A construction method for preparing oriented graphene aerogel at low cost

Abstract

The present invention discloses a construction method for preparing an oriented graphene aerogel at low cost. The method adopts a two-step method to prepare a graphene aerogel with an oriented structure, solves the problems of incomplete orientation of the skeleton without a skeleton, easy destruction of the skeleton, and wrinkling and agglomeration of graphene sheets during the traditional compression orientation process. By using the traditional sol-gel method, adding a foaming agent, and adopting a low-cost green method without freeze-drying, a graphene aerogel with a regular structure is prepared. Subsequently, the uniaxial compression induced by bilateral confinement is used to orient the graphene sheets along the direction perpendicular to the force, and a graphene aerogel with an oriented structure is prepared.

Description

Technical Field

[0001] The present invention belongs to the field of thermal interface materials, and relates to a method for constructing a high-performance thermal interface material, specifically to a method for constructing an oriented graphene aerogel with low cost. Background Art

[0002] Graphene oxide has excellent dispersibility and can form a uniformly dispersed liquid. Due to the special structural characteristics of two-dimensional layered materials or one-dimensional materials, their properties are highly anisotropic. Therefore, for the full application of high performance, the design of the oriented structure is extremely important. Usually, the preparation of the oriented structure requires a certain external force induction. Under the action of the external force, the lamellae deflect and are arranged in an oriented manner along the direction of the force. Common external forces include extrusion force, tensile force, shear force, electric field force, magnetic field force, or the induction force in the growth direction during the crystallization of ice crystals, etc. In addition to external force induction, due to the special liquid crystal property of graphene oxide, special structures can be spontaneously formed, including chemical reduction method, evaporation self-assembly, etc., all of which can realize the oriented structure of two-dimensional lamellae.

[0003] Applying an external force field to the composite material or porous material to induce the orientation of the lamellae is a very convenient and effective orientation method. Usually, the preparation of the oriented structure can be achieved by means of biaxial stretching, extrusion or compression. Usually, after the filler and the polymer are uniformly mixed, the internal filler is well oriented under the action of the biaxial tensile force. This is mainly because during the deformation process of the polymer, the contact friction force between the polymer and the filler drives the filler to deflect under the condition of polymer tensile deformation, realizing the orientation of one-dimensional or two-dimensional materials. In addition, under the action of the extrusion force, due to the large specific surface area of the two-dimensional lamellae, they are in a paving state in the polymer matrix and can achieve the orientation of the lamellae under the action of the force. When the graphene sheets form a three-dimensional connected network structure by other means, under the condition of uniaxial pressure, due to the special two-dimensional layered structure, good oriented arrangement can be achieved, and with the increase of the pressure, the deflection degree of the graphene sheets is different, and the oriented structure also changes. Generally speaking, applying an external field force can realize the preparation of the graphene oriented structure, which is convenient and efficient. Although the mechanical compression method can easily obtain the oriented structure, the skeleton will be damaged during the mechanical compression process, and the full oriented structure can only be achieved under a relatively high pressure. In addition, due to the complexity of the structure, when the axial pressure acts, the internal mechanism is prone to uneven stress, resulting in an unclear internal oriented structure or different from the surface structure. The large compression force will increase the density of the three-dimensional orientation result while realizing the oriented structure, making the structure more rigid. When the modulus of the composite material is required, it will cause an increase in the modulus of the composite material and a decrease in elasticity.

[0004] To solve the problems of low orientation degree of the three-dimensional connected network structure, skeleton damage, and complex ice template orientation, the present invention proposes a simple and low-cost construction method for preparing oriented graphene aerogel. Combining the green and environmentally friendly sol-gel method with the axial compression method, a two-step method is used to prepare a regular structure and orientation, and a low-density and highly oriented graphene aerogel is prepared. Summary of the Invention

[0005] To achieve the preparation of graphene aerogel with an oriented structure, the present invention provides a low-cost construction method for preparing oriented graphene aerogel. To achieve the orientation of graphene sheets under the action of pressure, first, a cellular structure with regular arrangement is prepared by the traditional foaming method, and then through axial compression, the graphene sheets are oriented in the direction perpendicular to the pressure direction to obtain a low-density and highly oriented graphene aerogel.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] A low-cost construction method for preparing oriented graphene aerogel, comprising the following steps:

[0008] Step 1: Mix graphene oxide solution with a foaming agent and a reducing agent, and then perform mechanical foaming.

[0009] In this step, the concentration of graphene oxide used to ensure the skeleton strength of the graphene aerogel is above 15 mg / ml.

