CN109370155B - Field-induced nonlinear conductive composite material preparation method, prepared composite material and application - Google Patents

Abstract

The invention discloses a field-induced nonlinear conductive composite material preparation method, the prepared composite material and application thereof, and relates to the field of nonlinear conductive composite materials. The steps are as follows: take KH560, ethanol and deionized water to obtain solution A; add GO to solution A, and react at 75-85 ° C for 3-5 h to obtain suspension B; add alkali to suspension B to make pH=10, add hydrazine hydrate , after dispersion, heated to 85-95 ℃ and reacted for 5-7h to obtain suspension C, washed, suction filtered, and the filter cake was dried to obtain RKGO powder; RKGO powder, epoxy resin E-51 and acetone were mixed to obtain suspension D, react at 75-85 ℃ until the acetone is volatilized and completely cooled to 45-50 ℃, add 2-ethyl-4-methylimidazole liquid, react, and solidify after air extraction to obtain a composite material; the RKGO filling mass fraction in the composite material is 0.75 %‑1.50%. The preparation method is simple, the cost is low, the reaction time is short, and it is easy to prepare in large quantities; the prepared composite material is light in weight, good in uniformity, and high in conductive nonlinear coefficient, and can be used for overvoltage protection, lightning surge protection, anti-static and self-adaptive Electromagnetic pulse protection field.

Description

Field-induced nonlinear conductive composite material preparation method, prepared composite material and application

technical field

The invention relates to the field of nonlinear conductive composite materials, in particular to a method for preparing a reduced modified graphene/epoxy resin field-induced nonlinear conductive composite material, the prepared composite material and applications.

Background technique

In recent years, large-scale integrated circuits have been widely used in military electronic information equipment, which has greatly improved the informatization and intelligence of electronic systems and equipment. At the same time, with the continuous development and application of electromagnetic pulse weapons (EMP) such as high-power microwaves, the electromagnetic environment in space is getting worse and worse, and the electromagnetic environment effects of electronic systems and equipment are becoming more and more significant. Therefore, doing a good job of electromagnetic protection is the key to ensuring the normal performance of electronic systems and equipment.

As an effective barrier against electromagnetic threats, electromagnetic protection materials are one of the effective means to solve electromagnetic protection. The traditional electromagnetic protection material uses its absorption, attenuation or reflection to the incident electromagnetic wave to isolate the electromagnetic wave from the protected electronic equipment, so as to achieve the purpose of electromagnetic protection. But such materials shield both useful and malicious electromagnetic signals, hindering the normal communication of electronic devices with the outside world. Therefore, how to deal with the contradiction between the normal sending and receiving signals of electronic equipment and the overvoltage, lightning surge, electrostatic discharge and strong electromagnetic pulse protection attack has become the key to solving the problem.

Liu Peiguo of National Defense University of Science and Technology proposed an energy selective surface structure (ESS), using a PIN diode to construct an energy selective surface and preliminarily verified the effectiveness of the electromagnetic energy selective surface, but due to the slow response time and turn-on delay of the diode material itself and other drawbacks, making it difficult to achieve effective protection against instantaneous electromagnetic pulses. The essence of the energy selective surface is to realize the metal/insulator phase transition induced by the electromagnetic field from the material level, and its impedance changes. In theory, low-impedance materials are needed to efficiently shield electromagnetic waves, and high-impedance materials are needed to efficiently transmit electromagnetic waves. These are two completely different requirements. In order for one material to meet both requirements, the material must be It has the characteristics of variable impedance, that is, it is in a high resistance state under the irradiation of low-power and weak-field safe electromagnetic waves, and suddenly changes to a low-resistance state under the irradiation of high-power and strong field harmful electromagnetic waves. Information and material systems that produce optimal response functions are often referred to as environment-adaptive intelligent electromagnetic protection materials. For fast rising edge, narrowband electromagnetic pulses, the phase transition response time of the material must be no slower than the pulse duration to ensure effective protection.

