention, as shown in fig. 1, where the preparation method of the graphene heat-conducting foam includes:
Step S1, coating graphene oxide slurry on a substrate to obtain a graphene oxide coating;
s2, drying the graphene oxide coating to ensure that the graphene oxide coating is not completely dried, wherein the drying treatment comprises normal-temperature drying or/and heating drying;
step S3, freeze-drying the incompletely dried graphene oxide coating to obtain graphene oxide heat-conducting foam;
and S4, performing heat treatment on the graphene oxide heat-conducting foam to obtain the graphene oxide heat-conducting foam.
In the step S1 and the step S2, the drying treatment may be performed after the continuous multilayer coating, or the single coating may be performed, that is, a layer of the drying treatment is applied, that is, the effect, the coating efficiency, the drying efficiency, etc. obtained from the invention are obtained, and in the later stage, the single coating is preferably selected for the orientation effect of the graphene by combining with the high polymer and stacking the high polymer layer by layer into blocks and then cutting the block, which is easy to operate, that is, in a preferred embodiment, as shown in fig. 2, the preparation method of the graphene heat-conducting foam comprises:
step S10, coating a layer of graphene oxide slurry on a substrate to obtain a layer of graphene oxide coating;
Step S20, drying the graphene oxide coating to ensure that the graphene oxide coating is not completely dried, wherein the drying treatment comprises normal-temperature drying or/and heating drying;
step S30, repeating the step S1 and the step S2 for a plurality of times to obtain an incompletely dried multilayer graphene oxide coating;
step S40, freeze-drying the incompletely dried multilayer graphene oxide coating to obtain graphene oxide heat-conducting foam;
and S50, performing heat treatment on the graphene oxide heat-conducting foam to obtain the graphene oxide heat-conducting foam.
In the above embodiments, the graphene oxide slurry may be obtained by dispersing the graphene oxide filter cake in a solvent, where the solvent is water or other solvents including a mixture of one or more of ethanol, methanol, DMF, or NMP.
In one embodiment, a method of preparing graphene oxide slurry includes:
preparing a graphene oxide filter cake by a Hummers method, wherein the solid content of the graphene oxide filter cake is 45-55 wt.%, and the rest is solvent water, and the molar ratio of oxygen to carbon in the solid content is 0.6-0.7, for example, the graphene oxide filter cake produced by Hemsy sixth element materials science and technology Co., ltd, da Cheng graphite Co., etc.;
And further dispersing the graphene oxide filter cake with water to prepare graphene oxide slurry.
In one embodiment, a method of preparing a graphene oxide slurry having a solids content of 4wt.% to 6wt.% includes:
dispersing the graphene oxide filter cake in water by adopting a stirring mode (such as mechanical stirring), wherein the stirring speed is preferably more than 600 revolutions per minute, and the stirring and dispersing time is 1-5 hours;
after dispersion, the defoaming treatment is performed by combining vacuum and stirring, preferably, the defoaming time is more than 30min, the vacuum pump is adopted for vacuumizing, and the vacuum degree is 0.095-0.099 MPa.
In the above embodiments, the drying treatment may be performed by an oven, a tunnel furnace, a heating plate, or the like, and the drying time is determined according to the drying temperature, the solid content of the non-dried graphene oxide coating, and the solid content of the dried graphene oxide coating, for example, the solid content and the drying temperature of the non-dried graphene oxide coating are measured; measuring the solid content of the graphene oxide coating after different drying times; obtaining a curve of the solid content of the graphene oxide coating and the drying time by adopting a curve fitting mode, for example, plotting by adopting multiple points (such as 5 points); the drying time for controlling the solid content of the graphene oxide coating layer to be in the range of 40wt.% to 75wt.% is obtained by the above-described curve, for example, the drying time for the solid content of the graphene oxide coating layer to be 40wt.% is obtained by the curve of the solid content of the graphene oxide coating layer versus the drying time.
In the above embodiments, the freeze-drying apparatus was a freeze-dryer, and the manufacturer was Haihai micro-mechanical Co., ltd.
In the above embodiments, the heat treatment may be performed by a high temperature furnace, graphitization furnace, acheson furnace, or the like, and the heat treatment temperature may reach a temperature of 3000 ℃.
