阅读说明：本技术 一种基于表面功能化处理的电场自适应复合材料及其制备方法 (Electric field self-adaptive composite material based on surface functionalization treatment and preparation method thereof ) 是由 胡军 何金良 袁之康 赵孝磊 杨霄 李琦 张波 孟鹏飞 郝层层 史善哲 闪琪琪 于 2020-07-17 设计创作，主要内容包括：本发明公开了一种基于表面功能化处理的电场自适应复合材料及其制备方法,制备方法首先制备ZnO压敏微球,然后对ZnO压敏微球进行表面改性,最后利用表面改性的ZnO压敏微球得到高温硫化固体硅橡胶基体的复合材料,或者高温固化环氧树脂基体的复合材料,由于对ZnO压敏微球进行表面功能化处理,引入了官能团,使得表面改性的ZnO压敏微球与基体间形成共价键,两者之间除了存在物理连接外,也存在化学连接,因此表面改性的ZnO压敏微球与基体之间的界面结合强度得到明显增加,本发明的制备方法得到的复合材料在具有优异的电学特性的基础上,能够有效地提高复合材料的机械性能和热学特性,具有广泛的应用价值。(The invention discloses an electric field self-adaptive composite material based on surface functionalization treatment and a preparation method thereof, the preparation method firstly prepares ZnO pressure-sensitive microspheres, then carries out surface modification on the ZnO pressure-sensitive microspheres, and finally obtains the composite material of a high-temperature vulcanized solid silicon rubber matrix or the composite material of a high-temperature cured epoxy resin matrix by utilizing the surface-modified ZnO pressure-sensitive microspheres, because the surface functionalization treatment is carried out on the ZnO pressure-sensitive microspheres and functional groups are introduced, covalent bonds are formed between the surface-modified ZnO pressure-sensitive microspheres and the matrix, and besides physical connection and chemical connection exist between the surface-modified ZnO pressure-sensitive microspheres and the matrix, the interface bonding strength between the surface-modified ZnO pressure-sensitive microspheres and the matrix is obviously increased, the composite material obtained by the preparation method of the invention can effectively improve the mechanical property and the thermal property of the composite material on the basis of having excellent electrical property, has wide application value.)

1. A preparation method of an electric field self-adaptive composite material based on surface functionalization treatment is characterized by comprising the following steps:

1) preparing ZnO pressure-sensitive microspheres: ZnO and Bi are mixed₂O₃、MnO₂、Co₂O₃、Cr₂O₃、SiO₂、Sb₂O₃And Al₂O₃Mixing and calcining to obtain ZnO pressure sensitive microspheres;

2) surface modification of ZnO pressure sensitive microspheres: dispersing the ZnO pressure-sensitive microspheres in a solvent, adding a coupling agent into the mixed solution, and separating after complete reaction to obtain surface-modified ZnO pressure-sensitive microspheres;

3) preparing a composite material: mixing silicon rubber, a vulcanizing agent and the surface-modified ZnO pressure-sensitive microspheres to prepare a composite material of a high-temperature vulcanized solid silicon rubber matrix; or, the epoxy resin, the curing agent and the surface modified ZnO pressure sensitive microspheres are prepared into the composite material of the high-temperature cured epoxy resin matrix by vacuum pouring.

2. The method according to claim 1, wherein ZnO and Bi in step 1) are used₂O₃、MnO₂、Co₂O₃、Cr₂O₃、SiO₂、Sb₂O₃And Al₂O₃Is 95: 1: 0.5: 1: 0.4: 1: 1: 0.1.

3. the method according to claim 1 or 2, wherein the step 1) is performed by first adding ZnO and Bi₂O₃、MnO₂、Co₂O₃、Cr₂O₃、SiO₂、Sb₂O₃And Al₂O₃Mixing, putting into a ball mill, and adding absolute ethyl alcohol for ball milling; then adding an organic adhesive into the ball-milled slurry, and pouring the mixture into a spray granulator for spray granulation to obtain spherical particles; secondly, placing the spherical particles into a calcining furnace for sintering and then cooling; finally, screening the sintered product to obtain the ZnO pressure-sensitive microspheres with the diameter of 10-200 mu m.

4. The preparation method according to claim 1, wherein in the step 2), the ZnO pressure sensitive microspheres are firstly added into the solvent, so that the ZnO pressure sensitive microspheres are uniformly dispersed in the solvent; then adding a coupling agent into the mixed solution for reaction; and finally, after the reaction is completed, carrying out centrifugal separation to obtain the surface modified ZnO pressure sensitive microsphere.

