Three-dimensional ordered macroporous structure electromagnetic wave-absorbing material and preparation method thereof

Abstract

The invention discloses a three-dimensional ordered macroporous structure electromagnetic wave-absorbing material and a preparation method thereof, the material comprises a carbon material, the material structure presents a three-dimensional ordered porous structure, and the aperture is 490-505 nm; the method comprises the following steps: step 1, preparing a three-dimensional ordered polymethyl methacrylate (PMMA) template; step 2, preparing the electromagnetic wave-absorbing material with the three-dimensional ordered macroporous structure; the electromagnetic wave-absorbing material has the advantages of being simple to prepare, high in dielectric loss capacity, high in reflection loss and wide in effective absorption bandwidth; the problem that conductive current generated in an alternating electromagnetic field environment is limited by a skin effect due to the fact that the conductivity of a carbon material is too high is solved. The higher the electric conductivity is, the smaller the skin depth is, and the reflection of the material to incident electromagnetic waves is enhanced, so that poor impedance matching is caused, the improvement of the electromagnetic wave absorption performance of the material is not facilitated, and the development of the carbon material is greatly limited.

Description

Technical Field

[0001] The present invention belongs to the field of materials, and particularly relates to a three-dimensional ordered macroporous structure electromagnetic wave absorbing material and a preparation method thereof. Background Art

[0002] Electromagnetic waves have been widely applied in fields such as communication and electronic devices due to their ability to acquire, transmit, process, and store information, greatly improving the quality of human life and social benefits. However, the accompanying electromagnetic pollution has become an urgent problem to be solved. Nevertheless, electromagnetic wave absorbing materials that can convert incident electromagnetic energy into other forms of energy such as heat energy have gradually attracted the attention of researchers. An excellent electromagnetic wave absorbing material should have characteristics such as a wide effective absorption bandwidth, strong absorption intensity, thin coating thickness, and light weight. In order to find an absorbing material with perfect performance, in the past few decades, researchers have conducted extensive research on materials such as carbon materials, ferrites, and metal alloys in an electromagnetic field environment.

[0003] Traditional electromagnetic wave absorbing materials, such as magnetic materials like ferrites and metal alloys, although having strong magnetic loss capabilities, are not suitable for large-scale commercial applications due to disadvantages such as high weight, high density, low chemical stability, narrow absorption bandwidth, and poor corrosion resistance of metal particles. However, carbon materials, due to advantages such as low density, good conductivity, light weight, and strong loss capabilities, are considered the most promising absorbing materials and have become a research hotspot in the field of absorbing materials. However, due to the too high conductivity of carbon materials, the conduction current generated in an alternating electromagnetic field environment will be restricted by the "skin effect". The higher the conductivity, the smaller the skin depth, the stronger the reflection of the incident electromagnetic wave by the material, resulting in poor impedance matching, which is not conducive to improving the electromagnetic wave absorption performance of the material and greatly limits the development of carbon materials. Summary of the Invention

[0004] The technical problems to be solved by the present invention are: to provide a three-dimensional ordered macroporous structure electromagnetic wave absorbing material and a preparation method thereof to solve the problems that the conductivity of carbon materials is too high, and the conduction current generated in an alternating electromagnetic field environment will be restricted by the "skin effect". The higher the conductivity, the smaller the skin depth, the stronger the reflection of the incident electromagnetic wave by the material, resulting in poor impedance matching, which is not conducive to improving the electromagnetic wave absorption performance of the material and greatly limits the development of carbon materials.

[0005] The technical solution of the present invention is:

[0006] A three-dimensional ordered macroporous structure electromagnetic wave absorbing material, the material composition includes a carbon material, and the material structure presents a three-dimensional ordered porous structure with a pore diameter of 490 - 505 nm.

[0007] Preparation method of electromagnetic wave absorbing material with three-dimensional ordered macroporous structure, the method comprising:

[0008] Step 1, preparation of three-dimensional ordered polymethyl methacrylate (PMMA) template;

[0009] Step 2, preparation of electromagnetic wave absorbing material with three-dimensional ordered macroporous structure.