Fig. 3 is a schematic diagram of an embodiment of a flowchart of a method for preparing a graphene thermal pad according to the present invention, where, as shown in fig. 3, the method for preparing a graphene thermal pad includes:
step S100, immersing a high polymer into the graphene heat-conducting foam obtained by the preparation method of the graphene heat-conducting foam in each embodiment, wherein the graphene which is arranged in an oriented manner of-45 degrees to 45 degrees in the transverse direction in the graphene heat-conducting foam is not less than 60 percent as shown in figure 4;
step S200, stacking a plurality of impregnated graphene heat-conducting foams layer by layer, pressing, bonding and forming along the stacking direction, and curing to obtain a graphene heat-conducting block, wherein preferably, before curing, pressure is applied to the bonded and formed multi-layer graphene heat-conducting foam;
and S300, cutting the graphene heat conduction blocks into pieces along the stacking direction to obtain the graphene heat conduction gasket.
In order to illustrate the technical effects of the present invention, the following specific examples and comparative examples were carried out, and performance tests were carried out, specifically:
1. the test method of the transverse thermal diffusivity comprises the following steps: testing by using a German relaxation-resistant laser heat conduction instrument with the model of LFA467 and a lactate sample stage, wherein the test model is a Cowan model and pulse correction, specifically, cutting a sample (graphene heat conduction foam or graphene heat conduction gasket) into a plurality of small pieces with the size of 5 multiplied by 10mm along the normal direction; sequentially arranging a plurality of small pieces into a sample station (square 10.0 mm); the sample stage was placed in LFA467 for testing under the following condition parameters: the temperature is 25 ℃, the light spot is 8.9mm, the voltage is 260V, and the pulse width is 1000 mu s.
2. The test method of the longitudinal thermal diffusivity comprises the following steps: adopting a German relaxation-resistant laser heat conduction instrument, wherein the model is LFA467, and adopting a circular sample stage for testing, wherein the test model is a Cowan model+pulse correction, specifically, the sample is directly sampled along the normal direction, and the sample size is phi 10mm; samples were placed on a sample stage and placed in LFA467 for testing under the following conditions: the temperature is 25 ℃, the light spot is 8.9mm, the voltage is 260V, and the pulse width is 1000 mu s.
3. The specific heat capacity test method comprises the following steps: the specific heat test is carried out by adopting a German relaxation-resistant DSC214 type differential scanning calorimeter, and the test process is as follows: firstly, taking an empty crucible matched with the DSC214, and directly placing the empty crucible into the DSC214 to serve as a blank test for testing; step two, DSC program software is opened, the initial temperature is set to be 0 ℃, the temperature is kept for 10 minutes, the temperature is increased to 50 ℃ at the heating rate of 10 ℃/min, and then the temperature is cooled along with the furnace, so that a base line is obtained; thirdly, placing 11mg of sapphire standard sample in the same blank crucible, and testing according to the same temperature program to obtain a DSC curve of the standard sample; taking out a sapphire standard sample, taking about 11mg (the error is not more than +/-10%) of a sample to be tested, placing the sample into the same crucible, and testing according to the same temperature program to obtain a DSC curve of the sample; and fifthly, directly calculating the specific heat capacity of the sample at 25 ℃ by adopting DSC software (the principle is a specific heat comparison method).
4. The density testing method refers to GB 4472-1984 for testing the density of a sample, the water drainage method is adopted for testing, and the quality of the same sample in air and water is tested respectively, and the density value is obtained by dividing the quality of the same sample in air and the quality of the same sample in water.
5. The longitudinal thermal conductivity or the transverse thermal conductivity of the graphene thermal conductivity foam is calculated by adopting the following formula:
K＝λ·C p ·ρ
Wherein, the K-heat conductivity coefficient is expressed as W/(m.K);
lambda-thermal diffusivity in mm 2 /s；
C p Specific heat capacity, unit J/g/K;
Pi-Density in g/cm 3 。
6. For thermal resistance testing, for convenience of comparison, the thickness processing of the graphene heat conduction gasket is uniformly controlled to be 1mm, and the application thermal resistance (the sum of the intrinsic thermal resistance and the contact thermal resistance of the upper surface and the lower surface of the graphene heat conduction gasket) of the graphene heat conduction gasket under the pressure of 40psi is tested through ASTMD 5470;
the equipment used was LW-9389 (Taiwan Rake Co., ltd.) which required the sample length and width dimensions to be 25.4X25.4 mm, and was cut directly or die-cut to the above dimensions, and the temperature used for the test was 80 ℃.
