A preparation method of a carbon-based aerogel wave-absorbing superstructure based on microstructure / macrostructure enhancement strategy

Abstract

The application discloses a preparation method of a carbon-based aerogel wave-absorbing superstructure based on a microstructure / macrostructure enhancement strategy, and the method comprises the following steps: firstly, carboxymethyl chitosan and carboxylated carbon nanotubes are put into deionized water to obtain a suspension; secondly, carbon fibers are added to obtain a carbon fiber suspension; thirdly, a crosslinking agent is added, and the mixture is stirred and aged, and then frozen to obtain a frozen aerogel; fourthly, the frozen aerogel is thawed, solvent is replaced, and then dried; and finally, the wave-absorbing superstructure is engraved. In the application, carbon nanotubes and carbon fibers are used as reinforcing phases, and the carbon-based aerogel is prepared by covalent crosslinking and bonding. The structure of the carbon-based aerogel is enhanced on the microscale and the macroscale, the mechanical properties of the carbon-based aerogel are improved, the electromagnetic wave absorption capacity of the carbon-based aerogel wave-absorbing superstructure is enhanced by combining with the superstructure excipient, and the carbon-based aerogel wave-absorbing superstructure is suitable for a thermal protection material interlayer in a complex electromagnetic environment.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing superstructures, specifically relating to a method for preparing carbon-based aerogel absorbing superstructures based on micro / macro structural enhancement strategies. Background Technology

[0002] In recent years, with the rapid development of electromagnetic technology, electromagnetic pollution has gradually become one of the sources of pollution posing a serious threat to human health, electronic equipment, and military security. Electromagnetic absorbing materials can effectively solve the pollution problem caused by electromagnetic waves, but the complexity and severity of their applications place higher demands on their practicality. In some applications, absorbing materials must possess heat resistance, thermal insulation, low density, and good mechanical properties. Developing multifunctional absorbing materials has become a key research focus and challenge in electromagnetic absorbing materials. In recent years, the unique microstructure of aerogels has provided new ideas for the design of electromagnetic wave absorbing materials and holds promise for solving the technical challenges faced by traditional electromagnetic wave absorbing materials. Based on the inherent properties of aerogels, assembling various electromagnetic absorbers into aerogels has become an effective strategy for developing high-performance, multifunctional electromagnetic wave absorbing materials.

[0003] In existing research on aerogel-based electromagnetic wave absorbing materials, the microwave absorption performance in the low-frequency range (especially 2GHz–6GHz) is not ideal. Electromagnetic superstructure absorbers, as a novel electromagnetic wave absorption scheme, can achieve perfect impedance matching through structural design and have the advantage of tunable resonant frequency, effectively enhancing the electromagnetic wave absorption capability of materials. However, how to achieve good superstructure shaping of aerogels remains a challenge. Therefore, combining the advantages of aerogel absorbing materials with the design concept of electromagnetic superstructure absorbers through a simple and easy-to-implement method holds promise as a novel electromagnetic pollution solution capable of achieving multifunctional and ultra-strong electromagnetic wave absorption. Summary of the Invention

[0004] The technical problem this invention aims to solve is to address the shortcomings of the prior art by providing a method for preparing carbon-based aerogel absorbing superstructures based on a micro / macro structural enhancement strategy. This method uses carbon nanotubes and carbon fibers as reinforcing phases, covalently cross-linked to prepare carbon-based aerogels, thereby enhancing the carbon-based aerogel structure at both the micro and macro scales, improving its mechanical properties. Furthermore, by combining physical laser etching with superstructure shaping to achieve structural design, the electromagnetic wave absorption capability of the carbon-based aerogel absorbing superstructure is enhanced, solving the problems of traditional absorbing materials having limited functionality, excessive mass, and narrow absorption frequency bands.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing carbon-based aerogel microwave absorbing superstructures based on micro / macro structure enhancement strategies, characterized in that the method includes the following steps:

[0006] Step 1: Place carboxymethyl chitosan and carboxylated carbon nanotubes into deionized water, and then perform magnetic stirring and ultrasonic dispersion in sequence to obtain a uniform suspension.

