Nanometer aerogel material with excellent wave absorption and infrared stealth performance and preparation method thereof

Abstract

The application provides a kind of nanometer aerogel material and preparation method thereof with excellent wave-absorbing and infrared stealth performance, which is composed of a silicon-containing polymer matrix with high cross-linking density and carbon nanomaterials, the carbon nanomaterials are uniformly dispersed in the silicon-containing polymer matrix, the silicon-containing polymer matrix is adsorbed on the surface of the carbon nanomaterials to form an organic-inorganic hybrid structure, the nanometer aerogel material has a nano-scale pore structure, and the porosity is 90% to 95%. The nanometer aerogel material has both wave-absorbing and infrared stealth performance. The application can solve the problem that the existing technology cannot effectively integrate thermal radiation blocking performance and electromagnetic wave absorption performance into one material system, and can simultaneously improve the EMW absorption performance and infrared stealth performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of polymer nanocomposite microwave absorption and infrared stealth materials, and relates to nanoaerogel materials with both excellent microwave absorption and infrared stealth properties and their preparation methods. Background Technology

[0002] To prepare materials that possess both excellent electromagnetic wave (EMW) absorption and infrared (IR) stealth properties, two key issues need to be considered: (1) EMW absorbing materials require low reflectivity and high absorptivity, while IR stealth materials require high reflectivity and low IR absorptivity. Since these two principles are completely opposite, combining EMW absorption and IR stealth in one material seems very challenging; (2) The absorbed EMW energy is converted into Joule heat, leading to an increase in temperature, which deteriorates the IR stealth performance of the material. This also increases the difficulty of preparing materials with both excellent EMW absorption and IR stealth properties. Therefore, integrating thermal radiation blocking and EMW absorption structures into a single material system is of great significance for developing multifunctional materials with excellent thermal infrared stealth and EMW absorption properties.

[0003] Porous polymer materials possess numerous advantages such as light weight, flexibility, and corrosion resistance, and are currently widely used in many fields. Among them, nano-aerogel materials (materials with nanoscale air distribution) can be used to block heat conduction and infrared signals due to their unique structure, including nanopore size, high specific surface area, and high porosity. For infrared stealth materials, the nanopore size of nano-aerogel materials induces the Knudsen effect, which greatly restricts the free movement of air molecules, thereby effectively reducing the heat conduction and heat convection of nano-aerogel materials. According to the Stefan-Boltzmann theory, a high specific surface area is beneficial to enhancing the infrared wave reflection of the material and improving its infrared stealth performance, while a high porosity is beneficial to reducing the heat conduction of the material and improving electromagnetic wave impedance matching, thus potentially improving both the infrared stealth and electromagnetic wave absorption performance of the material. However, no relevant methods have been reported to date. This invention addresses this problem, aiming to develop nanomaterials that simultaneously possess excellent wave absorption and infrared stealth properties. Summary of the Invention

[0004] To address the problem that existing technologies struggle to effectively integrate thermal radiation blocking performance and electromagnetic wave absorption performance into a single material system, this invention provides a nano-aerogel material with both excellent wave absorption and infrared stealth properties, along with its preparation method, thereby simultaneously improving the material's EMW absorption performance and infrared stealth performance.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0006] A nano-aerogel material with excellent microwave absorption and infrared stealth properties is disclosed. The nano-aerogel material is composed of a silicon-containing polymer matrix with high cross-linking density and carbon nanomaterials. The carbon nanomaterials are uniformly dispersed in the silicon-containing polymer matrix. The silicon-containing polymer matrix is ​​adsorbed on the surface of the carbon nanomaterials to form an organic-inorganic hybrid structure. The nano-aerogel material has a nanoscale porous structure with a porosity of 90% to 95%. The nano-aerogel material has both microwave absorption and infrared stealth properties.

[0007] In the above-mentioned technical solution for a nano-aerogel material with both excellent wave absorption and infrared stealth properties, the volume content of carbon nanomaterials in the nano-aerogel material is 1.6 vol.% to 1.9 vol.%, where the volume content of carbon nanomaterials is calculated by taking into account the volume of the air phase in the nano-aerogel material.

[0008] In the above-mentioned technical solution of nano-aerogel materials with excellent wave absorption and infrared stealth properties, the carbon nanomaterial is a one-dimensional carbon nanomaterial (e.g., fibrous carbon nanomaterial) or a two-dimensional carbon nanomaterial (e.g., sheet-like carbon nanomaterial).

[0009] In the above-mentioned technical solution for nano-aerogel materials with both excellent wave absorption and infrared stealth properties, the crosslinking density of the silicon-containing polymer matrix with high crosslinking density should meet the requirements for constructing a nanoporous structure. A feasible silicon-containing polymer matrix is ​​polyvinyltrimethylsilane.