[0010] The preparation method of the three-dimensional ordered polymethyl methacrylate (PMMA) template in Step 1 comprises:

[0011] Step 1.1, in an N2 environment, add 25 mL of absolute ethanol, 50 mL of methyl methacrylate, and 215 mL of deionized water into a five-necked flask. When the temperature rises to 80 °C, keep the temperature constant and stir for 2 h;

[0012] Step 1.2, dissolve 0.25 g of potassium persulfate in 10 mL of deionized water, add it into the five-necked flask in Step 1.1 and continue stirring for 2 h to obtain polymethyl methacrylate microspheres;

[0013] Step 1.3, place the polymethyl methacrylate dispersion in a beaker and let it stand at room temperature for 4 - 5 months to obtain a three-dimensional ordered polymethyl methacrylate template;

[0014] The preparation method of the electromagnetic wave absorbing material with three-dimensional ordered macroporous structure comprises:

[0015] Step 2.1, dissolve 0.096 g of anhydrous sodium carbonate in 8 mL of formaldehyde solution;

[0016] Step 2.2, dissolve 6 g of resorcinol particles in the solution in Step 2.1 and obtain a light yellow resorcinol-formaldehyde resin solution by magnetic stirring;

[0017] Step 2.3, put the three-dimensional ordered polymethyl methacrylate (PMMA) template into a beaker, add the resorcinol-formaldehyde resin solution along the edge of the beaker. Stop adding when the liquid level of the solution rises to half of the template, and take out the template after standing for 1 h;

[0018] Step 2.4, after sucking dry the solution on the surface of the template, place it in an oven and cure at 80 °C for 1 day;

[0019] Step 2.5, in an argon environment, place the cured template in a tubular furnace and anneal for 2 h, the heat treatment temperature is 700 °C, and the heating rate is 5 °C / min to obtain an electromagnetic wave absorbing material with three-dimensional ordered macroporous structure.

[0020] Advantages of the present invention:

[0021] 1. The electromagnetic wave absorbing material with a three-dimensional ordered macroporous structure has excellent impedance matching performance and a unique microstructure. The preparation process is simple, and it also maintains excellent dielectric loss ability, showing excellent electromagnetic wave absorption performance.

[0022] 2. The electromagnetic wave absorbing material with a three-dimensional ordered macroporous structure has the characteristics of a large specific surface area, a rich pore structure, excellent dielectric properties, and low density. At the same time, the ordered macroporous structure can not only optimize impedance matching but also enhance the multiple losses of the material to electromagnetic waves, achieving a good electromagnetic wave absorption effect.

[0023] 3. The carbon material itself has the characteristic of light weight. The electromagnetic wave absorbing material with a three-dimensional ordered macroporous structure of the present invention is a light-weight porous electromagnetic wave absorber, which not only has a light mass and a low loading amount but also has a wide effective absorption bandwidth and a strong loss ability.

[0024] 4. The dielectric loss tangent of the electromagnetic wave absorbing material with a three-dimensional ordered macroporous structure of the present invention is 0.3 - 0.7 in the range of 2 - 18 GHz, showing excellent dielectric loss performance. The fabricated absorber has a maximum reflection loss of -49.82 dB at a single matching thickness, and the effective absorption bandwidth can reach 4.56 GHz.

[0025] 5. The present invention uses the template method to prepare the electromagnetic wave absorbing material with a three-dimensional ordered macroporous structure, which can adjust the pore size of the material according to actual needs, and then adjust the electromagnetic wave absorption performance, having good industrial application prospects.

[0026] The electromagnetic wave absorbing material of the present invention has the advantages of simple preparation, strong dielectric loss ability, strong reflection loss, and a wide effective absorption bandwidth; it solves the problem that due to the too high conductivity of the carbon material, the conduction current generated in an alternating electromagnetic field environment will be restricted by the "skin effect". The higher the conductivity, the smaller the skin depth, the stronger the reflection of the incident electromagnetic wave by the material, resulting in poor impedance matching and being not conducive to improving the electromagnetic wave absorption performance of the material, which greatly limits the development of carbon materials and other technical problems. Description of the Drawings

[0027] Figure 1 In Figure a, it is a PMMA template, in Figure b, it is an SEM image of the electromagnetic wave absorbing material with a three-dimensional ordered macroporous structure prepared in Example 1, and in Figure c, it is a Mapping image of the electromagnetic wave absorbing material with a three-dimensional ordered macroporous structure prepared in Example 1;

