CN113845751A

CN113845751A - Epoxy resin-based electromagnetic shielding composite material and preparation method and application thereof

Info

Publication number: CN113845751A
Application number: CN202111126249.3A
Authority: CN
Inventors: 邹华维; 张浩若; 衡正光; 陈洋
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2021-09-24
Filing date: 2021-09-24
Publication date: 2021-12-28
Anticipated expiration: 2041-09-24
Also published as: CN113845751B

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

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

Technical Field

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

Background

With the development of communication electronic technology, electronic devices are widely applied in various fields such as entertainment and communication, the size of the electronic devices is smaller and the number of the electronic devices is larger, and a large amount of electromagnetic radiation generated in a limited space can cause electromagnetic interference between the devices, cause device failure and aging of electronic components, and also affect human health and the surrounding environment. Therefore, measures are required to reduce the harm of electromagnetic interference. At present, the main approach to eliminate the electromagnetic interference hazard is to shield it with electromagnetic shielding material.

The traditional electromagnetic shielding material is mainly a metal material and has excellent electromagnetic wave reflection capability, but the metal density is high, the cost is high, and the mechanism of reflection shielding is likely to cause secondary reflection pollution of electromagnetic waves. The novel polymer-based electromagnetic shielding composite material has good application prospect due to light weight, excellent corrosion resistance, easy processing and manufacture and the like.

Epoxy resin has excellent mechanical properties, adhesive strength, good electrical insulation, thermal stability, high solvent resistance, and is easy to process, and thus, composite electromagnetic shielding composite materials modified by using epoxy resin as a matrix are widely used. At present, a common modification means is to add a conductive material into epoxy resin, so that the epoxy resin has electromagnetic shielding performance. However, at present, the commonly used conductive fillers such as metal, carbon nanotube and the like are often dispersed in the epoxy resin matrix, so that an ideal conductive transmission network structure is difficult to form, and the conductive performance and the electromagnetic shielding effect of the composite material are limited.

The self-assembly behavior of amorphous Block Copolymer (BCP) in solution is an effective method for constructing high-precision functional nano-scale objects, especially when the BCP contains a crystalline block, the BCP can form a low-dimensional structure such as a rod micelle, and can even spontaneously extend and grow to form nano-fibers in a selective solvent. The poly-3-hexylthiophene (P3HT) has high hole mobility and is one of the most widely studied semiconductor polymers, and if the characteristics of BCP and the advantages of P3HT can be utilized to construct BCP with a P3HT block, so that stacked one-dimensional nanofibers are constructed in an epoxy resin matrix to form a nanofiber network structure with conductivity, excellent conductivity and electromagnetic shielding effect can be expected to be realized with a low filler addition amount. However, on the one hand, the high mobility of P3HT is largely due to its property of forming compact crystalline regions, and on the other hand, the behavior of BCP containing P3HT block self-assembling to form nanofibers is influenced by various factors, which when compounded, can result in grain boundaries and defects in the composite material, hinder charge transport, affect conductivity, even destroy nanofiber morphology, and result in failure to form a desired nanofiber network structure.

Therefore, how to effectively control the form of the nanofibers to prepare the epoxy resin-based composite material with the nanofiber network structure can obtain excellent conductivity and electromagnetic shielding performance under the condition of low addition of the conductive filler, and further research is still needed.

Disclosure of Invention

The invention aims to provide an epoxy resin-based electromagnetic shielding composite material with a conductive network structure formed by nano fibers.

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

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

more preferably, the diblock copolymer containing the poly-3-hexylthiophene block 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) to 1, preferably (0.6-3) to 1; or the mass ratio of the poly-3-hexylthiophene to the polycaprolactone block is 1: 1.

Further, the composite material is prepared from the following raw materials: a block copolymer, an epoxy resin and a curing agent; the mass fraction of the block copolymer in the total raw materials is 5-50%, preferably 25%; 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 of the epoxy resin to the curing agent is 1-2: 1.

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

Furthermore, the nano-fiber structure is formed by self-assembly of a block copolymer, and then is uniformly mixed with epoxy resin and a curing agent and is cured;

preferably, the nanofiber 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 is (0.5-5) to (0.5-5), and the preferable ratio is 1: 1.

