1. A preparation method of an ultra-thick heat-conducting graphene film is characterized by comprising the following steps:

1) adding chitosan into the graphene oxide water slurry to obtain modified graphene oxide slurry;

2) punching conical bulges on a substrate, and assembling the modified graphene oxide slurry on the substrate to obtain a graphene oxide film with bulges;

3) laminating and pressurizing a plurality of graphene oxide films to form an ultra-thick graphene oxide sheet, and heating for thermal reduction treatment;

4) and heating and graphitizing the graphene sheet after thermal reduction in a protective atmosphere to finally form a compact graphene film.

2. The method for preparing the ultra-thick heat-conducting graphene film according to claim 1, wherein the mass concentration of graphene oxide in the graphene oxide aqueous slurry is 1-6 wt.%, and the concentration of chitosan in the modified graphene oxide slurry is 0.2-2 wt.%.

3. The method for preparing the ultra-thick heat-conducting graphene film according to claim 1, wherein the substrate is made of polytetrafluoroethylene.

4. The method for preparing the ultra-thick heat-conducting graphene film according to claim 1, wherein the thermal reduction treatment is heating to 1200 ℃ at a rate of 1 ℃/min.

5. The method for preparing the ultra-thick heat-conducting graphene film according to claim 1, wherein the heating graphitization is specifically heating to 2200-3100 ℃ at a speed of 5 ℃/min.

Background

The rapid development of integrated circuits has made heat dissipation of electronic devices a common problem. Taking a smart phone as an example, the peak power consumption of the smart phone in the age of 5G can reach more than 10W. Heat accumulation is easily formed at high-power parts such as a Central Processing Unit (CPU), a baseband chip and the like. If heat is not removed from these areas by effective means, localized hot spots will be created, which in turn affect the performance and lifetime of the device. The plane heat conduction capability of graphite is extremely high, and the characteristic is very beneficial to transverse temperature equalization of local heat, so that the artificial graphite film is widely used as a heat dissipation material in electronic products such as smart phones and the like. The technical principle is that the graphite film diffuses local heat to the whole large plane in a heat conduction mode, so that the heat flow density is reduced, and local hot spots are eliminated. The heat spreading capability of the graphite film (i.e., the transfer of heat by thermal conduction) during this process can be described by the following equation:

where Δ T is the temperature difference, δ is the distance of thermal conduction, S is the width of the graphite film, and h is the thickness of the graphite film. Where δ and S are most often limited by the physical dimensions of the device. Therefore, the key point of preparing the graphite film with high heat diffusion capacity is to simultaneously improve the heat conductivity and the thickness.

The graphene is a graphite crystal with a hexagonal honeycomb structure, and the theoretical thermal conductivity of the graphene can reach more than 3000W/mK. Once the graphene is assembled into a graphene film with a certain thickness, the graphene film can be used as a new-generation heat dissipation material. Mainstream preparation methods of graphene include vapor deposition, graphene oxide and other technical routes. The graphene oxide is prepared by using graphene oxide slurry as a precursor, assembling graphene oxide into a GO thin film, and then obtaining the heat-conducting graphene film by high-temperature reduction and other technologies. It is therefore a common general knowledge of many engineers to greatly increase the thermal conductivity and thickness of thermally conductive graphene films.

To obtain a super-thick graphene film, a super-thick graphene oxide film must be first manufactured. The mechanism of graphene oxide film formation is known as follows: and a complete and compact thin film is formed between the graphene oxide sheet layers under the action of hydrogen bonds. Since most of the oxygen-containing functional groups of the graphene oxide are located at the edges of the particles, the graphene oxide is very easy to form a film in the facing direction and is not easy to accumulate in the thickness direction. Taking the suction filtration method as an example, the graphene oxide film is about 50 microns thick after being subjected to suction filtration for 60 hours. Therefore, the preparation of the ultra-thick graphene oxide film becomes an industry common problem.

Academic journal Crbon,2020 (167): 270-277 reports a method for preparing an ultra-thick graphene oxide film by using high-concentration graphene oxide slurry, and then a heat-conducting graphene thick film is prepared by subsequent high-temperature heat treatment. However, the graphene oxide slurry is a weakly acidic positively charged hydrosol, and is easily agglomerated and layered after the concentration exceeds 2 wt.%, so that the high-concentration graphene oxide slurry is not easy to exist stably. Crbon,2020 (167), 249-255 reports a method for preparing an ultra-thick graphene oxide membrane by using a hydrogen bond activation technology. The technical principle is that graphene oxide slurry is subjected to suction filtration to form a film, the obtained graphene oxide film is soaked in water and then is laminated, a thick graphene oxide film is formed after slow drying, and a heat-conducting graphene thick film is prepared through subsequent high-temperature treatment.