[0010] In the above-mentioned technical solution of nano-aerogel material with excellent wave absorption and infrared stealth properties, the pore size of the nano-aerogel material is 30-40 nm.

[0011] In the above-mentioned technical solution for nano-aerogel materials that combine excellent wave absorption and infrared stealth properties, the specific surface area of ​​the nano-aerogel material is 550–600 m². 2 / g.

[0012] In the above-mentioned technical solution for a nano-aerogel material possessing both excellent wave absorption and infrared stealth properties, the density of the nano-aerogel material is 0.15–0.18 g / cm³. 3 .

[0013] In the above-mentioned technical solution for nano-aerogel materials that combine excellent wave absorption and infrared stealth properties, the compressive modulus of the nano-aerogel material is 2.7 to 3.6 MPa.

[0014] In the above-mentioned technical solution for nano-aerogel materials that combine excellent wave absorption and infrared stealth properties, the thermal conductivity of the nano-aerogel material is 35–42 mW·m. -1 K -1 .

[0015] This invention also provides a method for preparing the above-mentioned nano-aerogel material with both excellent microwave absorption and infrared stealth properties, comprising the following steps:

[0016] (1) Dissolve a silicon-containing polymer matrix with high crosslinking density in a solvent to obtain a silicon-containing polymer matrix solution; uniformly disperse carbon nanomaterials in a solvent to obtain a carbon nanomaterial dispersion; thoroughly mix the silicon-containing polymer matrix solution and the carbon nanomaterial dispersion, then add ammonia to induce the decomposition of the spirolines; after adding ammonia and mixing evenly, obtain a gel precursor solution; transfer the gel precursor solution to a mold and place it in an oven at 35-45°C until the gel precursor solution transforms into a gel state to obtain a wet gel; immerse the obtained wet gel in a solvent for aging.

[0017] In this step, the ratio of the silicon-containing polymer matrix solution to the carbon nanomaterial dispersion is controlled so that the volume percentage of carbon nanomaterials in the silicon-containing polymer matrix solution and the carbon nanomaterial dispersion is less than 1.9 vol.%, and the amount of ammonia added is controlled so that the molar ratio of water to Si element in the silicon-containing polymer matrix is ​​(5~10):1.

[0018] (2) The sample aged in step (1) is dried with supercritical carbon dioxide to obtain a nano-aerogel material with both excellent wave absorption and infrared stealth properties.

[0019] In the above-mentioned technical solution for preparing nano-aerogel materials with both excellent microwave absorption and infrared stealth properties, the principle for controlling the ratio of silicon-containing polymer matrix solution to carbon nanomaterial dispersion in step (1) is to ensure that the volume content of carbon nanomaterials in the final prepared nano-aerogel material is 1.6 vol.% to 1.9 vol.%. However, considering that the sample will shrink in volume during the preparation process, the ratio of silicon-containing polymer matrix solution to carbon nanomaterial dispersion in step (1) should be controlled so that the volume percentage of carbon nanomaterials in the mixture of silicon-containing polymer matrix solution and carbon nanomaterial dispersion is less than 1.9 vol.%. Generally, depending on the difference in the degree of sample shrinkage during the preparation process, it is feasible to control the ratio of silicon-containing polymer matrix solution to carbon nanomaterial dispersion in step (1) so that the volume percentage of carbon nanomaterials in the mixture of silicon-containing polymer matrix solution and carbon nanomaterial dispersion is between 1.0 vol.% and 1.8 vol.%.

[0020] In the above-mentioned technical solution for preparing nano-aerogel materials with both excellent wave absorption and infrared stealth properties, the solvent in step (1) is preferably anhydrous ethanol. The main function of immersing the obtained wet gel in the solvent for aging in step (1) is to further increase the crosslinking density of the silicon-containing polymer matrix (e.g., polyvinyltrimethylsilane).

[0021] In the above-mentioned technical solution for preparing nano-aerogel materials with both excellent wave absorption and infrared stealth properties, the concentration of the silicon-containing polymer matrix solution is 0.1–0.2 g / mL, and the concentration of the carbon nanomaterial dispersion is 1–60 mg / mL.

[0022] In the above-mentioned technical solution for preparing nano-aerogel materials with both excellent wave absorption and infrared stealth properties, the aging time in step (1) is 20-30h.

[0023] In the above-mentioned technical solution for preparing nano-aerogel materials with both excellent microwave absorption and infrared stealth properties, when the silicon-containing polymer matrix is ​​polyvinyltrimethylsilane, a feasible method for preparing polyvinyltrimethylsilane is as follows:

[0024] The thermal initiator is dissolved in vinyltrimethoxysilane monomer, and the mass ratio of thermal initiator to vinyltrimethoxysilane monomer is controlled to be 1:(5-10). The mixture is stirred and reacted at 150-160°C for 3-5 hours under a nitrogen atmosphere. Unreacted thermal initiator and vinyltrimethoxysilane monomer are removed to obtain the final product.