5. The preparation method according to claim 1 or 4, wherein the solvent in the step 2) is n-heptane, the coupling agent is gamma-aminopropyltriethoxysilane, and the mass ratio of the ZnO pressure-sensitive microspheres to the coupling agent to the solvent is as follows: 5: 1: 35.

6. the preparation method according to claim 1, wherein in the step 3), the silicone rubber, the vulcanizing agent and the surface-modified ZnO pressure-sensitive microspheres are firstly added into an internal mixer for internal mixing, and then the mixed material after internal mixing is placed into a mold for shaping; secondly, putting the molded die into a flat vulcanizing machine for vulcanization; and finally, placing the vulcanized mold sample into a cold press for cooling treatment and then demolding to obtain the high-temperature vulcanized solid silicone rubber matrix composite material.

7. The preparation method according to claim 1 or 6, wherein the mass ratio of the silicone rubber, the vulcanizing agent and the surface-modified ZnO pressure-sensitive microspheres in the step 3) is as follows: 100: 1: (200-400).

8. The preparation method according to claim 1, characterized in that in the step 3), the surface-modified ZnO pressure-sensitive microspheres are uniformly mixed and preheated in a high-temperature oven; then uniformly mixing the epoxy resin, the curing agent and the surface modified ZnO pressure sensitive microsphere mixture, and then carrying out vacuum treatment; secondly, pouring the mixed solution after the vacuum treatment into a preheated mould for vacuum treatment again; placing the mold after vacuum treatment into a high-temperature oven again for curing treatment and then demolding; and finally, putting the sample obtained by demoulding into a high-temperature oven again for secondary curing to obtain the composite material of the high-temperature cured epoxy resin matrix.

9. The preparation method according to claim 1 or 8, wherein the mass ratio of the epoxy resin, the curing agent and the surface-modified ZnO pressure-sensitive microspheres in the step 3) is as follows: 100: 38: (200-400).

10. A composite material produced by the production method according to any one of claims 1 to 9.

Technical Field

The invention relates to the technical field of composite material preparation, in particular to an electric field self-adaptive composite material based on surface functionalization treatment and a preparation method thereof.

Background

The electric field self-adaptive material has wide prospect in the application of high-voltage equipment due to the nonlinear electrical characteristics, the self-adaptive characteristic of the electric field self-adaptive material is that the electrical parameters of the electric field self-adaptive material can be changed along with an external electric field, and when the space electric field at a certain position of the material has the tendency of being obviously higher than the average electric field in the adjacent area, the conductivity or the dielectric constant of the material at the position can be obviously improved, so that the electric field intensity at the position is reduced, and the effect of a uniform electric field can be achieved. The influence of the electrical parameters of the conventional material on the electric field distribution of the equipment belongs to an open loop process, once the influence of disturbance factors such as temperature change, material aging and the like is met, the final electric field distribution is easy to deviate from an expected or designed scheme due to the fact that the process has no feedback mechanism, and the reason that the stability of the traditional capacitance voltage-sharing method on the change of the material parameters is poor is provided. However, for the electric field adaptive material, because there is a negative feedback link that the electric field distribution can also affect the electrical parameters of the material in turn, the process is a closed loop adjustment process, which can achieve better effect of improving the electric field distribution and has stronger stability to disturbance factors, i.e., the electric field adaptive material has excellent electrical characteristics, and in addition, the electric field adaptive material needs to have lower heating and loss, i.e., the electric field adaptive material needs to have excellent mechanical properties and thermal properties, so as to embody better performance when applied to high voltage equipment. Therefore, it is necessary to design a new electric field adaptive composite material to have excellent mechanical and thermal properties on the basis of having excellent electrical properties.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides an electric field self-adaptive composite material based on surface functionalization treatment and a preparation method thereof.

In order to achieve the above object, the present invention provides a method for preparing an electric field adaptive composite material based on surface functionalization treatment, comprising the following steps:

1) preparing ZnO pressure-sensitive microspheres: ZnO and Bi are mixed₂O₃、MnO₂、Co₂O₃、Cr₂O₃、SiO₂、Sb₂O₃And Al₂O₃Mixing and calcining to obtain ZnO pressure sensitive microspheres;

2) surface modification of ZnO pressure sensitive microspheres: dispersing the ZnO pressure-sensitive microspheres in a solvent, adding a coupling agent into the mixed solution, and separating after complete reaction to obtain surface-modified ZnO pressure-sensitive microspheres;

3) preparing a composite material: mixing silicon rubber, a vulcanizing agent and the surface-modified ZnO pressure-sensitive microspheres to prepare a composite material of a high-temperature vulcanized solid silicon rubber matrix; or, the epoxy resin, the curing agent and the surface modified ZnO pressure sensitive microspheres are prepared into the composite material of the high-temperature cured epoxy resin matrix by vacuum pouring.