Disclosure of Invention

Aiming at the defects in the prior art, the invention starts from the principle of graphene oxide film forming, and by taking the special brick-mud structure and the special spike shape of pearl oyster shell as reference according to the bionic design principle, chitosan is introduced as a binder in the process of graphene oxide film forming, and meanwhile, a microscopic spike is constructed on the surface of a graphite oxide film in the process of film forming, so that the binding force between each layer of an inorganic thin sheet in the process of graphene oxide film forming is enhanced, an ultra-thick graphene oxide assembly is obtained, and the ultra-thick heat-conducting graphene film is obtained in the subsequent heat treatment process.

In order to achieve the technical purpose, the invention specifically adopts the following technical scheme:

a preparation method of an ultra-thick heat-conducting graphene film comprises the following steps:

1) adding chitosan into the graphene oxide water slurry to obtain modified graphene oxide slurry;

2) punching conical bulges on a substrate, and assembling the modified graphene oxide slurry on the substrate to obtain a graphene oxide film with bulges;

3) laminating and pressurizing a plurality of graphene oxide films to form an ultra-thick graphene oxide sheet, and heating for thermal reduction treatment;

4) and heating and graphitizing the graphene sheet after thermal reduction in a protective atmosphere to finally form a compact graphene film.

The mass concentration of the graphene oxide in the graphene oxide water slurry is 1-6 wt.%.

The concentration of chitosan in the modified graphene oxide slurry is 0.2-2 wt.%.

The substrate is preferably a polytetrafluoroethylene material.

The thickness of the graphene oxide film in the step (2) is 10-300 microns.

The graphene oxide sheet is 300-6000 microns thick.

The thermal reduction treatment is to heat up to 1200 ℃ at a speed of 1 ℃/min. The thermal reduction process of the graphene oxide is to heat the graphene oxide film to high temperature in vacuum or inert atmosphere to remove non-carbon atoms.

The heating graphitization is to heat up to 2200-3100 ℃ at the speed of 5 ℃/min to form a compact graphene film.

The invention has the beneficial effects that:

according to the invention, graphene oxide is modified by chitosan, the binding force between each layer of inorganic thin sheets in the graphene oxide film forming process is enhanced, an ultra-thick graphene oxide assembly is obtained, a bionic principle is utilized in the wet chemical film forming process, a graphene oxide film with a spike shape on the surface is obtained, and the ultra-thick graphene oxide film is formed by heat treatment, high-temperature repair and graphitization after stacking and assembling, so that the ultra-thick heat-conducting graphene film is obtained, the thickness of the obtained graphene film can reach more than 500 micrometers, the heat conductivity can reach 1146W/mK, and the ultra-thick graphene oxide film can be used for the heat dissipation design of high-power electronic equipment.

Drawings

FIG. 1 is a process flow for preparing an ultra-thick graphene oxide film according to the present invention;

FIG. 2 is a super-thick graphene oxide film formed by compacting multiple graphene oxide layers according to the present invention;

fig. 3 is an X-ray diffraction pattern of the ultra-thick graphene film in example 1 of the present invention.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to specific embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

According to the invention, the ultra-thick graphene oxide film is prepared according to the bionic design principle, chitosan is added into graphene oxide slurry, and the chitosan can be dissolved in acidic graphene oxide slurry. Preparing the graphene oxide slurry into a film by means of suction filtration, blade coating and the like, controlling the appearance of the graphite oxide film, and introducing 'spikes' on the surface of the graphite oxide film; and then stacking a plurality of graphene oxide films, wherein each graphene oxide film forms a tightly combined thick film under the combined action of the adhesive and the mechanical embedding. The product is then graphitized. The graphene oxide film is converted into a high heat conduction type (the volume density is more than or equal to 1.6 g/cm) by the technology³) The graphene thick film of (2).