[0010] The reducing agent used in this step is ascorbic acid, and it can also be other reducing agents that promote gelation, such as potassium hydroxide, hydroiodic acid, hydrazine hydrate, sodium borohydride, etc.

[0011] The foaming agent used in this step is a surfactant, which can be one or more of polyglucosides such as alkyl glucoside or decyl glucoside.

[0012] In this step, the mass ratio of graphene oxide solution to the reducing agent is 1:1 - 10.

[0013] In this step, the mass ratio of graphene oxide solution to the foaming agent is 1:2 - 5, and the solution foaming is achieved by the high-speed stirring method, with a rotation speed of 1500 - 2000 rad / min.

[0014] In this step, the volume expansion of the solution is 2 - 3 times the initial volume.

[0015] Step 2: Heat the expanded mixed solution to react and convert it into graphene oxide hydrogel.

[0016] In this step, the mixed solution is heated in air at 50 - 70 °C for 2 - 4 h without obvious shrinkage.

[0017] Step 3: After cooling the hydrogel to room temperature for thermal equilibrium, place it in a freezing device for freezing.

[0018] In this step, the hydrogel is frozen in an environment of -20 to -30 °C, generally for 4 to 6 h (it is recommended to limit it to a specific range) to enhance the strength of the framework structure.

[0019] In this step, the sample is frozen in a container with low thermal conductivity to avoid damage to the cellular structure caused by temperature gradient. The cellular structure in this step is like Figure 3 the structure in the first row, a hollow structure similar to cells, interconnected through cell walls to form a connected network structure.

[0020] Step 4: After thawing the frozen hydrogel, heat it under air conditions to further reduce the graphene oxide hydrogel, and then place it in a freezing device for freezing.

[0021] Step 5: Wash the reduced hydrogel with deionized water to remove the internal solution, and dry it at room temperature or under heating conditions.

[0022] In this step, the hydrogel washed with deionized water is dried in air at 50 to 70 °C for about 5 to 10 h, and finally a graphene hydrogel with a cellular structure is obtained.

[0023] Step 6: Place the cellular graphene aerogel obtained in Step 5 in a compression mold, perform uniaxial compression, and carry out orientation.

[0024] In this step, the compression mold is made of stainless steel and is confined on both sides to ensure that the aerogel deforms only along the compression direction.

[0025] Step 7: Under vacuum or inert atmosphere, subject the oriented aerogel to high-temperature treatment at 1000 to 3000 °C for about 2 to 4 h (specific range) to further improve the crystallinity of the aerogel, thereby improving the thermal conductivity.

[0026] The present invention uses a two-step method to prepare a graphene aerogel with an oriented structure. Using the traditional sol-gel method, a foaming agent is added, and a low-cost green method without freeze-drying is used to prepare a graphene aerogel with a regular structure. Subsequently, uniaxial compression with confinement on both sides is used to induce the graphene sheets to orient along the direction perpendicular to the force, and a graphene aerogel with an oriented structure is prepared.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. After the chemical hydrothermal reduction of the present invention, partial reduction realizes the interaction between graphene oxide sheets while maintaining the interaction between graphene oxide sheets, forming a hybrid hydrogel. Multiple freeze-thaw cycles enhance the structural mechanical strength, enabling it to be unaffected by capillary action during the air-drying process and maintaining a complete structure. This avoids conventional freeze-drying and simplifies the preparation process.

[0029] 2. The present invention can prepare samples of different sizes by designing molds of different sizes, enabling the preparation of large-size samples.

[0030] 3. The present invention uses a foaming method combined with a sol-gel method to prepare a cellular structure with a regular structure before compression orientation. Compared with traditional random porous aerogels, it can ensure that graphene sheets are fully unfolded in the aerogel and do not undergo damage or wrinkling deformation during compression. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flowchart for the preparation of a graphene aerogel with a vertical structure;

[0032] Figure 2 is a diagram of a compression device for a graphene aerogel with a vertical structure;

[0033] Figure 3 is an SEM of the vertical force direction during the compression of the sample in Example 1.