7. The graphene heat-conducting gasket is cut into a sample with the length and width dimension of 100X 10mm, and the two ends of the sample are fixed on a TM2101V5.06 tensile machine (source: suzhou European standard instruments Co., ltd.) to carry out tensile test on the transverse tensile strength of the graphene heat-conducting gasket, wherein the tensile rate is 0.2mm/min.
Example 1
In this embodiment, the preparation process parameters of the graphene heat-conducting foam are as follows:
the graphene oxide filter cake is a graphene oxide filter cake of a company of science and technology, sixth element materials, changzhou;
the solvent of the graphene oxide slurry is water;
The solid content of the graphene oxide slurry was 2wt.%;
the drying treatment equipment is an oven;
the drying temperature is normal temperature;
the drying time is 7h8min; controlling the solid content of the graphene oxide coating to be 40wt.% after the drying treatment;
the freeze drying equipment is a freeze dryer;
the freeze-drying air pressure is 50 mTorr;
the freeze drying time is 12 hours;
the heat treatment equipment is a graphitization furnace;
the temperature of the heat treatment is 2400 ℃, and the heat treatment time is 2 hours;
the thickness of the graphene heat conduction foam is 0.3mm;
through testing, the obtained graphene heat-conducting foam has the following relevant properties:
density: 0.082g/cm 3 ；
Specific heat capacity: 0.996J/g/K;
lateral thermal diffusivity: 362.24mm 2 /s；
Lateral thermal conductivity: 31.39W/(mK);
after the graphene heat-conducting foam is combined with the high polymer, stacking and curing the graphene heat-conducting foam layer by layer to form graphene heat-conducting blocks, and cutting the graphene heat-conducting blocks along the stacking direction to prepare the graphene heat-conducting gasket, wherein the preparation process conditions are as follows:
the high molecular polymer is polydimethylsiloxane (source: national drug reagent network CAS number: 9016-00-6 brand: ALFA);
impregnating at normal pressure;
the curing temperature is 60 ℃;
the content of the high molecular polymer was 60wt.%;
through testing, the obtained graphene heat conduction gasket has the following relevant performances:
Applying thermal resistance: 0.814K cm 2 /W；
Transverse tensile strength: 4.25MPa.
Example 2
In this embodiment, the preparation process parameters of the graphene heat-conducting foam are as follows:
the graphene oxide filter cake is a graphene oxide filter cake of a company of science and technology, sixth element materials, changzhou;
the solvent of the graphene oxide slurry is water;
the solid content of the graphene oxide slurry was 8wt.%;
the drying treatment equipment is an oven;
the drying temperature is 80 ℃;
the drying time is 2h12min;
controlling the solid content of the graphene oxide coating to be 75wt.% after the drying treatment;
the freeze drying equipment is a freeze dryer;
the freeze-drying air pressure is 300 mTorr;
the freeze drying time is 72 hours;
the heat treatment equipment is a graphitization furnace;
the temperature of the heat treatment is 2600 ℃, and the heat treatment time is 4 hours;
the thickness of the graphene heat conduction foam is 5mm;
through testing, the obtained graphene heat-conducting foam has the following relevant properties:
density: 0.122g/cm 3 ；
Specific heat capacity: 0.991J/g/K;
lateral thermal diffusivity: 321.28mm 2 /s；
Lateral thermal conductivity: 38.84W/(mK);
after the graphene heat-conducting foam is combined with the high polymer, stacking and curing the graphene heat-conducting foam layer by layer to form graphene heat-conducting blocks, and cutting the graphene heat-conducting blocks along the stacking direction to prepare the graphene heat-conducting gasket, wherein the preparation process conditions are as follows:
The high molecular polymer is polydimethylsiloxane (source: american Dow Corning model: DC 1503);
vacuum impregnation is adopted, and the vacuum degree is 0.099MPa;
the curing temperature is 200 ℃;
the content of high molecular polymer was 20wt.%;
through testing, the obtained graphene heat conduction gasket has the following relevant performances:
applying thermal resistance: 0.795K cm 2 /W；
Transverse tensile strength: 4.66MPa.