The invention refers to the special brick-mud structure and the special spike shape of the shell of the pearl oyster, 95 percent of the chemical components of the shell of the pearl oyster are flaky inorganic substances, but can be stacked into a thick shell layer with millimeter thickness and excellent mechanical property. The reason for this includes two parts: firstly, the special 'brick-mud structure' is that the flaky inorganic calcium carbonate is 'brick' and organic matters such as chitosan and the like are 'mud' playing a role in adhesion. Secondly, the flaky surface has special 'spike' appearance, and the 'spike' is beneficial to the embedding between the inorganic sheets.

Chitosan is introduced as a binder in the film forming process of graphene oxide, and microscopic spikes are constructed on the surface of the graphite oxide film in the film forming process. The method can obviously enhance the binding force among all layers of the inorganic thin sheet in the film forming process of the graphene oxide, obtain the ultra-thick graphene oxide assembly, and obtain the ultra-thick heat-conducting graphene film in the subsequent heat treatment process.

As shown in fig. 1, the invention provides a preparation method of an ultra-thick heat-conducting graphene film, which comprises the following steps:

1) adding chitosan into graphene oxide water slurry with the mass concentration of 1-6 wt.%, wherein the solid content of the chitosan is 0.2-2 wt.%, and obtaining modified graphene oxide slurry;

2) punching conical protrusions on a substrate, and assembling the modified graphene oxide slurry on the substrate to form a graphene oxide film with protrusions and the thickness of 10-300 microns;

3) laminating and pressurizing a plurality of graphene oxide films, forming a 300-6000 micron graphene oxide sheet (shown in figure 2) by each graphene oxide film under the embedding action of a high molecular auxiliary agent and a spike, heating to 1200 ℃ at the speed of 1 ℃/min, and removing non-carbon atoms;

4) and heating the graphene sheet subjected to thermal reduction to 2200-3100 ℃ at a speed of 5 ℃/min under a protective atmosphere to form a compact graphene film.

Example 1

1) Graphene oxide slurry with the average sheet diameter of 2 microns and the mass concentration of 1.0 wt.% is used as a precursor, and chitosan with the solid content of 1 wt.% is added into the graphene oxide slurry to form viscous slurry.

2) Conical protrusions are punched on the teflon substrate, and the height of the protrusions is about 5 microns. Coating the chitosan modified graphene oxide slurry on a patterned polytetrafluoroethylene substrate to form a film with the thickness of 50 microns, and uncovering the graphene oxide film, wherein the surface of the graphene film also has obvious 'spikes'.

3) And (3) laminating 6 layers of graphene oxide, pressurizing to 5Mp, heating to 60 ℃, and keeping the temperature and pressure for 1 hour to form a tightly combined multilayer graphene oxide film with the thickness of 300 microns.

4) Cutting the graphene oxide thick film into a square with the size of 100 multiplied by 100mm, putting the square into a graphite mold, heating to 1200 ℃ at the speed of 1 ℃/min, and preserving heat for 30 minutes after the target temperature is reached. The thermal reduction treatment is completed.

5) And (3) taking out the reduced graphene oxide film obtained in the step (4), weighing the film, putting the film into a graphite mold, and heating the film to 2200 ℃ at the speed of 5 ℃/min. And after the target temperature is reached, keeping the temperature for 120 minutes to finish the graphitization treatment. The volume density of the graphene film after graphitization treatment can reach 1.8g/cm³The thickness was 120 μm and the thermal conductivity was 855.0W/mK.

As shown in fig. 3, the characteristic size L of the inner graphite crystallite can be calculated by the scherrer equation, where L is 150 nm.

Example 2

1) Graphene oxide slurry with the average sheet diameter of 0.5 micron and the mass concentration of 1.5 wt.% is used as a precursor, and chitosan with the solid content of 2 wt.% is added into the graphene oxide slurry to form viscous slurry.

2) Conical protrusions are punched on the teflon substrate, and the height of the protrusions is about 10 microns. Coating the chitosan modified graphene oxide slurry on a patterned polytetrafluoroethylene substrate to form a film with the thickness of 60 microns, and uncovering the graphene oxide film, wherein the surface of the graphene film also has obvious 'spikes'.

3) And laminating 10 layers of graphene oxide, pressurizing to 5Mp, heating to 60 ℃, and keeping the temperature and pressure for 1 hour to form a tightly combined multilayer graphene oxide film with the thickness of 600 microns.

4) Cutting the graphene oxide thick film into a square with the size of 100 multiplied by 100mm, putting the square into a graphite mold, heating to 1200 ℃ at the speed of 1 ℃/min, and preserving heat for 30 minutes after the target temperature is reached. The thermal reduction treatment is completed.