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

Further, the soluble dopant is copper trifluoromethanesulfonate, tetrafluoro-tetracyanoterephthalylene or lithium bistrifluoromethanesulfonylimide, and is preferably copper trifluoromethanesulfonate.

Furthermore, the composite material containing the soluble dopant is obtained by self-assembling the block copolymer to form a nanofiber structure, uniformly mixing the nanofiber structure with epoxy resin and a curing agent, curing the mixture, and soaking the mixture in a solution containing the soluble dopant. Preferably, the nanofiber 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; the volume ratio of the good solvent to the poor solvent is (0.5-5) to (0.5-5), and the preferable ratio is 1: 1.

The invention also provides a preparation method of the composite material, which 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;

(2) adding an epoxy resin curing system into a dispersion liquid of a block copolymer, uniformly mixing, evaporating a solvent, reacting at 30-50 ℃ for 10-15 h, reacting at 50-70 ℃ for 2-6 h, curing, and annealing;

preferably, the good solvent of the dispersion liquid of the block copolymer in the step (1) is tetrahydrofuran or chloroform, the poor solvent is acetone or anisole, and the volume ratio of the good solvent to the poor solvent is (0.5-5): (0.5-5), more preferably 1: 1; the annealing conditions in the step (2) are as follows: annealing at 140-160 deg.C for 50-70 min.

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

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 invention also provides the application of the composite material in an electromagnetic shielding material.

The invention has the beneficial effects that: according to the invention, the nano fibrous conductive polymer structure is formed by self-assembling the block copolymer in the solution, and then the nano fibrous conductive polymer structure is compounded into the epoxy resin matrix to prepare the composite material, so that a network conductive fiber structure is formed in the epoxy resin matrix, and the improvement of the conductive performance is facilitated. The composite material is further soaked in a dopant solution, high conductivity and high electromagnetic shielding performance are realized, the conductivity is as high as 1.94S/m, the electromagnetic shielding efficiency of the composite material with the thickness of 1.1mm is averagely as high as 23.8dB under the condition that the P3HT-b-PCL is only 25 wt% (namely the addition of the conductive filler P3HT is only 12.5 wt%), 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 a very good application value in the field of electromagnetic shielding materials.

The soluble dopant is a dopant with solubility greater than 1mg/mL in water or organic.

The term "nanofiber" as used herein means a one-dimensional structure having no limitation in the longitudinal direction, but limited to 100 nm or less in the transverse direction.

The 'network structure' and 'conductive network structure' described in the invention refer to: the nano-fibers with certain length in the longitudinal direction form a three-dimensional structure with nodes through staggering and overlapping, and one or more nano-fibers are connected between every two nodes.

Obviously, many modifications, substitutions, and variations are possible in light of the above teachings of the invention, without departing from the basic technical spirit of the invention, as defined by the following claims.

The present invention will be described in further detail with reference to the following examples. This should not be understood as limiting the scope of the above-described subject matter of the present invention to the following examples. All the technologies realized based on the above contents of the present invention belong to the scope of the present invention.

Drawings

FIG. 1 shows the NMR spectrum of P3 HT-b-PCL.

FIG. 2 shows the results of the thermogravimetric test of P3 HT-b-PCL.

FIG. 3 is an optical photograph and principle (a-c) and microstructure characterization (d, e') of P3HT-b-PCL nanofiber preparation by crystallization-driven self-assembly (CDSA).

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

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

FIG. 6 shows the bending properties (a) of doped nanofiber composites of the present invention; the mechanical property characterization of the nanofiber composite material with different contents before and after doping (b), and the influence of the concentration of copper trifluoromethanesulfonate and the content of the segmented copolymer nanofiber on the direct-current conductivity of the composite film (c).

FIG. 7 shows the electromagnetic shielding performance (a) and the electromagnetic wave absorption coefficient (b) of the composite film doped with 25 wt% of the block copolymer nanofiber, the power coefficient (c) of the absorption coefficient and the reflection coefficient, and the effect (d-f) of different preparation methods (comparative example 1(without CDSA), comparative example 2(without CDSA-processed), comparative example 3(CDSA), example 1 (CDSA-analyzed), and example 4 (CDSA-analyzed-processed)) on the dielectric performance of the composite film.

