CN113845751B - Epoxy resin-based electromagnetic shielding composite material and preparation method and application thereof - Google Patents

Abstract

The invention provides an epoxy resin-based composite material with high conductivity and high electromagnetic shielding performance, which is an epoxy resin-based composite material containing a nanofiber-shaped conductive polymer formed by self-assembling a block copolymer in a solution, wherein the nanofiber-shaped conductive polymer forms a network structure in the composite material. The invention realizes high conductivity and high electromagnetic shielding performance by preparing nano fibrous conductive polymer nano filler, compounding the nano fibrous conductive polymer nano filler with an epoxy resin system and further soaking the nano fibrous conductive polymer nano filler in a dopant solution. Compared with other epoxy resin materials compounded with conductive fillers, the continuous conductive network has very excellent conductive performance and electromagnetic shielding capability under the condition of low filler addition amount, and the main electromagnetic shielding mechanism is an absorption mechanism, so that secondary pollution caused by strong electromagnetic wave reflection can be avoided, and the composite material has very excellent application prospect in the field of electromagnetic shielding materials.

Description

A kind of epoxy resin-based electromagnetic shielding composite material and its preparation method and application

technical field

The invention belongs to the field of composite materials, and in particular relates to an epoxy resin-based electromagnetic shielding composite material and its preparation method and application.

Background technique

With the development of communication electronic technology, electronic equipment has become more and more widely used in many fields such as entertainment and communication. It will cause electromagnetic interference between equipment, cause equipment failure and aging of electronic components, and also affect human health and the surrounding environment. Therefore, certain measures need to be taken to reduce the harm of electromagnetic interference. At present, the main way to eliminate the harm of electromagnetic interference is to use electromagnetic shielding materials to shield it.

Traditional electromagnetic shielding materials are mainly metal materials, which have excellent electromagnetic wave reflection capabilities, but metals have high density and high cost, and the mechanism of reflection shielding is likely to cause secondary reflection pollution of electromagnetic waves. The new polymer-based electromagnetic shielding composite material has a good application prospect because of its light weight, excellent corrosion resistance, easy processing and manufacturing.

Epoxy resin has excellent mechanical properties, adhesive strength, good electrical insulation, thermal stability, high solvent resistance, and is easy to process. Therefore, composite electromagnetic shielding composite materials modified with epoxy resin as a matrix are widely used application. At present, the commonly used modification method is to add conductive materials to the epoxy resin, so that the epoxy resin has electromagnetic shielding properties. However, currently commonly used conductive fillers such as metals and carbon nanotubes are often dispersed in the epoxy resin matrix, making it difficult to form an ideal conductive transmission network structure, which limits the conductive performance and electromagnetic shielding effect of composite materials.

The self-assembly behavior of amorphous block copolymers (BCP) in solution is an effective method to construct high-precision functional nanoscale objects, especially when BCP contains crystalline blocks, which can form low-dimensional structures such as rod micelles. In selective solvents, nanofibers can even be spontaneously elongated and grown. Poly-3-hexylthiophene (P3HT) has high hole mobility and has become one of the most widely studied semiconducting polymers. If the properties of BCP and the advantages of P3HT can be used to construct BCP with P3HT block, it will Constructing stacked one-dimensional nanofibers in the epoxy resin matrix to form a conductive nanofiber network structure is expected to achieve excellent electrical conductivity and electromagnetic shielding effect with a low amount of filler added. However, on the one hand, the high mobility of P3HT is largely due to its property of forming compact crystalline domains, and on the other hand, the self-assembly behavior of BCPs containing P3HT blocks to form nanofibers is affected by many factors. When it is compounded, it will cause grain boundaries and defects in the composite material, which will hinder the charge transport, affect the electrical conductivity, and even destroy the nanofiber morphology, resulting in the failure to form an ideal nanofiber network structure.

Therefore, how to effectively control the morphology of nanofibers, prepare epoxy resin-based composites with nanofiber network structure, and obtain excellent electrical conductivity and electromagnetic shielding performance at a low addition of conductive fillers still needs further research.

Contents of the invention

The object of the present invention is to provide an epoxy resin-based electromagnetic shielding composite material with a conductive network structure composed of nanofibers.

The invention provides a conductive polymer/epoxy resin-based composite material, which is an epoxy resin-based composite material containing a nanofibrous conductive polymer, and the nanofibrous conductive polymer is formed by a block copolymer in a solution Formed by self-assembly, the nanofibrous conductive polymer forms a network structure in the composite material.