Further, ZnO and Bi in the step 1)₂O₃、MnO₂、Co₂O₃、Cr₂O₃、SiO₂、Sb₂O₃And Al₂O₃Is 95: 1: 0.5: 1: 0.4: 1: 1: 0.1.

further, the step 1) firstly prepares ZnO and Bi₂O₃、MnO₂、Co₂O₃、Cr₂O₃、SiO₂、Sb₂O₃And Al₂O₃Mixing, putting into a ball mill, and adding absolute ethyl alcohol for ball milling; then adding an organic adhesive into the ball-milled slurry, and pouring the mixture into a spray granulator for spray granulation to obtain spherical particles; secondly, placing the spherical particles into a calcining furnace for sintering and then cooling; finally, screening the sintered product to obtain the ZnO pressure-sensitive microspheres with the diameter of 10-200 mu m.

Further, in the step 2), the ZnO pressure sensitive microspheres are added into a solvent to uniformly disperse the ZnO pressure sensitive microspheres in the solvent; then adding a coupling agent into the mixed solution for reaction; and finally, after the reaction is completed, carrying out centrifugal separation to obtain the surface modified ZnO pressure sensitive microsphere.

Further, the solvent in the step 2) is n-heptane, the coupling agent is gamma-aminopropyltriethoxysilane, and the mass ratio of the ZnO pressure-sensitive microspheres to the coupling agent to the solvent is as follows: 5: 1: 35.

further, in the step 3), firstly, adding the silicon rubber, the vulcanizing agent and the surface-modified ZnO pressure-sensitive microspheres into an internal mixer for internal mixing, and then placing the internally mixed material into a mold for shaping; secondly, putting the molded die into a flat vulcanizing machine for vulcanization; and finally, placing the vulcanized mold sample into a cold press for cooling treatment and then demolding to obtain the high-temperature vulcanized solid silicone rubber matrix composite material.

Further, the mass ratio of the silicon rubber, the vulcanizing agent and the surface modified ZnO pressure sensitive microspheres in the step 3) is as follows: 100: 1: (200-400).

Further, in the step 3), the ZnO pressure sensitive microspheres with the modified surfaces are uniformly mixed and preheated in a high-temperature oven; then uniformly mixing the epoxy resin, the curing agent and the surface modified ZnO pressure sensitive microsphere mixture, and then carrying out vacuum treatment; secondly, pouring the mixed solution after the vacuum treatment into a preheated mould for vacuum treatment again; placing the mold after vacuum treatment into a high-temperature oven again for curing treatment and then demolding; and finally, putting the sample obtained by demoulding into a high-temperature oven again for secondary curing to obtain the composite material of the high-temperature cured epoxy resin matrix.

Further, the mass ratio of the epoxy resin, the curing agent and the surface modified ZnO pressure sensitive microspheres in the step 3) is as follows: 100: 38: (200-400).

The invention also provides a composite material prepared by the preparation method.

Compared with the prior art, the preparation method firstly prepares the ZnO pressure sensitive microspheres, then carries out surface modification on the ZnO pressure sensitive microspheres, and finally obtains the composite material of the high-temperature vulcanized solid silicon rubber matrix or the composite material of the high-temperature cured epoxy resin matrix by utilizing the surface modified ZnO pressure sensitive microspheres; in addition, after the ZnO pressure-sensitive microspheres are subjected to surface functionalization treatment, the interface bonding strength of the matrix and the ZnO pressure-sensitive microspheres is increased, the number of defects in the composite material is reduced, and the reduction of the number of defects means the reduction of the content of air in the composite material due to the low thermal conductivity of the air, so that the thermal conductivity of the composite material is increased; and chemical connection is formed between the ZnO pressure-sensitive microspheres and the matrix, so that the scattering of phonons at the interface is reduced, the thermal resistance at the interface is reduced, and the thermal conductivity of the composite is increased.

Drawings

FIG. 1 is an XPS spectrum of a composite material without and with surface functionalization;

FIG. 2 is Si_2pIs reacted with N_1sXPS energy spectrum;

FIG. 3 is an SEM image of ZnO pressure sensitive microspheres and composite materials thereof;

FIG. 4 is a plot of the current-voltage characteristics of different samples;

FIG. 5 is a stress-strain curve for various samples;

fig. 6 is a graph of thermal conductivity for different samples.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. 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.