Fig. 8 is a scanning electron microscope characterization of a sample mixed and instilled as a thin film without crystallization-driven self-assembly by directly adding all components to chloroform.

Detailed Description

The poly 3-hexylthiophene-polycaprolactone diblock copolymer (P3HT-b-PCL) used in the examples of the present invention was either a commercially available product purchased or was prepared by chemical synthesis by one skilled in the art using known knowledge and experimental means via the following reaction route:

(1)2, 5-dibromo-3-hexylthiophene reacts with a tert-butyl magnesium chloride solution, and a catalyst Ni (dppp) Cl is added₂Then adding a vinyl magnesium bromide solution for reaction to obtain vinyl-terminated 3-hexylthiophene (P3 HT-vin):

(2) p3HT-vin and 9-borabicyclo [3.3.1 ]]Nonane (9-BBN) was reacted with NaOH, 30% H in that order₂O₂The solution is acted to prepare the hydroxyl-terminated poly 3-hexylthiophene (P3 HT-OH).

(3) Catalysis with P3HT-OHAgent Sn (Oct)₂Initiating an epsilon-caprolactone (epsilon-CL) ring-opening reaction under the action of the (P3) and the epsilon-caprolactone (epsilon-CL) to prepare the diblock copolymer of the P3HT and the PCL, wherein the mass ratio of the P3HT-OH to the epsilon-caprolactone (epsilon-CL) is 1: the relative molecular mass ratio of P3HT and PCL block of P3HT-b-PCL is (0.5-4) to 1, preferably (0.6-3) to 1.

The chemical structures of the synthesized intermediate and P3HT-b-PCL were confirmed by 1H NMR spectroscopy, and as shown in FIG. 1, the polymerization Degrees (DP) of P3HT and PCL blocks were determined to be 27 and 41, respectively, and the relative molecular masses of P3HT and PCL repeating units were 148 and 114, respectively, which were calculated to give a mass ratio of 1: 1. The polymers prepared were also characterized by thermogravimetric analysis (TGA) and the results (figure 2) showed that the maximum weight loss temperatures of PCL and P3HT blocks were determined to be 307 and 473 ℃ with the same mass of weight loss in the two stages being 1: 1. The synthesis of P3HT-b-PCL gave very high yields (95.8%), so the results of 1HNMR and TGA were consistent with a 1:1 synthetic feed ratio. That is, the content of the conductive filler P3HT in the finally prepared P3HT-b-PCL is 50%, namely, when the addition amount of the P3HT-b-PCL in the composite material is 25 wt%, the addition amount of the conductive filler P3HT is only 12.5 wt%.

Example 1 preparation of P3 HT-b-PCL/epoxy resin composite Material of the invention

1. Preparation of P3HT-b-PCL nanofiber Dispersion (Crystal driven self-Assembly CDSA)

First, 10 mg of a dried powder of P3HT-b-PCL and 5 ml of tetrahydrofuran were added to a 10 ml vial, sufficiently 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 mixture was allowed to mature at room temperature for 48 hours and then shaken for 5 minutes to obtain a stable and homogeneous dispersion.

2. Preparation of P3 HT-b-PCL/epoxy resin composite film

An epoxy resin curing system (mass ratio of E51 and D-230: 10: 3, ensuring that the molar ratio of the epoxy resin E51 to the reactive groups on the curing agent D-230 is 1: 1) was added to the micellar dispersion of P3HT-b-PCL, with the mass ratio of P3HT-b-PCL to the epoxy resin curing system being 1: 3(P3HT-b-PCL content 25 wt%), and mixed thoroughly by shaking. The mixture was then drop cast onto different substrates to obtain coatings of different thicknesses. After complete evaporation of the solvent, the epoxy system curing reaction was carried out in a blast furnace at 40 ℃ for 12 hours plus 60 ℃ for 4 hours, and finally, while ensuring complete curing, thermal annealing was carried out by raising the temperature to 150 ℃ and maintaining it for 1 hour. The membrane material was obtained by peeling from the teflon substrate.

Example 2 preparation of P3 HT-b-PCL/epoxy resin composite Material of the 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, and the composite material with the P3HT-b-PCL content of 5 wt% is prepared.

