CNTs / rGO / PI composite wave-absorbing foam with directional aperture structure and preparation method of CNTs / rGO / PI composite wave-absorbing foam

Abstract

The invention discloses CNTs / rGO / PI composite wave-absorbing foam with a directional aperture structure and a preparation method of the CNTs / rGO / PI composite wave-absorbing foam, and belongs to the technical field of wave-absorbing materials.Graphene oxide, carboxylated multi-walled carbon nanotubes and other raw materials are ultrasonically dispersed into prepared PAAs water and then ultrasonically stirred to be uniform, directional freezing is conducted, then freeze-drying treatment and thermal reduction treatment are conducted, and the CNTs / rGO / PI composite wave-absorbing foam with the directional aperture structure is obtained. The CNTs / rGO / PI composite wave-absorbing foam with the directional aperture structure is obtained by adding the directional aperture structure into the CNTs / rGO / PI composite wave-absorbing foam, the shape and the average internal diameter of the composite wave-absorbing foam are controllable, the density is as low as 0.002-1.2 g / cm < 3 >, the CNTs / rGO / PI composite wave-absorbing foam has an electromagnetic wave absorbing effect at 2-18GHz, the wave-absorbing bandwidth reaches 8.4 GHz when the thickness is 3.6 mm, and the whole Ku wave band and most X wave bands are covered by the CNTs / rGO / PI composite wave-absorbing foam. The composite foam is simple in preparation process, low in cost and suitable for large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave absorbing materials, and in particular to a CNTs / rGO / PI composite absorbing foam with a directional pore structure and a preparation method thereof. Background Art

[0002] With the change and progress of technology, the understanding of electromagnetic waves has become deeper and their applications have become more extensive. Radio waves are mainly used for communication; infrared rays are mainly used for infrared-guided missiles, thermal imagers, and remote control, etc.; visible light presents various colors in life and is the basis for all organisms to observe things; ultraviolet rays are used for disinfection in medicine, to verify the authenticity of banknotes, measure distances, and flaw detection in engineering in life; X-rays are used for CT scans, and gamma rays are used to cause atomic transitions to generate new rays, etc.; microwaves are mainly used in radar, aerospace, and 5G, etc. Due to their extensive applications in life and military, they have become a major research hotspot at present.

[0003] With the continuous in-depth research in the field of electromagnetic protection materials by researchers, the demand for various properties of microwave absorbing materials is also increasing. In order to adapt to the application prospects of miniaturization, lightweight, and flexibility of modern electronic and electrical equipment, there is an urgent need for lightweight and effective electromagnetic protection materials. An ideal electromagnetic absorption material should simultaneously have a thin thickness, a wide absorption bandwidth, a strong absorption intensity, and a light weight. In addition to the above, it should also have strong antioxidant, thermal stability, and mechanical stability to meet the needs of life and military. Therefore, it is crucial to select the correct matrix and absorbent for the absorbing material. Microwave absorbing materials are generally divided into ceramic microwave absorbing materials, carbon-based microwave absorbing materials, ferromagnetic microwave absorbing materials, and other types of microwave absorbing materials. Ferromagnetic microwave absorbing materials have the advantages of large amounts of raw materials, low cost, and simple manufacturing methods, but there are several recognized disadvantages, such as high density and poor temperature adaptability, which are not conducive to their practical applications. Ceramic absorbing materials can be used in high-temperature environments, but they still have obvious disadvantages, such as high density, which limits their development. Different from the above materials, carbon-based microwave absorbing materials naturally have advantages such as good dielectric constant, low density, and large specific surface area. Especially carbon-based foam materials, such as graphene foam and carbon nanotube foam, have extremely low weight and density close to air (1.2mg / cm 3), as well as excellent broadband microwave absorption performance. Due to its low density and good microwave absorption performance, it has become a popular research material. Moreover, it can be compounded with other absorbents in two-component or multi-component systems, and the material structure can be designed to improve impedance matching and enhance internal loss to obtain better microwave absorption performance. For example, Chinese patents CN110272719A and CN109573988A respectively disclose several carbon-based composite aerogel materials, but their shapes cannot be artificially controlled, and the fragile characteristics of carbon-based aerogels limit their development. Therefore, it is necessary to seek a flexible wave-absorbing aerogel material. Summary of the Invention

