A method for manufacturing a graphene film having a thermal rectification function

Abstract

The application discloses a manufacturing method of a graphene film with a thermal rectification function, relates to the technical field of micro-nano scale thermal conductivity regulation, and is characterized in that natural graphene is used as a raw material, and graphene micro-pieces with different sizes are prepared through an electrolytic stripping method; and a film composed of graphene micro-pieces with different sizes is continuously prepared on a substrate through a coating process or a spraying plating process. The application adopts a bionics method, imitates the pore structure of bamboo with a thermal rectification effect, selects graphene material as a heat conductor, utilizes the principle that the thermal conductivities of graphene micro-pieces with different sizes are different, adjusts relevant parameters to realize the size gradient distribution of the graphene micro-pieces, and prepares the graphene film with gradually increasing thermal conductivities, so that the graphene film has the function of thermal rectification, the problem of low rectification value of a traditional thermal rectifier is solved, and efficient control of heat flow is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-nano scale thermal conductivity regulation, and particularly relates to a manufacturing method of a graphene film with thermal rectification function. BACKGROUND

[0002] Thermal rectification refers to the fact that the thermal conductivity of a material in two directions is not equal, that is, the heat flow is easier to transfer along a certain direction, and when reversed, the thermal resistance is larger, and the heat flow is not easy to transfer. This is like a diode in electricity, which enables unidirectional heat transfer, and this feature can be utilized to achieve efficient control and management of heat flow.

[0003] Bamboo, which is very common in our daily life, has thermal rectification effect. When the cross section of the bamboo is observed under an optical microscope, it can be found that there are pore structures of different sizes in the bamboo, and the pore structures close to the inner wall of the bamboo are more than those close to the outer wall of the bamboo. The size and quantity of the pore structures gradually increase from outside to inside. Since the larger the pore structure is, the lower the thermal conductivity is, the thermal conductivity of the bamboo gradually increases from inside to outside, so heat absorption is easier and heat dissipation is more difficult. Therefore, the bamboo has good heat preservation performance and is widely used in buildings and daily life.

[0004] Thermal rectifiers were first introduced in 1936. The traditional thermal rectification mechanism is based on the dependence of the thermal conductivity of two different materials on different temperatures. However, most of the demonstration results based on this mechanism show that the rectification rate is very low. In addition, it is almost impossible to know the thermal conductivity of each part of the thermal rectifier in nanoscale devices. In this case, it is very necessary to develop new strategies for high-performance thermal rectifiers.

[0005] Graphene is a two-dimensional material with a single atomic layer thickness, and it has attracted much attention due to its unique electrical, optical, mechanical, and thermal properties. Studies have found that the thermal conductivity of graphene can be as high as 5300 (W / m·K), which is higher than that of graphite bulk and diamond, and is the highest value of thermal conductivity among known materials. With the in-depth theoretical research and the progress of measurement technology, it has been found that single-layer graphene has higher thermal conductivity than graphite bulk, which is related to its special phonon scattering mechanism, so it has become an important research object for verifying and developing phonon heat conduction theory. SUMMARY

[0006] In view of the above problems and technical requirements, the present application provides a manufacturing method of a graphene film with thermal rectification function, and the technical scheme of the present application is as follows:

[0007] The manufacturing method of the graphene film with thermal rectification function comprises the following steps:

[0008] The graphene microsheets of different sizes are electrolytically exfoliated to obtain graphene oxide dispersion liquid;

[0009] The graphene film with the size gradient distribution of graphene microsheets is prepared by using the graphene oxide dispersion liquid, and the thermal conductivity of the graphene film increases in turn along the direction of the size distribution.

[0010] A further technical solution is to electrolytically exfoliate graphene microsheets of different sizes to obtain the graphene oxide dispersion liquid, including:

[0011] Electrochemically layering the graphene microsheets of different sizes;

[0012] Oxidizing the obtained porous graphene net, wherein the porous refers to the existence of nanoscale pores between graphene microsheets;

[0013] Pouring the oxidized porous graphene net into deionized water, and exfoliating the oxidized porous graphene net by stirring to obtain the graphene oxide dispersion liquid.

[0014] A further technical solution is to electrochemically layer the graphene microsheets of different sizes, including:

[0015] Dispersing the graphene microsheets of different sizes into an electrolyte in an electrochemical reaction cell;

[0016] Inserting two electrodes into the electrolyte, and applying a constant current to electrochemically layer the graphene microsheets at a constant temperature.