Further, the above-mentioned block copolymer is a block copolymer containing a conjugated segment; preferably, the block copolymer containing a conjugated segment is a diblock copolymer containing a poly-3-hexylthiophene block ;

More preferably, the above-mentioned diblock copolymer containing poly 3-hexylthiophene block is poly 3-hexylthiophene-polycaprolactone diblock copolymer, and the relative ratio of poly 3-hexylthiophene and polycaprolactone block The molecular mass ratio is (0.5-4):1, preferably (0.6-3):1; or, the mass ratio of the poly-3-hexylthiophene to the polycaprolactone block is 1:1.

Further, the above-mentioned composite material is made of the following raw materials: block copolymer, epoxy resin and curing agent; the mass fraction of the block copolymer in the total raw materials is 5% to 50%, preferably 25%; the The mass ratio of the epoxy resin to the curing agent is 10:(0.1-8), or the molar ratio of the reactive functional groups between the epoxy resin and the curing agent is (1-2):1.

Preferably, the epoxy resin curing agent is a polyetheramine curing agent.

Furthermore, it is obtained by self-assembling the block copolymer to form a nanofiber structure, mixing it with epoxy resin and curing agent and curing it;

Preferably, the nanofibrous structure is formed by self-assembly of the block copolymer in a mixed solvent of a good solvent and a poor solvent; more preferably, the good solvent is tetrahydrofuran or chloroform, and the poor solvent is acetone or anisole ; The volume ratio of the good solvent to the poor solvent (0.5-5): (0.5-5), preferably 1:1.

Furthermore, the above composite material also contains a soluble dopant, the content of which is 1-10%, preferably 5%.

Furthermore, the above-mentioned soluble dopant is copper trifluoromethanesulfonate, tetrafluoro-tetracyano-terephthalmethane or lithium bistrifluoromethanesulfonylimide, preferably copper trifluoromethanesulfonate.

Further, the above-mentioned composite material containing soluble dopant is self-assembled by the block copolymer to form a nanofibrous structure, mixed uniformly with epoxy resin and curing agent and cured, and then mixed in the solution containing soluble dopant Soak the resulting. Preferably, the nanofibrous structure is formed by self-assembly of a block copolymer in a mixed solvent of a good solvent and a poor solvent; more preferably, the good solvent is tetrahydrofuran or chloroform, and the poor solvent is acetone or anisole; Said good solvent and poor solvent volume ratio (0.5～5):(0.5～5), preferably 1:1.

The present invention also provides the preparation method of above-mentioned composite material, comprises the following steps:

(1) The block copolymer self-assembles to form a dispersion of nanofibers in a mixed solvent of a good solvent and a poor solvent;

(2) Add the epoxy resin curing system to the dispersion of the block copolymer and mix evenly. After evaporating the solvent, react at 30-50°C for 10-15h, and then react at 50-70°C for 2-6h to cure and anneal;

Preferably, the good solvent of the dispersion of the block copolymer described in step (1) is tetrahydrofuran or chloroform, the poor solvent is acetone or anisole, and the good solvent and poor solvent volume ratio (0.5～5): (0.5～5 ), more preferably 1:1; the annealing condition in step (2) is: annealing at 140-160° C. for 50-70 min.

Further, the above method also includes soaking the material obtained in step (2) in a solution containing a soluble dopant, treating at 30-50° C. for 20-40 minutes, and then drying.

Preferably, the solvent of the solution containing the soluble dopant is acetonitrile, and the concentration of the soluble dopant is 20-65 mg/mL.

The present invention also provides the application of the above-mentioned composite material in electromagnetic shielding materials.

Beneficial effects of the present invention: the present invention forms a nanofibrous conductive polymer structure through the self-assembly of the block copolymer in the solution, and then compounded into the epoxy resin matrix to prepare a composite material, forming a network in the epoxy resin matrix The conductive fiber structure is conducive to the improvement of electrical conductivity. Further immersion in the dopant solution realizes high conductivity and high electromagnetic shielding performance, the conductivity is as high as 1.94S/m, and under the addition of only 25wt% P3HT-b-PCL (that is, the addition of the conductive filler P3HT is only 12.5 wt%), the electromagnetic shielding efficiency of the composite material of the present invention with a thickness of 1.1mm is as high as 23.8dB on average, and the main mechanism of its electromagnetic shielding is an absorption mechanism, which can avoid strong electromagnetic wave reflections and cause secondary pollution, and has great advantages in the field of electromagnetic shielding materials Good application value.