[0025] This invention first uses free radical polymerization to prepare a silicon-containing polymer matrix (e.g., polyvinyltrimethylsilane, PVTMS) with high inorganic crosslinking points. The high crosslinking density of the silicon-containing polymer matrix is ​​beneficial for preparing aerogels with nanopores and high specific surface areas, and the organic-inorganic hybrid molecular structure is beneficial for improving the mechanical properties of the nanoaerogel material. Then, a wet gel is prepared using the spinodal decomposition method, which can effectively improve the sol-gel transition rate. Finally, the nanoaerogel material is prepared by scCO2 drying, endowing the material with a nanoporous structure and high specific surface area. This nanoaerogel material has nanopores, high specific surface area, high porosity, and an organic-inorganic hybrid structure that enhances mechanical properties. Among these, the nanopores are beneficial for effectively blocking heat conduction and heat convection, the abundant heterogeneous interfaces are beneficial for infrared reflection and EMW absorption, and the high porosity is beneficial for enhancing the EMW impedance matching of the material. These factors enable the nanoaerogel material of this invention to have both excellent microwave absorption performance and infrared stealth performance.

[0026] Compared with the prior art, the technical solution provided by the present invention can produce the following beneficial technical effects:

[0027] 1. This invention provides a nano-aerogel material with both excellent microwave absorption and infrared stealth properties. The nano-aerogel material is composed of a silicon-containing polymer matrix with high cross-linking density and carbon nanomaterials. The carbon nanomaterials are uniformly dispersed in the silicon-containing polymer matrix, and the silicon-containing polymer matrix adsorbs onto the surface of the carbon nanomaterials, forming an organic-inorganic hybrid structure. This nano-aerogel material has a nanoscale pore structure with a pore size of 30–40 nm and a porosity of 90%–95%. This nano-aerogel material features nanopore size, high specific surface area, and high porosity. The nanopore size effectively blocks heat conduction and convection, the abundant heterogeneous interfaces facilitate infrared reflection and EMW absorption, and the high porosity enhances the EMW impedance matching of the material. These factors enable the nano-aerogel material of this invention to simultaneously possess excellent microwave absorption and infrared stealth properties. Furthermore, the organic-inorganic hybrid structure in the nano-aerogel material of this invention enhances the mechanical properties of the material, which is beneficial for improving the material's application performance in practical scenarios.

[0028] 2. Experiments have confirmed that the nano-aerogel material provided by this invention possesses excellent thermal infrared stealth performance. When covered on the surface of a thermal infrared signal source at a temperature of 100.1℃, it achieves excellent thermal infrared stealth performance (ΔT reaches 60.7℃). Simultaneously, the nano-aerogel material provided by this invention also exhibits excellent EMW absorption performance, with low reflection loss and good impedance matching in the Ku band (12.4-18GHz). In particular, when the volume content of MWCNT is 1.7 vol.% and the porosity is 91.7%, the effective absorption bandwidth covers the entire Ku band (12.4-18GHz), with a reflection loss as low as -36.1 dB for electromagnetic waves at a frequency of 14.6 GHz, and a corresponding impedance matching close to 1. The material thickness is 2 mm.

[0029] 3. This invention also provides a method for preparing the aforementioned nano-aerogel material with both excellent microwave absorption and infrared stealth properties. First, a silicon-containing polymer matrix (e.g., polyvinyltrimethylsilane, PVTMS) with high inorganic crosslinking points is prepared using free radical polymerization. Then, a wet gel is prepared using the spinodal decomposition method. Finally, the nano-aerogel material is obtained by scCO2 drying, thus constructing a nanoporous structure around the carbon nanomaterial network structure for the first time. This invention provides a new approach for preparing nano-aerogel materials with both excellent microwave absorption and infrared stealth properties.