[0017] A further technical solution is to oxidize the obtained porous graphene net, including:

[0018] At a first temperature, adding an oxidizing agent into a mixture of the porous graphene net and the electrolyte, and performing an oxidation process without stirring when the temperature rises to a second temperature;

[0019] After the oxidation lasts for a period of time, filtering and collecting the oxidation product, and washing with deionized water;

[0020] Adding a certain amount of hydrochloric acid, and performing a mesh filtration on the suspension to obtain the oxidized porous graphene net.

[0021] A further technical solution is to prepare the graphene film with the size gradient distribution of graphene microsheets by using the graphene oxide dispersion liquid, including:

[0022] Repeated execution: taking a certain amount of the dispersion liquid from the graphene oxide dispersion liquid and placing it at the center of the base of a rotating table; turning on the rotating table to uniformly spread the dispersion liquid on the entire base, and then the graphene microsheets of different sizes in the dispersion liquid are arranged from small to large in size along the center of the base to the outside;

[0023] Until the graphene oxide film with the required thickness is obtained;

[0024] The graphene film with the gradient distribution of the microsheet size is obtained by reducing the graphene oxide film.

[0025] The further technical solution is to prepare the graphene film with the gradient distribution of the microsheet size by using the graphene oxide dispersion solution, including:

[0026] The graphene microsheets in the graphene oxide dispersion solution are centrifuged and layered according to the size by using the sucrose solution with the density gradient distribution, and each layer corresponds to a microsheet size.

[0027] The centrifuged dispersion solution of each layer is sprayed to the specified area of the transfer platform in sequence by the directional moving transfer platform, and the graphene oxide film is obtained.

[0028] The graphene film with the gradient distribution of the microsheet size is obtained by reducing the graphene oxide film.

[0029] The further technical solution is to prepare the graphene film with the gradient distribution of the microsheet size by using the graphene oxide dispersion solution, including:

[0030] The sucrose solution with the density gradient distribution is added to the centrifugal tube, and then the graphene oxide dispersion solution is placed on the uppermost layer of the sucrose solution; after centrifugation, the graphene microsheets with the same size in the dispersion solution are distributed in the corresponding density of the sucrose solution, and are layered and arranged from small to large along the tube opening to the tube bottom.

[0031] The further technical solution is to reduce the graphene oxide film, including:

[0032] The graphene oxide film is immersed in a proper amount of reducing agent, and heated by the water bath method for a certain time; the graphene oxide film is repeatedly washed by a proper amount of ethanol solution and deionized water until the PH is about 7; and the reduced graphene film is obtained after air drying.

[0033] The further technical solution is that the method further includes:

[0034] The prepared graphene film with the gradient distribution of the microsheet size is placed in the thermal conductivity measuring instrument, and the thermal rectification value of the graphene film is calculated.

[0035] The beneficial technical effects of the present application are:

[0036] The application provides a new method for manufacturing a graphene film with a thermal rectification function. The method is based on bionics, imitates the pore structure of bamboo with a thermal rectification effect, selects graphene as a heat conductor, uses the principle that the thermal conductivities of graphene microsheets of different sizes are different, realizes size gradient distribution of the graphene microsheets in two ways, and prepares the graphene film with the thermal conductivity gradually increasing from the large size to the small size, so that the graphene film has the thermal rectification function, the problem of low rectification value of a traditional thermal rectifier is solved, and efficient control of heat flow is realized. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a manufacturing method flowchart provided by the first embodiment of the application.

[0038] Figure 2 is a manufacturing method flowchart provided by the second embodiment of the application.

[0039] Figure 3 is an electrolytic oxidation peeling schematic diagram provided by the application.

[0040] Figure 4 is a coating method film preparation schematic diagram provided by the application.

[0041] Figure 5 is a different size microsheet distribution schematic diagram provided by the application.

[0042] Figure 6 is a density gradient of a sucrose solution and a microsheet distribution schematic diagram after centrifugation provided by the application.

[0043] Figure 7 is a spray plating film preparation schematic diagram provided by the application.

[0044] Figure 8 is a zoned film preparation schematic diagram provided by the application. DETAILED DESCRIPTION

[0045] The specific embodiments of the application are further described below with reference to the accompanying drawings.

[0046] Embodiment one: a graphene film with a size gradient is prepared by using a coating method.

[0047] Please refer to Figure 1 The embodiment provides a manufacturing method of a graphene film with a thermal rectification function, and comprises the following steps:

[0048] Step 1: graphene microsheets of different sizes are electrolytically peeled to obtain graphene oxide dispersion.