[0034] In the figure, 1: graphene aerogel; 2: compression direction; 3: compression mold. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The technical solutions of the present invention will be further described below in conjunction with the embodiments, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0036] Example 1

[0037] This example provides a construction method for low-cost preparation of oriented graphene aerogel. As Figure 1 shown, the specific steps of the method are as follows:

[0038] 1) Preparation of graphene oxide dispersion: Weigh 4 g of flake graphite and place it in a beaker. Pour 450 ml of concentrated sulfuric acid and 50 ml of phosphoric acid into the beaker to prepare a mixed solution I, and stir at room temperature for 40 min. Place the beaker in a water bath for water bath heating, and add 18 g of potassium permanganate to the mixed solution I in 8 portions to obtain a mixed solution II. Keep the mixed solution II at a constant temperature of 70 °C for heating, take it out after 16 h and cool it at room temperature. After cooling to room temperature, slowly pour the mixed solution II into 700 ml of ice water mixed with hydrogen peroxide, let it stand for 24 h, filter off the supernatant, and take the lower layer solution for centrifugal washing to obtain a high-concentration graphene oxide solution. Finally, disperse the washed high-concentration graphene oxide solution in deionized water to obtain a graphene oxide dispersion with a concentration of 20 mg / mL for standby. Place the prepared graphene oxide dispersion in an environment at 11 °C for thermal equilibrium. The preparation method of 700 ml of ice water mixed with hydrogen peroxide is to dissolve 6 ml of hydrogen peroxide solution with a mass fraction of 30% in water to form a mixed solution III of 700 ml, and place the mixed solution III in a refrigerator at a sub-zero environment for freezing to obtain ice water mixed with hydrogen peroxide.

[0039] 2) Foaming of graphene oxide solution: Mix 200 g of graphene oxide solution with a concentration of 16 mg / ml, 6.4 g of foaming agent and 6.4 g of reducing agent, and use a stirrer to carry out mechanical foaming at a rotation speed of 1500 rad / min. Move the stirring head during the stirring process to ensure uniform foaming. When the solution volume expands to 2.75 times the original volume, control the volume and stir for 30 min.

[0040] 3) Preparation of graphene oxide hydrogel: Place the foamed graphene oxide mixture in an open container, seal it with plastic wrap, etc., and leave 5 holes with a diameter of 0.5 mm to release the reaction gas. Place the mixed solution in an air condition at 60 °C for preforming treatment for 3 h. Wait until the sample forms a jelly-like shape, separate it from the container and take out the sample.

[0041] 4) Place the hydrogel sample in a container with low thermal conductivity to avoid the influence of temperature gradient on the sample structure during the freezing process. Place the container in a refrigerator at -20 °C and freeze it completely.

[0042] 5) After thawing the frozen sample, place it in an air condition at 60 °C for reaction for 4 h. Repeat step 4) and then continue to place it in an air condition at 60 °C for reaction for 6 h, and react at 80 °C for 6 h.

[0043] 6) Washing and drying of hydrogel: After cooling the hydrogel, add 500 ml of deionized water to soak and wash it. Heat the solution during washing, the heating temperature is 65 °C, soak for 15 min, wash 4 times, take out the hydrogel, and heat and dry it in a blast drying oven at 60 °C to obtain a graphene aerogel with a cellular structure.

[0044] 7) Aerogel orientation: Place the aerogel in a compression mold, compress the volume to 75% of the original volume, keep the pressure for 12 h, and then remove the sample.

[0045] 8) Thermal reduction of oriented aerogel: Under nitrogen protection, treat the aerogel at 1200 °C.

[0046] Measure the thermal conductivity of the thermal interface material prepared in this example. When the volume fraction of graphene is 1.8 vol.%, the thermal conductivity in the vertical direction can reach 1 W / m·K, and the horizontal thermal conductivity is 0.2 W / m·K, showing anisotropy in thermal conductivity.

[0047] Example 2

[0048] This example provides a construction method for preparing oriented graphene aerogel at low cost, as Figure 1 shown, the specific steps of the method are as follows:

[0049] 1) Preparation of graphene oxide dispersion: Weigh 4 g of flake graphite and place it in a beaker. Pour 450 ml of concentrated sulfuric acid and 50 ml of phosphoric acid into the beaker to prepare a mixed solution I, and stir at room temperature for 40 min. Place the beaker in a water bath for water bath heating, add 18 g of potassium permanganate to the mixed solution I in 8 portions to obtain a mixed solution II, keep the mixed solution II at a constant temperature of 70 °C for heating, take it out after 16 h and cool it at room temperature. After cooling to room temperature, slowly pour the mixed solution II into 700 ml of hydrogen peroxide mixed ice water, let it stand for 24 h, filter off the supernatant, and take the lower layer solution for centrifugal washing to obtain a high-concentration graphene oxide solution. Finally, disperse the washed high-concentration graphene oxide solution in deionized water to obtain a graphene oxide dispersion with a concentration of 20 mg / mL for standby. Place the prepared graphene oxide dispersion in an environment at 11 °C for thermal equilibrium. The preparation method of 700 ml of hydrogen peroxide mixed ice water is to dissolve 6 ml of hydrogen peroxide solution with a mass fraction of 30% in water to form a mixed solution III, and place the mixed solution III in a refrigerator at a sub-zero environment for freezing to obtain hydrogen peroxide mixed ice water.