[0030] 4. By combining the nano-aerogel material provided by this invention with a highly conductive graphene film, a double-layer PVTMS@MWCNT / Graphene double-layer EMI shielding material can be obtained. Experiments have confirmed that this double-layer EMI shielding material has excellent electromagnetic shielding and wave absorption performance. Under the condition of a thickness of 2.06 mm, the average absorption-reflection ratio is 25.4, and the low reflection bandwidth is 4.1 GHz (Reflection less than 0.1). Attached Figure Description

[0031] Figure 1 Figures (a) and (b) are SEM images of the PVTMS nanoaerogel material prepared in Comparative Example 1 and the PVTMS@MWCNT nanoaerogel material prepared in Example 1, respectively. Figure 1 Figure (c) shows digital micrographs of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents. Figure 1 Figure (d) shows the thermal conductivity and porosity of PVTMS nanoaerogel materials and PVTMS@MWCNT nanoaerogel materials with different MWCNT contents. Figure 1 Figure (e) is an infrared thermograph of PVTMS@MWCNT-1.7 vol.% at different surface temperatures. Figure 1 Figure (f) shows the compressive mechanical properties of PVTMS nanoaerogel materials and PVTMS@MWCNT nanoaerogel materials with different MWCNT contents. Figure 1 Figures (g) and (h) show the total XPS and C1s XPS spectra of PVTMS nanoaerogel material and PVTMS@MWCNT nanoaerogel material with different MWCNT contents, respectively.

[0032] Figure 2 The linear shrinkage rate and density of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents are shown.

[0033] Figure 3 Figures (a) and (b) show the test results of the real and imaginary parts of the dielectric constant of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents. Figure 3 Figure (c) shows the average real and imaginary parts of the dielectric properties of PVTMS@MWCNT nanoaerogel materials in the Ku band with different MWCNT contents. Figure 3 Figure (d) shows the attenuation constant (α) of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents. Figure 3 Figures (e) to (h) and (e') to (h') show the test results of 3D and 2D microwave absorption properties of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents, respectively. Figure 3 The (e”) to (h”) figures show the impedance matching (Z) of PVTMS@MWCNT nanoaerogel materials with different thicknesses and different MWCNT contents. in / Z0).

[0034] Figure 4 Figures (a) and (b) show the nitrogen adsorption-desorption isotherms and pore size distribution curves of PVTMS aerogel and PVTMS@MWCNT-1.7 vol.%. Figure (c) shows the temperature of the hot stage before and after covering the sample with PVTMS@MWCNT-1.7 vol.%. Figure (d) shows photographs of the sample before and after covering it with PVTMS@MWCNT-1.7 vol.%. Figure 4 Figure (e) illustrates the infrared stealth mechanism of the PVTMS@MWCNT nanoaerogel material. Figure 4 Figures (f) to (i) show thermal infrared images taken before, 0 min, 8 min, and 16 min after covering the hot stage with PVTMS@MWCNT-1.7 vol.%.

[0035] Figure 5 Figures (a) to (c) are schematic diagrams of double-layer PVTMS@MWCNT / graphene electromagnetic interference shielding materials of different thicknesses. Figure 5 Figure (d) is a schematic diagram of the graphene film. Figure 5 Figures (a') to (d') show the EMI shielding effectiveness (SE) of double-layer PVTMS@MWCNT / graphene electromagnetic interference shielding materials and graphene films of different thicknesses. Figure 5 Figures (a”) to (d”) show the SE values ​​corresponding to reflectance (R), transmission (T), and absorption (A) of double-layer PVTMS@MWCNT / graphene electromagnetic interference shielding materials and graphene films of different thicknesses. Figure 5 Figures (a”’) to (d”’) show the A / R ratios of SE for double-layer PVTMS@MWCNT / graphene electromagnetic interference shielding materials and graphene films of different thicknesses. Detailed Implementation

[0036] The following examples further illustrate the nano-aerogel material with excellent microwave absorption and infrared stealth properties described in this invention, as well as its preparation method. The examples described below are merely some embodiments of this invention, not all embodiments. Based on the invention's content and embodiments, other embodiments obtained by those skilled in the art without inventive effort are all within the scope of protection of this invention.

[0037] In the following examples and comparative examples, the thermal initiators di-tert-butyl peroxide (DTBP, 98%) and vinyltrimethoxysilane (VTMS, 98%) were purchased from Sigma Aldrich. The solvents anhydrous ethanol (100%) and alkaline catalysts ammonia (28%–30% (NH3), ACS grade) were purchased from GreenField Global and VWR, respectively. All chemicals were used as is. Multi-walled carbon nanotubes (MWCNTs, diameter: 9.5 nm, length: 1.5 μm) were purchased from Nanocyl SA (NC7000TM), Belgium. Drying was performed using scCO2 (purity ≥99%, Linde gas).

[0038] Example 1

[0039] In this embodiment, PVTMS@MWCNT nanoaerogel materials with both excellent microwave absorption and infrared stealth properties are prepared through the following steps:

[0040] (1) Preparation of PVTMS by free radical polymerization

[0041] The thermal initiator di-tert-butyl peroxide (DTBP) was dissolved in the monomer vinyltrimethoxysilane (VTMS) with the mass ratio of DTBP to VTMS controlled at 1:10. The resulting solution was poured into a four-necked flask equipped with a condenser and a stirrer and reacted for 3 hours at 150°C and 200 rpm under a nitrogen atmosphere. After that, the four-necked flask was placed in a vacuum oven at 150°C to remove unreacted monomer and thermal initiator, yielding polyvinyltrimethylsilane (PVTMS).