Example 3
In this embodiment, the preparation process parameters of the graphene heat-conducting foam are as follows:
the graphene oxide filter cake is a graphene oxide filter cake of a company of science and technology, sixth element materials, changzhou;
the solvent of the graphene oxide slurry is water;
the solid content of the graphene oxide slurry was 4wt.%;
the drying treatment equipment is an oven;
the drying temperature is 70 ℃;
the drying time is 37min;
controlling the solid content of the graphene oxide coating to be 50wt.% after the drying treatment;
the freeze drying equipment is a freeze dryer;
the freeze-drying air pressure is 100 mTorr;
the freeze drying time is 18h;
the heat treatment equipment is a graphitization furnace;
the temperature of the heat treatment is 2800 ℃ and the heat treatment time is 5 hours;
the thickness of the graphene heat conduction foam is 1mm;
through testing, the obtained graphene heat-conducting foam has the following relevant properties:
Density: 0.104g/cm 3 ；
Specific heat capacity: 0.993J/g/K;
lateral thermal diffusivity: 407.31mm 2 /s；
Lateral thermal conductivity: 40.71W/(mK);
after the graphene heat-conducting foam is combined with the high polymer, stacking and curing the graphene heat-conducting foam layer by layer to form graphene heat-conducting blocks, and cutting the graphene heat-conducting blocks along the stacking direction to prepare the graphene heat-conducting gasket, wherein the preparation process conditions are as follows:
the polymer is dimethyl diphenyl polysiloxane (source: CAS number: 68083-14-7, manufacturer: guangzhou Yuanzha New Material Co., ltd.);
high-pressure impregnation is adopted, and the pressure is 2MPa;
the curing temperature is 70 ℃;
the content of high molecular polymer was 50wt.%;
through testing, the obtained graphene heat conduction gasket has the following relevant performances:
applying thermal resistance: 0.773K cm 2 /W；
Transverse tensile strength: 5.05MPa.
Example 4
In this embodiment, the preparation process parameters of the graphene heat-conducting foam are as follows:
the graphene oxide filter cake is a graphene oxide filter cake of a company of science and technology, sixth element materials, changzhou;
the solvent of the graphene oxide slurry is water;
the solid content of the graphene oxide slurry was 6wt.%;
the drying treatment equipment is an oven;
the drying temperature is 75 ℃;
the drying time is 1h23min;
Controlling the solid content of the graphene oxide coating to be 70wt.% after the drying treatment;
the freeze drying equipment is a freeze dryer;
the freeze-drying air pressure is 200 mTorr;
the freeze drying time is 36h;
the heat treatment equipment is a graphitization furnace;
the temperature of the heat treatment is 2900 ℃, and the heat treatment time is 4 hours;
the thickness of the graphene heat conduction foam is 3mm;
through testing, the obtained graphene heat-conducting foam has the following relevant properties:
density: 0.117g/cm 3 ；
Specific heat capacity: 0.992J/g/K;
lateral thermal diffusivity: 394.15mm 2 /s；
Lateral thermal conductivity: 47.27W/(mK);
after the graphene heat-conducting foam is combined with the high polymer, stacking and curing the graphene heat-conducting foam layer by layer to form graphene heat-conducting blocks, and cutting the graphene heat-conducting blocks along the stacking direction to prepare the graphene heat-conducting gasket, wherein the preparation process conditions are as follows:
the polymer is alpha, omega-dihydroxyl polymethyl (3, 3-trifluoropropyl) siloxane (source: CAS number: 68607-77-2, manufacturer: zhengzhou alpha chemical Co., ltd.);
high-pressure impregnation is adopted, and the pressure is 8MPa;
the curing temperature is 150 ℃;
the content of high molecular polymer was 30wt.%;
through testing, the obtained graphene heat conduction gasket has the following relevant performances:
The application thermal resistance is as follows: 0.742K cm 2 /W；
The transverse tensile strength is: 5.17MPa.