[0007] Step 2: Add the carbon fiber to the suspension obtained in Step 1 and disperse it by ultrasonication to obtain a carbon fiber suspension.

[0008] Step 3: Add 4-(4,6-dimethoxy[1,3,5]triazine-2-yl)-4-methylmorpholine chloride hydrate to the carbon fiber suspension obtained in Step 2 and stir magnetically, then age and freeze to obtain cryo-aerogel;

[0009] Step 4: Thaw the frozen aerogel obtained in Step 3 in ethanol, perform three solvent replacements with acetone, and then dry it at room temperature and pressure to obtain carbon-based aerogel.

[0010] Step 5: Place the carbon-based aerogel obtained in Step 4 under the laser light source of a laser engraving machine to engrave a superstructure pattern, thereby obtaining a carbon-based aerogel absorbing superstructure.

[0011] This invention uses carboxymethyl chitosan (CMCS) as raw material, carboxylated carbon nanotubes (CNTs) and carbon fibers (CF) as micro and macro reinforcing phases, respectively, and 4-(4,6-dimethoxy[1,3,5]triazine-2-yl)-4-methylmorpholine chloride hydrate (DMTMM) as a carboxyl activator. First, CMCS and carboxylated carbon nanotubes are fully dispersed in deionized water. The carboxyl groups are beneficial to promoting the uniform dispersion of carboxylated carbon nanotubes and improving the uniformity of carbon-based aerogels. Then, carbon fibers are added and dispersed, and then the carboxyl activator is added to induce coupling between CMCS, which has abundant amino and carboxyl functional groups on its surface, and carboxylated carbon nanotubes, which have carboxyl functional groups on their surface. This results in a strong crosslinking between the two, and the carbon fibers are uniformly dispersed in the strong crosslinking network, forming a uniform skeletal structure, thus obtaining a carbon-based aerogel. On the one hand, the strong cross-linked network formed at the microscale by carboxylated carbon nanotubes and carboxymethyl chitosan in this carbon-based aerogel effectively dissipates external stress, and the carboxylated carbon nanotubes play a reinforcing role at the microscale, significantly reducing the shrinkage of the carbon-based aerogel, improving its structure, and enhancing its mechanical properties. On the other hand, carbon fibers, due to their high strength and high modulus, improve the axial and radial load-bearing capacity of the carbon-based aerogel and overcome excessive shrinkage caused by capillary forces, playing a reinforcing role at the microscale and improving its mechanical properties. Therefore, the synergistic effect of carbon nanotubes and carbon fibers enhances the internal structure of the carbon-based aerogel, thereby enhancing its mechanical properties at both the micro and macro scales, resulting in a low shrinkage rate (6.3%) and ultra-low density (0.025 g / cm³). 3 ) and low thermal conductivity (25.15 mW·m -1 ·K -1 Next, based on the excellent dielectric properties of carbon nanotubes and carbon fibers, and combined with the superstructure design concept, a laser engraving method was used to achieve aerogel superstructure shaping, endowing carbon-based aerogels with periodic structures, obtaining aerogel microwave absorbing superstructures, effectively improving their low-frequency microwave absorption performance, and enabling them to achieve ultra-wideband (almost covering S, C, X and Ku bands), wide temperature (-20℃ to 200℃), and wide-angle (5° to 40° incident angle) microwave absorption characteristics.

[0012] The above-described method for preparing a carbon-based aerogel absorbing superstructure based on a micro / macro structure enhancement strategy is characterized in that, in step one, the mass ratio of carboxymethyl chitosan to carboxylated carbon nanotubes is 8:1 to 4, and the length of the carboxylated carbon nanotubes is 10 μm to 20 μm. By limiting the mass ratio of carboxymethyl chitosan to carboxylated carbon nanotubes, the method avoids situations where too few carboxylated carbon nanotubes fail to provide microscopic enhancement, or too many lead to excessively high dielectric constants that negatively impact the absorption effect of the product.