[0004] The object of the present invention is to provide a CNTs / rGO / PI composite wave-absorbing foam with a relatively wide effective absorption bandwidth and low absorption peaks, and to provide a method for preparing a graphene / multi-walled carbon nanotube composite wave-absorbing foam with a certain flexibility and oriented pore size, which has a simple process flow and low cost.

[0005] To achieve the above object, the present invention provides a method for preparing a CNTs / rGO / PI composite wave-absorbing foam with an oriented pore structure, comprising the following steps:

[0006] 1) After ultrasonic dispersing graphene oxide and carboxylated multi-walled carbon nanotubes in water, a mixed solution is obtained. The mixed solution is placed in a vacuum environment for static treatment to obtain a graphene oxide / carboxylated multi-walled carbon nanotube suspension A;

[0007] 2) 4,4'-Diaminodiphenyl ether is dissolved in dimethylacetamide solution, and an appropriate amount of pyromellitic dianhydride is added. After stirring evenly at low temperature, the molar ratio of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride is controlled. The obtained PAA solution is poured into deionized water so that PAA precipitates out in water;

[0008] 3) The PAA obtained in step 2) is dissolved in deionized water with the help of ethylenediamine to obtain solution B;

[0009] 4) The solution A and solution B obtained in steps 1) and 2) are mixed, and the suspension is subjected to directional freezing and freeze-drying treatments in sequence to obtain a CNTs / GO / PAA foam;

[0010] 5) The CNTs / GO / PAA foam obtained in step 4) is subjected to thermal reduction treatment to obtain a CNTs / rGO / PI composite wave-absorbing foam.

[0011] Preferably, in the above preparation method of the CNTs / rGO / PI composite absorbing foam with a directional pore structure, the mass ratio of carbon nanotubes to graphene oxide in step 1) is 50:0 to 0:50; among them, graphene oxide is prepared by the hummer method, and carbon nanotubes are conventional commercially available products; the concentration of graphene oxide and carbon nanotubes in the solution in step 1) is 5 mg / ml to 20 mg / ml; when freeze-drying, too little graphene oxide and carboxylated carbon nanotube solution is likely to cause shrinkage of the foam, while too much graphene oxide and carbon nanotube solution is difficult to be uniformly dispersed in the solution and is prone to rupture.

[0012] Preferably, in the above preparation method of the CNTs / rGO / PI composite absorbing foam with a directional pore structure, the molar ratio of water, 4,4'-diaminodiphenyl ether and pyromellitic dianhydride in step 2) is 100:99, and this molar ratio is the optimal ratio for the formation of PAA.

[0013] Preferably, in the above preparation method of the CNTs / rGO / PI composite absorbing foam with a directional pore structure, the concentration of the PAA solution in step 3) is lower than 35 mg / ml. Too high a concentration will make the density of the foam too high and make it prone to rupture.

[0014] Preferably, in the above preparation method of the CNTs / rGO / PI composite absorbing foam with a directional pore structure, the mixed suspension solution of solution A and solution B in step 4) is contained in a regular upward-opening container in the directional freezing device, and the refrigeration device is a high-thermal-conductivity planar bulk solid, such as aluminum, gold, copper, silver, 1070 aluminum alloy, 6063 aluminum alloy, H96 copper-zinc alloy, gold-silver alloy.

[0015] Preferably, in the above preparation method of the CNTs / rGO / PI composite absorbing foam with a directional pore structure, the thermal conductivity of the high-thermal-conductivity planar bulk solid is greater than 180 W / mK; the regular upward-opening container is a glassware, and polymer ware is likely to cause the foam to adhere to the wall.

