CN112442340A

CN112442340A - Preparation method of heat-conducting filler three-dimensional framework, three-dimensional framework and high-molecular composite material

Info

Publication number: CN112442340A
Application number: CN201910828937.0A
Authority: CN
Inventors: 卢咏来; 李京超; 林驭韬; 张朝旭; 咸越; 赵秀英; 张立群
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2019-09-03
Filing date: 2019-09-03
Publication date: 2021-03-05

Abstract

The invention discloses a preparation method of a three-dimensional framework of a heat-conducting filler, the three-dimensional framework and a high-molecular composite material. The preparation method comprises the following steps: uniformly mixing the graphene oxide aqueous dispersion and the heat-conducting filler, adding a reducing agent and a surfactant, and uniformly stirring; then stirring and foaming, sealing and reducing the foaming liquid to obtain hydrogel, drying, and finally carrying out heat treatment on the dried gel. The invention prepares the heat-conducting filler three-dimensional porous network with reduced graphene oxide as a framework by combining an aqueous phase surfactant foaming method and the gelation of graphene oxide, injects high molecules into the filler framework by a vacuum-assisted impregnation method, and finally cures to obtain the corresponding high heat-conducting polymer composite material. The method has simple process, the obtained composite material has a continuous heat conduction network inside, and the heat conduction is isotropic and is far superior to the traditional randomly dispersed sample.

Description

Preparation method of heat-conducting filler three-dimensional framework, three-dimensional framework and high-molecular composite material

Technical Field

The invention relates to the technical field of heat conduction materials, in particular to a preparation method of a three-dimensional framework of a heat conduction filler, the three-dimensional framework and a high polymer composite material.

Background

With the increasingly obvious trend of integration and miniaturization of electronic and optical systems, effective heat dissipation becomes a key problem. Generally, system overheating is reduced or prevented by using a Thermal Interface Material (TIM) between the heat source (i.e., the working device unit) and the heat sink. Therefore, a high thermal conductivity TIM is critical to achieving reliable, long-lived microelectronic devices. In addition, with the coming of the 5G era, the data transmission amount of electronic devices such as mobile phones and the like is greatly increased, which will continuously increase the overheating risk of smart phones. Studies have shown that 5G is 2.5 times as much as 4G, only from the point of view of chip power consumption, which means that heat conduction/dissipation will be a huge obstacle and challenge for smart device development in the future!

The random distribution of the filler in the matrix of the composite material obtained by means of conventional mechanical mixing and the like often makes the thermal conductivity of the material difficult to reach a higher level, and the traditional processing method can not meet the production requirement of the high thermal conductivity polymer material more and more. In recent years, researchers develop methods such as an ice template method, a 3D mold pressing method, an aerogel method and the like to successfully construct a three-dimensional network of a heat-conducting filler in a polymer matrix, and prepare various high-molecular composite materials with high heat conductivity. However, these methods for constructing a three-dimensional network often have disadvantages such as complicated processing methods and difficulty in industrial scale-up, and for example, freeze-drying is required.

Graphene is the substance with the highest thermal conductivity so far, and therefore, it is the material of choice as a thermally conductive filler to improve the thermal conductivity of polymers. Graphene oxide is one of the commonly used raw materials for preparing graphene, and the production cost thereof is continuously reduced with the efforts of the industry in recent years, so that the graphene oxide gradually has the precondition of industrialization. The unique property that graphene oxide can be gelatinized through thermal reduction is also used for constructing a heat-conducting three-dimensional network by a plurality of heat-conducting researchers, but the existing method usually needs a process means with higher difficulty such as freeze drying and the like, the heat conduction is anisotropic, and higher heat conductivity is only shown in a certain direction, so that the practical feasibility of the method is greatly restricted.

Disclosure of Invention

The invention provides a preparation method of a heat-conducting filler three-dimensional framework, the three-dimensional framework and a high-molecular composite material, and aims to solve the problems of complex process, heat-conducting anisotropy and the like of a heat-conducting framework material in the prior art. The invention prepares the heat-conducting filler three-dimensional porous network with reduced graphene oxide as a framework by combining an aqueous phase surfactant foaming method and gelation of graphene oxide, injects a polymer into the filler framework by a vacuum-assisted impregnation method, and finally cures to obtain the corresponding high-heat-conducting polymer composite material.

The invention aims to provide a preparation method of a three-dimensional framework of a heat-conducting filler.