[0049] Step 1.1: graphene microsheets of different sizes are electrochemically layered.

[0050] AsFigure 3 As shown, the graphene microsheets of different sizes are dispersed into electrolyte (H2SO4) by continuous magnetic stirring in the electrochemical reaction cell. Two electrodes are inserted into the electrolyte (insertion depth of 5 cm), and a constant current (5 A) is applied to perform the electrochemical delamination of graphene microsheets under water circulation temperature control (25 °C).

[0051] Alternatively, the lateral size (length) of the graphene microsheets selected in this embodiment ranges from 30 to 280 microns. For example, the lateral size is increased by 50 microns, and a certain number of graphene microsheets are selected from each of 30 microns, 80 microns, 130 microns, 180 microns, 230 microns, and 280 microns to achieve the size gradient change of the graphene film.

[0052] Step 1.2: The obtained fresh porous graphene network is used as a raw material for oxidation treatment.

[0053] First, the excess electrolyte in the electrochemical delamination process is removed for the next electrochemical delamination. At a first temperature (e.g., 5 °C), an oxidizing agent (potassium permanganate) is added to the mixture of the porous graphene network and the electrolyte under continuous stirring. When the temperature rises to a second temperature (e.g., 35 °C), the stirring is terminated, and the oxidation process is performed without stirring. After the oxidation lasts for a period of time (e.g., 40 minutes), the oxidation product is collected by filtration to remove the remaining oxidizing agent, which can reduce the water-enhanced oxidation of graphite, and the oxidation product is initially washed with deionized water, i.e., the oxidation product is placed in deionized water, and hydrogen peroxide (30%) is added dropwise to consume the excess manganese ions. Finally, a certain amount of hydrochloric acid (30%) is added, and the suspension is subjected to mesh filtration to obtain an oxidized porous graphene network. Here, the porous refers to the existence of nanoscale pores between graphene microsheets.

[0054] Step 1.3: The oxidized porous graphene network is poured into deionized water and washed to a neutral state by spontaneous sedimentation. Finally, the oxidized porous graphene network is exfoliated in water by stirring to obtain an oxidized graphene dispersion.

[0055] Step 2: The graphene film with a size gradient distribution of microsheets is prepared using the obtained oxidized graphene dispersion.

[0056] Step 2.1: A certain amount of the dispersion is taken from the oxidized graphene dispersion and placed at the center of the rotating stage base. Specifically, the prepared oxidized graphene dispersion is transferred to a syringe, the position of the syringe is corrected until it is aligned with the center of the lower quartz substrate of the rotating stage, and then the syringe is opened, so that a certain amount of the oxidized graphene dispersion is dropped onto the center of the lower quartz substrate.

[0057] Step 2.2: The rotating stage is turned on to evenly spread the dispersion on the entire substrate.

[0058] After the graphene oxide dispersion is stabilized on the quartz substrate, the rotating table is turned on. Under the action of centrifugal force, the graphene oxide dispersion is evenly coated on the entire quartz substrate. The greater the mass, the greater the centrifugal force, so the graphene microsheets of different sizes in the dispersion are arranged from small to large along the center of the substrate to the outside, as shown in FIG. 3. Figure 4

[0059] After the first layer of liquid film is stabilized, the rotation of the rotating table is stopped. The operations of steps 2.1 and 2.2 are repeated until the graphene oxide film of the desired thickness is obtained.

[0060] Step 2.3: Reducing the graphene oxide film to obtain a graphene film with a gradient distribution of microsheet sizes.

[0061] After the rotation is stopped, the graphene oxide film is removed for natural air drying. An appropriate amount of reducing agent (HI acid) is extracted using a syringe and injected into a beaker until the graphene oxide film is immersed, and a water bath method is used for heating for a certain period of time. Then, an appropriate amount of ethanol solution and deionized water are repeatedly washed to the graphene oxide film until the PH is about 7. After drying again, a reduced graphene film is obtained, as shown in FIG. 4. Figure 5

[0062] As can be seen from the figure, the inter-sheet pores of large-size microsheets are larger than those of small-size microsheets. Since the larger the pore structure, the lower the thermal conductivity, the thermal conductivity of the prepared graphene film increases in turn along the direction of smaller size distribution.