The "soluble dopant" in the present invention refers to a dopant whose solubility in water or organic matter is greater than 1 mg/mL.

The "nanofiber" mentioned in the present invention refers to a one-dimensional structure that is limited to less than 100 nanometers in the transverse direction and not limited in the longitudinal direction.

The "network structure" and "conductive network structure" in the present invention refer to: a three-dimensional structure with nodes formed by interlacing and overlapping nanofibers with a certain length in the longitudinal direction, and there are one or more nanofibers between each two nodes. connect.

Apparently, according to the above content of the present invention, according to common technical knowledge and conventional means in this field, without departing from the above basic technical idea of the present invention, other various forms of modification, replacement or change can also be made.

The above-mentioned content of the present invention will be further described in detail below through specific implementation in the form of examples. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following examples. All technologies realized based on the above contents of the present invention belong to the scope of the present invention.

Description of drawings

Figure 1 is the H NMR spectrum of P3HT-b-PCL.

Fig. 2 is the thermogravimetric test result of P3HT-b-PCL.

Figure 3 is the optical photographs and principles (a-c) and microstructural characterization (d, e, e') of P3HT-b-PCL nanofibers prepared by crystallization-driven self-assembly (CDSA).

Figure 4 is the optical image (a-b) of the epoxy composite solution and composite material containing P3HT-b-PCL block copolymer nanofibers, and the scanning electron microscope characterization (c) of the composite material.

Figure 5 shows the chemical principle (a-c) and XPS, EDS-mapping microstructure characterization (d-h) of doping nanowires with copper trifluoromethanesulfonate in acetonitrile solution.

Figure 6 shows the bending performance (a) of the nanofiber composite material after doping of the present invention; the mechanical property characterization (b) of the nanofiber composite material with different contents before and after doping, and the concentration and block of copper trifluoromethanesulfonate Effect of the content of copolymer nanofibers on the DC conductivity of the composite film (c).

Fig. 7 is the electromagnetic shielding performance (a) and the electromagnetic wave absorption coefficient (b) after doping containing 25wt% block copolymer nanofiber composite film, the power coefficient (c) of absorption coefficient and reflection coefficient and different preparation methods (comparative example 1 (without CDSA), comparative example 2 (without CDSA-doped), comparative example 3 (CDSA), embodiment 1 (CDSA-annealed), embodiment 4 (CDSA-annealed-doped)) on the influence of composite film dielectric properties (d-f).

Figure 8 is a scanning electron microscope characterization of a sample that was directly added to chloroform and dripped into a thin film without crystallization-driven self-assembly.

Detailed ways

The poly-3-hexylthiophene-polycaprolactone diblock copolymer (P3HT-b-PCL) used in the embodiments of the present invention is to purchase commercially available products, or through the following reaction route, by those skilled in the art with known knowledge and experiments Means homemade by chemical synthesis:

(1) 2,5-dibromo-3-hexylthiophene reacts with tert-butylmagnesium chloride solution, adds catalyst Ni(dppp)Cl ₂ , and then adds vinylmagnesium bromide solution to react to obtain vinyl-terminated 3-hexylthiophene ( P3HT-vin):

(2) P3HT-vin reacts with 9-boronbicyclo[3.3.1]nonane ( ₉ -BBN), and then reacts with NaOH and 30% _H2O2 solution in turn to prepare hydroxyl-terminated poly-3-hexylthiophene (P3HT-OH).

(3) Use P3HT-OH to initiate the ring-opening reaction of ε-caprolactone (ε-CL) under the action of catalyst Sn(Oct) ₂ , the mass ratio of P3HT-OH and ε-caprolactone (ε-CL) 1:1, the diblock copolymer of P3HT and PCL is obtained: the relative molecular mass ratio of P3HT and PCL block of P3HT-b-PCL is (0.5～4):1, preferably (0.6～3):1 .