The method comprises the following steps:

uniformly mixing the graphene oxide aqueous dispersion and the heat-conducting filler, adding a reducing agent and a surfactant, and uniformly stirring; then stirring and foaming, sealing and reducing the foaming liquid to obtain hydrogel, drying, and finally carrying out heat treatment on the dried gel.

Wherein the content of the first and second substances,

the graphene oxide of the present invention generally refers to graphene oxide prepared by various conventional methods (such as modified hummers method), wherein the graphene oxide concentration in the preferred graphene oxide aqueous dispersion is 2mg/ml-20 mg/ml.

The heat-conducting filler in the invention can be selected from the heat-conducting fillers existing in the prior art, and is preferably one or a combination of hexagonal boron nitride, cubic boron nitride, graphene nanosheets, graphite, carbon fibers, carbon nanotubes, aluminum oxide, zinc oxide, metallic silver, metallic copper, silicon carbide, beryllium oxide, aluminum nitride, carbon nitride, diamond, magnesium oxide, MXene and other heat-conducting fillers. The mass ratio of the heat-conducting filler to the graphene oxide is 1-100: 1; preferably (5-80): 1;

the reducing agent in the invention can be selected from graphene reducing agents existing in the prior art, and is preferably one or a combination of common weak reducing agents for graphene oxide such as ascorbic acid, ethylenediamine, pyrrole and the like; the mass ratio of the reducing agent to the graphene oxide is (0.5-5): 1; preferably (1-3): 1.

the surfactant in the invention can be selected from surfactants existing in the prior art, including all ionic and nonionic surfactants, preferably one or a combination of sodium dodecyl benzene sulfonate, various alkyl glucosides, dodecyl ammonium bromide, potassium oleate soap, alkylphenol polyoxyethylene ether (OP, NP, TX) series emulsifiers, fatty alcohol polyoxyethylene ether (AEO) series emulsifiers, (peregal) series emulsifiers, sorbitan fatty acid ester polyoxyethylene ether (Tween series) emulsifiers, sorbitan fatty acid ester (span series) emulsifiers, coconut oil diethanolamide (6501) emulsifiers and the like. The dosage of the surfactant is 0.2-5 g added in each 100ml of graphene dispersion liquid.

Preferably:

the reduction temperature is 65-90 ℃, and the reduction time is 15min-6 h.

The heat treatment temperature is 60-2000 ℃, and the heat treatment time is 1min-5 h.

The invention also aims to provide the three-dimensional framework of the heat-conducting filler prepared by the method.

The invention also aims to provide a high polymer composite material containing the heat-conducting three-dimensional framework.

The composite material is prepared by a method comprising the following steps:

immersing a heat-conducting filler three-dimensional framework in a liquid polymer or a solution thereof, and completely degassing and curing in a vacuum environment to obtain the polymer composite material containing the heat-conducting three-dimensional framework;

the liquid polymer is one of liquid silicon rubber, liquid epoxy resin and liquid polyurethane.

The basic principle of the invention is that the characteristic that the aqueous solution of the surfactant can be foamed under high-speed stirring is utilized, and simultaneously, the graphene oxide and the heat-conducting filler in the system also have a certain foam stabilizing function, so that stable filler foaming liquid can be formed after foaming. Pouring the foaming liquid into a mold with a certain shape, sealing, reducing at a certain temperature, gelatinizing in the reduction process of the graphene oxide to form hydrogel with a regular shape and a porous structure inside, and directly drying the obtained hydrogel in a hot air state. And drying to obtain the three-dimensional filler skeleton network. In order to further improve the thermal conductivity of the three-dimensional filler skeleton network, the graphene can be further reduced by heat treatment. And finally, immersing the three-dimensional network into liquid polymer, degassing in a vacuum state, and vulcanizing the degassed composite material at a certain temperature to obtain the high-thermal-conductivity polymer composite material with a perfect three-dimensional skeleton network inside.

The technical scheme adopted by the invention is as follows:

uniformly stirring or ultrasonically mixing the graphene oxide aqueous dispersion and the heat-conducting filler, adding a reducing agent and a surfactant, and uniformly stirring. Then the stirring speed is increased to foam, and the foaming liquid is poured into a container, sealed and reduced at a certain temperature. And (3) putting the hydrogel obtained by reduction into an oven for drying, and finally, putting the dried aerogel into a high-temperature heat treatment.