In fact, the field-induced (or electro-)resistive material has the variable impedance characteristic of the above-mentioned adaptive electromagnetic protection material, that is, the resistance of the material changes drastically with the electric field (voltage) or current and exhibits nonlinear conductive characteristics. The polymer matrix composites have nonlinear conductive properties under the action of an electric field, especially under the action of a strong electric field, the nonlinear conductive properties of the composites are more obvious. For filled polymer conductive composites, the intrinsic properties of fillers (or components) are the key factors affecting the macroscopic effective properties of the materials. In recent years, with the development of functional composite materials, it has been found that incorporating an appropriate amount of metal oxide, nano-metal or alloy powder into some polymer materials will make such polymer-based nanocomposites nonlinear under electric field induction. It has good application prospects as an adaptive intelligent electromagnetic protection material. In China, Zou Weiqin et al. studied the conductive switching characteristics of polypropylene-based and polydichloride-based composite materials doped with Al or Ag micropowder earlier, and found that near a certain electric field threshold, the resistance value of the composite material increased with the change of the external electric field. The change of the amplitude, when the type, average particle size and volume ratio of the doped metal or alloy particles are different, has a great influence on the conductive switching characteristics of the composite material. Chen Guohua's team from Huaqiao University studied the nonlinear conductive behavior of epoxy resin/graphite nanosheet conductive composites under the action of an electric field, and found that the conductivity of the composite system has strong nonlinearity to an applied electric field, and the nonlinear conductivity of this system is The behavior gives a theoretical explanation.

Graphene, as a two-dimensional carbon nanomaterial (one dimension in space is at the nanoscale, while the other two dimensions are macroscopic), has both the excellent electrical conductivity, thermal conductivity and stability of bulk graphite. Chemical properties, as well as new characteristics of two-dimensional nanomaterials, ultra-high specific surface area, high light transmittance and high electron mobility, unique physical and chemical properties, in polymer functional materials, optical materials, catalysts and high-performance solar cells, etc. It has a very wide range of applications and is one of the most popular and promising materials at present. The use of graphene to develop adaptive nonlinear conductive composites has potential applications. The ultra-high specific surface area and ultra-lightweight characteristics of graphene make it have a lower percolation threshold when used as a filler. Since graphene is easy to agglomerate in organic solvents and is difficult to be compatible, it is necessary to solve the intrinsic properties of graphene and improve the matrix. The problem of balance between compatibility can be used to prepare adaptive nonlinear conductive materials.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a preparation method of field-induced nonlinear conductive composite material, the prepared composite material and application. The preparation method has the advantages of simple process, simple operation, low cost, short reaction time and easy mass preparation The prepared composite material is light in weight, good in uniformity and high in conductive nonlinear coefficient, and can be used in the fields of overvoltage protection, lightning surge protection, anti-static and adaptive electromagnetic pulse protection.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is: a method for making a field-induced nonlinear conductive composite material, comprising the following steps:

(1) Take epoxy silane coupling agent KH560, ethanol and deionized water, and disperse to obtain solution A;

(2) adding graphene oxide into solution A, after dispersion, reacting at 75-85 °C for 3-5 hours to obtain modified graphene oxide suspension B;

(3) Add alkaline solution to suspension B to keep the pH value of suspension B alkaline, add hydrazine hydrate to suspension B, disperse at room temperature, heat to 85-95 ℃ and stir for 5-7 hours to obtain Suspension C, washing, suction filtration, and freeze-drying the filter cake to obtain the reduced modified graphene powder;

(4) Mix and disperse the reduced modified graphene powder, epoxy resin E-51 and acetone to obtain suspension D, which is reacted at 75-85 °C until the acetone is completely volatilized and then cooled to 45-50 °C, adding 2-ethyl-4-methylimidazole liquid, reacting, vacuuming the bubbles and curing to obtain the reduced modified graphene-epoxy field nonlinear conductive composite material;

The content of the modified graphene powder after reduction in the field-induced nonlinear conductive composite material is 0.75%-1.50%.

Preferably, the thickness of the graphene oxide is 0.6-1.0 nm, the diameter of the sheet layer is 0.5-5 μm, the number of layers is 1-2, and the specific surface area is 1000-1217 m ² /g.