[0050] 2) Foaming of graphene oxide solution: Mix 200 g of graphene oxide solution with a concentration of 16 mg / ml with 6.4 g of foaming agent and 6.4 g of reducing agent, and perform mechanical foaming with a stirrer at a rotation speed of 1500 rad / min. During the stirring process, move the stirring head to ensure uniform foaming. When the solution volume expands to 2.75 times the original volume, control the volume and stir for 30 min.

[0051] 3) Preparation of graphene oxide hydrogel: Place the foamed graphene oxide mixture in an open container, seal it with plastic wrap, etc., and leave 5 holes with a diameter of 0.5 mm to release the reaction gas. Place the mixed solution under air conditions at 60 °C for preforming for 3 h. Wait until the sample forms a jelly-like state, separate it from the container, and then take out the sample.

[0052] 4) Place the hydrogel sample in a container with low thermal conductivity to avoid temperature gradient during the freezing process affecting the sample structure. Place the container in a -20 °C refrigerator and freeze it completely.

[0053] 5) After thawing the frozen sample, place it under air conditions at 60 °C for reaction for 4 h. Repeat step 4), and then continue to place it under air conditions at 60 °C for reaction for 6 h, and react at 80 °C for 6 h.

[0054] 6) Washing and drying of the hydrogel: After cooling the hydrogel, add 500 ml of deionized water to soak and wash it. Heat the solution during washing, with the heating temperature being 65 °C, soak for 15 min, wash 4 times, then take out the hydrogel and heat and dry it in a 60 °C blast drying oven to obtain a graphene aerogel with a cellular structure.

[0055] 7) Aerogel orientation: Place the aerogel in a compression mold, compress the volume to 75% of the original volume, keep the pressure for 12 h, and then remove the sample.

[0056] 8) Thermal reduction of the oriented aerogel: Under nitrogen protection, treat the aerogel at 2500 °C.

[0057] Test the thermal conductivity of the thermal interface material prepared in this example. When the graphene volume fraction is 1.8 vol.%, the thermal conductivity in the vertical direction can reach 5 W / m·K, and the horizontal thermal conductivity is 1.2 W / m·K, showing the anisotropy of the thermal conductivity.

[0058] Example 3

[0059] This example provides a construction method for low-cost preparation of oriented graphene aerogel, as Figure 1 shown. The specific steps of the method are as follows:

[0060] 1) Preparation of graphene oxide dispersion: Weigh 4 g of flake graphite and place it in a beaker. Pour 450 ml of concentrated sulfuric acid and 50 ml of phosphoric acid into the beaker to prepare a mixed solution Ⅰ, and stir it at room temperature for 40 min. Place the beaker in a water bath for water bath heating. Add 18 g of potassium permanganate to the mixed solution Ⅰ in 8 portions to obtain a mixed solution Ⅱ. Heat the mixed solution Ⅱ at a constant temperature of 70 °C, take it out after 16 h and cool it at room temperature. After cooling to room temperature, slowly pour the mixed solution Ⅱ into 700 ml of hydrogen peroxide mixed with ice water. Let it stand for 24 h, then filter off the supernatant, and take the lower layer solution for centrifugal washing to obtain a high-concentration graphene oxide solution. Finally, disperse the washed high-concentration graphene oxide solution in deionized water to obtain a graphene oxide dispersion with a concentration of 20 mg / mL for standby. Place the prepared graphene oxide dispersion in an environment at 11 °C for thermal equilibrium. The preparation method of 700 ml of hydrogen peroxide mixed with ice water is to dissolve 6 ml of hydrogen peroxide solution with a mass fraction of 30% in water to form a mixed solution Ⅲ of 700 ml, and place the mixed solution Ⅲ in a refrigerator at a sub-zero environment for freezing to obtain hydrogen peroxide mixed with ice water.

[0061] 2) Foaming of graphene oxide solution: Mix 200 g of graphene oxide solution with a concentration of 16 mg / ml, 6.4 g of foaming agent and 6.4 g of reducing agent, and use a stirrer to carry out mechanical foaming at a rotation speed of 1500 rad / min. During the stirring process, move the stirring head to ensure uniform foaming. When the solution volume expands to 2.75 times the original volume, control the volume and stir for 30 min.