The embodiment of the invention provides a preparation method of an electric field self-adaptive composite material based on surface functionalization treatment, which comprises the following steps:

1) preparation of ZnO pressure-sensitive microspherePreparing: ZnO and Bi are mixed₂O₃、MnO₂、Co₂O₃、Cr₂O₃、SiO₂、Sb₂O₃And Al₂O₃Mixing and calcining to obtain ZnO pressure sensitive microspheres;

2) surface modification of ZnO pressure sensitive microspheres: dispersing the ZnO pressure-sensitive microspheres in a solvent, adding a coupling agent into the mixed solution, and separating after complete reaction to obtain surface-modified ZnO pressure-sensitive microspheres;

3) preparing a composite material: mixing silicon rubber, a vulcanizing agent and the surface-modified ZnO pressure-sensitive microspheres to prepare a composite material of a high-temperature vulcanized solid silicon rubber matrix; or, the epoxy resin, the curing agent and the surface modified ZnO pressure sensitive microspheres are prepared into the composite material of the high-temperature cured epoxy resin matrix by vacuum pouring.

Specifically, the preparation method of the ZnO pressure-sensitive microsphere in the step 1) comprises the following steps: firstly ZnO and Bi₂O₃、MnO₂、Co₂O₃、Cr₂O₃、SiO₂、Sb₂O₃And Al₂O₃Mixing, putting into a ball mill, and adding absolute ethyl alcohol for ball milling; then adding an organic adhesive into the ball-milled slurry, and pouring the mixture into a spray granulator for spray granulation to obtain spherical particles; secondly, placing the spherical particles into a calcining furnace for sintering and then cooling; finally, screening the sintered product to obtain the ZnO pressure-sensitive microspheres with the diameter of 10-200 mu m.

Preferably, ZnO and Bi in the step 1)₂O₃、MnO₂、Co₂O₃、Cr₂O₃、SiO₂、Sb₂O₃And Al₂O₃Is 95: 1: 0.5: 1: 0.4: 1: 1: 0.1.

specifically, the method for modifying the surface of the ZnO pressure-sensitive microsphere in the step 2) comprises the following steps: firstly, adding ZnO pressure-sensitive microspheres into a solvent to uniformly disperse the ZnO pressure-sensitive microspheres in the solvent; then adding a coupling agent into the mixed solution for reaction; and finally, after the reaction is completed, carrying out centrifugal separation to obtain the surface modified ZnO pressure sensitive microsphere.

Preferably, the solvent in the step 2) is n-heptane, the coupling agent is gamma-aminopropyltriethoxysilane, and the mass ratio of the ZnO pressure sensitive microspheres to the coupling agent to the solvent is as follows: 5: 1: 35.

specifically, the preparation method of the composite material of the high-temperature vulcanized solid silicone rubber matrix in the step 3) comprises the following steps: firstly, adding silicon rubber, a vulcanizing agent and surface-modified ZnO pressure-sensitive microspheres into an internal mixer for internal mixing, and then putting the internally mixed material into a mold for molding; secondly, putting the molded die into a flat vulcanizing machine for vulcanization; and finally, placing the vulcanized mold sample into a cold press for cooling treatment and then demolding to obtain the high-temperature vulcanized solid silicone rubber matrix composite material.

Preferably, the mass ratio of the silicone rubber, the vulcanizing agent and the surface modified ZnO pressure sensitive microspheres in the step 3) is as follows: 100: 1: (200-400).

Specifically, in the step 3), the ZnO pressure-sensitive microspheres with the modified surfaces are uniformly mixed and preheated in a high-temperature oven; then uniformly mixing the epoxy resin, the curing agent and the surface modified ZnO pressure sensitive microsphere mixture, and then carrying out vacuum treatment; secondly, pouring the mixed solution after the vacuum treatment into a preheated mould for vacuum treatment again; placing the mold after vacuum treatment into a high-temperature oven again for curing treatment and then demolding; and finally, putting the sample obtained by demoulding into a high-temperature oven again for secondary curing to obtain the composite material of the high-temperature cured epoxy resin matrix.

Preferably, the mass ratio of the epoxy resin, the curing agent and the surface modified ZnO pressure sensitive microspheres in the step 3) is as follows: 100: 38: (200-400).

In addition, the embodiment of the invention also provides a composite material prepared by the method.

According to the embodiment of the invention, as the ZnO pressure sensitive microspheres are subjected to surface functionalization treatment and functional groups are introduced, covalent bonds are formed between the surface-modified ZnO pressure sensitive microspheres and the matrix, and the surface-modified ZnO pressure sensitive microspheres and the matrix are chemically connected in addition to physical connection, the interface bonding strength between the surface-modified ZnO pressure sensitive microspheres and the matrix is obviously increased, stress conduction can be better carried out, and the breaking strength is greatly improved; in addition, after the ZnO pressure-sensitive microspheres are subjected to surface functionalization treatment, the interface bonding strength of the matrix and the ZnO pressure-sensitive microspheres is increased, the number of defects in the composite material is reduced, and the reduction of the number of defects means the reduction of the content of air in the composite material due to the low thermal conductivity of the air, so that the thermal conductivity of the composite material is increased; and chemical connection is formed between the ZnO pressure-sensitive microspheres and the matrix, so that the scattering of phonons at the interface is reduced, the thermal resistance at the interface is reduced, and the thermal conductivity of the composite is increased.