[0042] (2) Constructing nanoporous structures using cross-linking chemical reactions

[0043] PVTMS was dissolved in anhydrous ethanol to obtain a PVTMS solution with a concentration of 0.2 g / mL. The PVTMS solution was stirred at 40 °C for 0.5 h. MWCNTs were added to anhydrous ethanol and ultrasonically dispersed in a bath ultrasonic bath for 0.5 h to obtain a MWCNT dispersion. The PVTMS solution and MWCNT dispersion were mixed and stirred for 0.5 h. Then, ammonia water, an alkaline catalyst, was added at a molar ratio of water to Si in PVTMS (water / Si) of 8:1 to induce spinodal phase separation. After adding ammonia water, the mixture was stirred for 1 min. The resulting gel precursor solution was transferred to a mold. The mold containing the gel precursor solution was placed in an oven at 40 °C until the gel precursor solution transformed into a gel state, a process that takes approximately 10–12 h. The resulting wet gel was then aged in anhydrous ethanol for 24 h.

[0044] In this step, multiple sets of experiments were conducted. In each set of experiments, when mixing the PVTMS solution and the MWCNT dispersion, the amount of each was controlled (in step (1), the ratio of PVTMS solution to MWCNT dispersion was controlled so that the volume percentage of MWCNT in the mixture of PVTMS solution and MWCNT dispersion was between 0.9 vol.% and 2.0 vol.%), so that the volume content of MWCNT in the finally prepared PVTMS@MWCNT nanoaerogel material was 1.4 vol.%, 1.6 vol.%, 1.7 vol.%, 1.9 vol.%, and 2.1 vol.%, respectively.

[0045] (3) Supercritical carbon dioxide (scCO2) drying

[0046] The sample obtained by aging in step (2) was subjected to solvent exchange with liquid CO2 at a pressure of 10.34 MPa (1500 psi) and a temperature of 25°C. Finally, CO2 was released at a pressure of 10.34 MPa (1500 psi) and a temperature of 45°C to complete the drying process, resulting in disc-shaped PVTMS@MWCNT nanoaerogel material.

[0047] The PVTMS@MWCNT nanoaerogel materials prepared in each group of experiments in this embodiment are designated as PVTMS@MWCNT-1.4 vol.%, PVTMS@MWCNT-1.6 vol.%, PVTMS@MWCNT-1.7 vol.%, PVTMS@MWCNT-1.9 vol.%, and PVTMS@MWCNT-2.1 vol.%, respectively, based on the different volume contents of MWCNT.

[0048] Comparative Example 1

[0049] In this comparative example, PVTMS nanoaerogel material was prepared. The preparation process of this comparative example is basically the same as that of Example 1, except that MWCNT dispersion is not prepared or added in step (2).

[0050] Example 2

[0051] In this embodiment, the PVTMS@MWCNT nanoaerogel material prepared in Example 1 was characterized.

[0052] The microstructure of the PVTMS nanoaerogel material prepared in Comparative Example 1 and the PVTMS@MWCNT nanoaerogel material prepared in Example 1 was observed using scanning electron microscopy (SEM). The elemental content of the PVTMS nanoaerogel material and the PVTMS@MWCNT nanoaerogel material was determined using X-ray photoelectron spectroscopy (XPS). The thermal conductivity of the PVTMS nanoaerogel material and the PVTMS@MWCNT nanoaerogel material was measured using a hot-pan TPS2500S thermal constant analyzer. Infrared thermographs of PVTMS@MWCNT-1.7 vol.% (thickness 5.6 mm) at different surface temperatures were captured using a Fluke-Ti32S infrared imager.

[0053] Figure 1 Figures (a) and (b) are SEM images of the PVTMS nanoaerogel material prepared in Comparative Example 1 and the PVTMS@MWCNT nanoaerogel material prepared in Example 1, respectively. As can be seen from the figures, both exhibit nanoscale pore structures.

[0054] Figure 1 Figure (c) shows digital micrographs of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents. As can be seen from the figure, after drying with scCO2, the shrinkage of the PVTMS@MWCNT nanoaerogel materials decreases with increasing MWCNT content. Further testing of the linear shrinkage rate and density of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents yielded the following results: Figure 2 As shown, by Figure 2 It can be seen that after drying with scCO2, the shrinkage of the aerogel material decreases with increasing MWCNT content. Simultaneously, the density of the nano-aerogel also slightly decreases with increasing MWCNT content. The main reasons for this are as follows:

[0055] For nanoporous aerogel materials, capillary forces during solvent exchange are the primary cause of shrinkage. However, according to the multinuclear model, the migration rate of molecular chains decreases significantly with increasing MWCNT content due to adsorption at the nanofiller interface. Therefore, after adding MWCNTs, PVTMS can adsorb onto the MWCNT surface, forming a high-density absorption layer around the MWCNTs. This high-density absorption layer around the MWCNT network helps improve the strength of the solid framework and reduce the shrinkage rate during scCO2 drying.