Preferably, in solution A, the volume ratio of ethanol and deionized water is 2.5-3.5: 1.

Preferably, the mass ratio of graphene oxide and epoxy silane coupling agent KH560 is 9-11:1.

Preferably, the mass ratio of modified graphene oxide and hydrazine hydrate is 7-9: 10.

Preferably, in step (3), an alkaline solution is added to the suspension B to keep the pH of the suspension B between 9.5-10.5.

Further preferably, in step (3), an alkali solution is added to the suspension B to keep the pH value of the suspension B at 10.

Preferably, in step (3), the alkali solution is KOH solution; the washing is washing with ethanol and deionized water; and the freeze drying is vacuum drying in a vacuum freeze dryer at -50° C. for 24 hours.

Preferably, the mass ratio of epoxy resin E-51 and 2-ethyl-4-methylimidazole is 100: 3-5.

Preferably, in the suspension B, the ratio of the grams of epoxy resin E-51 to the milliliters of acetone is 0.9-1.1:10.

Application of the solid polymer matrix composite material prepared by the above field-induced nonlinear conductive composite material preparation method: the composite material is used in the fields of overvoltage protection, lightning surge protection, anti-static and adaptive electromagnetic pulse protection.

In the present invention, graphene oxide is abbreviated as GO, modified graphene oxide is abbreviated as KGO, and modified graphene after reduction is abbreviated as RKGO.

The beneficial effects produced by the above technical solutions are:

(1) The preparation method of the modified graphene/epoxy resin field-induced nonlinear conductive composite material after the reduction of the present invention has the advantages of simple process, simple operation, low cost, short reaction time, and easy mass preparation; the obtained composite material Light weight, good uniformity and high nonlinear coefficient of conductivity, can be used in the fields of overvoltage protection, lightning surge protection, anti-static and adaptive electromagnetic pulse protection.

(2) The preparation method of the reduced modified graphene RKGO adopted in the present invention is simple in process, simple in operation, low in requirements for the experimental environment, low in cost, short in reaction time, easy to prepare in large quantities, and the prepared RKGO product is a single product. Layer or few-layer flake structure, with high aspect ratio, high purity, good uniformity and dispersion.

(3) The epoxy resin of the present invention adopts the E-51 model with high thermal stability and dielectric constant, which has high strength after curing, good solvent resistance, strong stability and excellent mechanical properties. The preparation of the field-induced nonlinear conductive composite material adopts the solution blending method, which has the advantages of simple process, easy operation, stable product quality and easy addition of additives.

(4) The present invention modifies and reduces graphene oxide with KH560 and hydrazine hydrate, and then fills the polymer matrix with a low concentration below the percolation threshold, so that the composite material appears as an insulating material to the outside under normal weak field conditions. , when the external field increases and the electron energy in the reduced modified graphene exceeds the potential barrier formed by the insulating matrix between the conductive fillers, a large number of tunnel electrons will be generated and conduct electricity, resulting in a significant conductive switching effect. The number of free tunneling electrons has surged, and the electrical conductivity and current-carrying capacity of the composite material have been greatly improved, so that the dual effects of the material’s critical field can be adjusted and the electrical conductivity can be greatly improved after the phase transition. The problem of low resistance characteristics provides technical support for effective overvoltage protection, lightning surge protection, anti-static and adaptive electromagnetic pulse protection.

Description of drawings

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments;

Fig. 1 is the TEM image of KGO suspension B prepared in Example 1 of the present invention;

Fig. 2 is the SEM image of the RKGO powder obtained in Example 1 of the present invention;

Fig. 3 is the TEM image of the RKGO suspension C prepared in the embodiment of the present invention 1;

4 is a micro-domain SEM image of the field-induced nonlinear conductive composite material with a RKGO filling mass fraction of 0.75% prepared in Example 1 of the present invention;

5 is a micro-domain SEM image of the field-induced nonlinear conductive composite material with RKGO filling mass fraction of 1.00% prepared in Example 2 of the present invention;

6 is a micro-domain SEM image of the field-induced nonlinear conductive composite material with a RKGO filling mass fraction of 1.50% prepared in Example 3 of the present invention;

FIG. 7 is a voltammetry diagram of field-induced nonlinear conductive composite materials prepared under different filling concentrations of RKGO composite particles of the present invention.