The production method of the present invention is described in detail below.

The preparation method of the ZnO pressure-sensitive microsphere comprises the following steps: first, ZnO and Bi are mixed₂O₃、MnO₂、Co₂O₃、Cr₂O₃、SiO₂、Sb₂O₃And Al₂O₃According to the following steps of 95: 1: 0.5: 1: 0.4: 1: 1: mixing the components according to the mole percentage of 0.1, putting the mixture into a ball mill, and adding absolute ethyl alcohol to perform ball milling for 8 hours; then, adding an organic adhesive into the ball-milled slurry, pouring the mixture into a spray granulator, and carrying out spray granulation to prepare spherical particles; secondly, placing the spherical particles obtained by spray granulation into a calcining furnace, heating to 1100-1400 ℃ at a temperature rise rate of 2-7 ℃/min, and cooling after sintering for 1-4 hours at a temperature drop rate of 1-3 ℃/min; and finally, screening the sintered product by a standard sieve to obtain the ZnO pressure-sensitive microspheres with the same crystal boundary characteristics and different sizes, wherein the particle diameter is between 10 and 200 mu m.

In this embodiment, γ -aminopropyltriethoxysilane (KH550) is used as a coupling agent, and n-heptane is used as a solvent to perform surface modification on the ZnO pressure-sensitive microspheres, thereby realizing functional treatment. The coupling agent is firstly subjected to hydrolysis reaction to generate silanol, and silanol hydroxyl and the hydroxyl on the surface of the ZnO pressure-sensitive microsphere are subjected to dehydration condensation reaction, so that the ZnO pressure-sensitive microsphere which is originally rich in hydrophilic hydroxyl is changed into oleophylic particles on the surface, and is easier to be compatible with the polymer, thereby increasing the interface bonding strength between the ZnO pressure-sensitive microsphere and the polymer and improving the interface characteristic. The coupling chemistry is as follows:

the specific surface modification functionalization treatment method comprises the following steps: firstly, adding 5 parts by mass of ZnO pressure-sensitive microspheres into 35 parts by mass of n-heptane, and carrying out magnetic stirring for 20-50 minutes to uniformly disperse the ZnO pressure-sensitive microspheres into the n-heptane; then adding 1 part by mass of silane coupling agent KH550 into the mixed solution, magnetically stirring at 25 ℃ at 500 revolutions per minute for 24 hours, and after the reaction is finished, separating out the ZnO pressure-sensitive microspheres in a centrifugal mode; and finally, in order to remove the unreacted coupling agent and the by-products remained on the surface of the ZnO pressure-sensitive microsphere, cleaning the ZnO pressure-sensitive microsphere subjected to surface treatment with absolute ethyl alcohol for three times, putting the cleaned particles into a vacuum drying oven, drying for 24 hours at the temperature of 50 ℃, and removing the excessive absolute ethyl alcohol to obtain the ZnO pressure-sensitive microsphere subjected to silane coupling treatment.

According to the specific application of different self-adaptive electric field regulation composite materials, different matrix materials are required to be selected for the composite materials, the composite materials mainly comprise two matrix materials of high-temperature vulcanized solid silicone rubber and thermosetting epoxy resin, and the composite materials corresponding to different matrixes have different characteristics. The compound taking the high-temperature vulcanized solid silicon rubber as the matrix has certain elasticity and can be applied to the position where strain occurs; the composite using the thermosetting epoxy resin as the matrix has high hardness and high mechanical strength, and can be used for supporting and other positions needing high mechanical strength. Different base materials have different preparation processes when the composite material is prepared.

The composite material of the high-temperature vulcanized solid silicone rubber matrix is generally prepared by two ways of open mixing and internal mixing, and in this embodiment, the internal mixing preparation method is exemplified, and specifically includes: firstly, silicon rubber, a vulcanizing agent and surface modified ZnO pressure sensitive microspheres are mixed according to the mass ratio: 100: 1: (200-400) adding the mixture into an internal mixer, and carrying out internal mixing for 0.5-2.0 hours; then, the mixed material is placed into a mould, and the moulding is carried out for 3 minutes at the normal temperature of 25 ℃ and under the pressure of 10 MPa; secondly, putting the molded die into a flat vulcanizing machine, and vulcanizing at 170 ℃ and 15 MPa; and finally, placing the vulcanized mold sample in a cold press for cooling treatment, and demolding to finish the preparation of the composite material of the high-temperature vulcanized solid silicone rubber matrix.