[0062] 3) Preparation of graphene oxide hydrogel: Place the foamed graphene oxide mixture in an open container, seal it with plastic wrap, etc., and leave 5 holes with a diameter of 0.5 mm to release the reaction gas. Place the mixed solution in an air condition at 60 °C for preforming treatment for 3 h. Wait until the sample forms a jelly-like shape, separate it from the container and take out the sample.

[0063] 4) Place the hydrogel sample in a container with low thermal conductivity to avoid the influence of temperature gradient on the sample structure during the freezing process. Place the container in a refrigerator at -20 °C for complete freezing.

[0064] 5) After thawing the frozen sample, place it in an air condition at 60 °C for reaction for 4 h. Repeat step 4) and then continue to place it in an air condition at 60 °C for reaction for 6 h, and react at 80 °C for 6 h.

[0065] 6) Washing and drying of hydrogel: After cooling the hydrogel, add 500 ml of deionized water to soak and wash it. During the washing, heat the solution, the heating temperature is 65 °C, soak for 15 min, wash 4 times, then take out the hydrogel and heat and dry it in a blast drying oven at 60 °C to obtain a graphene aerogel with a cellular structure.

[0066] 7) Aerogel orientation: Place the aerogel in a compression mold, compress the volume to 75% of the original volume, and remove the sample after maintaining the pressure for 12 h.

[0067] 8) Thermal reduction of oriented aerogel: Under nitrogen protection, treat the aerogel at 3000 °C.

[0068] Measure the thermal conductivity of the thermal interface material prepared in this example. When the graphene volume fraction is 1.8 vol.%, the thermal conductivity in the vertical direction can reach 7 W / m·K, and the horizontal thermal conductivity is 1.3 W / m·K, showing anisotropy in thermal conductivity.

Claims

1. A construction method for preparing an oriented graphene aerogel with low cost, characterized in that The method includes the following steps: Step 1: Mix graphene oxide solution, foaming agent and reducing agent according to a mass ratio of 1:2-5:1-10, conduct mechanical foaming, and heat and react the expanded mixed solution to convert it into graphene oxide hydrogel; Step 2: After cooling the hydrogel to room temperature, perform thermal equilibrium, conduct the first thermal reduction at 50-70 °C, and then place it in a freezing device in a low-thermal-conductivity container and freeze it at -20--30 °C; Step 3: After thawing the frozen hydrogel, heat it under air conditions to further reduce the graphene oxide hydrogel, and then place it in a freezing device in a low-thermal-conductivity container for freezing; Step 4: Wash the reduced hydrogel several times with deionized water, remove the internal solution, and dry it at room temperature or by heating to finally obtain a graphene aerogel with a cellular structure; Step 5: Place the cellular graphene aerogel obtained in Step 4 in a compression mold, perform uniaxial compression, and conduct orientation; Step 6: Under vacuum or inert atmosphere, perform high-temperature treatment on the oriented aerogel at 1000-3000 °C and keep it warm for 2-4 h to further improve the crystallinity of the aerogel, thereby improving the thermal conductivity.

2. The construction method for preparing an oriented graphene aerogel at low cost according to claim 1, characterized in that In the said Step 1, the concentration of the graphene oxide is 15-30 mg / ml.

3. The construction method for preparing an oriented graphene aerogel at low cost according to claim 1, characterized in that In the said Step 1, the reducing agent is one of ascorbic acid, potassium hydroxide, hydroiodic acid, hydrazine hydrate, sodium borohydride; the foaming agent is polyglucoside.

4. The construction method for preparing an oriented graphene aerogel at low cost according to claim 1, characterized in that In the said Step 1, the mechanical stirring speed is 1500-2000 rad / min, the stirring head moves up and down during the stirring process, and the volume expands to 2-3 times the original volume.

5. The construction method for preparing an oriented graphene aerogel at low cost according to claim 1, characterized in that In the said Step 2, the thermal reduction is carried out step by step. To avoid serious volume shrinkage, multiple freezings are required during the process.

6. The construction method for preparing the oriented graphene aerogel with low cost according to claim 1, characterized in that In the said Step 4, the drying method adopts direct air drying.

7. The construction method for preparing the oriented graphene aerogel at low cost according to claim 1, characterized in that In the said Step 5, the obtained graphene aerogel is axially compressed in a mold with two-sided confinement.

Images