Detailed ways

The main chemical reagents used in the examples are shown in Table 1. GO, KH560, KOH and hydrazine hydrate were used to synthesize RKGO; ethanol and deionized water were used to prepare the solvent required for the reaction and wash the suspension to obtain pure RKGO. ; Acetone and 2E4MZ were used to achieve the curing of composites.

Table 1 Main chemical reagents

Experimental reagents short name Specification Manufacturer/Supplier monolayer graphene oxide GO AR Suzhou Tanfeng Technology Epoxy silane coupling agent KH560 AR Sinopharm Group Chemical Reagent Co., Ltd. Hydrazine hydrate N₂H₄ AR Sinopharm Group Chemical Reagent Co., Ltd. Potassium hydroxide KOH AR Tianjin Comeo Chemical Reagent Co., Ltd. 2-Ethyl-4-methylimidazole 2E4MZ AR Shandong West Asia Chemical Co., Ltd. Ethanol AR Tianjin Yongda Chemical Reagent Co., Ltd. acetone AR Tianjin Yongda Chemical Reagent Co., Ltd. Epoxy resin E-51 ER AR Chuzhou Huisheng Electronic Materials Co., Ltd.

All reagents in the examples were not further purified, and the water used in the examples was deionized water.

Example 1

The method for preparing the reduced modified graphene/epoxy field nonlinear conductive composite material includes the following steps:

(1) First, pour 50ml of deionized water, 150ml of ethanol and 10mg of KH560 into a beaker, and ultrasonically disperse for 1h until KH560 is completely hydrolyzed to obtain mixed solution A.

(2) Then 100 mg of GO was added to solution A, after ultrasonic dispersion, heated to 80 °C and stirred for 4 h to obtain KGO suspension B.

(3) A small amount of KOH solution was added to suspension B to make the system pH=10, and 147.06 mg of hydrazine hydrate was added to suspension B, dispersed at room temperature, and heated to 90 °C for magnetic stirring reaction for 6 hours to obtain RKGO suspension C.

(4) After washing the suspension C with ethanol and deionized water, and suction filtration for three times, it was put into a vacuum freeze dryer at -50 °C for vacuum drying for 24 hours to obtain a black RKGO powder.

(5) Pour 50 mg of RKGO, 100 ml of acetone and 9.57 g of epoxy resin E-51 into a beaker and seal the mouth of the beaker with plastic wrap, ultrasonically disperse it for about 30 minutes to obtain suspension D, then heat it to 80°C and stir for 4 hours, and then remove it Cling film, continue to heat and stir until the suspension D no longer generates bubbles and becomes a black uniform viscous liquid, so as to ensure the complete evaporation of acetone, and obtain a liquid composite material system.

(6) The liquid composite material system prepared in step (5) was cooled to 45°C, poured into 0.38g of 2E4MZ liquid, stirred and reacted at 45°C for 1 min, and then poured into the mold that had been coated with the release agent in advance, and added to the vulcanizer. Press down and stand at room temperature for 24 hours, and then stand at 100 °C for 4 hours before demoulding to obtain a field-induced nonlinear conductive composite material with a mass fraction of RKGO of 0.75%.

Example 2

The method for preparing the reduced modified graphene/epoxy field nonlinear conductive composite material includes the following steps:

The first (1)-(4) are the same as those in Example 1.

(5) Pour 100 mg of RKGO, 100 ml of acetone and 9.52 g of epoxy resin E-51 into a beaker, seal the mouth of the beaker with plastic wrap, disperse it ultrasonically for about 30 minutes to obtain suspension D, then heat it to 80°C and stir for 4 hours, and then remove the preservation film, continue to heat and stir until the acetone evaporates completely to obtain a liquid composite material system.