The compound of the high-temperature curing epoxy resin matrix is prepared by adopting a vacuum pouring process, and specifically comprises the following steps: firstly, mechanically stirring surface-modified ZnO pressure-sensitive microspheres to uniformly mix the surface-modified ZnO pressure-sensitive microspheres; then, the filler mixture is put into a high-temperature oven and preheated for 4 hours at 130 ℃; secondly, the epoxy resin, the curing agent and the surface modified ZnO pressure sensitive microspheres are prepared according to the mass ratio: 100: 38: (200-400) mixing at 130 ℃, and mechanically stirring to uniformly disperse the mixture; thirdly, placing the mixture into a vacuum oven for vacuumizing for 15 minutes, pouring the mixed solution into a preheated mold after the vacuum treatment is finished, performing vacuum treatment again for 10 minutes, and removing residual gas in the mold cavity; thirdly, placing the vacuum-treated mould into a high-temperature oven at 130 ℃ for curing treatment, and demoulding after curing for 12 hours; and finally, putting the demoulded sample into a high-temperature oven at 130 ℃ again for secondary curing, wherein the secondary curing time is 16 hours, and curing the compound of the epoxy resin matrix at high temperature.

Taking the composite material of a silicon rubber matrix as an example, selecting ZnO pressure-sensitive microspheres with volume fractions of 35%, 40%, 45% and 50% and particle diameters of 10-30 μm, preparing four samples of SR/ZnO-35%, SR/ZnO-40%, SR/ZnO-45% and SR/ZnO-50% without surface functionalization treatment, and preparing the four samples of SR/ZnO-S-35%, SR/ZnO-S-40%, SR/ZnO-S-45% and SR/ZnO-S-50% by performing the surface functionalization treatment by using the preparation method of the embodiment, wherein the specific names and the compositions (phr) are as follows:

the above samples were subjected to X-ray photoelectron spectroscopy (XPS) to analyze the effect of the surface functionalization treatment, see FIG. 1, FIG. 1 is an XPS spectrum of a composite material without the surface functionalization treatment and the surface functionalization treatment, see FIG. 2, and FIG. 2 (a) is Si_2p(ii) XPS spectrum, (b) is N_1sXPS spectrum, by analyzing the appearance of new Si after surface functionalization_2pAnd N_1sPeak, indicating that the silane coupling agent KH550 was successfully grafted onto the ZnO varistor microsphere surface.

In order to judge the interface bonding strength between the ZnO varistor microsphere and the substrate, the appearance of the section of the sample is judged by SEM after the sample is stretched, so as to explain the bonding strength between the ZnO varistor microsphere and the substrate. Before and after the surface functionalization treatment, the tensile section SEM of the ZnO pressure sensitive microsphere and the composite is shown in figure 3, wherein (a) is the ZnO pressure sensitive microsphere without surface treatment, (b) and (c) are ZnO pressure sensitive microsphere composite materials without surface treatment, (d) is the ZnO pressure sensitive microsphere with surface treatment, and (e) and (f) are ZnO pressure sensitive microsphere composite materials with surface treatment. For the composite material with the particle surface not subjected to surface functionalization treatment, most of ZnO pressure-sensitive microspheres are separated from the matrix silicon rubber as can be seen from FIG. 3; even if the ZnO pressure sensitive microspheres are not separated, air gaps can be seen between the ZnO pressure sensitive microspheres and the matrix, which shows that the ZnO pressure sensitive microspheres are easy to separate from the matrix under the action of external force, and the interface bonding strength between the ZnO pressure sensitive microspheres and the matrix is low. As for the composite material with the surface functionalized treatment, the graph shows that even under the action of tensile force, the ZnO pressure-sensitive microspheres are still combined with the matrix tightly, and only a few ZnO pressure-sensitive microspheres form air gaps at the interface between the ZnO pressure-sensitive microspheres and the matrix.