[0013] The aforementioned method for preparing a carbon-based aerogel absorbing superstructure based on a micro / macro structure enhancement strategy is characterized in that, in step two, the mass ratio of carboxylated carbon nanotubes in the suspension to the added carbon fibers is 5:3-6, and the length of the carbon fibers is 6 mm. This invention effectively overcomes the excessive shrinkage of carbon-based aerogels by adding carbon fibers for macroscopic enhancement. Furthermore, by controlling the proportion of added carbon fibers, it avoids excessive carbon fibers from depositing at the bottom of the crosslinking system, which would lead to uneven shrinkage of the carbon-based aerogel. Simultaneously, by selecting short-cut carbon fibers for easy dispersion and forming a uniform aerogel skeleton, the shrinkage rate of the carbon-based aerogel is reduced.

[0014] The above-mentioned method for preparing a carbon-based aerogel microwave absorbing superstructure based on a micro / macro structure enhancement strategy is characterized in that the ultrasonic dispersion time in step two is 1 hour.

[0015] The above-mentioned method for preparing a carbon-based aerogel microwave absorbing superstructure based on a micro / macro structure enhancement strategy is characterized in that the mass ratio of 4-(4,6-dimethoxy[1,3,5]triazine-2-yl)-4-methylmorpholine chloride hydrate to carboxymethyl chitosan in the carbon fiber suspension in step three is 1:1.

[0016] The above-mentioned method for preparing a carbon-based aerogel microwave absorbing superstructure based on a micro / macro structure enhancement strategy is characterized in that the magnetic stirring time in step three is 5 min, the aging temperature is 45℃ and the time is 3 h, and the freezing temperature is -20℃ and the time is 24 h.

[0017] The method for preparing a carbon-based aerogel microwave absorbing superstructure based on a micro / macro structure enhancement strategy is characterized in that the drying time in step four is 24 hours.

[0018] The aforementioned method for fabricating a carbon-based aerogel absorbing superstructure based on a micro / macro structure enhancement strategy is characterized in that the superstructure pattern in step five is stepped or cylindrical. By fabricating periodic structures on carbon-based aerogels to generate edge diffraction and electromagnetic wave resonance, the electromagnetic wave loss capability of the carbon-based aerogel absorbing superstructure is enhanced, and the electromagnetic wave absorption frequency band is broadened.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. This invention is based on a micro- and macro-structure enhancement strategy. Carbon nanotubes and carbon fibers are used as reinforcing phases to prepare carbon-based aerogels through covalent cross-linking. This enhances the structure of the carbon-based aerogel at both the micro and macro scales, improving its mechanical properties. By combining physical laser etching with superstructure shaping to achieve structural design, the electromagnetic wave absorption capability of the carbon-based aerogel superstructure is enhanced. This carbon-based aerogel superstructure exhibits excellent electromagnetic wave loss capability, with an effective absorption bandwidth that almost covers the S to Ka band. It also possesses wide-angle and wide-temperature electromagnetic wave absorption performance, realizing the integration of ultra-lightweight, heat-insulating, self-extinguishing, load-bearing, and highly efficient electromagnetic wave absorption in aerogel.

[0021] 2. This invention utilizes carbon nanotubes and carbon fibers to enhance the aerogel structure at both the microscopic and macroscopic scales, respectively. Compared to conventional freeze-drying or supercritical drying for aerogel preparation, this invention can obtain carbon-based aerogels using only atmospheric pressure drying. Compared to conventional methods of forming carbon-based aerogels by high-temperature carbonization of organic matrices, this invention directly covalently crosslinks carbon nanotubes, eliminating the need for complex high-temperature carbonization and simplifying the preparation process. Furthermore, this invention chemically crosslinks carbon nanotubes and introduces carbon fibers, both of which are excellent dielectric materials. Therefore, the dielectric properties of the aerogel can be easily altered by changing their content, enabling optimized design of the dielectric properties of carbon-based aerogels.

[0022] 3. The carbon-based aerogel obtained by this invention has a shrinkage rate of only 6.25% and a density of only 0.025 g / cm³. 3 The low shrinkage rate ensures that the carbon-based aerogel has low density, which meets the requirements of "thin, light, wide and strong" for microwave absorbing materials. At the same time, the low density indicates that the carbon-based aerogel has more pores, which is conducive to the repeated reflection and scattering of electromagnetic waves in the pores, thus improving the microwave absorption performance of the carbon-based aerogel microwave absorbing superstructure. Moreover, the carbon-based aerogel has a simple preparation process, the drying process is easy to achieve, and it has good large-scale preparation capability.