The chemical structures of the synthesized intermediates and P3HT-b-PCL were confirmed by 1H NMR spectroscopy, as shown in Figure 1, the degrees of polymerization (DP) of the P3HT and PCL blocks were determined to be 27 and 41, respectively, and the repeating units of P3HT and PCL were determined to be 27 and 41 respectively. The relative molecular masses are 148 and 114 respectively, and the calculated mass ratio of the two is 1:1. The as-prepared polymers were also characterized by thermogravimetric analysis (TGA), and the results (Fig. 2) showed that the maximum weight loss temperatures of the PCL and P3HT blocks were determined to be 307 and 473 °C, and the masses of the two stages of weight loss were also 1: 1. The synthesis of P3HT-b-PCL has a high yield (95.8%), so the results of 1HNMR and TGA are consistent with the synthesis ratio of 1:1. That is to say, in the final P3HT-b-PCL, the content of conductive filler P3HT is 50%, that is, when the addition of P3HT-b-PCL in the composite material is 25wt%, the addition of conductive filler P3HT is only 12.5 wt%.

Embodiment 1, the preparation of P3HT-b-PCL/epoxy resin composite material of the present invention

1. Preparation of P3HT-b-PCL nanofiber dispersion (crystallization-driven self-assembly CDSA)

First, 10 mg of dry powder of P3HT-b-PCL and 5 mL of THF were added to a 10 mL vial, fully dissolved by slight heating, and then cooled to room temperature. Subsequently, 5 mL of acetone was slowly added dropwise to the dissolved P3HT-b-PCL solution through a thin tube connected to a constant flow pump. The above mixture was allowed to mature at room temperature for 48 hours, then shaken for 5 minutes to obtain a stable and uniform dispersion.

2. Preparation of P3HT-b-PCL/epoxy composite film

Add the epoxy resin curing system (the mass ratio of E51 and D-230 is 10:3, ensure that the molar ratio of the reactive groups on the epoxy resin E51 and curing agent D-230 is 1:1) to P3HT-b- In the micellar dispersion of PCL, the mass ratio of P3HT-b-PCL to epoxy resin curing system is 1:3 (P3HT-b-PCL content 25wt%), and they are thoroughly mixed by shaking. This mixture is then drip-cast onto different substrates to obtain coatings of varying thickness. After the solvent is completely evaporated, the curing reaction of the epoxy system is carried out in the blast furnace, the temperature is 40°C, 12 hours, 60°C, 4 hours, and finally, under the condition of ensuring complete curing, the temperature is increased to 150°C and kept for 1 hour. thermal annealing. Membrane material was obtained by exfoliation from a Teflon substrate.

Embodiment 2, the preparation of P3HT-b-PCL/epoxy resin composite material of the present invention

Referring to the preparation method of Example 1, the mass ratio of P3HT-b-PCL to the epoxy resin curing system is 1:19, that is, a composite material with a P3HT-b-PCL content of 5wt% is prepared.

Embodiment 3, the preparation of P3HT-b-PCL/epoxy resin composite material of the present invention

Referring to the preparation method of Example 1, the mass ratio of P3HT-b-PCL to the epoxy resin curing system is 3:17, namely a composite material with a P3HT-b-PCL content of 15 wt%.

Embodiment 4, preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 1 was immersed in a 65 mg/mL copper trifluoromethanesulfonate (Cu(OTf) ₂ ) acetonitrile solution, and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Embodiment 5, preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 1 was immersed in a 20 mg/mL copper trifluoromethanesulfonate (Cu(OTf) ₂ ) acetonitrile solution, and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Embodiment 6, preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 1 was immersed in a 35 mg/mL acetonitrile solution of copper trifluoromethanesulfonate (Cu(OTf) ₂ ), and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Embodiment 7, preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 1 was immersed in a 50 mg/mL acetonitrile solution of copper trifluoromethanesulfonate (Cu(OTf) ₂ ), and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Embodiment 8, preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 2 was immersed in a 65 mg/mL acetonitrile solution of copper triflate (Cu(OTf) 2 ), and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Embodiment 9, preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 2 was immersed in a 20 mg/mL copper trifluoromethanesulfonate (Cu(OTf) ₂ ) acetonitrile solution, and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Embodiment 10, preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 2 was immersed in a 35 mg/mL copper trifluoromethanesulfonate (Cu(OTf)2) acetonitrile solution, and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Example 11, Preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 2 was immersed in a 50 mg/mL copper trifluoromethanesulfonate (Cu(OTf) ₂ ) acetonitrile solution, and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Embodiment 12, preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 3 was immersed in a 65 mg/mL copper trifluoromethanesulfonate (Cu(OTf) ₂ ) acetonitrile solution, and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Example 13, Preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 3 was immersed in a 20 mg/mL copper trifluoromethanesulfonate (Cu(OTf) ₂ ) acetonitrile solution, and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Example 14, Preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 3 was immersed in a 35 mg/mL acetonitrile solution of copper triflate (Cu(OTf) ₂ ), and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Example 15, Preparation of P3HT-b-PCL/epoxy resin composite material doped by the present invention