[0028] Figure 2 is the XRD pattern of the electromagnetic wave absorbing material with a three-dimensional ordered macroporous structure prepared in Example 1;

[0029] Figure 3 is the dielectric constant pattern of the electromagnetic wave absorbing material with a three-dimensional ordered macroporous structure prepared in Example 1;

[0030] Figure 4 Reflection loss diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in Example 1;

[0031] Figure 5 Dielectric constant diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in Comparative Example 1;

[0032] Figure 6 Reflection loss diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in Comparative Example 1;

[0033] Figure 7 Dielectric constant diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in Comparative Example 2;

[0034] Figure 8 Reflection loss diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in Comparative Example 2;

[0035] Figure 9 Attenuation constant diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing materials prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0036] Figure 10 Impedance matching diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing materials prepared in Example 1, Comparative Example 1 and Comparative Example 2. Detailed implementation mode

[0037] A three-dimensional ordered macroporous structure electromagnetic wave absorbing material and a preparation method thereof according to the present invention mainly have the following characteristics:

[0038] (1) An electromagnetic wave absorbing material with a three-dimensional ordered macroporous structure having a pore diameter of 490 - 505 nm is prepared by a template method and a high-temperature pyrolysis method;

[0039] (2) The pyrolysis temperature of the 3DOM structure material is adjusted, and different pyrolysis temperatures adjust the dielectric constant of the material and optimize the impedance matching;

[0040] (3) The 3DOM structure carbon material induces the incident electromagnetic wave to perform multiple reflections and scatterings inside the material, promoting the attenuation and dissipation of the electromagnetic wave;

[0041] (4) The three-dimensional ordered macroporous structure electromagnetic wave absorbing material has a unique microstructure and a simple preparation process;

[0042] (5) The three-dimensional ordered macroporous structure electromagnetic wave absorbing material has excellent impedance matching performance and strong electromagnetic wave attenuation performance, making it have excellent electromagnetic wave absorption performance.

[0043] Example 1:

[0044] The three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared by the present invention mainly includes a carbon material, and its structure presents a three-dimensional ordered porous structure with a pore diameter of 490 - 505 nm.

[0045] This embodiment provides a preparation method of a three-dimensional ordered macroporous structure electromagnetic wave absorbing material, including the following steps:

[0046] Step 1: Preparation of a three-dimensional ordered polymethyl methacrylate (PMMA) template.

[0047] Step 1.1: Under an N2 environment, add 25 mL of absolute ethanol, 50 mL of methyl methacrylate, and 215 mL of deionized water into a five-necked flask. When the temperature rises to 80 °C, keep the temperature unchanged and stir for 2 h.

[0048] In the present invention, the preparation of polymethyl methacrylate microspheres requires an anaerobic environment to avoid oxidation of the microspheres during the emulsion polymerization reaction, resulting in non-uniform particle sizes. Therefore, in the present invention, N2 is introduced into the five-necked flask and stirred for 2 h to expel the oxygen in the flask.

[0049] The reactant ratio of 25 mL of absolute ethanol, 50 mL of methyl methacrylate, and 215 mL of deionized water and the environment of 80 °C adopted in the present invention are necessary conditions for synthesizing polymethyl methacrylate microspheres with a particle size of 480 - 530 nm, which are determined through multiple preliminary experiments. Only under these parameters can the polymethyl methacrylate microspheres with a particle size of 480 - 530 nm be prepared with uniform particle sizes.

[0050] Step 1.2: Dissolve 0.25 g of potassium persulfate in 10 mL of deionized water, and quickly add it to the five-necked flask in Step 1.1, and continue to stir for 2 h to obtain polymethyl methacrylate microspheres;

[0051] Step 1.3: Place the polymethyl methacrylate dispersion in a beaker and leave it at room temperature for 4 - 5 months. This process is to allow the water to naturally evaporate at room temperature (20 - 25 °C), and rely on the gravitational force to make the polymethyl methacrylate microspheres arrange uniformly to form an ordered microsphere structure, and a three-dimensional ordered polymethyl methacrylate template can be obtained.

[0052] Step 2: Preparation of a three-dimensional ordered macroporous structure electromagnetic wave absorbing material.