Example 3 preparation of P3 HT-b-PCL/epoxy resin composite Material of the 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, and the composite material with the P3HT-b-PCL content of 15 wt% is prepared.

Example 4 preparation of doped P3 HT-b-PCL/epoxy composite Material of the invention

The membrane material prepared in example 1 was immersed in 65mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 5 preparation of doped P3 HT-b-PCL/epoxy composite according to the invention

The membrane material prepared in example 1 was immersed in 20mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 6 preparation of doped P3 HT-b-PCL/epoxy composite Material of the invention

The film material obtained in example 1 was usedThe batch was immersed in 35mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 7 preparation of doped P3 HT-b-PCL/epoxy composite according to the invention

The membrane material prepared in example 1 was immersed in 50mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 8 preparation of doped P3 HT-b-PCL/epoxy composite according to the invention

The membrane material prepared in example 2 was immersed in a 65mg/mL acetonitrile solution of copper trifluoromethanesulfonate (Cu (OTf)2) and held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 9 preparation of doped P3 HT-b-PCL/epoxy composite according to the invention

The membrane material prepared in example 2 was immersed in 20mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 10 preparation of doped P3 HT-b-PCL/epoxy composite Material of the invention

The membrane material prepared in example 2 was immersed in a 35mg/mL acetonitrile solution of copper trifluoromethanesulfonate (Cu (OTf)2) and maintained at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 11 preparation of a doped P3 HT-b-PCL/epoxy composite according to the invention

The membrane material prepared in example 2 was immersed in 50mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 12 preparation of doped P3 HT-b-PCL/epoxy composite according to the invention

The membrane material prepared in example 3 was immersed in 65mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 13 preparation of a doped P3 HT-b-PCL/epoxy composite according to the invention

The membrane material prepared in example 3 was immersed in 20mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 14 preparation of a doped P3 HT-b-PCL/epoxy composite according to the invention

The membrane material prepared in example 3 was immersed in 35mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Example 15 preparation of doped P3 HT-b-PCL/epoxy composite Material of the invention

The membrane material prepared in example 3 was immersed in 50mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Comparative example 1: preparation of P3HT-b-PCL nanofiber solution: first, 10 mg of a dried powder of P3HT-b-PCL and 10 ml of tetrahydrofuran were added to a 10 ml vial, sufficiently dissolved by slight heating, and then cooled to room temperature to obtain a solution. The remaining steps refer to example 1, and a composite material is prepared.

Comparative example 2: the composite material obtained in comparative example 1 was immersed in 65mg/mL of copper trifluoromethanesulfonate (Cu (OTf)₂) And held at 40 ℃ for 30 minutes. The film was then removed from the solution and dried thoroughly in a forced air oven at 40 ℃.

Comparative example 3: referring to the method of example 1, a composite material was obtained without annealing treatment after curing.

The beneficial effects of the present invention are demonstrated by the following experimental examples.

Experimental example 1, characterization of P3HT-b-PCL Crystal-driven self-Assembly into nanofiber Structure

The procedure described in step 1 of example 1 was followed: 10 mg of a dried powder of P3HT-b-PCL and 5 ml of tetrahydrofuran were added to a 10 ml vial, sufficiently 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, and the morphology of the product in the resulting solution changed with time as shown in FIG. 3a, and it can be seen that the solution gradually changed from orange to purple with the continuous diffusion of the solvent, which is characteristic of micelle formation with crystalline P3HT nuclei. The diffusion diagram is shown in fig. 3 b. After completion of the diffusion crystallization, the whole system was in a steady state at room temperature (fig. 3 c). As can be seen from the observation results of the atomic force microscope (FIG. 3D) and the scanning electron microscope (FIGS. 3e and 3 e'), the P3HT-b-PCL of the present invention forms a nanofiber structure, and forms a staggered and overlapped structure, so that a large 3D nanofiber network can be constructed. Accordingly, the product prepared in comparative example 1 cannot form a nanofiber network structure, but forms an island structure, which is not favorable for improving the electrical conductivity (fig. 8).

Further, the state of the dispersion of P3HT-b-PCL and epoxy resin curing system uniformly mixed according to step 2 in example 1 is shown in FIG. 4a, and the morphology of the cured composite film is shown in FIG. 4 b. The invention successfully prepares the composite film of P3HT-b-PCL and epoxy resin.