The membrane material prepared in Example 3 was immersed in a 50 mg/mL acetonitrile solution of copper trifluoromethanesulfonate (Cu(OTf) ₂ ), and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Comparative Example 1: Preparation of P3HT-b-PCL nanofiber solution: first, 10 mg of dry powder of P3HT-b-PCL and 10 mL of THF were added to a 10 mL vial, fully dissolved by slight heating, and then cooled A solution was obtained at room temperature. The remaining steps refer to Example 1 to prepare a composite material.

Comparative Example 2: The composite material obtained in Comparative Example 1 was soaked in 65 mg/mL copper trifluoromethanesulfonate (Cu(OTf) ₂ ) in acetonitrile solution, and kept at 40° C. for 30 minutes. The films were then removed from the solution and dried thoroughly in a forced air oven at 40 °C.

Comparative example 3: Referring to the method of Example 1, no annealing treatment was performed after curing to obtain a composite material.

The beneficial effects of the present invention are demonstrated through experimental examples below.

Experimental example 1. Characterization of P3HT-b-PCL crystallization driven self-assembly into nanofiber structure

First, follow the method described in step 1 of Example 1: add 10 mg of dry powder of P3HT-b-PCL and 5 ml of tetrahydrofuran into a 10 ml vial, dissolve it fully by slight heating, and then cool to room temperature. Subsequently, 5 ml of acetone was slowly added dropwise to the dissolved P3HT-b-PCL solution through a thin tube connected to a constant-flow pump, and the product form in the obtained solution changed with time as shown in Figure 3a. It can be seen that It was found that the solution gradually changed from orange to purple as the solvent continued to diffuse, which is characteristic of the formation of micelles with crystalline P3HT cores. The schematic diagram of the diffusion is shown in Fig. 3b. After the diffusion crystallization is completed, the whole system exhibits a stable state at room temperature (Fig. 3c). It can be seen from the observation results of atomic force microscope (Fig. 3d) and scanning electron microscope (Fig. 3e, 3e') that the P3HT-b-PCL of the present invention forms a nanofiber structure, and forms interlaced and overlapping, and can construct a large 3D nanofiber network . Correspondingly, the product prepared in Comparative Example 1 cannot form a nanofiber network structure, but forms an island structure, which is not conducive to the improvement of electrical conductivity (Figure 8).

Further, the dispersion state of P3HT-b-PCL and epoxy resin curing system mixed uniformly according to step 2 in Example 1 is shown in Figure 4a, and the morphology of the cured composite film is shown in Figure 4b. It shows that the present invention has successfully prepared the composite film of P3HT-b-PCL and epoxy resin.

The product obtained in Example 4 was observed with a scanning electron microscope, and the result obtained is shown in Figure 4c.

As can be seen from the figure, in the composite material prepared by the present invention, there is an obvious fibrous network structure, which shows that after P3HT-b-PCL of the present invention is compounded with epoxy resin, further doping is not significant. The conductive network structure formed in the compound of the present invention plays a key role in the conductive performance and electromagnetic shielding performance of the material after destroying its nanofiber structure.

Experimental example 2, doping of copper trifluoromethanesulfonate

The structure and solution form of copper trifluoromethanesulfonate are shown in Figure 5a, and the state changes of P3HT-b-PCL/epoxy resin composite film before and after soaking in copper trifluoromethanesulfonate solution are shown in Figure 5b, The doping mechanism of copper methanesulfonate and P3HT is shown in Figure 5c.

The composite material prepared in Example 4 was subjected to X-ray photoelectron spectroscopy (XPS) experiments, and the results obtained are shown in Figure 5d-5g, combined with the results of X-ray energy spectroscopy (EDS) testing on the material interface (Figure 5h) , it can be proved that the acetonitrile solution of Cu(OTf) ₂ can effectively penetrate into the composite film and be well doped into the composite matrix of P3HT-b-PCL/epoxy resin, which contributes to the improvement of electrical conductivity.