[0063] Step 3: The prepared graphene film with a gradient distribution of microsheet sizes is placed in the "LF-R thermal conductivity measuring instrument". After the graphene film is heated by laser, the temperature rise change is measured. The LF-R thermal conductivity calculation formula is:

[0064]

[0065] In the formula, P1 and P2 are the powers of the two laser heating (W); h is the thickness of the single-layer graphene film (nm); and ΔT is the difference between the two local temperature rises (℃). The thermal conductivities from the center to the edge and from the edge to the center are measured in turn, and the thermal rectification value of the graphene film is calculated according to formula (2).

[0066]

[0067] In the formula, K represents the thermal conductivity of the graphene film, which is calculated by formula (1); and strong and weak represent the constraint strength of graphene from the polymer, respectively; K 弱→强 represents the corresponding thermal conductivity of the heat flow from the end of the graphene with weaker constraint to the end of the graphene with stronger constraint, i.e., the thermal conductivity of the heat transfer from the end of the polymer with thinner polymer to the end of the polymer with thicker polymer; and K 强→弱 ​​K indicates the thermal conductivity in the opposite direction.

[0068] Embodiment Two: Fabricating graphene film with size gradient by using spray coating method.

[0069] Please refer to Figure 2 As shown in the figure, the embodiment provides another method for fabricating graphene film with thermal rectification function, which includes the following steps:

[0070] Step 1: Electrolytically exfoliating graphene microsheets with different sizes to obtain graphene oxide dispersion.

[0071] The specific implementation of this step is the same as steps 1.1-1.3 of embodiment one, which will not be repeated here.

[0072] Step 2: Using graphene oxide dispersion to prepare graphene film with microsheet size gradient distribution.

[0073] Step 2.1: Using sucrose solution with density gradient distribution to centrifugally separate graphene microsheets in graphene oxide dispersion according to their sizes, with each layer corresponding to a microsheet size.

[0074] Specifically, sucrose solution with appropriate density (concentration) distribution is selected to achieve density gradient distribution. In this embodiment, sucrose solutions with density gradients of 20%-70% (i.e. 20%, 30%, 40%, 50%, 60%, 70%) are needed. In a Beckman centrifuge tube (i.e. polycarbonate centrifuge tube, inner diameter 11 mm, length 60 mm), sucrose solution with the above density gradient distribution is added, i.e. layer liquid with increasing density gradient (0.5 ml per layer) is added at the bottom of the tube, such as Figure 6 as shown in the figure.

[0075] Before ultracentrifugation, freshly prepared graphene oxide dispersion is placed in the uppermost layer of sucrose solution with density gradient. The centrifugation time is 5 minutes and the rotation speed is 50Krpm. After centrifugation, graphene microsheets of the same size in the dispersion are distributed in the sucrose solution with corresponding density, and are arranged in layers from small to large size from the tube opening to the bottom. As shown in the figure, Figure 6 the sizes of graphene microsheets are 30 microns, 80 microns, 130 microns, 180 microns, 230 microns, and 280 microns, respectively. When separating larger and heavier samples, sucrose solution with a larger gradient can be used.

[0076] Optionally, the separated graphene microsheets are made into sufficient and stable graphene dispersion for standby use.

[0077] Step 2.2: The directional moving transfer platform sprays each layer of the dispersion after centrifugation to the designated area of the transfer platform in turn to obtain graphene oxide film.

[0078] As Figure 7 shown, the uppermost graphene oxide dispersion liquid is transferred to the spraying device, the knob of the nozzle is adjusted to adjust the size of the sprayed liquid mist droplets, the first coating area (A area) of the conveying platform is moved under the nozzle, and the nozzle is continuously sprayed 35 cm above the substrate in the A area. At the same time, the lower conveying belt is stationary, and after the first size dispersion liquid (30 microns) is sprayed (A area is prepared), the second size dispersion liquid (80 microns) is supplemented. Then the nozzle is stationary, the conveying belt is rotated to the second coating area (B area) for processing. Cycle repeatedly until all sizes of graphene oxide dispersion liquid are sprayed, and six sizes of microsheet correspond to six continuous coating areas as Figure 8 shown.

[0079] Step 2.3: Reducing the graphene oxide film to obtain a graphene film with a gradient distribution of microsheet sizes.

[0080] After the coating is completed, the wet graphene oxide film is removed and naturally air dried. The subsequent reduction step is the same as step 2.3 of Example 1 and is not repeated here. The obtained reduced graphene film is as Figure 5 shown, and the thermal conductivity increases in turn along the direction of smaller size distribution.

[0081] Step 3: Place the prepared graphene film with a gradient distribution of microsheet sizes in a thermal conductivity measuring instrument, and calculate the thermal rectification value of the graphene film.