[0016] Preferably, in the above preparation method of the CNTs / rGO / PI composite absorbing foam with a directional pore structure, the freeze-drying condition in step 4) is to dry for 24 to 96 h in an environment with a temperature below -20°C and a vacuum degree below 0.1 Pa.

[0017] Preferably, in the above preparation method of the CNTs / rGO / PI composite absorbing foam with a directional pore structure, the thermal reduction treatment process in step 5) is: heat treatment is carried out at a temperature of 150 to 500°C under a protective atmosphere.

[0018] A kind of CNTs / rGO / PI composite absorbing foam with a directional pore structure is obtained by the above preparation method.

[0019] Therefore, the present invention adopts the above-mentioned CNTs / rGO / PI composite absorbing foam with a directional pore structure and its preparation method to obtain a CNTs / rGO / PI composite absorbing foam that is light, flexible, has a directional pore structure, and has a relatively wide effective absorption bandwidth and low absorption peak, and provides a method for preparing a flexible CNTs / rGO / PI composite absorbing foam with a directional pore structure by using directional freezing and freeze-drying techniques. The present invention combines CNTs and rGO to form a CNTs / rGO / PI foam, with a density as low as 0.002 - 1.2 g / cm 3 , which has an electromagnetic wave absorption effect at 2 - 18 GHz, and the absorption bandwidth covers 9.6 GHz - 18 GHz (X-band to Ku-band), and the thickness is only 3.6 mm. The addition of CNTs improves the conductivity of the material and enhances the conductive loss; the heterointerface between rGO and CNTs generates a strong interfacial polarization effect, and the two cooperate to optimize the impedance matching, forming a multi-loss mechanism of "conductive loss + dielectric loss + interfacial polarization", significantly broadening the absorption bandwidth and enhancing the absorption intensity. The carbon-based foam itself has an extremely low density, and the composite structure further reduces the weight through the three-dimensional pore structure design. At the same time, the one-dimensional structure of CNTs is intertwined with the two-dimensional sheets of rGO, which can improve the fragility of a single rGO aerogel and enhance the flexibility of the material to meet the requirements of flexible applications. Through directional freezing and thermal reduction treatment, a porous interconnected structure is formed, increasing the multiple reflections and scattering of electromagnetic waves inside and extending the energy dissipation path; the reasonable ratio of composite components (CNTs / rGO) balances the dielectric constant and magnetic permeability, solving the impedance mismatch problem of single materials.

[0020] The technical solutions of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0021] Figure 1 It is the SEM image of CNTs / rGO / PI.

[0022] Figure 2 It is the SEM image of the directional freezing of CNTs / rGO / PI

[0023] Figure 3 It is the schematic diagram of the directional freezing of CNTs / rGO / PI.

[0024] Figure 4 It is the wave absorption performance of Comparative Example 1 CNTs / PI.

[0025] Figure 5 It is the wave absorption performance of Comparative Example 2 rGO / PI after heat treatment at 300 °C.

[0026] Figure 6 The microwave absorption performance of 3rGO / PI as a comparative example after heat treatment at 400 °C.

[0027] Figure 7 The microwave absorption performance diagram of CNTs / rGO / PI in Example 1. Detailed implementation mode

[0028] In order to better understand the above technical solutions, the following will combine the accompanying drawings of the specification and specific implementation modes to make a detailed description of the above technical solutions. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms of "a", "the" and "said" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. "Plurality" generally includes at least two.

[0030] It should also be noted that the term "comprises", "comprising" or any other variation thereof is intended to cover a non-exclusive inclusion, so that a commodity or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such commodity or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the commodity or device comprising the element.