Example 5
In this embodiment, the preparation process parameters of the graphene heat-conducting foam are as follows:
the graphene oxide filter cake is a graphene oxide filter cake of a company of science and technology, sixth element materials, changzhou;
the solvent of the graphene oxide slurry is water;
the solid content of the graphene oxide slurry is 5wt.%;
the drying treatment equipment is an oven;
the drying temperature is 80 ℃;
the drying time is 46min;
controlling the solid content of the graphene oxide coating to be 60wt.% after the drying treatment;
the freeze drying equipment is a freeze dryer;
the freeze-drying air pressure is 150 mTorr;
the freeze drying time is 24 hours;
the heat treatment equipment is a graphitization furnace;
the heat treatment temperature is 3000 ℃, and the heat treatment time is 8 hours;
the thickness of the graphene heat-conducting foam is 2mm;
through testing, the obtained graphene heat-conducting foam has the following relevant properties:
density: 0.109g/cm 3 ；
Specific heat capacity: 0.993J/g/K;
lateral thermal diffusivity: 462.72mm 2 /s；
Lateral thermal conductivity: 50.08W/(mK);
after the graphene heat-conducting foam is combined with the high polymer, stacking and curing the graphene heat-conducting foam layer by layer to form graphene heat-conducting blocks, and cutting the graphene heat-conducting blocks along the stacking direction to prepare the graphene heat-conducting gasket, wherein the preparation process conditions are as follows:
The high molecular polymer is alpha, omega-dihydroxy polydimethylsiloxane (source: wohenchen Jiali biotechnology Co., ltd.);
high-pressure impregnation is adopted, and the pressure is 7MPa;
the curing temperature is 100 ℃;
the content of high molecular polymer was 45wt.%;
through testing, the obtained graphene heat conduction gasket has the following relevant performances:
the application thermal resistance is as follows: 0.701K cm 2 /W；
The transverse tensile strength is: 5.64MPa.
Comparative example 1
In this comparative example, the preparation process parameters of the graphene heat-conducting foam are as follows:
the graphene oxide filter cake is a graphene oxide filter cake of a company of science and technology, sixth element materials, changzhou;
the solvent of the graphene oxide slurry is water;
the solid content of the graphene oxide slurry was 4wt.%;
the drying treatment equipment is an oven;
the drying temperature is 70 ℃;
the drying time is 8h and 49min;
controlling the solid content of the graphene oxide coating to be less than 0.1wt.% after the drying treatment, and treating the graphene oxide coating as completely dried;
the heat treatment equipment is a graphitization furnace;
the temperature of the heat treatment is 2800 ℃ and the heat treatment time is 5 hours;
the thickness of the graphene heat conduction foam is 1mm;
after combining graphene heat conduction foam with a high polymer, stacking and solidifying the graphene heat conduction foam layer by layer to form graphene heat conduction blocks, and cutting the graphene heat conduction blocks along the stacking direction to prepare the graphene heat conduction gasket, wherein the preparation process conditions are as follows:
The polymer is dimethyl diphenyl polysiloxane (source: CAS number: 68083-14-7, manufacturer: guangzhou Yuanzha New Material Co., ltd.);
high-pressure impregnation is adopted, and the pressure is 2MPa;
the curing temperature is 70 ℃;
the content of high molecular polymer was 50wt.%;
through testing, the obtained graphene heat conduction gasket has the following relevant performances:
applying thermal resistance: 1.351K cm 2 /W；
Transverse tensile strength: 0.86MPa;
comparative example 1 the graphene oxide coating was directly and completely dried, without freeze-drying treatment, and the other conditions were the same as in example 3. Because the freeze drying process is not adopted, the inside of the obtained graphene heat conduction foam is mainly closed pores with smaller size, so that the combination of a high polymer and graphene is poor, the thermal resistance of the prepared graphene heat conduction gasket is larger, and the application thermal resistance is 1.351K & cm 2 and/W, while the transverse tensile strength is small, the transverse tensile strength is only 0.86MPa.
Comparative example 2
In this comparative example, the preparation process parameters of the graphene heat-conducting foam are as follows:
the graphene oxide filter cake is a graphene oxide filter cake of a company of science and technology, sixth element materials, changzhou;
the solvent of the graphene oxide slurry is water;
The solid content of the graphene oxide slurry was 6wt.%;
the freeze drying equipment is a freeze dryer;
the freeze-drying air pressure is 200 mTorr;
freeze drying for 64h;
the heat treatment equipment is a graphitization furnace;
the temperature of the heat treatment is 2900 ℃, and the heat treatment time is 4 hours;
the thickness of the graphene heat conduction foam is 3mm;
through testing, the obtained graphene heat-conducting foam has the following relevant properties:
density: 0.034g/cm 3 ；
Specific heat capacity: 1.032J/g/K;
lateral thermal diffusivity: 102.42mm 2 /s；
Lateral thermal conductivity: 3.59W/(mK);
comparative example 2 the graphene oxide coating was applied and then subjected to a freeze-drying treatment as it is, without the step of the drying treatment according to the present invention, and the other conditions were the same as in example 4. The interior of the obtained graphene heat conduction foam is extremely fluffy due to the direct adoption of freeze drying treatment, the orientation of graphene is poor, the transverse heat conduction coefficient of the graphene heat conduction foam is only 3.59W/(m.K), and the high heat conduction requirement (more than or equal to 20W/(m.K)) of the graphene heat conduction gasket is difficult to meet.