[0082] The specific calculation method of this step is the same as the calculation method provided in step 3 of Example 1 and is not repeated here.

[0083] Finally, the thermal rectification values calculated by the two examples are shown in Table 1.

[0084] Table 1. Thermal rectification calculation values of the prepared graphene film

[0085] Serial number Thermal rectification value γ Example one 0.26 Example two 0.31

[0086] The above is only a preferred embodiment of the present application, and the present application is not limited to the above examples. It can be understood that other improvements and changes directly derived or thought of by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. A method for manufacturing a graphene film with thermal rectification function, characterized in that, The method includes: Electrolytic exfoliation of graphene microsheets of different sizes yielded a graphene oxide dispersion. The preparation of graphene films with a gradient distribution of micro-flake size using the aforementioned graphene oxide dispersion includes: Repeat the process: Take a certain amount of the graphene oxide dispersion and place it at the center of the rotating stage substrate; turn on the rotating stage to spread the dispersion evenly on the entire substrate, and the graphene micro flakes of different sizes in the dispersion will be arranged from the center of the substrate outwards in order of increasing size; Until a graphene oxide film of the desired thickness is obtained; The graphene oxide film was reduced to obtain a graphene film with a gradient distribution of micro-flap size; Or include: Using a sucrose solution with a density gradient distribution, the graphene micro-flakes in the graphene oxide dispersion are centrifuged and layered according to size, with each layer corresponding to a micro-flake size; A directional moving conveyor platform sequentially sprays the centrifuged dispersion into a designated area of ​​the conveyor platform to obtain a graphene oxide film. The graphene oxide film was reduced to obtain a graphene film with a gradient distribution of micro-flap size; The thermal conductivity of the graphene film increases sequentially along the direction of smaller size distribution.

2. The method for manufacturing a graphene film with thermal rectification function according to claim 1, characterized in that, The electrolytic exfoliation of graphene microsheets of different sizes to obtain a graphene oxide dispersion includes: Electrochemically layering of graphene microsheets of different sizes; The obtained porous graphene network is subjected to oxidation treatment, where porous refers to the presence of nanoscale pores between graphene microsheets. The porous graphene oxide mesh was poured into deionized water and stirred to peel off the porous graphene oxide mesh, thus obtaining a graphene oxide dispersion.

3. The method for manufacturing a graphene film with thermal rectification function according to claim 2, characterized in that, Electrochemical layering of graphene microsheets of different sizes, including: Graphene microsheets of different sizes are dispersed in an electrolyte in an electrochemical reaction cell; Two electrodes were inserted into the electrolyte and a constant current was applied to perform electrochemical delamination of graphene microsheets at a constant temperature.

4. The method for manufacturing a graphene film with thermal rectification function according to claim 2, characterized in that, The obtained porous graphene network is subjected to oxidation treatment, including: At the first temperature, the oxidant is added to the mixture of porous graphene mesh and electrolyte, and an oxidation process without stirring is carried out when the temperature rises to the second temperature. After oxidation has continued for a period of time, the oxidized product is collected by filtration and rinsed with deionized water. Add a certain amount of hydrochloric acid and filter the suspension through a mesh to obtain oxidized porous graphene mesh.

5. The method for manufacturing a graphene film with thermal rectification function according to claim 1, characterized in that, Using a sucrose solution with a density gradient distribution, the graphene microflakes in the graphene oxide dispersion are centrifuged and separated according to size, including: A sucrose solution with a density gradient is added to a centrifuge tube, and the graphene oxide dispersion is placed on top of the sucrose solution. After centrifugation, graphene microflakes of the same size in the dispersion are distributed in sucrose solutions of corresponding densities and are arranged in layers from small to large size along the tube opening to the bottom of the tube.

6. The method for manufacturing a graphene film with thermal rectification function according to claim 1, characterized in that, The reduction of the graphene oxide film includes: Immerse the graphene oxide film in an appropriate amount of reducing agent and heat it in a water bath for a certain period of time; repeatedly wash the graphene oxide film with an appropriate amount of ethanol solution and deionized water until the pH is approximately 7; after air drying, the reduced graphene film is obtained.

7. The method for manufacturing a graphene film with thermal rectification function according to any one of claims 1-6, characterized in that, The method further includes: The obtained graphene film with a gradient distribution of micro-sheet size was placed in a thermal conductivity meter, and the thermal rectification value of the graphene film was calculated.

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