[0023] 4. The carbon-based aerogel microwave absorbing superstructure prepared by this invention has excellent microwave absorption and mechanical properties, far exceeding most existing aerogel materials, and is suitable as a thermal protection material interlayer for use in complex electromagnetic environments.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a comparison chart of the shrinkage rates of the CF-C / C aerogel prepared in Example 1 of the present invention and the CMCS / CNTs aerogel prepared in Comparative Example 1.

[0026] Figure 2This is a microscopic morphology image of the CF-C / C aerogel prepared in Example 1 of the present invention.

[0027] Figure 3 This is a microscopic morphology diagram of the CMCS / CNTs aerogel prepared in Comparative Example 1 of the present invention.

[0028] Figure 4 The infrared spectra of CMCS, CNTs, the prepared CF-C / C aerogel in Example 1 of the present invention, and the CMCS / CNTs aerogel prepared in Comparative Example 1 are shown.

[0029] Figure 5 The images show the TG curves of the CF-C / C aerogel prepared in Example 1 of this invention and the CMCS / CNTs aerogel prepared in Comparative Example 1.

[0030] Figure 6 The images show DSC diagrams of the CF-C / C aerogel prepared in Example 1 and the CMCS / CNTs aerogel prepared in Comparative Example 1.

[0031] Figure 7 This is a diagram showing the real part of the dielectric constant of the CF-C / C aerogels prepared in Examples 1 and 17-19 of this invention.

[0032] Figure 8 This is a diagram showing the imaginary part of the dielectric constant of the CF-C / C aerogels prepared in Examples 1 and 17-19 of this invention.

[0033] Figure 9 The images show physical diagrams of the carbon-based aerogel absorbing superstructures prepared in Examples 1 and 20 of this invention, as well as schematic diagrams of the corresponding stepped and cylindrical unit structures.

[0034] Figure 10 The simulation and measured reflectivity loss diagrams are shown for the stepped unit structure in the carbon-based aerogel absorbing superstructure prepared in Example 1 of this invention.

[0035] Figure 11 The simulation and measured reflectivity loss diagrams are shown for the stepped unit structure in the carbon-based aerogel absorbing superstructure prepared in Example 20 of this invention.

[0036] Figure 12 The diagram shows the reflectivity loss of the unit structure in the carbon-based aerogel absorbing superstructure prepared in Examples 1 and 20 of this invention under different incident angles.

[0037] Figure 13 The graph shows the reflectivity loss of the unit structure in the carbon-based aerogel absorbing superstructure prepared in Examples 1 and 20 of this invention at different temperatures. Detailed Implementation

[0038] Example 1

[0039] This embodiment includes the following steps:

[0040] Step 1: Carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:2 until the mass concentration is 1.5%. The mixture is then magnetically stirred and ultrasonically dispersed to obtain a uniform suspension.

[0041] Step 2: Add carbon fiber (CF) to the suspension obtained in Step 1 and ultrasonically disperse for 1 hour to obtain a carbon fiber suspension; the mass ratio of carboxylated carbon nanotubes to added carbon fiber in the suspension is 5:5.

[0042] Step 3: Add 4-(4,6-dimethoxy[1,3,5]triazin-2-yl)-4-methylmorpholine chloride hydrate to the carbon fiber suspension obtained in Step 2 and stir magnetically for 5 min. Then, place it in a constant temperature drying oven and age at 45℃ for 3 h, and then freeze it in a -20℃ environment for 24 h to obtain a cryogel. The mass ratio of 4-(4,6-dimethoxy[1,3,5]triazin-2-yl)-4-methylmorpholine chloride hydrate to carboxymethyl chitosan in the carbon fiber suspension is 1:1.

[0043] Step 4: Thaw the frozen aerogel obtained in Step 3 in ethanol, and perform three solvent replacements with acetone. Then dry it at room temperature and pressure for 24 hours to obtain carbon fiber reinforced carboxymethyl chitosan / carboxylated carbon nanotube composite aerogel, denoted as CF-C / C aerogel.