The stirring in the invention is not limited to equipment, and for example, a special foaming machine can be used for stirring, and a common stirring paddle can be used for stirring. The stirring speed and time during foaming are determined according to actual conditions, stable foaming can be ensured, and the foaming multiplying power is generally 1.5-5 times for foaming.

The heat treatment process of the dried aerogel is not limited by heat treatment equipment and heat treatment temperature, and can be carried out in an oven or a furnace if the heat treatment is carried out at a lower temperature (less than 350 ℃); if the temperature is higher, the heat treatment is carried out in a furnace with better sealing property under the protection of inert gas, and the maximum heat treatment temperature is not more than 2000 ℃.

The invention discloses a method for preparing a high polymer composite material containing a three-dimensional framework of a heat-conducting filler, which comprises the following specific processes: immersing the three-dimensional filler skeleton in a liquid high-molecular solution, placing the three-dimensional filler skeleton in a vacuum environment, completely degassing, taking out the three-dimensional filler skeleton, and curing at a certain temperature.

The polymer adopted by the invention is one of liquid silicon rubber, liquid epoxy resin and liquid polyurethane, the liquid polymer can be directly used for vacuum impregnation, and can also be prepared into solutions with various concentrations for reuse according to actual conditions, and the selected solvent is not limited, such as cyclohexane, ethyl acetate and the like.

The dipping, degassing and curing can adopt the prior process method, and the vacuum-assisted dipping and degassing time of the invention is preferably 1-12 h.

The curing temperature and time adopted by the invention are determined according to the type of the cured macromolecule, and can be determined by technical personnel according to actual conditions.

The invention has the advantages of

1. The method for preparing the filler framework by combining the surfactant foaming method and the graphene oxide gelation is mild in condition, simple and easy to operate and easy to implement industrially.

2. The filler network prepared by the foaming method is isotropic, and the thermal conductivity in all directions can be improved.

3. The heat transfer of the filler framework network can be effectively enhanced by utilizing the three-dimensional network structure of the graphene supporting filler framework.

Drawings

FIG. 1 is a schematic view of a scanning electron microscope showing a brittle fracture surface of a three-dimensional filler skeleton prepared in example 1.

FIG. 2 is a schematic view of the brittle fracture surface of the composite material prepared in example 1 under a scanning electron microscope.

Detailed Description

The present invention will be further described with reference to the following examples.

While the present invention will be described in detail and with reference to the specific embodiments thereof, it should be understood that the following detailed description is only for illustrative purposes and is not intended to limit the scope of the present invention, as those skilled in the art will appreciate numerous insubstantial modifications and variations therefrom.

Comparative example 1

Adding 9.3 g of hexagonal boron nitride sheets and 90.7 g of liquid silicon rubber added with curing agent into a planetary stirrer at the same time, vacuumizing and stirring uniformly, pouring into a mould, and curing at 100 ℃ for 2 hours to obtain the silicon rubber composite material containing 9.3 wt% of boron nitride.

Comparative example 2

Adding 17.6 g of graphene nanosheet and 82.4 g of liquid epoxy resin added with a curing agent into a planetary stirrer at the same time, vacuumizing and uniformly stirring, pouring into a mold, and curing at 100 ℃ for 2 hours to obtain the epoxy resin composite material containing 17.6 wt% of graphene nanosheet.

Comparative example 3

28.7 g of alumina and 71.3 g of liquid polyurethane added with curing agent are added into a planetary mixer at the same time, the mixture is vacuumized and stirred evenly, poured into a mould and cured for 2 hours at 100 ℃ to obtain the polyurethane composite material containing 28.7 wt percent of alumina.

The starting materials used in the examples are all commercial products.

Example 1

Uniformly stirring or ultrasonically mixing 500ml of graphene oxide aqueous dispersion with the concentration of 2mg/ml and 50g of hexagonal boron nitride sheets in a beaker, then adding 1 g of ascorbic acid and 2 g of alkyl glycoside aqueous dispersion (50 wt%) and continuously stirring to be uniform at a low rotating speed (below 600 revolutions per minute) by using a stirring paddle. The rotating speed is increased to 1500 r/min, stirring and foaming are carried out for about 5min, the foaming liquid obtained at the moment is poured into a container and sealed, and the container is placed in a 65 ℃ blast oven to be reduced for 6 hours. And continuously putting the taken-out foaming hydrogel into a blast oven at 60 ℃ for drying. The dried gel was then heat treated in a forced air oven at 200 ℃ for 5 hours. Immersing the obtained gel in liquid silicon rubber which is uniformly mixed with a curing agent, putting the liquid silicon rubber into a vacuum oven, vacuumizing and degassing for 2 hours at normal temperature, taking out the aerogel impregnated with the silicon rubber, and vulcanizing for 1 hour at 100 ℃ to obtain the composite material containing 9.3 wt% of the filler.