The scanning electron microscope observation of the product obtained in example 4 gave the results shown in FIG. 4 c.

As can be seen from the figure, the composite material prepared by the invention has an obvious fibrous network structure, which shows that the P3HT-b-PCL is further doped after being compounded with the epoxy resin, and the nanofiber structure of the PCL is not obviously damaged, and the conductive network structure formed in the composite plays a key role in the conductive performance and the electromagnetic shielding performance of the material.

Experimental example 2 doping of copper trifluoromethanesulfonate

The structure and the solution form of the copper trifluoromethanesulfonate are shown in fig. 5a, the state change of the P3 HT-b-PCL/epoxy resin composite film before and after soaking in the copper trifluoromethanesulfonate solution is shown in fig. 5b, and the doping action mechanism of the copper trifluoromethanesulfonate and the P3HT is shown in fig. 5 c.

The composite material obtained in example 4 was subjected to X-ray photoelectron spectroscopy (XPS) experiments, and the results are shown in FIGS. 5d to 5g, and in combination with the results of X-ray spectroscopy (EDS) tests on the material interface (FIG. 5h), it was confirmed that Cu (OTf)₂The acetonitrile solution can effectively permeate into the composite membrane and be well doped into a P3 HT-b-PCL/epoxy resin composite matrix, and the conductivity is improved.

Experimental example 3 characterization of the Properties of the composite Material of the invention

The composite material of example 4 of the present invention was bent and as can be seen from fig. 6a, the material exhibited very excellent toughness. Further, mechanical property tests of examples 1 and 3 (before doping), examples 4 and 12 (after doping) show that after doping, although the mechanical strength of the material is reduced, the elongation at break is increased, and the toughness of the material is still maintained at an excellent level (fig. 6 b).

The results of conducting the electrical conductivity tests on the composites of examples 4-15 are shown in fig. 6 c. As can be seen, Cu (OTf)₂The concentration of (A) has little influence on the conductivity of the material, and the material can basically reach saturation after being soaked for 30min at the concentration of 65 mg/mL. And with the increase of the addition amount of P3HT-b-PCL, the conductivity of the composite material is improved, and the highest conductivity can reach 1.94S/m. In contrast, the composite thin film without a nanofiber structure (comparative example 1) did not have conductivity even after doping.

The electromagnetic shielding performance and dielectric constant were further developed and the results are shown in FIGS. 7a-7 b. The total electromagnetic Shielding Effect (SET) of the doped composite film containing 25 wt% of the nanofiber structure P3HT-b-PCL in the X wave band (8.2-12.4GHz) is increased along with the increase of the thickness, and the average value of 23.8dB is obtained in the X wave band with the thickness of 1.1 mm. Since the content of P3HT in the block copolymer is 50%, the above-mentioned performance is realized when the content of the block copolymer in the composite film is 12.5 wt%, which is the best performance of the conductive polymer/epoxy resin composite system reported at present and is superior to most of the carbon nano-material/epoxy composite system containing equivalent filler content. Compared with the electromagnetic shielding material of the epoxy resin matrix reported in various documents at present, the electromagnetic shielding material of the invention achieves very excellent electromagnetic shielding effect under the condition of low addition amount of the conductive filler and the thickness of only 1.1 mm. As shown in table 1.

TABLE 1 comparison of electromagnetic shielding performance with epoxy resin-based electromagnetic shielding materials reported in the prior art

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also, when an electromagnetic wave reaches the surface of a shielding material, there are three shielding mechanisms, i.e., reflection (SER), absorption (SEA), and multiple reflection (SEM), which can be ignored when SET is greater than 15 dB. Fig. 7b shows the SER and SEA contributions to SET at different thicknesses. In all cases, the value of SEA is dominant, while SER is less than 2 dB. To further clarify the EMI shielding mechanism of the composite film, power coefficients of the corresponding absorption coefficient (a) and reflection coefficient (R) were calculated from the S-parameters, which are used to represent the ability of the shielding material to absorb, reflect and transmit microwaves, and to evaluate the power balance of microwave and aerogel interactions, it can be seen from fig. 7c that the composite film containing doped nanofibers has a high absorption coefficient a, greater than 0.7. Meanwhile, R and a show gradual increase and decrease, respectively. And A is always greater than R, consistent with the results for EMI SE (SEA > SER). Therefore, the main shielding mechanism of the CDSA nanofiber composite membrane is absorption, so that secondary pollution caused by large-scale reflection of electromagnetic waves can be avoided.