The longitudinal performance of the graphene heat-conducting foam was further tested by the same method:
longitudinal thermal diffusivity: 45.62mm 2 /s；
Calculating to obtain the longitudinal heat conductivity coefficient: 1.60W/(mK);
the thermal conductivity in the longitudinal direction was also lower, so the decrease in thermal conductivity in the transverse direction of the graphene thermal conductive foam in comparative example 2 did not result in a higher thermal conductivity in the longitudinal direction, and therefore the high thermal conductivity requirements for preparing graphene thermal conductive gaskets could not be met in either the transverse or longitudinal directions.
Comparative example 3
In this comparative example, the preparation process parameters of the graphene heat-conducting foam are as follows:
the graphene oxide filter cake is a graphene oxide filter cake of a company of science and technology, sixth element materials, changzhou;
the solvent of the graphene oxide slurry is water;
the solid content of the graphene oxide slurry is 5wt.%;
directly placing graphene oxide slurry into a container for normal-temperature drying;
the heat treatment equipment is a graphitization furnace;
the heat treatment temperature is 3000 ℃, and the heat treatment time is 8 hours;
the thickness of the graphene heat-conducting foam is 2mm;
through testing, the obtained graphene heat-conducting foam has the following relevant properties:
density: 0.023g/cm 3 ；
Specific heat capacity: 1.072J/g/K;
lateral thermal diffusivity: 86.43mm 2 /s；
Lateral thermal conductivity: 2.13W/(mK);
longitudinal thermal diffusivity: 77.30mm 2 /s；
Calculating to obtain the longitudinal heat conductivity coefficient: 1.91W/(mK);
comparative example 3 the graphene oxide slurry was directly placed in a container, and coating, drying and freeze-drying treatments were not performed, except that the conditions were the same as in example 5. In this embodiment, the processes such as coating, drying and freeze drying are not adopted, so that the obtained graphene heat conduction foam does not have any orientation, and the heat conduction performance in the transverse direction and the longitudinal direction are poor, so that the graphene heat conduction foam cannot be used for preparing a graphene heat conduction gasket.
Comparative example 4
In this comparative example, the preparation process parameters of the graphene oxide slurry are as follows:
the graphene oxide filter cake is a graphene oxide filter cake of a company of science and technology, sixth element materials, changzhou;
the solvent of the graphene oxide slurry is water;
the solid content of the graphene oxide slurry is 0.2wt.%;
the solid content of the graphene oxide slurry of comparative example 4 was 0.2wt.%, and since the graphene oxide slurry was too low in solid content, the slurry was too thin, a significant flow phenomenon occurred after coating, and the graphene oxide coating could not be maintained, and the conditions for the next preparation step were not provided.
Comparative example 5
In this comparative example, the preparation process parameters of the graphene oxide slurry are as follows:
the graphene oxide filter cake is a graphene oxide filter cake of a company of science and technology, sixth element materials, changzhou;
the solvent of the graphene oxide slurry is water;
the solid content of the graphene oxide slurry was 12wt.%;
the solid content of the graphene oxide slurry of comparative example 5 was 12wt.%, and since the solid content of the graphene oxide slurry was too high, the slurry was too thick to be normally coated, resulting in failure to form a continuous graphene oxide coating, and the conditions for performing the next preparation step were not provided.
In the prior art, although pores can be controlled by direct freeze drying, graphene orientation is poor because graphene oxide in a slurry coating does not undergo an orientation self-assembly process. On the other hand, if the freeze drying is not performed and the self-assembly is performed by completely oxidizing the graphene, the internal pores of the obtained graphene heat conduction foam cannot be controlled, and the pores are mostly closed pores, which is unfavorable for the later compounding with materials such as polymers, because the polymers are difficult to be immersed in the pores.
According to the invention, the coated graphene oxide coating realizes directional self-assembly in the drying treatment process, and the graphene oxide is semi-directional in the drying treatment process due to incomplete drying, and then the semi-directional structure is maintained through freeze drying, so that the porous structure inside the graphene heat-conducting foam is formed through freeze drying, and the high polymer with any viscosity is easy to be immersed into the porous structure.