[0056] Figure 1Figure (d) shows the thermal conductivity and void fraction of PVTMS nanoaerogel materials and PVTMS@MWCNT nanoaerogel materials with different MWCNT contents. As can be seen from the figure, with the increase of MWCNT content, the void fraction (volume percentage of air phase in the nanoaerogel material) of the aerogel material increases from 90.9% to 92%, and the thermal conductivity also increases from 25.3 mW·m -1 K -1 Increased to 42.4 mW·m -1 K -1 The increased porosity can be attributed to the enhanced strength of the solid skeleton surrounding MWCNT, leading to a decrease in shrinkage ratio, while the increased thermal conductivity can be attributed to the high thermal conductivity of MWCNT. However, due to its high porosity (high air content) and nanopore size (Knudsen effect), PVTMS@MWCNT nanoaerogel materials still exhibit low thermal conductivity.

[0057] Depend on Figure 1 Figure (e) shows infrared thermographs of PVTMS@MWCNT-1.7 vol.% at different surface temperatures. As can be seen from the figure, the use of PVTMS@MWCNT nanoaerogel material with low thermal conductivity can effectively block heat transfer, thereby inhibiting the evaporation of water from the flowers on the surface of the nanoaerogel material.

[0058] Figure 1 Figure (f) shows the compressive modulus of PVTMS nanoaerogel material and PVTMS@MWCNT nanoaerogel material with different MWCNT contents. As can be seen from the figure, the mechanical properties of the aerogel material are improved by adding MWCNT to form a solid absorption layer.

[0059] Figure 1 Figures (g) and (h) show the total XPS and C1s XPS spectra of the PVTMS nanoaerogel material and the PVTMS@MWCNT nanoaerogel material with different MWCNT contents. The characteristic peak of C1s at 284.8 eV is significantly increased, which can be attributed to the addition of MWCNTs (containing C=C or CC). The added carbon nanofiller MWCNT is beneficial to the construction of the EMW absorption structure, thereby effectively absorbing the incident EMW.

[0060] Example 3

[0061] In this embodiment, the EMW absorption performance of the PVTMS@MWCNT nanoaerogel material (monolayer) prepared in Example 1 was tested.

[0062] The real and imaginary parts of the dielectric constant (ε′ and ε″) and permeability (μ′ and μ″) of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents were tested in the Ku band (12.4-18 GHz) using a PNA-X network analyzer (Keysight N5232B). The EMW absorption performance (reflection loss, RL) of the material was calculated using equations (1) to (2). The EMW attenuation capability of the material was characterized by the attenuation constant α, which was calculated using equation (3).

[0063]

[0064]

[0065]

[0066] In equations (1) to (3), Z in Z0 is the input impedance of the material, Z0 is the free space impedance (377Ω), and μ is the input impedance of the material. r and ε r ε′ and ε″ are the complex permeability and permittivity, respectively; f and d are the frequency (Hz) of the applied electromagnetic wave and the thickness (m) of the material, respectively; c is the speed of light (m / s); ε′ and ε″ are the real and imaginary parts of the permittivity of the material in the Ku band (12.4-18GHz); μ′ and μ″ are the real and imaginary parts of the permeability of the material in the Ku band (12.4-18GHz).

[0067] Figure 3 Figures (a) and (b) show the test results of the real and imaginary parts of the dielectric constant of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents. Figure 3 Figure (c) shows the average real and imaginary parts of the dielectric properties of PVTMS@MWCNT nanoaerogel materials in the Ku band under different MWCNT contents. As can be seen from the figure, both the real part (ε′) and the imaginary part (ε″) of the dielectric constant of the PVTMS@MWCNT nanoaerogel material increase with increasing MWCNT content. The increase in the dielectric constant of the PVTMS@MWCNT nanoaerogel material can be attributed to the increase in MWCNT content, while the increase in dielectric loss can be attributed to the increase in conductive loss in the PVTMS@MWCNT nanoaerogel material with increasing MWCNT content.

[0068] Figure 3 Figure (d) shows the attenuation constant (α) of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents. As can be seen from the figure, the attenuation constant increases with the increase of MWCNT content, which is due to the conduction loss of MWCNT.