[0031] The present invention provides a preparation method of a CNTs / rGO / PI composite microwave absorption foam with a directional pore structure, comprising the following steps:

[0032] 1) After ultrasonic dispersing graphene oxide and carboxylated multi-walled carbon nanotubes in water, a mixed solution is obtained, and the mixed solution is placed in a vacuum environment for static treatment to obtain a graphene oxide / carboxylated multi-walled carbon nanotube suspension A;

[0033] 2) Dissolve 4,4'-diaminodiphenyl ether in a dimethylacetamide solution, add an appropriate amount of pyromellitic dianhydride, stir evenly at a low temperature, control the molar ratio of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride, and pour the obtained PAA solution into deionized water so that PAA precipitates out in water;

[0034] 3) Dissolve the PAA obtained in step 2) in deionized water with the help of triethylamine to obtain solution B;

[0035] 4) mixing the solution A and the solution B obtained in step 1) and step 2), and sequentially subjecting the suspension to directional freezing and freeze drying to obtain CNTs / GO / PAA foam;

[0036] 5) subjecting the CNTs / GO / PAA foam obtained in step 4) to thermal reduction treatment to obtain a CNTs / rGO / PI composite microwave absorbing foam.

[0037] To further optimize the above technical solution, in step 1), the mass ratio of carbon nanotubes to graphene oxide is 50:0 to 0:50; wherein, graphene oxide is prepared by the Hummer method, and carbon nanotubes are conventional commercial products; in step 1), the concentration of graphene oxide and carbon nanotubes in the solution is 5 mg / ml to 20 mg / ml; during freeze drying, too little graphene oxide and carboxylated carbon nanotube solution is likely to cause shrinkage of the foam, while too much graphene oxide and carbon nanotube solution is difficult to be evenly dispersed in the solution and is likely to break.

[0038] To further optimize the above technical solution, the molar ratio of water 4,4'-diaminodiphenyl ether to pyromellitic anhydride in step 2) is 100:99, which is the optimal ratio for the generation of PAA.

[0039] To further optimize the above technical solution, the concentration of the PAA solution in step 3) is lower than 35 mg / ml. Too high a concentration will make the density of the foam too high, making it easy to break.

[0040] To further optimize the above technical solution, the mixed suspension solution of solution A and solution B in step 4) is contained in a regular upwardly open container in a directional freezing device, and the refrigeration device is a planar block solid with high thermal conductivity, such as aluminum, gold, copper, silver, 1070 aluminum alloy, 6063 aluminum alloy, H96 copper-zinc alloy, and gold-silver alloy.

[0041] To further optimize the above technical solution, the thermal conductivity of the high thermal conductivity planar block solid is greater than 180W / mK; the regular upwardly open container is a glass container, and polymer containers easily cause foam to stick to the wall.

[0042] To further optimize the above technical solution, the freeze-drying conditions in step 4) are drying for 24 to 96 hours in an environment with a temperature below -20°C and a vacuum degree below 0.1 Pa.

[0043] In order to further optimize the above technical solution, the thermal reduction treatment process in step 5) is: heat treatment at a temperature of 150 to 500° C. under a protective atmosphere.

[0044] A kind of CNTs / rGO / PI composite absorbing foam with a directional pore structure is obtained by the above preparation method.

[0045] In order to introduce in more detail a kind of CNTs / rGO / PI composite absorbing foam with a directional pore structure and its preparation method provided by the embodiments of the present invention, the following will be described in combination with specific embodiments.

[0046] Comparative Example 1

[0047] 1) After ultrasonic dispersing the raw materials including 20 mg of carboxylated multi-walled carbon nanotubes in 50 ml of water, a mixed solution is obtained. The mixed solution is placed in a vacuum environment for static treatment to obtain a carboxylated multi-walled carbon nanotube suspension A.

[0048] 2) 4,4'-Diaminodiphenyl ether is dissolved in dimethylacetamide solution, and a certain amount of pyromellitic dianhydride is added. It is stirred evenly at low temperature, and the molar ratio of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride is controlled. The obtained PAA solution is poured into deionized water, so that PAA precipitates out in water.

[0049] 3) 500 mg of the PAA obtained in step 2) is dissolved in 50 ml of deionized water with the help of ethylenediamine to obtain solution B.

[0050] 4) The solution A and solution B obtained in step 1) and step 2) are mixed, ultrasonicated for 30 minutes, stirred for 5 h, the suspension is poured into a petri dish, and the petri dish is placed on a copper plate at -80 °C for directional freezing, and then freeze-dried for 48 h to obtain CNTs / PAA foam.