5) And (3) taking out the reduced graphene oxide film obtained in the step (4), weighing the film, putting the film into a graphite mold, and heating the film to 2800 ℃ at a speed of 5 ℃/min. And after the target temperature is reached, keeping the temperature for 60 minutes to finish the graphitization treatment. The volume density of the graphene film after graphitization treatment can reach 1.87g/cm³The thickness was 245 μm and the thermal conductivity was 931.3W/mK.

Example 3

1) Graphene oxide slurry with the average sheet diameter of 100 micrometers and the mass concentration of 6.0 wt.% is used as a precursor, and chitosan with the solid content of 0.2 wt.% is added into the graphene oxide slurry to form viscous slurry.

2) Conical protrusions are punched on the teflon substrate, and the height of the protrusions is about 20 microns. Coating the chitosan modified graphene oxide slurry on a patterned polytetrafluoroethylene substrate to form a film with the thickness of 100 microns, and uncovering the graphene oxide film, wherein the surface of the graphene film also has obvious 'spikes'.

3) And laminating 10 layers of graphene oxide, pressurizing to 5Mp, heating to 60 ℃, and keeping the temperature and pressure for 1 hour to form a tightly combined multilayer graphene oxide film with the thickness of 1000 microns.

4) Cutting the graphene oxide thick film into a square with the size of 100 multiplied by 100mm, putting the square into a graphite mold, heating to 1200 ℃ at the speed of 1 ℃/min, and preserving heat for 30 minutes after the target temperature is reached. The thermal reduction treatment is completed.

5) And (3) taking out the reduced graphene oxide film obtained in the step (4), weighing the film, putting the film into a graphite mold, and heating the film to 3100 ℃ at a speed of 5 ℃/min. And after the target temperature is reached, keeping the temperature for 20 minutes to finish the graphitization treatment. The volume density of the graphene film after graphitization treatment can reach 2.0g/cm³The graphene film thickness was 473 microns, and the thermal conductivity was 1057.5W/mK.

Example 4

1) Graphene oxide slurry with the average sheet diameter of 30 micrometers and the mass concentration of 3.0 wt.% is used as a precursor, and chitosan with the solid content of 1.5 wt.% is added into the graphene oxide slurry to form viscous slurry.

2) Conical protrusions are punched on the teflon substrate, and the height of the protrusions is about 10 microns. Coating the chitosan modified graphene oxide slurry on a patterned polytetrafluoroethylene substrate to form a film with the thickness of 100 microns, and uncovering the graphene oxide film, wherein the surface of the graphene film also has obvious 'spikes'.

3) And (3) laminating 12 layers of graphene oxide, pressurizing to 5Mp, heating to 60 ℃, and keeping the temperature and pressure for 1 hour to form a tightly combined multilayer graphene oxide film with the thickness of 1200 microns.

4) Cutting the graphene oxide thick film into a square with the size of 100 multiplied by 100mm, putting the square into a graphite mold, heating to 1200 ℃ at the speed of 1 ℃/min, and preserving heat for 30 minutes after the target temperature is reached. The thermal reduction treatment is completed.

5) And (3) taking out the reduced graphene oxide film obtained in the step (4), weighing the film, putting the film into a graphite mold, and heating the film to 2500 ℃ at the speed of 5 ℃/min. And after the target temperature is reached, keeping the temperature for 60 minutes to finish the graphitization treatment. The volume density of the graphene film after graphitization treatment can reach 1.98g/cm³The graphene film thickness was 509 microns and the thermal conductivity was 947.1W/mK.

Example 5

1) Graphene oxide slurry with the average sheet diameter of 20 micrometers and the mass concentration of 1.0 wt.% is used as a precursor, and chitosan with the solid content of 0.5 wt.% is added into the graphene oxide slurry to form viscous slurry.

2) Conical protrusions are punched on the teflon substrate, and the height of the protrusions is about 10 microns. Coating the chitosan modified graphene oxide slurry on a patterned polytetrafluoroethylene substrate to form a film with the thickness of 100 microns, and uncovering the graphene oxide film, wherein the surface of the graphene film also has obvious 'spikes'.

3) And laminating 10 layers of graphene oxide, pressurizing to 5Mp, heating to 60 ℃, and keeping the temperature and pressure for 1 hour to form a tightly combined multilayer graphene oxide film with the thickness of 1000 microns.