Performing electrical characteristic verification on different samples to obtain voltammetry characteristic curves of different samples, as shown in fig. 4, (a) is a voltammetry characteristic curve of a ZnO pressure sensitive microsphere surface-treated composite material and an unprepared composite material with a volume fraction of 35%, (b) is a voltammetry characteristic curve of a ZnO pressure sensitive microsphere surface-treated composite material and an unprepared composite material with a volume fraction of 40%, (c) is a voltammetry characteristic curve of a ZnO pressure sensitive microsphere surface-treated composite material and an unprepared composite material with a volume fraction of 45%, (d) is a voltammetry characteristic curve of a ZnO pressure sensitive microsphere surface-treated composite material and an unprepared composite material with a volume fraction of 50%, and threshold field strengths and nonlinear coefficients of the samples are shown in the following table:

sample (I)	Threshold field strength (V/mm)	Coefficient of non-linearity
			SR/ZnO-S-35％	2141	13.9
SR/ZnO-S-40％	1892	12.4
			SR/ZnO-S-45％	1672	12.2
SR/ZnO-S-50％	1369	9.2
			SR/ZnO-35％	2019	13.0
SR/ZnO-40％	1801	11.7
			SR/ZnO-45％	1573	10.0
SR/ZnO-50％	1314	9.4

From the above table and fig. 4, it can be seen that, no matter whether the ZnO pressure sensitive microspheres are surface-treated or not, the threshold field strength of the composite material gradually decreases with the increase of the volume fraction of the ZnO pressure sensitive microspheres, and the increase of the volume fraction of the ZnO pressure sensitive microspheres shortens the conductive path in the composite material, thereby reducing the threshold field strength. Under different volume fractions, the threshold field intensity of the ZnO pressure-sensitive microsphere surface functionalization treatment composite material is slightly higher than that of the composite material which is not subjected to ZnO pressure-sensitive microsphere surface functionalization treatment. On one hand, the surface functionalization treatment increases the bonding strength of the ZnO pressure-sensitive microspheres and the substrate interface, increases the pressure of the substrate on the ZnO pressure-sensitive microspheres, so that the contact between the ZnO pressure-sensitive microspheres is tighter, and reduces the interface contact resistance. On the other hand, the ZnO pressure-sensitive microspheres are coated by the matrix more uniformly through surface functionalization treatment, so that a silicon rubber matrix material exists among the ZnO pressure-sensitive microspheres, and the existence of the matrix among the ZnO pressure-sensitive microspheres leads to the increase of interface contact resistance. The interaction of these two aspects results in a slight increase in the threshold field strength of the surface-functionalized composite material. Because the size of the ZnO pressure sensitive microsphere is micron grade, the agglomeration tendency among particles is smaller. Therefore, the surface functionalization treatment has limited improvement on the dispersibility of the ZnO pressure-sensitive microspheres in the matrix, so that the influence on the threshold field intensity is small, and the influence on the integrally formed conductive path is hardly generated by only changing the contact resistance between the interfaces. Compared with the composite material with the non-functionalized surface, the composite material with the functionalized surface of the particles has larger nonlinear coefficient, which shows that the composite material with the functionalized surface has better pressure equalizing effect.

The mechanical property verification is performed on different samples to obtain stress-strain curves of the different samples, as shown in fig. 5, (a) is the stress-strain curve of the ZnO pressure-sensitive microsphere surface-treated composite material with the volume fraction of 35% and the non-surface-treated composite material, (b) is the stress-strain curve of the ZnO pressure-sensitive microsphere surface-treated composite material with the volume fraction of 40% and the non-surface-treated composite material, (c) is the stress-strain curve of the ZnO pressure-sensitive microsphere surface-treated composite material with the volume fraction of 45% and the non-surface-treated composite material, (d) is the stress-strain curve of the ZnO pressure-sensitive microsphere surface-treated composite material with the volume fraction of 50% and the non-surface-treated composite material, and the mechanical parameters of the different samples are shown in the following table:

it can be seen from the above table and fig. 5 that the elongation at break and tensile strength at break of the composites, whether surface treated or not, decrease with increasing volume fraction of filler and the initial modulus increases with increasing volume fraction. This is because the integral number of the ZnO pressure sensitive microspheres increases, the interconnection between the substrates decreases, and the interconnection between the substrates and the ZnO pressure sensitive microspheres increases. On one hand, the matrix has elasticity and can generate elastic strain under the action of external force, the ZnO pressure-sensitive microspheres have smaller elasticity, hardly generate strain under the action of external force and cannot be stretched and increased, and the breaking elongation of the composite material is determined by the proportion of the matrix in the direction of the action of tensile force. The higher the proportion of matrix in the stress transmission path, the greater the elongation at break. On the other hand, since the ZnO pressure sensitive microspheres are in the order of micrometers, the specific surface area is relatively small, and the strength between the substrate and the matrix is greater than the bonding strength between the substrate and the ZnO pressure sensitive microspheres, the tensile strength at break decreases as the integral number of the ZnO pressure sensitive microspheres increases. Because the hardness of the ZnO pressure-sensitive microspheres is far higher than that of the matrix, the initial modulus of the composite material is increased along with the increase of the volume fraction of the ZnO pressure-sensitive microspheres.