Experimental example 3, performance characterization of the composite material of the present invention

The composite material of Example 4 of the present invention is bent, and it can be seen from Fig. 6a that the material exhibits very excellent toughness. And further to the mechanical property test of embodiment 1, embodiment 3 (before doping) and embodiment 4, embodiment 12 (after doping) finds, after doping, although the mechanical strength of material reduces to some extent, fracture The toughness of the material remained at an excellent level despite the increase in elongation (Fig. 6b).

The electrical conductivity test was carried out on the composite materials of Examples 4-15, and the results are shown in FIG. 6c. It can be seen that the concentration of Cu(OTf) ₂ has little effect on the conductivity of the material, and the concentration of 65mg/mL can basically reach saturation after soaking for 30min. With the increase of P3HT-b-PCL addition, the electrical conductivity of the composite material increases, and the highest electrical conductivity can reach 1.94S/m. In contrast, the composite film without nanofibrous structure (Comparative Example 1) was not conductive even after doping.

Further electromagnetic shielding performance and dielectric constant, the results are shown in Figure 7a-7b. The total electromagnetic shielding effect (SET) in the X-band (8.2-12.4GHz) of the doped composite film containing 25wt% nanofibrous structure P3HT-b-PCL increases with the thickness, and the X-band with a thickness of 1.1 mm is obtained an average of 23.8dB. Since the content of P3HT in the block copolymer is 50%, it achieves the above performance when the content in the composite film is 12.5wt%, which is the best performance of the conductive polymer/epoxy resin composite system that has been reported so far, and It is superior to most carbon nanomaterials/epoxy composite systems with comparable filler content. Compared with the epoxy resin matrix electromagnetic shielding materials reported in many literatures at present, the present invention achieves a very excellent electromagnetic shielding effect under the low addition amount of conductive filler and a thickness of only 1.1 mm. As shown in Table 1.

Table 1 compares the electromagnetic shielding performance of epoxy resin-based electromagnetic shielding materials reported in the prior art

References in Table 1:

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3.M.S.Cao, J.Yang, W.L.Song, D.Q.Zhang, B.Wen, H.B.Jin, Z.L.Hou and J.Yuan, ACSAppl Mater Interfaces, 2012, 4, 6949-6956.

4. Y. Huang, N. Li, Y. Ma, F. Du, F. Li, X. He, X. Lin, H. Gao and Y. Chen, Carbon, 2007, 45, 1614-1621.

5. H. Zhang, Z. Heng, J. Zhou, Y. Shi, Y. Chen, H. Zou and M. Liang, Chem. Eng. J., 2020, 398

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Moreover, when the electromagnetic wave reaches the surface of the shielding material, there are three shielding mechanisms, namely reflection (SER), absorption (SEA) and multiple reflection (SEM). When SET is greater than 15dB, SEM can be ignored. Figure 7b shows the contribution of SER and SEA to SET at different thicknesses. In all cases, the value of SEA is dominant, while SER is less than 2dB. In order to further clarify the EMI shielding mechanism of the composite film, the power coefficients of the corresponding absorption coefficient (A) and reflection coefficient (R) were calculated from the S parameters, which were used to represent the ability of the shielding material to absorb, reflect, and transmit microwaves, and Evaluating the power balance of the microwave-airgel interaction, it can be seen from Figure 7c that the composite film containing doped nanofibers has a high absorption coefficient A, greater than 0.7. At the same time, R and A showed a gradual increase and decrease, respectively. And A is always greater than R, which is consistent with the results of EMI SE (SEA>SER). Therefore, the main shielding mechanism of the CDSA nanofiber composite film is absorption, which can avoid secondary pollution caused by a large number of reflections of electromagnetic waves.

Further, it can be seen from the dielectric performance test results in Figures 7d-7f that the conductive polymer in the composite film does not have a nanofiber structure and is not doped (Comparative Example 1) or has a nanofiber structure but is not doped (Comparative Example 3, Example 1), the dielectric property is relatively poor, and it is difficult to meet the requirements of conduction and electromagnetic shielding. However, the composite material (Example 1) with the nanofiber network structure of the present invention can provide a basis for further doping to significantly improve the conductivity and dielectric properties. Although the dielectric properties of the composite material (Example 4, Comparative Example 3) doped with copper trifluoromethanesulfonate have been improved, on the basis of the nanofiber network structure obtained in Example 1, further doping obtained The dielectric properties of the composite material (Example 4) with a nanofiber conductive network structure show very significant advantages, and it is a material with excellent electrical conductivity and excellent electromagnetic shielding performance.