[0044] Step 5: The carbon fiber reinforced carboxymethyl chitosan / carboxylated carbon nanotube composite aerogel obtained in Step 4 is made into a plate with a length × width of 180mm × 180mm. Then, a laser etching machine is used to etch a stepped periodic structure on the surface of the plate to obtain a carbon-based aerogel microwave absorbing superstructure.

[0045] Comparative Example 1

[0046] The difference between this comparative example and Example 1 is that the carbon fiber addition and ultrasonic dispersion process in step two were not performed. Instead, the suspension obtained in step one was directly subjected to the magnetic stirring, aging, and freezing processes of adding 4-(4,6-dimethoxy[1,3,5]triazine-2-yl)-4-methylmorpholine chloride hydrate in step three, as well as the thawing, solvent replacement, and drying processes in step four, to obtain a carboxymethyl chitosan / carboxylated carbon nanotube composite aerogel, denoted as CMCS / CNTs aerogel.

[0047] Example 2

[0048] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:2 until the mass concentration is 0.5%.

[0049] Example 3

[0050] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:2 until the mass concentration is 1.0%.

[0051] Example 4

[0052] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:2 until the mass concentration is 2.0%.

[0053] Example 5

[0054] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:1 until the mass concentration is 0.5%.

[0055] Example 6

[0056] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:1 until the mass concentration is 1.0%.

[0057] Example 7

[0058] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:1 until the mass concentration is 1.5%.

[0059] Example 8

[0060] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:1 until the mass concentration is 2.0%.

[0061] Example 9

[0062] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:3 until the mass concentration is 0.5%.

[0063] Example 10

[0064] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:3 until the mass concentration is 1.0%.

[0065] Example 11

[0066] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:3 until the mass concentration is 1.5%.

[0067] Example 12

[0068] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:3 until the mass concentration is 2.0%.

[0069] Example 13

[0070] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:4 until the mass concentration is 0.5%.

[0071] Example 14

[0072] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:4 until the mass concentration is 1.0%.

[0073] Example 15

[0074] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:4 until the mass concentration is 1.5%.

[0075] Example 16

[0076] The difference between this embodiment and Embodiment 1 is that in step one, carboxymethyl chitosan (CMCS) and carboxylated carbon nanotubes (CNTs) are added to deionized water at a mass ratio of 8:4 until the mass concentration is 2.0%.

[0077] Example 17

[0078] The difference between this embodiment and Embodiment 1 is that the mass ratio of carboxylated carbon nanotubes to added carbon fibers in the suspension in step two is 5:3.

[0079] Example 18

[0080] The difference between this embodiment and Embodiment 1 is that the mass ratio of carboxylated carbon nanotubes to added carbon fibers in the suspension in step two is 5:4.

[0081] Example 19

[0082] The difference between this embodiment and Embodiment 1 is that the mass ratio of carboxylated carbon nanotubes to added carbon fibers in the suspension in step two is 5:6.

[0083] Example 20

[0084] The difference between this embodiment and embodiment 1 is that in step five, a laser etching machine is used to etch a cylindrical periodic structure on the surface of the flat plate to obtain a carbon-based aerogel microwave absorbing superstructure.

[0085] Figure 1 This is a comparison chart of the shrinkage rates of the CF-C / C aerogel prepared in Example 1 and the CMCS / CNTs aerogel prepared in Comparative Example 1. Figure 1 It can be seen that, in molds of the same diameter, the diameter D of the CF-C / C aerogel prepared by carbon fiber reinforcement in Example 1 is 37.5 mm, while the diameter D of the CMCS / CNTs aerogel prepared in Comparative Example 1 is 33.5 mm. The two show a significant difference in shrinkage rate. According to calculation, the shrinkage rate of the CF-C / C aerogel prepared by carbon fiber reinforcement in Example 1 is as low as 6.25%, indicating that the macroscopic reinforcement of the aerogel by carbon fiber in this invention significantly reduces the shrinkage rate of the aerogel.