(6) The liquid composite material system prepared in step (5) was cooled to 45°C, poured into 0.38g of 2E4MZ liquid, stirred and reacted at 45°C for 1 min, and then poured into the mold that had been coated with the release agent in advance, and added to the vulcanizer. Press down and stand at room temperature for 24 hours, and then stand at 100 °C for 4 hours before demoulding to obtain a field-induced nonlinear conductive composite material with a mass fraction of RKGO of 1.00%.

Example 3

The method for preparing the reduced modified graphene/epoxy field nonlinear conductive composite material comprises the following steps:

The first (1)-(4) are the same as those in Example 1.

(5) Pour 150mg of RKGO, 100ml of acetone and 9.47g of epoxy resin E-51 into a beaker and seal the mouth of the beaker with plastic wrap, disperse it ultrasonically for about 30 minutes to obtain suspension D, then heat it to 80°C and stir for 4 hours, and then remove the preservation film, continue to heat and stir until the acetone evaporates completely to obtain a liquid composite material system.

(6) The liquid composite material system prepared in step (5) was cooled to 45°C, poured into 0.38g of 2E4MZ liquid, stirred and reacted at 45°C for 1 min, and then poured into the mold that had been coated with the release agent in advance, and added to the vulcanizer. Press down and stand at room temperature for 24 hours, and then stand at 100 °C for 4 hours before demoulding to obtain a field-induced nonlinear conductive composite material with a mass fraction of RKGO of 1.50%.

Structural characterization and performance testing of KGO, RKGO and field-induced nonlinear conductive composites

1. Characterization of the prepared KGO structure:

Fig. 1 is the TEM image of KGO suspension B prepared in Example 1 of the present invention; the present invention adopts JEM-2100 type transmission electron microscope (Transmission Electron Microscopy, TEM) produced by Japan JEOL Microscopy Co., Ltd. to analyze the KGO product in suspension The microstructure was observed and analyzed. It can be seen from Fig. 1 that the generated KGO is dominated by a single-layer structure, the diameter of the lamella is about 1-2 μm, the agglomeration is small, the wrinkles are small, the uniformity and dispersion are good, and the good microscopic properties of the initial material GO are basically maintained. structure.

2. Structure characterization of the prepared RKGO:

Fig. 2 is the SEM image of the RKGO powder obtained in Example 1 of the present invention; the present invention adopts the GeminiSEM 300 scanning electron microscope (Scanning Electron Microscopy, SEM) produced by Carl Zeiss Microscopy Co., Ltd. in Germany to analyze the RKGO product powder. The microstructure was observed and analyzed. It can be seen from Figure 2 that the resulting RKGO powder has a significantly smaller sheet diameter than GO due to the reduction effect of hydrazine hydrate, but basically it still exists in a single-layer structure with less agglomeration and less folds, indicating that the The modification of the joint agent KH560 has a good protective effect on the microstructure of KGO, and greatly reduces the damage to its structure by reduction.

3 is a TEM image of the RKGO suspension C prepared in Example 1 of the present invention. The present invention still adopts the JEM-2100 transmission electron microscope (Transmission Electron Microscopy, TEM) produced by Japan JEOL Microscopy Co., Ltd. It can be seen from Figure 3 that the monolayer structure of most RKGOs is well maintained, which can be confirmed in combination with the SEM images of RKGO, indicating that the modification of the coupling agent KH560 plays a very important role in the protection of the KGO microstructure.

3. Microstructure characterization of the reduced modified graphene/epoxy field nonlinear conductive composites

In order to better observe the distribution state of RKGO in field-induced nonlinear conductive composites, SEM characterization analysis was performed on samples with filling mass fractions of 0.75%, 1.00%, and 1.50%, as shown in Figure 4-6.

According to the analysis of Figure 4-6, RKGO is generally uniformly distributed in the field-induced nonlinear conductive composite material, with good dispersion and no obvious agglomeration. more potential conductive paths. Due to the small filling mass fraction of RKGO and the insulating interface generated by the epoxy resin matrix between the RKGOs, it will not conduct electricity when the external field strength is low. The insulating-metal phase transition makes the composite material from a high resistance state suddenly change to a low resistance state, resulting in an obvious nonlinear conductive behavior.