[0053] Step 2.1: Dissolve 0.096 g of anhydrous sodium carbonate in 8 mL of formaldehyde solution. This step is to create a suitable alkaline environment, and at the same time, formaldehyde is a necessary drug for synthesizing novolac resin;

[0054] Step 2.2: Dissolve 6 g of resorcinol particles into the solution in Step 2.1 through magnetic stirring to obtain a light yellow resorcinol-formaldehyde resin solution, which is the precursor solution. In an alkaline environment, resorcinol reacts with formaldehyde solution to produce novolac resin;

[0055] Step 2.3: Place a PMMA template of a certain size into a beaker, and add the resorcinol-formaldehyde resin solution along the edge of the beaker. Stop adding when the liquid level of the solution reaches half of the template, and take out the template after standing for 1 h. In the present invention, the capillary action is utilized to suck the resorcinol-formaldehyde resin solution, i.e., novolac resin, into the pores of the template, filling the pores between the template spheres, so as to obtain a three-dimensional ordered macroporous structure by removing the template spheres through high-temperature pyrolysis;

[0056] Step 2.4: After sucking dry the excess solution on the surface of the template, place it in an oven and cure it at 80 °C for 1 day to cure the novolac resin;

[0057] Step 2.5: Under an argon atmosphere, place the cured template in a tubular furnace and anneal it for 2 h. The heat treatment temperature is 700 °C, and the heating rate is 5 °C / min to obtain a three-dimensional ordered macroporous structure electromagnetic wave absorbing material.

[0058] This process is to obtain the carbonized novolac resin. Therefore, an argon atmosphere is selected to avoid the oxidation and disappearance of the carbon material in the air. 700 °C is the optimal reaction temperature selected after comparing other carbonization temperatures. The wave absorbing performance of the carbon material obtained at this temperature is better.

[0059] In the present invention, the cured template is in the gaps between the template spheres of the precursor solution, and the template is removed through annealing treatment to obtain a three-dimensional ordered macroporous structure electromagnetic wave absorbing material.

[0060] Figure 1 Figure a of this is the PMMA template prepared in Example 1. It can be seen that the template microspheres are of uniform size, arranged orderly, and the diameter is about 523 nm. Figure b is the SEM image of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in Example 1. It can be seen that the wave absorbing material prepared in Example 1 presents a three-dimensional ordered macroporous structure, the pore size is uniform and the pores communicate with each other. Figure c is the Mapping image of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in Example 1. It can be seen that the wave absorbing material is composed of C element and O element.

[0061] Figure 2 This is the XRD pattern of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in Example 1. It can be seen that due to the low graphitization degree of the carbon material, there are two diffraction broad peaks belonging to the (002) crystal plane and (100) crystal plane of graphite carbon near 23° and 43° in the wave absorbing material of Example 1, which indicates that the wave absorbing material prepared in Example 1 is amorphous carbon.

[0062] Figure 3 Dielectric constant diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in Example 1 (loading amount of the wave absorbing material is 20%). It can be seen that in the frequency range of 2 - 18 GHz, the real part of the dielectric constant of the wave absorbing material is 9 - 13, and the imaginary part is 2.8 - 4.4, indicating that the material has strong electromagnetic energy storage and electromagnetic energy dissipation capabilities, and can effectively absorb and dissipate the incident electromagnetic wave through internal loss mechanisms (such as multiple reflection losses).

[0063] Figure 4 Reflection loss diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in Example 1. It can be seen that the strongest reflection loss (RL min ) is -49.82 dB (thickness is 3.2 mm), and the effective absorption bandwidth (EAB) reaches 4.56 GHz (thickness is 1.7 mm), covering most of the frequency bands in the Ku band.

[0064] Comparative Example 1:

[0065] The difference from Example 1 is that the heat treatment temperature is 600 °C.

[0066] Figure 5 Dielectric constant diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in this comparative example (loading amount of the wave absorbing material is 20%). It can be seen that the real part of the dielectric constant of the wave absorbing material prepared in this comparative example is about 2.0 in the whole frequency band range, and the imaginary part is about 0, with very low absorption and loss of electromagnetic waves, almost a wave-transparent material.

[0067] Figure 6 Reflection loss diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in this comparative example. It can be seen that the absorption bandwidth of the sample is 0, and the reflection loss is almost 0, with extremely poor absorption performance of electromagnetic waves, and the absorption performance is much smaller than that of the wave absorbing material in Example 1.

[0068] Comparative Example 2:

[0069] The difference from Example 1 is that the heat treatment temperature is 800 °C.