[0051] 5) The CNTs / PAA foam obtained in step 4) is subjected to thermal reduction treatment at 300 °C with a heating rate of 5 °C / min in a nitrogen atmosphere to obtain CNTs / PI composite absorbing foam.

[0052] 6) The obtained CNTs / PI foam is made into a coaxial ring sample (the inner diameter of the coaxial ring sample is 3 mm and the outer diameter is 7 mm). The electromagnetic parameters of the sample are measured by a vector network analyzer, and then the absorbing performance of the material is calculated by CST STUDIO SUITE software. Figure 4 The absorbing performance diagram of the CNTs / PI composite absorbing foam at 1.7 mm is shown. It can be clearly seen that due to the small content of carbon nanotubes, the absorbing performance is poor.

[0053] Comparative Example 2

[0054] 1) After ultrasonic dispersing 500 mg of graphene oxide in 50 ml of water, a mixed solution is obtained. The mixed solution is placed in a vacuum environment for static treatment to obtain a carboxylated multi-walled carbon nanotube suspension A.

[0055] 2) Dissolve 4,4'-diaminodiphenyl ether in dimethylacetamide solution, add a certain amount of pyromellitic dianhydride, stir evenly at low temperature, control the molar ratio of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride, and pour the obtained PAA solution into deionized water to precipitate PAA in water.

[0056] 3) Dissolve 500 mg of the PAA obtained in step 2) in 50 ml of deionized water with the help of ethylenediamine to obtain solution B.

[0057] 4) Mix solution A and solution B obtained in step 1) and step 2), ultrasonicate for 30 minutes, stir for 5 h, pour the suspension into a petri dish, place the petri dish on a copper plate at -80 °C for directional freezing, and then perform freeze-drying treatment for 48 h to obtain rGO / PAA foam.

[0058] 5) Heat-treat the rGO / PAA foam obtained in step 4) at 300 °C with a heating rate of 5 °C / min in a nitrogen atmosphere to obtain rGO / PI composite wave-absorbing foam.

[0059] 7) Prepare the obtained rGO / PI foam into coaxial ring samples (the inner diameter of the coaxial ring samples is 3 mm and the outer diameter is 7 mm), measure the electromagnetic parameters of the samples by a vector network analyzer, and then calculate the wave-absorbing performance of the material by CST STUDIO SUITE software. Figure 5 The wave-absorbing performance diagram of the rGO / PI composite wave-absorbing foam at 4.7 mm is shown. It can be clearly seen that the wave-absorbing performance has been improved, but the bandwidth is relatively narrow.

[0060] Comparative Example 3

[0061] 1) After ultrasonic dispersing 500 mg of graphene oxide in 50 ml of water, a mixed solution is obtained. The mixed solution is placed in a vacuum environment for static treatment to obtain a carboxylated multi-walled carbon nanotube suspension A.

[0062] 2) Dissolve 4,4'-diaminodiphenyl ether in dimethylacetamide solution, add a certain amount of pyromellitic dianhydride, stir evenly at low temperature, control the molar ratio of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride, and pour the obtained PAA solution into deionized water to precipitate PAA in water.

[0063] 3) Dissolve 500 mg of the PAA obtained in step 2) in 50 ml of deionized water with the help of triethylenetetramine to obtain solution B.

[0064] 4) Mix solution A and solution B obtained in steps 1) and 2), ultrasonicate for 30 minutes, stir for 5 h, pour the suspension into a petri dish, place the petri dish on a copper plate at -80 °C for directional freezing, and then perform freeze-drying for 48 h to obtain rGO / PAA foam.

[0065] 5) Heat-treat the rGO / PAA foam obtained in step 4) at 400 °C with a heating rate of 5 °C / min in a nitrogen atmosphere to obtain rGO / PI composite wave-absorbing foam.