[0086] Figure 2 This is a microstructure image of the CF-C / C aerogel prepared in Example 1 of this invention. Figure 2 The two images on the right show the distribution of N and O elements in CF-C / C aerogels. Figure 3 This is a microstructure image of the CMCS / CNTs aerogel prepared in Comparative Example 1 of this invention. Figure 2 and Figure 3 It can be seen that both CF-C / C aerogel and CMCS / CNTs aerogel have highly porous structures, compared to Figure 3 CMCS / CNTs aerogel, Figure 2 In the CF-C / C aerogel, the carbon fibers (CF) with robust mechanical properties are uniformly dispersed in the aerogel matrix, providing a uniform skeletal structure for the aerogel. The pore size distribution in the skeletal structure is within the range of several hundred micrometers, with high porosity and good air-filling properties, giving the CF-C / C aerogel its ultra-lightweight properties. At the same time, the skeletal structure provided by CF enhances the cross-linked aerogel network, thereby reducing the shrinkage rate of the CF-C / C aerogel.

[0087] Figure 4The images show the infrared spectra of CMCS, CNTs, the prepared CF-C / C aerogel in Example 1 of this invention, and the CMCS / CNTs aerogel prepared in Comparative Example 1. Figure 4 It can be seen that at 3413cm -1 2900cm -1 and 1580cm -1 Stretch vibrations of OH / NH2, CH / CH2, and COOH groups are observed nearby, at 900 cm⁻¹. -1 Up to 1030cm -1 Multiple absorption peaks related to carbohydrate structure were observed within the range; simultaneously, different characteristic peaks corresponding to amide bonds appeared in the infrared spectra of CF-C / C aerogel and CMCS / CNTs aerogel: located at 1646 cm⁻¹. -1 (Amide I band, C=O extension of acetyl group), 1529cm -1 (Amide II band, NH extension) and 1255cm -1 (Amino III, CN extension) indicates that a covalent cross-linking chemical reaction occurs between the amino group of CMCS and the carboxyl group of CNTs, forming an amide bond.

[0088] The thermal stability of the aerogel was verified in air using thermogravimetric analysis (TG) and differential scanning calorimetry (DSC), and the results are as follows: Figure 5 and Figure 6 As shown.

[0089] Figure 5 The images show the TG curves of the CF-C / C aerogel prepared in Example 1 and the CMCS / CNTs aerogel prepared in Comparative Example 1. Figure 6 The images show DSC diagrams of the CF-C / C aerogel prepared in Example 1 and the CMCS / CNTs aerogel prepared in Comparative Example 1. Figure 5 and Figure 6It can be seen that the weight loss of CMCS / CNTs aerogel and CF-C / C aerogel exhibits three distinct stages: during the initial temperature rise to 100℃, both aerogels show slight weight loss, mainly due to the evaporation of adsorbed water within the aerogel; as the temperature rises to 350℃, significant weight loss is observed in both aerogels, with the maximum heat fluxes of CMCS / CNTs aerogel and CF-C / C aerogel at 314.7℃ and 304.3℃, respectively. Due to the depolymerization and decomposition of the aerogel polymer chains, the weight losses of CMCS / CNTs aerogel and CF-C / C aerogel are 26%. 5% and 28.4%; after 400℃, due to further decomposition and carbonization of the aerogel polymer chains, both CMCS / CNT aerogel and CF-C / C aerogel experienced significant secondary weight loss, with maximum heat fluxes at 498.8℃ and 526.8℃, respectively; ultimately, during the entire heating process, the carbon residue rates of CMCS / CNTs aerogel and CF-C / C aerogel were 17.1% and 37.1%, respectively; indicating that the incorporation of carbon fiber (CF) into CMC / CNTs aerogel has minimal impact on decomposition, and in practical applications, the maximum operating temperature of CF-C / C aerogel is controlled at 200℃ to ensure its thermal stability.

[0090] Figure 7 This is a graph showing the real part of the dielectric constant of the CF-C / C aerogels prepared in Examples 1 and 17-19 of this invention. Figure 8 This is a diagram showing the imaginary part of the dielectric constant of the CF-C / C aerogels prepared in Examples 1 and 17-19 of this invention. Figure 7 and Figure 8 It can be seen that as the content of CNTs with excellent conductivity increases, a conductive network is gradually formed, and the defect dipole polarization on CNTs leads to an upward trend in both the real part ε′ and the imaginary part ε″ of the dielectric constant, resulting in a significant increase in the dielectric constant of CF-C / C aerogel, thus ensuring its dielectric properties.