[0069] Figure 3 Figures (e) to (h) and (e') to (h') show the test results of 3D and 2D microwave absorption properties of PVTMS@MWCNT nanoaerogel materials with different MWCNT contents, respectively. Figure 3 The (e”) to (h”) figures show the impedance matching (Z) of PVTMS@MWCNT nanoaerogel materials with different thicknesses and different MWCNT contents. in As shown in the figure, with the increase of MWCNT content, the absorption performance of PVTMS@MWCNT nanoaerogel material for EMW first increases and then decreases; with the increase of MWCNT content, the impedance matching (Z0) of PVTMS@MWCNT nanoaerogel material decreases. in / Z0) gradually decreases. For example Figure 3 As shown in Figure (f”), the impedance matching of PVTMS@MWCNT-1.7 vol.% reaches 1, indicating that the EMW has relatively low reflection at the air / material interface, and the reduction in reflectivity is beneficial to the absorption of the EMW. Therefore, as Figure 3 As shown in Figures (f) and (f'), by adjusting the MWCNT content of the PVTMS@MWCNT nanoaerogel material, the optimal EMW absorption performance (full Ku band, RL) can be obtained. min = -36.1dB, thickness is 2mm).

[0070] Example 4

[0071] In this embodiment, the nitrogen adsorption-desorption isotherm and pore size distribution curve of the PVTMS@MWCNT nanoaerogel material prepared in Example 1 were tested, as well as its infrared stealth performance.

[0072] The pore size distribution and surface area of ​​PVTMS nanoaerogel materials and PVTMS@MWCNT nanoaerogel materials were determined using the BET (Brunall-Emmett-Taylor) test method of Autosorb IQ. Figure 4 Figures (a) and (b) show the nitrogen adsorption-desorption isotherms and pore size distribution curves for the PVTMS aerogel prepared in Example 1 and the PVTMS@MWCNT-1.7 vol.% prepared in Example 1. Figure 4 As shown in Figure (a), all samples exhibit type IV isotherms, a characteristic of mesoporous materials. The hysteresis loops are generated by capillary condensation in mesopores with diameters greater than 4 nm. Nitrogen adsorption-desorption analysis is also used to measure the specific surface area and pore size of samples, such as... Figure 4 As shown in Figure (b), PVTMS@MWCNT-1.7 vol.% has a high specific surface area of ​​approximately 559 m². 2 / g, with pore size in the range of 30–40 nm.

[0073] To characterize the infrared stealth properties of the PVTMS@MWCNT nanoaerogel material prepared in Example 1, PVTMS@MWCNT-1.7 vol.% was covered on a hot stage at different temperatures (67.1 °C, 82.4 °C and 100.1 °C), and thermal infrared images were captured.

[0074] At fixed set temperatures (67.1℃, 82.4℃, and 100.1℃), the temperature of the hot stage before covering the PVTMS@MWCNT-1.7 vol.% sample, and the temperature detected on the sample surface after covering, are shown as follows: Figure 4 Figure (c) shows the photographs taken without PVTMS@MWCNT-1.7 vol.% on the hot plate and with PVTMS@MWCNT-1.7 vol.% on the hot plate, respectively. Figure 4 The left and right figures are shown in (d) of the diagram. (From...) Figure 4 As shown in Figure (c), when the PVTMS@MWCNT-1.7 vol.% sample was covered on the hot stage, the temperature signal detected by the temperature sensor was greatly reduced, and ΔT reached 60.7℃. Figure 4 Figures (f) to (i) show thermal infrared images taken before, 0 min, 8 min, and 16 min after covering the hot stage with PVTMS@MWCNT-1.7 vol.%.

[0075] Figure 4 Figure (e) illustrates the infrared stealth mechanism of PVTMS@MWCNT nanoaerogel materials. Generally, heat transfer mechanisms include thermal radiation, thermal conduction, and thermal convection. For PVTMS@MWCNT nanoaerogel materials, the high specific surface area and high porosity are beneficial for blocking thermal radiation through reflection and reducing solid-phase thermal conduction, respectively, while the nanopore size is beneficial for blocking gas-phase thermal conduction and thermal convection through the Knudsen effect. Therefore, PVTMS@MWCNT nanoaerogel materials possess excellent infrared stealth performance.

[0076] Example 5

[0077] In this embodiment, a double-layer PVTMS@MWCNT / graphene electromagnetic interference shielding material was prepared, and the electromagnetic interference (EMI) shielding performance of the material was tested.

[0078] (1) First, a graphene film with excellent conductivity and EMW reflectivity was prepared by solvent casting and thermal reduction. The specific preparation method can be found in the references [Nano Research.15(6),4902-4908(2022), Advanced Materials.29(27),1700589(2017), Applied Physics Reviews.10(1),(2023)]. The thickness of the prepared graphene film was approximately 0.03 mm. Then, the graphene film (reflective layer) was glued to the lower surface of the PVTMS@MWCNT-1.7 vol.% prepared in Example 1, thus preparing bilayer PVTMS@MWCNT / graphene electromagnetic interference shielding materials with three thicknesses.