[0066] 6) Prepare the obtained rGO / PI foam into coaxial ring samples (the inner diameter of the coaxial ring samples is 3 mm and the outer diameter is 7 mm), measure the electromagnetic parameters of the samples by a vector network analyzer, and then calculate the wave-absorbing performance of the material through CST STUDIO SUITE software. Figure 6 The wave-absorbing performance diagram of the rGO / PI composite wave-absorbing foam at 5 mm is shown. It can be clearly seen that the wave-absorbing performance has been improved, but the bandwidth is relatively narrow.

[0067] Example 1

[0068] 1) After ultrasonically dispersing the raw materials including 500 mg of graphene oxide and 20 mg of carboxylated multi-walled carbon nanotubes in 50 ml of water, a mixed solution is obtained. Place the mixed solution in a vacuum environment for static treatment to obtain carboxylated multi-walled carbon nanotube suspension A.

[0069] 2) Dissolve 4,4'-diaminodiphenyl ether in a dimethylacetamide solution, add a certain amount of pyromellitic dianhydride, stir evenly at low temperature, control the molar ratio of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride, and pour the obtained PAA solution into deionized water to precipitate PAA in the water.

[0070] 3) Dissolve 500 mg of the PAA obtained in step 2) in 50 ml of deionized water with the help of triethylenetetramine to obtain solution B.

[0071] 4) Mix solution A and solution B obtained in steps 1) and 2), ultrasonicate for 30 minutes, stir for 5 h, pour the suspension into a petri dish, place the petri dish on a copper plate at -80 °C for directional freezing, and then perform freeze-drying for 48 h to obtain CNTs / rGO / PAA foam.

[0072] 5) The CNTs / rGO / PAA foam obtained in step 4) is subjected to thermal reduction treatment at 300° C. and a heating rate of 5° C. / min in a nitrogen atmosphere to obtain a CNTs / rGO / PI composite absorbing foam.

[0073] 6) The obtained CNTs / rGO / PI foam was prepared into a coaxial ring sample (the inner diameter of the coaxial ring sample was 3 mm and the outer diameter was 7 mm), the electromagnetic parameters of the sample were measured by a vector network analyzer, and then the wave absorption performance of the material was calculated by CSTSTUDIOSUITE software. Figure 7 The wave absorption performance diagram of CNTs / rGO / PI foam at 3.6mm is shown. It can be clearly seen that the bandwidth is from 9.6GHz to 18GHz, and the wave absorption performance is excellent. This is because the addition of carbon nanotubes not only improves the conductivity of the foam, but also strengthens the interface polarization effect, thereby obtaining better wave absorption performance.

[0074] As can be seen from the above, in Comparative Example 1, only 20 mg of carboxylated multi-walled carbon nanotubes were used. Due to the low content of carbon nanotubes, the conductivity and interface polarization effect of the material were weak, resulting in insufficient absorption intensity ( Figure 4 The absorption performance is poor). A single carbon nanotube material needs to have a sufficient content to effectively improve the absorption performance, but it is easily limited by the dispersion and content ratio when used alone.

[0075] In Comparative Examples 2 and 3, 500 mg of graphene oxide was used. Although the wave absorption performance was improved by thermal reduction treatment (300°C, 400°C), the wave absorption bandwidth was narrow ( Figure 5 , Figure 6 Although a single rGO material has a certain dielectric loss capacity, it lacks multiple loss mechanisms (such as conductive loss and interfacial polarization synergy), resulting in insufficient bandwidth and difficulty in meeting broadband absorption requirements.

[0076] The present invention adopts the above-mentioned CNTs / rGO / PI composite absorbing foam with directional pore structure and its preparation method to compound CNTs and rGO to form CNTs / rGO / PI foam with a density as low as 0.002-1.2 g / cm 3 , has electromagnetic wave absorption effect in 2-18GHz, and the absorption bandwidth covers 9.6GHz-18GHz (X band to Ku band), and the thickness is only 3.6mm. The addition of CNTs improves the conductivity of the material and enhances the conductive loss; the heterogeneous interface of rGO and CNTs produces a strong interface polarization effect, and the two synergistically optimize the impedance matching, forming a multi-loss mechanism of "conductive loss + dielectric loss + interface polarization", which significantly broadens the absorption bandwidth and improves the absorption intensity.