Compared with the composite material without surface treatment, the composite material with the surface treatment has the advantages that the breaking tensile strength is obviously increased, the breaking elongation is slightly reduced, and the integral mechanical property is obviously improved. This is because the ZnO pressure sensitive microspheres are subjected to surface treatment to introduce functional groups, so that covalent bonds are formed between the ZnO pressure sensitive microspheres and the matrix. Compared with untreated ZnO pressure-sensitive microspheres, the matrix and the ZnO pressure-sensitive microspheres are chemically connected except for physical connection, so that the interface bonding strength between the ZnO pressure-sensitive microspheres and the matrix is obviously increased, stress conduction can be better performed, and the breaking strength is greatly improved. Compared with the treated composite material, the interface bonding strength between the untreated composite material ZnO pressure-sensitive microspheres and the matrix is poor, and under the action of external force, gaps are formed between the ZnO pressure-sensitive microspheres and the matrix interface, so that stress concentration is generated, and the breaking strength is reduced.

For the compound of ZnO pressure sensitive microsphere surface treatment, because of the increase of the interface bonding strength, under the action of external force, the phenomenon that the ZnO pressure sensitive microsphere is separated from the matrix or the position of the filler is moved rarely occurs, the matrix and the ZnO pressure sensitive microsphere are relatively fixed, the transmission path of the external force is formed by the ZnO pressure sensitive microsphere and the matrix together, and the elasticity of the ZnO pressure sensitive microsphere is very small, so that the elongation at break of the whole composite material is slightly reduced. For the composite material without surface treatment on the surface of the ZnO pressure-sensitive microsphere, under the action of external force, the ZnO pressure-sensitive microsphere can be separated from or displaced with the matrix, so that a stress transmission path consisting of the matrix is easier to form, the proportion of the matrix in the stress transmission path is increased, and the elongation at break of the composite material is increased.

The improvement of the thermal conductivity is beneficial to heat dissipation and is beneficial to practical application, the thermal conductivity of the composite material mainly depends on the thermal conductivity of the ZnO pressure-sensitive microspheres and the matrix and the condition of the interface of the ZnO pressure-sensitive microspheres and the matrix, so that the thermal conductivity of each sample is analyzed, and the thermal conductivity of different samples is shown in figure 6. Compared with a silicon rubber matrix, the ZnO pressure-sensitive microsphere has higher thermal conductivity. Thus, it can be seen that the thermal conductivity increases with increasing volume fraction of ZnO pressure sensitive microspheres for the surface treated and untreated ZnO pressure sensitive microsphere composites. This is because the increase in volume fraction of the ZnO pressure sensitive microspheres promotes the formation of thermally conductive pathways within the composite, thereby increasing the thermal conductivity of the composite.

When the volume fraction of the ZnO pressure sensitive microspheres is low (35%), the thermal conductivity of the surface-functionalized composite is slightly increased (1.0%) compared to the composite with the unfunctionalized surface. For the composite material with the volume fraction of ZnO pressure-sensitive microspheres of 45 percent and 50 percent, the thermal conductivity of the composite material subjected to surface functionalization treatment is respectively improved by 6.5 percent and 5.4 percent compared with the thermal conductivity of the composite material not subjected to surface functionalization treatment. The interface thermal resistance is influenced by the combination degree of the ZnO pressure-sensitive microspheres and the substrate interface, and further the thermal conductivity of the composite material is influenced. On one hand, after surface functionalization treatment, the interface bonding strength of the matrix and the ZnO pressure-sensitive microsphere is increased, and the number of internal defects of the composite material is reduced. Since the thermal conductivity of air is low, a reduction in the number of defects means a reduction in the internal air content, thereby increasing the thermal conductivity of the composite material. On the other hand, the ZnO pressure-sensitive microspheres and the matrix form chemical connection through surface functionalization treatment, so that phonon scattering at the interface is reduced, thermal resistance at the interface is reduced, and the thermal conductivity of the composite material is increased.

In conclusion, the ZnO pressure-sensitive microspheres are subjected to surface functionalization treatment, so that the mechanical and thermal properties of the composite material are obviously improved while the composite material keeps excellent electrical properties. Compared with the composite material with the non-functionalized surface, the composite material with the functionalized surface has the advantages that the tensile strength is generally improved by 20 percent and the thermal conductivity is also improved to some extent under the same volume fraction of the ZnO pressure-sensitive microspheres. The result shows that on the basis of the original multi-performance regulation and control, the surface of the ZnO pressure-sensitive microsphere is subjected to functional treatment, so that the mechanical performance and the heat dissipation characteristic can be effectively improved, and meanwhile, the excellent electrical characteristic is kept.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.