[0079] (2) The EMI shielding performance of the graphene film and the prepared double-layer PVTMS@MWCNT / graphene electromagnetic interference shielding material were tested respectively, and the results are as follows: Figure 5 As shown.

[0080] for Figure 5 As shown in Figures (d), (d'), (d'), (d'), and (d'), due to the very high conductivity of the graphene film, most of the incident EMW is reflected at the air / graphene film interface (average R = 0.98). However, for the bilayer PVTMS@MWCNT / graphene electromagnetic interference shielding material, the reflection (SER) is greatly reduced, and almost all of the total EMI shielding (SET) comes from absorption (SEA). Figure 5 As shown in Figures (b”) and (b”’), the ~2 mm thick bilayer PVTMS@MWCNT / graphene electromagnetic interference shielding material exhibits the best EMW absorption performance in electromagnetic interference shielding applications. The maximum A / R is 72.3, and the average A / R in the Ku band is 25.4. The effective EMW absorption bandwidth (EBW, A / R>10) is 4.13 GHz. This demonstrates that the nano-aerogel material provided by this invention also shows great potential in preparing bilayer materials with excellent electromagnetic interference shielding performance (primarily absorption).

Claims

1. A nano-aerogel material possessing both excellent wave absorption and infrared stealth properties, characterized in that, This nano-aerogel material is composed of a silicon-containing polymer matrix with high cross-linking density and carbon nanomaterials. The carbon nanomaterials are uniformly dispersed in the silicon-containing polymer matrix. The silicon-containing polymer matrix is ​​adsorbed on the surface of the carbon nanomaterials to form an organic-inorganic hybrid structure. This nano-aerogel material has a nanoscale pore structure with a porosity of 90%~95%. This nano-aerogel material has both wave absorption properties and infrared stealth properties. The volume content of carbon nanomaterials in this nano-aerogel material is 1.6 vol.%~1.9 vol.%; the pore size of the nano-aerogel material is 30~40 nm; the silicon-containing polymer matrix is ​​polyvinyltrimethoxysilane; This nano-aerogel material was prepared by the following method: (1) Polyvinyltrimethoxysilane was dissolved in a solvent to obtain a silicon-containing polymer matrix solution; carbon nanomaterials were uniformly dispersed in the solvent to obtain a carbon nanomaterial dispersion; the silicon-containing polymer matrix solution and the carbon nanomaterial dispersion were thoroughly mixed, and then ammonia was added to induce the decomposition of the spiking lines. After adding ammonia and mixing evenly, a gel precursor solution was obtained. The gel precursor solution was transferred to a mold and heated at 35~45°C. o The wet gel was placed in an oven at C until the gel precursor solution turned into a gel state; the wet gel was then immersed in a solvent for aging. In this step, the ratio of the silicon-containing polymer matrix solution to the carbon nanomaterial dispersion is controlled so that the volume percentage of carbon nanomaterials in the mixture of the silicon-containing polymer matrix solution and the carbon nanomaterial dispersion is less than 1.9 vol.%, and the amount of ammonia added is controlled so that the molar ratio of water to Si element in the silicon-containing polymer matrix is ​​(5~10):

1. (2) Dry the aged sample in step (1) with supercritical carbon dioxide to obtain the final product.

2. The nano-aerogel material with excellent wave absorption and infrared stealth properties according to claim 1, characterized in that, The carbon nanomaterial is either a one-dimensional carbon nanomaterial or a two-dimensional carbon nanomaterial.

3. The nano-aerogel material with excellent wave absorption and infrared stealth properties according to claim 1, characterized in that, The concentration of the silicon-containing polymer matrix solution is 0.1~0.2 g / mL, and the concentration of the carbon nanomaterial dispersion is 1~60 mg / mL.

4. The nano-aerogel material with excellent wave absorption and infrared stealth properties according to claim 1, characterized in that, The aging time in step (1) is 20~30 h.

5. The nano-aerogel material with excellent wave absorption and infrared stealth properties according to claim 1, characterized in that... The preparation of polyvinyltrimethoxysilane is as follows: A thermal initiator is dissolved in a vinyltrimethoxysilane monomer, and the mass ratio of the thermal initiator to the vinyltrimethoxysilane monomer is controlled to be 1:(5~10). The mixture is then heated at 150~160°C under a nitrogen atmosphere. o Stir the reaction at C for 3-5 h to remove unreacted thermal initiator and vinyltrimethoxysilane monomer, and the product is obtained.

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