[0091] Figure 9 The images show physical models of the carbon-based aerogel absorbing superstructures prepared in Examples 1 and 20 of this invention, along with corresponding schematic diagrams of stepped and cylindrical unit structures. Figure 9It can be seen that the carbon-based aerogel absorbing superstructure prepared in Example 1 has a stepped periodic unit structure (denoted as CF-C / CS). The heights of the two gradient layers in the stepped periodic unit structure are defined as h1 and h2, respectively, and the side lengths are defined as d and d / 2, respectively. The carbon-based aerogel absorbing superstructure prepared in Example 20 has a cylindrical periodic unit structure (denoted as CF-C / CC). In the cylindrical periodic unit structure, the heights of the two gradient layers are defined as h1 and h2, respectively, and the diameter of the cylinder is defined as d. Further detection of electric and magnetic field intensity distribution and energy loss density distribution revealed that the diameter and side length of each unit structure have little effect on the absorption bandwidth, only slightly altering the absorption intensity. Increasing the thickness and height h1 and h2 of the unit structure helps shift the absorption band to lower frequencies. Simultaneously, a large amount of electromagnetic wave energy accumulates at the edges of each unit structure, indicating that the periodic unit structure sculpted in this invention enhances the edge diffraction effect, thereby improving microwave loss performance. Furthermore, microwave loss is concentrated at the edges of the top structure, the top, and the sides of the lower gradient layers within the unit structure. Thus, the resonance in the stepped periodic unit structure and the edge diffraction effect at the edges of the gradient layers help generate more absorption frequencies, thereby achieving broadband microwave absorption.

[0092] Parametric modeling was performed on the stepped unit structure of the carbon-based aerogel absorbing superstructure prepared in Example 1 and the cylindrical unit structure of the carbon-based aerogel absorbing superstructure prepared in Example 20. The electric and magnetic field intensity distributions were simulated and analyzed. Following the principle of maximizing absorption bandwidth, the parameters d = 36 mm, h1 = 12 mm, and h2 = 16 mm were determined for the stepped unit structure CF-C / CS, and the parameters d = 30 mm, h1 = 16 mm, and h2 = 12 mm were determined for the cylindrical unit structure CF-C / CS. The reflection loss of the carbon-based aerogel absorbing superstructures prepared in Examples 1 and 20 was tested using the arc frame method. The simulation and measurement results of the frequency-dependent reflectivity of the carbon-based aerogel absorbing superstructures were compared. The results are shown below. Figure 10 and Figure 11 As shown.

[0093] Figure 10 The figures show the simulated and measured reflectivity loss of the stepped unit structure in the carbon-based aerogel absorbing superstructure prepared in Example 1 of this invention. Figure 11 The above figures show the simulated and measured reflectivity loss of the cylindrical unit structure in the carbon-based aerogel absorbing superstructure prepared in Example 20 of this invention. Figure 10 and Figure 11It can be seen that the simulated and measured reflectivity loss trends of each carbon-based aerogel absorbing superstructure are generally consistent. Moreover, the microwave absorption ranges of CF-C / CC and CF-C / CS below -10dB are 2.1GHz to 40.0GHz and 2.9GHz to 40.0GHz, respectively. In the S to Ka band, the effective microwave absorption coverage reaches 97.6% and 99.7%, respectively. This indicates that the carbon-based aerogel absorbing superstructure prepared in this invention has excellent electromagnetic wave loss capability, and the effective absorption bandwidth almost covers the S to Ka band.

[0094] Figure 12 The figures show the reflectivity loss of the unit structures in the carbon-based aerogel absorbing superstructures prepared in Examples 1 and 20 of this invention at different incident angles. Figure 12 It can be seen that when the incident angle increases from 10° to 40°, the absorption intensity of CF-C / CC and CF-C / CS increases, while the effective bandwidth remains unchanged. This indicates that CF-C / CS and CF-C / CC exhibit effective microwave absorption throughout the entire S to Ka band over a wide range of incident angles, demonstrating excellent wide-angle absorption characteristics.