4) Cutting the graphene oxide thick film into a square with the size of 100 multiplied by 100mm, putting the square into a graphite mold, heating to 1200 ℃ at the speed of 1 ℃/min, and preserving heat for 30 minutes after the target temperature is reached. The thermal reduction treatment is completed.

5) And (3) taking out the reduced graphene oxide film obtained in the step (4), weighing the reduced graphene oxide film, putting the film into a graphite mold, and heating the film to 2600 ℃ at a speed of 5 ℃/min. And after the target temperature is reached, keeping the temperature for 30 minutes to finish the graphitization treatment. The volume density of the graphene film after graphitization treatment can reach 1.90g/cm³The graphene film thickness is 433 microns and the thermal conductivity is 927.7W/mK.

Example 6

1) Graphene oxide slurry with the average sheet diameter of 50 micrometers and the mass concentration of 4.0 wt.% is used as a precursor, and chitosan with the solid content of 1 wt.% is added into the graphene oxide slurry to form viscous slurry.

2) Conical protrusions are punched on the teflon substrate, and the height of the protrusions is about 15 micrometers. Coating the chitosan modified graphene oxide slurry on a patterned polytetrafluoroethylene substrate to form a film with the thickness of 120 microns, and uncovering the graphene oxide film, wherein the surface of the graphene film also has obvious 'spikes'.

3) And (3) laminating 6 layers of graphene oxide, pressurizing to 5Mp, heating to 60 ℃, and keeping the temperature and pressure for 1 hour to form a tightly combined multilayer graphene oxide film with the thickness of 720 microns.

4) Cutting the graphene oxide thick film into a square with the size of 100 multiplied by 100mm, putting the square into a graphite mold, heating to 1200 ℃ at the speed of 1 ℃/min, and preserving heat for 30 minutes after the target temperature is reached. The thermal reduction treatment is completed.

5) And (3) taking out the reduced graphene oxide film obtained in the step (4), weighing the film, putting the film into a graphite mold, and heating the film to 2700 ℃ at a speed of 5 ℃/min. And after the target temperature is reached, keeping the temperature for 50 minutes to finish the graphitization treatment. The volume density of the graphene film after graphitization treatment can reach 1.95g/cm³The graphene film thickness was 515 microns and the thermal conductivity was 1032W/mK.

Example 7

1) Graphene oxide slurry with the average sheet diameter of 50 micrometers and the mass concentration of 4.0 wt.% is used as a precursor, and chitosan with the solid content of 1 wt.% is added into the graphene oxide slurry to form viscous slurry.

2) Conical protrusions are punched on the teflon substrate, and the height of the protrusions is about 15 micrometers. Coating the chitosan modified graphene oxide slurry on a patterned polytetrafluoroethylene substrate to form a film with the thickness of 120 microns, and uncovering the graphene oxide film, wherein the surface of the graphene film also has obvious 'spikes'.

3) And (3) laminating 12 layers of graphene oxide, pressurizing to 5Mp, heating to 60 ℃, and keeping the temperature and pressure for 1 hour to form a tightly combined multilayer graphene oxide film with the thickness of 1200 microns.

4) Cutting the graphene oxide thick film into a square with the size of 100 multiplied by 100mm, putting the square into a graphite mold, heating to 1200 ℃ at the speed of 1 ℃/min, and preserving heat for 30 minutes after the target temperature is reached. The thermal reduction treatment is completed.

5) And (3) taking out the reduced graphene oxide film obtained in the step (4), weighing the film, putting the film into a graphite mold, and heating the film to 2700 ℃ at a speed of 5 ℃/min. And after the target temperature is reached, keeping the temperature for 50 minutes to finish the graphitization treatment. The volume density of the graphene film after graphitization treatment can reach 2.01g/cm³The graphene film thickness is 571 microns, and the thermal conductivity is 1146W/mK.

The properties of the graphene films prepared in examples 1 to 7 of the present invention are shown in table 1.

Table 1 shows ultra-thick thermally conductive graphene films of the present invention

Examples	Thickness (micron)	Density (g/cm)3)	Thermal conductivity (Wm)-1K-1)
				1	120	1.80	855.0
2	245	1.87	931.3
				3	473	2.0	1057.5
4	509	1.98	947.1
				5	433	1.90	927.7
6	515	1.95	1032
				7	571	2.01	1146

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.