4. Test results and analysis of nonlinear voltammetric characteristics of the reduced modified graphene/epoxy field-induced nonlinear conductive composites

Figure 7 shows the nonlinear voltammetry curves of field-induced nonlinear conductive composites prepared with RKGO particles filling mass fractions of 0.75%, 1.00% and 1.50%, respectively. The results show that starting from 0.75wt%, different RKGO particles filling The composite materials with mass fractions all have obvious nonlinear conductive behavior, and with the increase of filling concentration, the conductive switching voltage of the composite materials decreases, and the corresponding nonlinear coefficients also change to varying degrees. Therefore, the field-induced nonlinear conductive composite material prepared by the present invention can exhibit good field-induced conductive switching properties at low filling mass fractions, and the more filling, the lower the critical field, which indicates that the modified graphene particles Filled composite materials can indeed effectively adjust the switching critical field strength of the material. Moreover, due to the low filling mass fraction and ultra-light filler characteristics, field-induced nonlinear conductive composites can not only achieve critical field regulation and greatly improve conductivity and current-carrying capacity, and have better prospects for cost reduction and ease of application.

Claims (10)

1. A method for preparing a field nonlinear conductive composite material is characterized by comprising the following steps: the method comprises the following steps:

(1) taking epoxy silane coupling agent KH560, ethanol and deionized water, and dispersing to obtain solution A;

(2) adding graphene oxide into the solution A, dispersing, and reacting at 75-85 ℃ for 3-5h to obtain a modified graphene oxide suspension B;

(3) adding an alkali solution into the suspension B to keep the pH value of the suspension B alkaline, adding hydrazine hydrate into the suspension B, dispersing at normal temperature, heating to 85-95 ℃, stirring and reacting for 5-7h to obtain a suspension C, washing, performing suction filtration, and freeze-drying a filter cake to obtain reduced modified graphene powder;

(4) mixing and dispersing the reduced modified graphene powder, epoxy resin E-51 and acetone to obtain a suspension D, reacting at 75-85 ℃, cooling to 45-50 ℃ after the acetone is completely volatilized, adding 2-ethyl-4-methylimidazole liquid, reacting, vacuumizing and curing to obtain the reduced modified graphene-epoxy resin field nonlinear conductive composite material;

the filling mass fraction of the reduced modified graphene powder in the field nonlinear conductive composite material is 0.75-1.50%.

2. The method for preparing field nonlinear conductive composite material as claimed in claim 1, wherein the graphene oxide has a thickness of 0.6-1.0nm, a lamella diameter of 0.5-5 μm, a number of layers of 1-2, a specific surface area of 1000-²/g。

3. The method of making a field nonlinear conductive composite material as recited in claim 1, wherein: in the solution A, the volume ratio of ethanol to deionized water is 2.5-3.5: 1.

4. The method of making a field nonlinear conductive composite material as recited in claim 1, wherein: the mass ratio of the graphene oxide to the epoxy silane coupling agent KH560 is 9-11: 1.

5. The method of making a field nonlinear conductive composite material as recited in claim 1, wherein: the mass ratio of the modified graphene oxide to the hydrazine hydrate is 7-9: 10.

6. The method for producing a field nonlinear conductive composite material as claimed in claim 1, wherein in the step (3), the alkali solution is KOH solution; washing is washing by using ethanol and deionized water; the freeze drying is vacuum drying at-50 deg.C for 24 hr in vacuum freeze dryer.

7. The method of making a field nonlinear conductive composite material as recited in claim 1, wherein: the mass ratio of the epoxy resin E-51 to the 2-ethyl-4-methylimidazole is 100: 3-5.

8. The method for producing a field nonlinear conductive composite material as claimed in claim 1, wherein a ratio of grams of the epoxy resin E-51 to milliliters of acetone in the suspension D is 0.9 to 1.1: 10.

9. A solid polymer matrix composite prepared by the method of any one of claims 1 to 8.

10. Use of a solid polymer matrix composite material prepared by the method of making a field-induced nonlinear conductive composite material as claimed in claim 9, wherein the composite material is used in the fields of overvoltage protection, lightning surge protection, static electricity prevention and adaptive electromagnetic pulse protection.

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