In summary, the present invention forms a nanofibrous conductive polymer structure through the self-assembly of block copolymers in a solution, and then composites them into an epoxy resin matrix to prepare a composite material, forming a network of nanofibers in the epoxy resin matrix structure, the prepared epoxy resin-based composite material with a conductive network structure composed of nanofibers is compared with other conductive filler composite epoxy resin materials, and its continuous conductive network makes it very excellent at low filler additions. Excellent conductivity and electromagnetic shielding ability, the conductivity is as high as 1.94S/m, and the electromagnetic shielding efficiency is as high as 23.8dB. The main shielding mechanism is absorption, which can avoid secondary pollution caused by a large number of reflections of electromagnetic waves. It has very excellent application prospects in the field of electromagnetic shielding materials .

Claims (8)

1. A conductive polymer/epoxy resin-based composite material is characterized in that the conductive polymer/epoxy resin-based composite material is an epoxy resin-based composite material containing a nanofiber-like conductive polymer, wherein the nanofiber-like conductive polymer forms a network structure in the composite material; the nanofiber-like conductive polymer is formed by self-assembly of a block copolymer in a solution; the block copolymer is a poly-3-hexylthiophene-polycaprolactone diblock copolymer, and the relative molecular mass ratio of the poly-3-hexylthiophene to the polycaprolactone block is (0.5-4): 1; the composite material is prepared by self-assembling the block copolymer to form a nanofiber structure, uniformly mixing the nanofiber structure with epoxy resin and a curing agent, curing, and soaking in a solution containing a soluble dopant; the soluble dopant is copper trifluoromethanesulfonate; the preparation method of the composite material comprises the following steps:

(1) Self-assembling the block copolymer in a mixed solvent of a good solvent and a poor solvent to form a dispersion liquid of the nanofiber; the good solvent of the dispersion liquid of the block copolymer is tetrahydrofuran, the poor solvent is acetone, and the volume ratio of the good solvent to the poor solvent is (0.5-5): 0.5-5);

(2) Adding the epoxy resin curing system into the dispersion liquid of the block copolymer, uniformly mixing, evaporating the solvent, reacting at 30-50 ℃ for 10-15h, reacting at 50-70 ℃ for 2-6h, curing, and annealing; the annealing conditions are as follows: annealing at 140-160 ℃ for 50-70min.

2. The composite material of claim 1, wherein the mass fraction of the block copolymer in the total raw material is 5% to 50%; the mass ratio of the epoxy resin to the curing agent is 10 (0.1-8).

3. The composite material of claim 1, wherein the good solvent and poor solvent are in a volume ratio of 1.

4. The composite material of claim 1, wherein the soluble dopant is present in an amount of 1 to 10%.

5. The composite material of claim 4, wherein the soluble dopant is present in an amount of 5%.

6. A method for preparing the composite material according to any one of claims 1 to 5, characterized by comprising the steps of:

(1) Self-assembling the block copolymer in a mixed solvent of a good solvent and a poor solvent to form a dispersion liquid of the nanofiber; the good solvent of the dispersion liquid of the block copolymer is tetrahydrofuran, the poor solvent is acetone, and the volume ratio of the good solvent to the poor solvent is (0.5-5): 0.5-5);

(2) Adding the epoxy resin curing system into the dispersion liquid of the block copolymer, uniformly mixing, evaporating the solvent, reacting at 30-50 ℃ for 10-15h, reacting at 50-70 ℃ for 2-6h, curing, and annealing; the annealing conditions are as follows: annealing at 140-160 ℃ for 50-70min;

the preparation method also comprises the step of soaking the material obtained in the step (2) in a solution containing a soluble dopant, processing at 30-50 ℃ for 20-40min, and drying.

7. The method according to claim 6, wherein the solvent of the solution containing the soluble dopant is acetonitrile, and the concentration of the soluble dopant is 20 to 65mg/mL.

8. Use of the composite material of any one of claims 1 to 5 in an electromagnetic shielding material.

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