The mode of preparing graphene heat-conducting foam in the prior art, namely coating-drying-heat treatment, is mainly a closed-pore structure because of small internal pores, and can be used for immersing a high-molecular polymer with certain viscosity (such as viscosity of more than 1000 cp) after being diluted by a solvent; in addition, some high molecular weight polymers have a viscosity of greater than 1000cp, but are not diluted with a suitable solvent and cannot be used for immersion without dilution; the invention prepares the open pore with larger pore structure through semi-drying and semi-freezing control pore structure adjustment, which can solve the problems, thereby expanding and extending the types and the range of the applied high polymer, not needing to be diluted (such as viscosity of 1000-10000 cp) before, and being directly applied when not being used for immersion before; therefore, the method not only widens the variety range of the applicable high polymer, improves the convenience of high polymer immersion, avoids pollution, high cost, complex process and the like caused by using solvents, but also enriches the diversity of the graphite/high polymer composite material.
According to the invention, the semi-coating drying and the semi-freeze drying are combined, so that the large-scale production can be realized, and the graphene heat-conducting foam with semi-directional arrangement inside can be obtained; the internal pore structure size of the obtained graphene heat-conducting foam can be controlled; the method is suitable for a wider range of high molecular polymers, and can be combined with high-viscosity high polymers to obtain a composite material and a heat-conducting gasket with stronger mechanical properties; after the high polymer is impregnated, the graphene can be better oriented by further simple pressing, so that the graphene has higher oriented heat conduction performance; after pressing, the combination of the graphene and the high-molecular polymer is tighter, and the performance, especially the mechanical performance, of the obtained graphene heat-conducting gasket is improved.
While the foregoing disclosure shows exemplary embodiments of the invention, it should be noted that various changes and modifications could be made herein without departing from the scope of the invention as defined by the appended claims. Furthermore, although elements of the invention may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.
Claims (18)
1. The preparation method of the graphene heat-conducting foam is characterized by comprising the following steps of:
Coating graphene oxide slurry on a substrate to obtain a graphene oxide coating, wherein the solid content of the graphene oxide slurry is 0.5-9.5 wt.%;
drying the graphene oxide coating to ensure that the graphene oxide coating is not completely dried, wherein the drying treatment comprises normal-temperature drying or/and heating drying, and the solid content of the graphene oxide coating is controlled to be 40-75 wt%;
and freeze-drying the incompletely dried graphene oxide coating to obtain graphene oxide heat-conducting foam, wherein the vacuum level of freeze-drying is as follows: the air pressure is 50-300mTorr, and the freeze drying time is 12-72h; preparing graphene oxide heat-conducting foam by adopting a semi-drying and semi-freezing preparation method, wherein the semi-drying refers to that the graphene oxide is coated and then is subjected to partial drying treatment, and the graphene oxide coating is not completely dried but a set amount of solvent is reserved; by semi-frozen is meant that the freeze-drying has been preceded by a semi-drying but still contains a set amount of solvent, in which case the freeze-drying process is performed;
carrying out heat treatment on the graphene oxide heat conduction foam to obtain graphene oxide heat conduction foam, wherein the heat treatment temperature is more than or equal to 2400 ℃; the heat treatment time is more than or equal to 2 hours, the thickness of the graphene heat conduction foam is 0.3-5mm, the graphene which is arranged in a-45-degree directional manner in the graphene heat conduction foam and the transverse direction reaches a set proportion, and the set proportion is not less than 60%.
2. The method of manufacturing according to claim 1, characterized in that the graphene oxide slurry has a solids content of 4wt.% to 6wt.%.
3. The method of claim 1, wherein the step of drying the graphene oxide coating such that the graphene oxide coating is not completely dried comprises:
the drying degree is controlled by controlling the solid content of the graphene oxide coating, and the higher the solid content is, the higher the drying degree is.
4. The method of claim 1, wherein the step of drying the graphene oxide coating such that the graphene oxide coating is not completely dried comprises:
and controlling the drying degree of the graphene oxide coating by controlling the proportion of the transverse heat conductivity coefficient and the longitudinal heat conductivity coefficient of the graphene oxide coating, wherein the larger the proportion is, the larger the drying degree is.
5. The preparation method according to claim 1, wherein the solid content of the graphene oxide coating is controlled to be 50wt.% to 70wt.%.
6. The method of claim 1, wherein the gas pressure is 100-200mTorr.
7. The method according to claim 1, wherein in the heat treatment, the heat treatment temperature is not less than 2800 ℃; the heat treatment time is more than or equal to 5 hours.