Further, as can be seen from the dielectric property test results of fig. 7d-7f, when the conductive polymer in the composite film has no nanofiber structure and is not doped (comparative example 1) or has a nanofiber structure and is not doped (comparative example 3 and example 1), the dielectric property is poor, and the requirements of conductivity and electromagnetic shielding are difficult to achieve. However, the composite material with the nanofiber network structure of the present invention (example 1) can provide a basis for further doping, significantly improving conductivity and dielectric properties. Although the dielectric properties of the composite materials (example 4 and comparative example 3) doped with copper trifluoromethanesulfonate are improved, the dielectric properties of the composite material (example 4) with the nanofiber conductive network structure obtained by further doping on the basis of the nanofiber network structure prepared in example 1 show very remarkable advantages, and the composite material is a material with excellent conductivity and excellent electromagnetic shielding performance.

In conclusion, the segmented copolymer is self-assembled in the solution to form the nano-fiber-shaped conductive polymer structure, and then the nano-fiber-shaped conductive polymer structure is compounded into the epoxy resin matrix to prepare the composite material, the network-shaped nano-fiber structure is formed in the epoxy resin matrix, and compared with epoxy resin materials compounded by other conductive fillers, the prepared epoxy resin-based composite material with the conductive network structure formed by the nano-fibers has very excellent conductive performance and electromagnetic shielding capability under the condition of low filler addition amount due to the continuous conductive network, the conductivity is as high as 1.94S/m, the electromagnetic shielding efficiency is as high as 23.8dB, the main shielding mechanism is absorption, secondary pollution caused by large reflection of electromagnetic waves can be avoided, and the application prospect in the field of electromagnetic shielding materials is very excellent.

Claims

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.

2. The composite material of claim 1, wherein the block copolymer is a block copolymer comprising conjugated segments; preferably, the block copolymer is a diblock copolymer containing a block of poly-3-hexylthiophene;

more preferably, the diblock copolymer containing the poly-3-hexylthiophene block 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.

3. The composite material according to claim 1 or 2, characterized in that it is made of the following raw materials: a block copolymer, an epoxy resin and a curing agent; the mass fraction of the segmented copolymer in the total raw materials is 5-50%; the mass ratio of the epoxy resin to the curing agent is 10 (0.1-8).

4. The composite material of claim 3, wherein the nanofiber structure is formed by self-assembly of the block copolymer, and then the nanofiber structure is uniformly mixed with epoxy resin and a curing agent and cured;

preferably, the nanofiber 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 is (0.5-5): (0.5-5), preferably 1: 1.

5. The composite material according to claim 1 or 2, further comprising a soluble dopant, wherein the content of the soluble dopant is 1 to 10%, preferably 5%.

6. Composite material according to claim 5, characterized in that the soluble dopant is copper triflate, tetrafluoro-tetracyanoterephthal-ane or lithium bistrifluoromethanesulfonylimide, preferably copper triflate.

7. The composite material of claim 5, wherein the nanofiber structure is formed by self-assembly of the block copolymer, then the nanofiber structure is uniformly mixed with epoxy resin and curing agent and cured, and then the mixture is soaked in a solution containing soluble dopant.

8. A method for preparing a composite material according to any one of claims 1 to 7, comprising the steps of:

preferably, the good solvent of the dispersion liquid of the block copolymer in the step (1) is tetrahydrofuran or chloroform, the poor solvent is acetone or anisole, and the volume ratio of the good solvent to the poor solvent is (0.5-5): (0.5-5); the annealing conditions in the step (2) are as follows: annealing at 140-160 deg.C for 50-70 min.

9. The preparation method according to claim 8, further comprising the steps of soaking the material obtained in the step (2) in a solution containing a soluble dopant, treating at 30-50 ℃ for 20-40 min, and drying;

10. Use of the composite material of any one of claims 1 to 7 in an electromagnetic shielding material.