[0070] Figure 7 Dielectric constant diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in this comparative example (loading amount of the wave absorbing material is 20%). It can be seen that the real part of the dielectric constant of the wave absorbing material prepared in this comparative example is 11.6 - 16.7 in the whole frequency band range, and the imaginary part is 4.9 - 10.7. The too high dielectric constant leads to enhanced reflection of electromagnetic waves and weakened impedance matching.

[0071] Figure 8Reflection loss diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material prepared in this comparative example. It can be seen that due to the too high dielectric constant, the absorption performance of the sample prepared in this comparative example is worse than that of the sample prepared in Example 1. The strongest reflection loss of the sample prepared in this comparative example is only -22.98 dB (thickness is 5.0 mm), and the effective absorption bandwidth is 2.72 GHz (thickness is 2.3 mm).

[0072] Figure 9 Attenuation constant diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing materials prepared in Example 1, Comparative Example 1 and Comparative Example 2. It can be seen that with the increase of the heat treatment temperature, the attenuation ability of the electromagnetic wave absorbing material to electromagnetic waves also gradually increases.

[0073] Figure 10 Impedance matching diagram of the three-dimensional ordered macroporous structure electromagnetic wave absorbing materials prepared in Example 1, Comparative Example 1 and Comparative Example 2. It can be seen that the impedance matching of the electromagnetic wave absorbing material prepared in Example 1 is the best, and the impedance matching of the electromagnetic wave absorbing material prepared in Comparative Example 1 is the worst. Due to the good impedance matching ability and strong electromagnetic wave attenuation performance, the electromagnetic wave absorbing material prepared in Example 1 has the optimal wave absorption performance.

Claims

1. A three-dimensional ordered macroporous structure electromagnetic wave absorbing material, characterized in that: The material composition includes carbon materials, and the material structure presents a three-dimensionally ordered porous structure with a pore size of 490 - 505 nm.

2. The preparation method of the three-dimensional ordered macroporous structure electromagnetic wave absorbing material according to claim 1, characterized in that: The method includes: Step 1, preparation of a three-dimensionally ordered polymethyl methacrylate (PMMA) template; Step 2, preparation of a three-dimensionally ordered macroporous structure electromagnetic wave absorbing material.

3. The preparation method of a three-dimensional ordered macroporous structure electromagnetic wave absorbing material according to claim 2, characterized in that: The preparation method of the three-dimensionally ordered polymethyl methacrylate (PMMA) template described in Step 1 includes: Step 1.1, in an N2 environment, add 25 mL of absolute ethanol, 50 mL of methyl methacrylate, and 215 mL of deionized water into a five-necked flask. When the temperature rises to 80 °C, keep the temperature constant and stir for 2 h; Step 1.2, dissolve 0.25 g of potassium persulfate in 10 mL of deionized water, add it to the five-necked flask in Step 1.1 and continue stirring for 2 h to obtain polymethyl methacrylate microspheres; Step 1.3, place the polymethyl methacrylate dispersion in a beaker and let it stand at room temperature for 4 - 5 months to obtain a three-dimensionally ordered polymethyl methacrylate template.

4. The preparation method of a three-dimensional ordered macroporous structure electromagnetic wave absorbing material according to claim 2, wherein: The preparation method of the three-dimensionally ordered macroporous structure electromagnetic wave absorbing material includes: Step 2.1, dissolve 0.096 g of anhydrous sodium carbonate in 8 mL of formaldehyde solution; Step 2.2, dissolve 6 g of resorcinol particles in the solution in Step 2.1 and obtain a light yellow resorcinol-formaldehyde resin solution by magnetic stirring; Step 2.3, place the three-dimensionally ordered polymethyl methacrylate (PMMA) template in a beaker, add the resorcinol-formaldehyde resin solution along the edge of the beaker. Stop adding when the liquid level of the solution rises to half of the template. After standing for 1 h, take out the template; Step 2.4, after sucking dry the solution on the surface of the template, place it in an oven and cure at 80 °C for 1 day; Step 2.5, in an argon environment, place the cured template in a tubular furnace and anneal for 2 h. The heat treatment temperature is 700 °C, and the heating rate is 5 °C / min to obtain a three-dimensionally ordered macroporous structure electromagnetic wave absorbing material.

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