8. A graphene heat-conducting foam, characterized in that the graphene is prepared by the preparation method of any one of claims 1-7, and the graphene inside the graphene heat-conducting foam is in orientation distribution.
9. The graphene thermal foam of claim 8, wherein the graphene thermal foam has a thickness of 1-3mm.
10. The graphene heat-conducting foam according to claim 8, wherein the graphene heat-conducting foam has a predetermined proportion of graphene arranged in a direction of-30 ° to 30 ° from the lateral direction.
11. The preparation method of the graphene heat conduction gasket is characterized by comprising the following steps of:
immersing a high molecular polymer in the graphene heat-conducting foam obtained by the preparation method in any one of claims 1-7, wherein the content of the high molecular polymer is 20-60 wt.% after the high molecular polymer is immersed;
stacking a plurality of impregnated graphene heat-conducting foam layers by layers, pressing, bonding and forming along the stacking direction, and curing to obtain a graphene heat-conducting block, wherein the curing temperature is 60-200 ℃;
cutting the graphene heat conduction blocks into pieces along the stacking direction to obtain graphene heat conduction gaskets;
wherein, still include:
at least one of vacuum impregnation, normal pressure impregnation and high pressure impregnation is adopted to impregnate the graphene heat conduction foam into the high molecular polymer, and the pressure of the high pressure impregnation is 0.5-10 MPa.
12. The method of claim 11, wherein pressure is applied to the adhesively formed multi-layer graphene thermal foam prior to curing.
13. The method according to claim 11, wherein the vacuum degree of vacuum impregnation is 0.095 to 0.099MPa.
14. The preparation method according to claim 11, wherein the content of the high molecular polymer after immersion is 30wt.% to 50wt.%.
15. A graphene heat-conducting gasket, characterized in that it is prepared by the preparation method of any one of claims 11 to 14, and comprises a plurality of layers of graphene heat-conducting foam and a high molecular polymer stacked along the thickness direction, wherein graphene inside the graphene heat-conducting foam is in orientation distribution, and the high molecular polymer is immersed in the graphene.
16. The graphene thermal pad of claim 15, wherein the high molecular polymer is at least one of epoxy, phenolic, furfural, polyurethane, acrylic, polybutene, and silicone.
17. The graphene thermal pad of claim 16, wherein the high molecular polymer is an organic silica gel.
18. The graphene thermal pad of claim 17, wherein the high molecular polymer is at least one of polydimethylsiloxane, α, ω -dihydroxypolydimethylsiloxane, dimethyldiphenylpolysiloxane, α, ω -dihydroxypolymethyl3, 3, 3-trifluoropropyl siloxane, and α, ω -divinylpolydimethylsiloxane.
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107010618A (en) * | 2017-04-28 | 2017-08-04 | 哈尔滨工业大学 | The preparation method and radiating film of a kind of high starch breeding alkene radiating film |
| CN110759739A (en) * | 2019-09-25 | 2020-02-07 | 三峡大学 | Preparation method of graphene ceramic composite material |
| CN113290958A (en) * | 2021-01-11 | 2021-08-24 | 常州富烯科技股份有限公司 | Graphene foam film enhanced heat conduction gasket and preparation method thereof |
| WO2022120587A1 (en) * | 2020-12-08 | 2022-06-16 | 中国科学院深圳先进技术研究院 | Preparation method for thermally conductive gaskets with high normal thermal conductivity and high elasticity |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107010618A (en) * | 2017-04-28 | 2017-08-04 | 哈尔滨工业大学 | The preparation method and radiating film of a kind of high starch breeding alkene radiating film |
| CN110759739A (en) * | 2019-09-25 | 2020-02-07 | 三峡大学 | Preparation method of graphene ceramic composite material |
| WO2022120587A1 (en) * | 2020-12-08 | 2022-06-16 | 中国科学院深圳先进技术研究院 | Preparation method for thermally conductive gaskets with high normal thermal conductivity and high elasticity |
| CN113290958A (en) * | 2021-01-11 | 2021-08-24 | 常州富烯科技股份有限公司 | Graphene foam film enhanced heat conduction gasket and preparation method thereof |
Non-Patent Citations (1)
| Title |
|---|
| 聚合物/定向石墨烯复合材料研究进展;吕青等;工程塑料应用;第44卷(第2期);140-144 * |
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