Example 2

Stirring or ultrasonically mixing 50ml of graphene oxide aqueous dispersion with the concentration of 20mg/ml and 5g of graphene nano-sheets uniformly in a beaker, then adding 2 g of ethylenediamine and 2.5 g of sodium dodecyl sulfate, and continuously stirring until the mixture is uniform at a low rotation speed (below 600 revolutions per minute) by using a stirring paddle. And (3) increasing the rotating speed to 1500 rpm, stirring and foaming for about 5min, pouring the foaming liquid obtained at the moment into a container, sealing, and reducing for 15min in a blowing oven at 90 ℃. And continuously putting the taken-out foaming hydrogel into a blast oven at 60 ℃ for drying. And continuously placing the dried gel in a blast oven for heat treatment at 2000 ℃ for 1 min. Immersing the obtained gel in a liquid epoxy resin monomer which is uniformly mixed with a curing agent, putting the gel into a vacuum oven, vacuumizing and degassing for 2 hours at normal temperature, taking out the aerogel impregnated with the epoxy resin, and curing for 1 hour at 100 ℃ to obtain the composite material containing 17.6 wt% of filler by mass fraction.

Example 3

100ml of graphene oxide aqueous dispersion with the concentration of 10mg/ml and 30g of alumina are stirred or ultrasonically mixed uniformly in a beaker, then 3 g of pyrrole and 1 g of alkylphenol polyoxyethylene are added and stirred continuously until the mixture is uniform at a low rotating speed (below 600 revolutions per minute) by a stirring paddle. The rotating speed is increased to 1500 r/min, stirring and foaming are carried out for about 5min, the foaming liquid obtained at the moment is poured into a container and sealed, and the container is placed in a blast oven with the temperature of 80 ℃ for reduction for 2 hours. And continuously putting the taken-out foaming hydrogel into a blast oven at 60 ℃ for drying. The dried gel was then heat treated in a forced air oven at 1000 ℃ for 2 hours. Immersing the obtained gel in liquid polyurethane which is uniformly mixed with a curing agent, putting the gel in a vacuum oven, vacuumizing and degassing for 2 hours at normal temperature, taking out the aerogel impregnated with the polyurethane, and vulcanizing at 100 ℃ for 1 hour to obtain the composite material containing 28.7 wt% of filler by mass fraction.

Example 4

200ml of graphene oxide aqueous dispersion with the concentration of 5mg/ml and 50g of metal copper powder are stirred or ultrasonically mixed uniformly in a beaker, then 2 g of ascorbic acid and 4g of potassium oleate soap are added and stirred continuously until the mixture is uniform by a stirring paddle at a low rotating speed (below 600 revolutions per minute). The rotating speed is increased to 1500 r/min, stirring and foaming are carried out for about 5min, the foaming liquid obtained at the moment is poured into a container and sealed, and the container is placed in a blast oven at the temperature of 85 ℃ for reduction for 2 hours. And continuously putting the taken-out foaming hydrogel into a blast oven at 60 ℃ for drying. The dried gel was then heat treated in a forced air oven at 60 ℃ for 2 hours. Immersing the obtained gel in liquid polyurethane which is uniformly mixed with a curing agent, putting the gel in a vacuum oven, vacuumizing and degassing for 2 hours at normal temperature, taking out the aerogel impregnated with the polyurethane, and vulcanizing at 100 ℃ for 1 hour to obtain the composite material containing the filler with the mass fraction of 23.5 percent.