[0077] The carbon-based foam itself has an extremely low density. The composite structure further reduces the weight through the three-dimensional pore structure design. At the same time, the one-dimensional structure of CNTs is intertwined with the two-dimensional sheets of rGO, which can improve the fragility of the single rGO aerogel and enhance the flexibility of the material to meet the requirements of flexible applications.

[0078] Through directional freezing and thermal reduction treatments, a porous interconnected structure is formed, increasing the multiple reflections and scattering of electromagnetic waves inside and extending the energy dissipation path. The reasonable ratio of composite components (CNTs / rGO) balances the dielectric constant and magnetic permeability, solving the impedance mismatch problem of single materials.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of CNTs / rGO / PI composite absorbing foam with a directional pore structure, characterized in that, Including the following steps: 1) After ultrasonic dispersing graphene oxide and carboxylated multi-walled carbon nanotubes in water, a mixed solution is obtained, and the mixed solution is placed in a vacuum environment for static treatment to obtain a graphene oxide / carboxylated multi-walled carbon nanotube suspension A; 2) 4,4'-Diaminodiphenyl ether is dissolved in N,N-dimethylacetamide solution, an appropriate amount of pyromellitic dianhydride is added, and the mixture is stirred evenly at low temperature. The molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is controlled. The obtained PAA solution is poured into deionized water so that PAA precipitates out in water; 3) The PAA obtained in step 2) is dissolved in deionized water with the help of ethylenediamine to obtain solution B; 4) The solution A and solution B obtained in step 1) and step 2) are mixed, and the suspension is subjected to directional freezing and freeze-drying treatments in sequence to obtain CNTs / GO / PAA foam; 5) The CNTs / GO / PAA foam obtained in step 4) is subjected to thermal reduction treatment to obtain a CNTs / rGO / PI composite microwave absorption foam.

2. The preparation method of a CNTs / rGO / PI composite absorbing foam with a directional pore structure according to claim 1, characterized in that, In step 1), the mass ratio of carbon nanotubes to graphene oxide is 50:0 to 0:50; the concentration of graphene oxide and carbon nanotubes in the solution in step 1) is 5 mg / ml to 20 mg / ml.

3. The preparation method of a CNTs / rGO / PI composite absorbing foam with a directional pore structure according to claim 1, characterized in that, In step 2), the molar ratio of water, 4,4'-diaminodiphenyl ether and pyromellitic dianhydride is 100:

99.

4. The preparation method of a CNTs / rGO / PI composite absorbing foam with a directional pore structure according to claim 1, characterized in that, In step 3), the concentration of the PAA solution is lower than 35 mg / ml.

5. The preparation method of a CNTs / rGO / PI composite absorbing foam with a directional pore structure according to claim 1, characterized in that, In step 4), the mixed suspension solution of solution A and solution B is filled in a regular upward-open container in the directional freezing device, and the refrigeration device is a high-thermal conductivity planar block solid.

6. The preparation method of a CNTs / rGO / PI composite absorbing foam with a directional pore structure according to claim 5, characterized in that, The thermal conductivity of the high-thermal conductivity planar block solid is greater than 180 W / mK; the regular upward-open container is a glassware.

7. The preparation method of a CNTs / rGO / PI composite absorbing foam with a directional pore structure according to claim 1, characterized in that, In step 4), the freeze-drying conditions are drying for 24 to 96 h in an environment with a temperature below -20 °C and a vacuum degree below 0.1 Pa.

8. The preparation method of a CNTs / rGO / PI composite absorbing foam with a directional pore structure according to claim 1, characterized in that, In step 5), the thermal reduction treatment process is: under a protective atmosphere, heat treatment is carried out at a temperature of 150 to 500 °C.

9. A CNTs / rGO / PI composite absorbing foam obtained by the preparation method according to any one of claims 1 to 8, characterized in that, It has a directional pore structure.

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