[0095] Figure 13 The graphs show the reflectivity loss of the unit structures in the carbon-based aerogel absorbing superstructures prepared in Examples 1 and 20 of this invention at different temperatures. Figure 13 The small image in the lower left corner of each reflectivity loss curve is a magnified detail of the boxed area. Figure 13 It can be seen that, unlike the usual phenomenon where temperature changes affect the dielectric constant of the absorbing material and thus its overall impedance matching performance, thereby altering reflectivity damage, when the ambient temperature is between -20℃ and 200℃, the temperature has only a slight effect on the effective bandwidth of the reflectivity of CF-C / CC and CF-C / CS in Examples 1 and 20 of this invention, exhibiting excellent microwave absorption performance over a wide temperature range.

[0096] In summary, the carbon-based aerogel absorbing superstructure prepared by this invention has excellent wide-angle and wide-temperature microwave absorption capabilities, and has great potential in dealing with electromagnetic threats in complex environments.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing carbon-based aerogel microwave absorbing superstructures based on micro / macro structure enhancement strategies, characterized in that, The method includes the following steps: Step 1: Carboxymethyl chitosan and carboxylated carbon nanotubes are placed in deionized water and magnetically stirred and ultrasonically dispersed in sequence to obtain a uniform suspension; the length of the carboxylated carbon nanotubes is 10μm~20μm. Step 2: Add the carbon fiber to the suspension obtained in Step 1 and disperse it ultrasonically to obtain a carbon fiber suspension; the length of the carbon fiber is 6 mm. Step 3: Add 4-(4,6-dimethoxy[1,3,5]triazine-2-yl)-4-methylmorpholine chloride hydrate to the carbon fiber suspension obtained in Step 2 and stir magnetically, then age and freeze to obtain cryo-aerogel; Step 4: Thaw the frozen aerogel obtained in Step 3 in ethanol, perform three solvent replacements with acetone, and then dry it at room temperature and pressure to obtain carbon-based aerogel. Step 5: Place the carbon-based aerogel obtained in Step 4 under the laser light source of a laser engraving machine to engrave a superstructure pattern, thereby obtaining a carbon-based aerogel absorbing superstructure.

2. The method for preparing a carbon-based aerogel microwave absorbing superstructure based on a micro / macro structure enhancement strategy according to claim 1, characterized in that, The mass ratio of carboxymethyl chitosan to carboxylated carbon nanotubes in step one is 8:1~4.

3. The method for preparing a carbon-based aerogel microwave absorbing superstructure based on a micro / macro structure enhancement strategy according to claim 1, characterized in that, In step two, the mass ratio of carboxylated carbon nanotubes to added carbon fibers in the suspension is 5:3~6.

4. The method for preparing a carbon-based aerogel absorbing superstructure based on a micro / macro structure enhancement strategy according to claim 1, characterized in that, The ultrasonic dispersion time in step two is 1 hour.

5. The method for preparing a carbon-based aerogel microwave absorbing superstructure based on a micro / macro structure enhancement strategy according to claim 1, characterized in that, In step three, the mass ratio of 4-(4,6-dimethoxy[1,3,5]triazine-2-yl)-4-methylmorpholine chloride hydrate to carboxymethyl chitosan in the carbon fiber suspension is 1:

1.

6. The method for preparing a carbon-based aerogel microwave absorbing superstructure based on a micro / macro structure enhancement strategy according to claim 1, characterized in that, The magnetic stirring time in step three is 5 minutes, the aging temperature is 45°C and the time is 3 hours, and the freezing temperature is -20°C and the time is 24 hours.

7. The method for preparing a carbon-based aerogel microwave absorbing superstructure based on a micro / macro structure enhancement strategy according to claim 1, characterized in that, The drying time described in step four is 24 hours.

8. The method for preparing a carbon-based aerogel microwave absorbing superstructure based on a micro / macro structure enhancement strategy according to claim 1, characterized in that, The superstructure pattern described in step five is either stepped or cylindrical.

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