Example 5

100ml of graphene oxide aqueous dispersion with the concentration of 10mg/ml and 60g of diamond powder are stirred or ultrasonically mixed uniformly in a beaker, then 2 g of pyrrole and 0.2 g of dodecyl ammonium bromide are added and continuously stirred until the mixture is uniform by a stirring paddle at a low rotating speed (below 600 revolutions per minute). The rotating speed is increased to 1500 r/min, stirring and foaming are carried out for about 5min, the foaming liquid obtained at the moment is poured into a container and sealed, and the container is placed in a blast oven at the temperature of 75 ℃ for reduction for 3 hours. And continuously putting the taken-out foaming hydrogel into a blast oven at 60 ℃ for drying. The dried gel was then heat treated in a forced air oven at 500 ℃ for 0.5 hour. Immersing the obtained gel in liquid polyurethane which is uniformly mixed with a curing agent, putting the gel in a vacuum oven, vacuumizing and degassing for 2 hours at normal temperature, taking out the aerogel impregnated with the polyurethane, and vulcanizing for 1 hour at 100 ℃ to obtain the composite material containing 37.2 wt% of filler by mass fraction.

Description of the test results

It can be seen from figure 1 that the three-dimensional filler network skeleton has a uniform distribution of about a hundred micron-sized pores left by surfactant foaming, with the boron nitride flakes clearly visible on the walls of the pores. As can be seen from fig. 2, silicone rubber is filled in each cell. Compared with the traditional method for randomly dispersing the filler, the filler three-dimensional network structure constructed by the foaming method can play a role of a heat conducting network in the rubber matrix, so that the heat conductivity of the rubber material is greatly improved.

The comparative examples and examples were tested for thermal conductivity (standard ASTM E1461) and the results are shown in table 1.

TABLE 1

As can be seen from the table, comparative examples 1-3 and examples 1-5, respectively, contain the same amount of filler mass fraction, and the comparative thermal conductivity can be seen to be significantly higher for the examples as a whole than for the comparative examples. Compared with the prior art, the heat conductivity of the alloy is improved by adopting the traditional double-planet stirring and mixing. In the embodiment, the filler three-dimensional network is constructed in the matrix, so that the thermal conductivity of the material is obviously improved.

While the present invention has been described in detail with reference to the foregoing examples, it is not intended to be limited to the details shown, since various equivalent modifications, such as changes in the proportions of the materials used, for example, in the case of fillers and surfactants, and in the case of processing the proportions of the materials used, for example, in the case of processing the invention in a different order of addition, can be made by those skilled in the art. Such equivalent modifications and substitutions are intended to be included within the scope of the present application.

Claims

1. A preparation method of a three-dimensional framework of a heat-conducting filler is characterized by comprising the following steps:

2. The method of claim 1, wherein:

the heat-conducting filler is one or a combination of hexagonal boron nitride, cubic boron nitride, graphene nanosheets, graphite, carbon fibers, carbon nanotubes, aluminum oxide, zinc oxide, metallic silver, metallic copper, silicon carbide, beryllium oxide, aluminum nitride, carbon nitride, diamond, magnesium oxide and MXene;

the reducing agent is one or a combination of ascorbic acid, ethylenediamine and pyrrole;

the surfactant is ionic or non-ionic.

3. The method of claim 2, wherein:

the surfactant is one or a combination of sodium dodecyl benzene sulfonate, alkyl glycoside, dodecyl ammonium bromide, potassium oleate soap, alkylphenol polyoxyethylene, fatty alcohol polyoxyethylene ether, peregal series emulsifier, sorbitan fatty acid ester polyoxyethylene ether, sorbitan fatty acid ester and coconut oil diethanolamide.

4. The method of claim 1, wherein:

the concentration of the graphene oxide aqueous dispersion is 2mg/ml-20 mg/ml.

5. The method of claim 1, wherein:

the mass ratio of the heat-conducting filler to the graphene oxide is 1-100: 1; preferably (5-80): 1;

the mass ratio of the reducing agent to the graphene oxide is (0.5-5): 1; preferably (1-3): 1;

the dosage of the surfactant is 0.2-5 g added in each 100ml of graphene dispersion liquid.

6. The method of claim 1, wherein:

the reduction temperature is 65-90 ℃, and the reduction time is 15min-6 h.

7. The method of claim 1, wherein:

8. A three-dimensional skeleton of a thermally conductive filler produced by the method according to any one of claims 1 to 7.

9. A polymer composite material using the thermally conductive three-dimensional skeleton according to claim 8, wherein the polymer composite material is prepared by a method comprising the steps of:

and immersing the heat-conducting filler three-dimensional framework in liquid polymer or a solution thereof, and completely degassing and curing the liquid polymer or the solution in a vacuum environment to obtain the polymer composite material containing the heat-conducting three-dimensional framework.

10. The polymer composite material containing a thermally conductive three-dimensional skeleton according to claim 9, wherein: