A microwave absorption-infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel and a preparation method thereof

Abstract

The application belongs to the technical field of microwave absorption-infrared stealth materials, and provides a microwave absorption-infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel and a preparation method thereof, which comprises the following steps: uniformly mixing MXene, a mixed silane coupling agent / dilute hydrochloric acid solution, CoZn-NC magnetic nanoparticles and a nanocellulose solution to obtain a mixed colloidal solution; injecting the mixed colloidal solution into a mold for directional freezing, and then drying and heat polymerizing to obtain the microwave absorption-infrared stealth material. The preparation method provided by the application selects nanocellulose as an aerogel matrix, uses transition metal carbide and CoZn-CN magnetic nanoparticles derived from ZIF-67@ZIF-8 core-shell MOF as dielectric-magnetic loss materials, and introduces a silane coupling agent to ensure that a precursor forms a uniform and stable colloidal solution; then, a three-dimensional network structure is formed through a directional freezing method, and nanocellulose-based dielectric-magnetic coupling aerogel is obtained after vacuum freeze drying and heat polymerization.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorption-infrared stealth materials technology, and relates to a microwave absorption-infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel and its preparation method. Background Technology

[0002] With the rapid development and application of modern communication technology and the electronics industry, electromagnetic waves, as one of the important information media, have been widely used in fields such as medicine, civilian use, 5G communication, radar, and navigation, bringing tremendous convenience to human life and significantly promoting the process of social intelligence. However, the explosive development of various electronic devices and the application of a large number of wireless communication technologies have also brought about major problems such as electromagnetic interference, electromagnetic radiation pollution, and electromagnetic information leakage. Therefore, electromagnetic radiation is considered to be the fifth largest pollution problem in the world today, and as electronic technology develops towards integration, high frequency, and miniaturization, the electromagnetic radiation problem is becoming increasingly serious. Therefore, it is necessary to effectively control the electromagnetic radiation generated by various devices such as search, identification, tracking, data transmission, and wireless communication. At the same time, the stealth capabilities of weaponry are crucial to improving the overall combat effectiveness of the army, navy, and air force and national defense security.

[0003] In recent years, microwave absorbing materials have attracted widespread attention from researchers to address electromagnetic pollution and national defense security issues. They can convert incident electromagnetic waves into heat or other forms of energy, thereby rapidly attenuating electromagnetic waves, reducing the radar cross-section of targets, and enhancing the stealth performance of equipment. However, traditional absorbing materials suffer from bottlenecks limiting their application, such as high material addition requirements, narrow absorption bandwidth, large matching thickness, and poor environmental stability. Therefore, there is an urgent need to develop a cost-effective and simplified absorbing material to meet practical needs.

[0004] Against this backdrop, aerogels, as a novel type of microwave absorbing material, possess unique advantages. Compared to traditional microwave absorbing materials, aerogels exhibit ultra-light weight and a highly designable porous structure. This porous structure helps suppress the skin effect and enhance multiple internal reflections and dissipation. Nanocellulose-based aerogels have attracted widespread attention due to their renewable source, environmental friendliness, non-toxicity, and ease of preparation. Furthermore, the abundant surface functional groups on nanocellulose can be cross-linked with other functional components and easily modified, thereby expanding their multifunctionality and application range. However, pristine nanocellulose-based aerogels inherently possess microwave transmission properties, thus requiring the addition of appropriate electromagnetic wave absorbers to enhance electromagnetic attenuation capabilities. Research indicates that coupling magnetic and dielectric loss media can effectively achieve high-performance impedance matching and improve the electromagnetic wave loss capability of composite materials.

[0005] Despite the numerous advantages of nanocellulose-based aerogels as microwave absorbing metamaterials, several challenges remain to be overcome. Firstly, further research is needed to optimize aerogel preparation methods and process parameters to achieve excellent impedance matching and a wider absorption bandwidth. Simultaneously, addressing the compatibility between microwave absorption and infrared stealth is also a research hotspot. Furthermore, the high strength and durability of aerogels in harsh environments require in-depth investigation to ensure their reliability in practical applications and their ability to withstand complex and changing external environments. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a microwave absorption-infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel and its preparation method. The preparation method provided by the present invention selects nanocellulose as the aerogel matrix, uses transition metal carbide (MXene) and ZIF-67@ZIF-8 core-shell MOF-derived CoZn-CN magnetic nanoparticles as dielectric-magnetic loss materials, and introduces a silane coupling agent to ensure that the precursor forms a uniform and stable colloidal solution. Then, a three-dimensional network structure is formed by directional freezing, followed by vacuum freeze-drying and thermal polymerization to obtain nanocellulose-based dielectric-magnetic coupling aerogel.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a microwave-absorbing infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel, the preparation method comprising:

[0009] MXene, a silane coupling agent / dilute hydrochloric acid mixed solution, CoZn-NC magnetic nanoparticles, and nanocellulose solution were mixed evenly to obtain a mixed colloidal solution. The mixed colloidal solution was injected into a mold for directional freezing, followed by drying and thermal polymerization to obtain the microwave absorbing-infrared stealth material.

[0010] This invention selects MXene, which has high conductivity, as the dielectric loss component. MXene has a large specific surface area, good dielectric properties, and low infrared emissivity, making it suitable for infrared stealth. Compared with other conductive materials such as graphene and carbon nanotubes, the aerogel materials prepared using the raw materials provided in this invention can achieve microwave absorption-infrared stealth compatibility, endowing the aerogel with multi-band stealth performance. ZIF-8@ZIF-67 core-shell MOF-derived CoZn-NC magnetic nanoparticles are selected as the magnetic loss component. The magnetic ZIF derivative significantly enhances the magnetic response and generates abundant carbon nanotubes in the shell after high-temperature carbonization, thereby improving interfacial polarization.

[0011] This invention constructs a multi-electromagnetic loss mechanism by dielectric coupling MXene with CoZn-NC magnetic nanoparticles. The magnetic loss introduced by CoZn-NC magnetic nanoparticles and the dielectric loss of MXene generate a synergistic enhancement effect. Anisotropic hierarchical channel structures are formed by directional freezing-induced formation of nanocellulose. At the same time, the interaction between MXene and nanocellulose and other components is achieved by using a silane coupling agent to realize the stable cross-linking of the three-dimensional network. This achieves synergistic optimization of electromagnetic parameters and impedance matching, resulting in a high-performance, lightweight, and efficient microwave absorbing material.

[0012] The preparation method provided by this invention constructs a directional multi-level pore structure, resulting in a microwave absorbing material with excellent absorption performance and good impedance matching. It exhibits a superior effective absorption bandwidth (EAB) of 6.25 GHz at a thickness of only 1.5 mm, covering 100% of the Ku band (12.4-18 GHz), with a minimum reflection loss below -30 dB. Furthermore, it possesses infrared stealth capabilities, remaining invisible to infrared detectors, achieving multi-band compatible stealth capabilities combining microwave absorption and infrared stealth. Secondly, the microwave absorption-infrared stealth material prepared by this invention exhibits excellent environmental adaptability, with a water contact angle as high as 150.6°, excellent reversible compressibility under strain conditions of 20-80%, and is difficult to ignite in air. Thirdly, the aerogel material prepared by this invention has a low density of only 0.0195 g / cm³. 3 Around 1.0 g / cm³, compared to traditional coating-type microwave absorbing materials (with a density of 1.0 g / cm³ after using paraffin binder). 3 Its density is significantly reduced.

[0013] It should be noted that the CoZn-NC magnetic nanoparticles and their preparation methods used in this invention have been disclosed in the prior art, and this invention does not impose specific requirements or limitations on them. Exemplarily, this invention provides the following optional preparation methods:

[0014] (1) 4.368 g of Co(NO3)2·6H2O, 4.64 g of Zn(NO3)2·6H2O and 4.208 g of 2-methylimidazole were dispersed in 15 mL, 15 mL and 30 mL of methanol, respectively, to obtain cobalt nitrate solution, zinc nitrate solution and 2-methylimidazole solution;

[0015] (2) Cobalt nitrate solution was added dropwise to 2-methylimidazole solution and the mixture was sonicated for 15 min. Then, zinc nitrate solution was added dropwise to the mixture and sonicated for 15 min. After standing at room temperature for 1 h, the purple solid was collected by centrifugation, washed 6 times with ethanol, and dried under vacuum at 60 °C for 12 h to obtain dodecahedron ZIF-67@ZIF-8.

[0016] (3) Place the dried ZIF-67@ZIF-8 into a tube furnace, introduce protective gas into the tube furnace, heat to 700°C at a heating rate of 5°C / min, keep warm for 2 hours, and then cool naturally to obtain the CoZn-NC magnetic nanoparticles used in this invention.

[0017] As a preferred embodiment of the present invention, the ratio of MXene, the silane coupling agent / dilute hydrochloric acid mixed solution, the CoZn-NC magnetic nanoparticles, and the nanocellulose solution is (100~150) mg:(0.1~1) mL:(100~150) mg:(10~15) g. For example, it can be 100 mg:0.1 mL:100 mg:10 g, 110 mg:0.3 mL:110 mg:11 g, 120 mg:0.5 mL:120 mg:12 g, 130 mg:0.7 mL:130 mg:13 g, 140 mg:0.9 mL:140 mg:14 g, or 150 mg:1 mL:150 mg:15 g. However, it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0018] For example, in the actual preparation process, the amount of MXene added to the mixed colloidal solution can be 100-150 mg, the amount of the silane coupling agent / dilute hydrochloric acid mixed solution added can be 0.1-1.0 mL, the amount of CoZn-NC magnetic nanoparticles added can be 100-150 mg, and the amount of nanocellulose solution added can be 5-20 g. Of course, those skilled in the art can proportionally increase or decrease the amount of each component added based on actual needs. Any adjustment of the amount added within the proportional range defined by this invention falls within the protection scope defined by this invention.

[0019] This invention specifically limits the ratio of MXene, silane coupling agent / dilute hydrochloric acid mixed solution, CoZn-NC magnetic nanoparticles and nanocellulose solution in the mixed colloidal solution to (100~150)mg:(0.1~1)mL:(100~150)mg:(10~15)g. Within this range, the microwave absorbing material prepared has the best comprehensive performance.

[0020] When the amount of MXene added is too low, it cannot form an effective conductive network in the matrix, resulting in insufficient conductivity loss, low dielectric constant, and significantly reduced microwave absorption performance. When the amount of MXene added is too high, it will cause the overall conductivity of the composite material to rise sharply, causing severe impedance mismatch, which will cause most electromagnetic waves to be reflected on the material surface and unable to enter the interior, thus also causing deterioration of microwave absorption performance.

[0021] Since silane coupling agents play a crucial role in crosslinking and reinforcing in aerogel formation, if the amount of silane coupling agent / dilute hydrochloric acid mixed solution added is too low, it will lead to insufficient crosslinking degree of the three-dimensional network of the aerogel, a fragile skeleton structure, and a significant decrease in mechanical properties. If the amount of silane coupling agent / hydrochloric acid water mixed solution added is too high, excessive silane coupling agent will undergo self-condensation to form redundant soft phases, destroying the porous structure of the aerogel, resulting in material shrinkage, increased density, and deterioration of thermal insulation performance.

[0022] When the amount of CoZn-NC magnetic nanoparticles added is too low, sufficient magnetic loss centers cannot be formed in the matrix, resulting in insufficient magnetic loss capacity of the material and a significant decrease in wave absorption performance. When the amount of CoZn-NC magnetic nanoparticles added is too high, the CoZn-NC magnetic nanoparticles are prone to agglomeration, which causes impedance mismatch and weakens the loss mechanism, also leading to deterioration of wave absorption performance.

[0023] Since nanocellulose plays a key role in constructing a three-dimensional skeleton network in aerogel formation, when the amount of nanocellulose solution added is too low, the aerogel skeleton structure becomes sparse and the support strength is insufficient, resulting in a significant decrease in mechanical properties and easy collapse during the drying process. When the amount of nanocellulose solution added is too high, excessive cross-linking hydrogen bonds between fibers are caused, which compresses and blocks the pore structure, resulting in an increase in material density, a decrease in specific surface area, and a deterioration in thermal insulation performance.

[0024] In a preferred embodiment of the present invention, MXene is titanium carbide.

[0025] As a preferred embodiment of the present invention, the silane coupling agent / dilute hydrochloric acid mixed solution is composed of a silane coupling agent and a dilute hydrochloric acid solution.

[0026] In some optional examples, the silane coupling agent comprises any one or a combination of at least two of vinyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, n-propyltrimethoxysilane, n-octyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or γ-aminopropyltriethoxysilane.

[0027] In some optional instances, the mass fraction of the silane coupling agent in the silane coupling agent / dilute hydrochloric acid mixture is 30 to 50 wt%, for example, it can be 30 wt%, 32 wt%, 34 wt%, 36 wt%, 38 wt%, 40 wt%, 42 wt%, 44 wt%, 46 wt%, 48 wt%, or 50 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] In some alternative instances, the pH of the dilute hydrochloric acid solution is 3 to 5, for example, it may be 3, 4 or 5, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0029] As a preferred technical solution of the present invention, the nanocellulose in the nanocellulose solution includes any one or a combination of at least two of TEMPO oxidized cellulose nanofibers, TEMPO oxidized cellulose nanocrystals, carboxylated cellulose nanofibers, phosphorylated cellulose nanofibers, carboxylated cellulose nanocrystals, or phosphorylated cellulose nanocrystals.

[0030] In some optional examples, the mass fraction of the nanocellulose solution is 0.5 to 2 wt%, for example, it may be 0.5 wt%, 0.7 wt%, 0.9 wt%, 1.1 wt%, 1.3 wt%, 1.5 wt%, 1.7 wt%, 1.9 wt%, or 2.0 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] As a preferred technical solution of the present invention, the stirring time of the mixed colloidal solution is 60~120min, for example, it can be 60min, 65min, 70min, 75min, 80min, 85min, 90min, 95min, 100min, 105min, 110min, 115min or 120min, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0032] This invention specifically limits the stirring time of the mixed colloidal solution to 60-120 min. The stirring process is crucial to ensure uniform dispersion and full reaction of the reactants. When the stirring time is less than 60 min, the reactants are unevenly dispersed, local components segregate, and it is difficult to form a uniform and stable microstructure. When the stirring time is more than 120 min, the excessive mechanical shearing action will destroy the already formed microstructure or trigger unnecessary side reactions, which will instead cause a decrease in the performance of the microwave absorbing material.

[0033] As a preferred technical solution of the present invention, the directional freezing operation process includes:

[0034] A mold containing a mixed colloidal solution is placed on a low-temperature freezing plate, and ice crystals grow from bottom to top, transforming the mixed colloidal solution from a liquid to a solid.

[0035] As a preferred technical solution of the present invention, the drying method is freeze drying.

[0036] In some optional instances, the freeze-drying temperature is ≤-60°C, for example, it may be -60°C, -61°C, -62°C, -63°C, -64°C, -65°C, -66°C, -67°C, -68°C, -69°C or -70°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0037] In some optional instances, the freeze-drying time is 24 to 72 hours, for example, 24 hours, 30 hours, 35 hours, 40 hours, 45 hours, 50 hours, 55 hours, 60 hours, 65 hours, 70 hours, or 72 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0038] As a preferred embodiment of the present invention, the thermal polymerization is carried out in a vacuum environment.

[0039] In some alternative instances, the temperature of the thermal polymerization is 100~120°C, for example, 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C or 120°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0040] This invention specifically limits the thermal polymerization temperature to 100~120°C. Since the thermal polymerization temperature directly affects the reaction kinetics of the hydrolysis and condensation of the silane coupling agent and the network structure of the final material, when the thermal polymerization temperature is below 100°C, the reaction activity is insufficient, resulting in low degree of condensation crosslinking, fragile gel skeleton, and difficulty in forming a stable three-dimensional network. When the thermal polymerization temperature is above 120°C, the reaction rate is too fast, resulting in local over-condensation, causing uneven network structure and increased internal stress, which makes the material prone to cracking and macroscopic shrinkage during the drying process.

[0041] In some optional instances, the thermal polymerization time is 100 to 150 min, for example, 100 min, 105 min, 110 min, 115 min, 120 min, 125 min, 130 min, 135 min, 140 min, 145 min or 150 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0042] This invention specifically limits the thermal polymerization time to 100-150 min. The thermal polymerization time directly determines the completion of the hydrolysis and condensation reaction of the silane coupling agent and the maturity of the network structure. When the thermal polymerization time is less than 100 min, the cross-linking of the silicon-oxygen network is insufficient, the strength of the gel skeleton is insufficient, and it is easy to collapse due to capillary force during the drying process. When the thermal polymerization time is more than 150 min, the excessively prolonged polymerization will lead to excessive shrinkage and aging of the network, making the gel brittle and reducing its porosity, which will damage its performance.

[0043] For example, the present invention provides a method for preparing a microwave-absorbing infrared stealth material based on dielectric-magnetic coupling aerogel, the preparation method specifically including the following steps:

[0044] (1) Add 0.1~1.0 mL of silane coupling agent / dilute hydrochloric acid mixed solution to 10~15 g of nanocellulose solution; wherein, the mass fraction of nanocellulose solution is 0.5~2 wt%, the mass fraction of silane coupling agent in silane coupling agent / dilute hydrochloric acid mixed solution is 30~50 wt%, and the pH of dilute hydrochloric acid is 3~5;

[0045] (2) Add 100~150mg of MXene and 100~150mg of CoZn-NC magnetic nanoparticles to the obtained mixed solution respectively, and stir vigorously for 60~120min to form a homogeneous and stable mixed colloidal solution;

[0046] (3) Pour the well-stirred mixed colloidal solution into a silicone-based mold and place the mold on a low-temperature freezing plate for freezing treatment (the low-temperature freezing plate is rapidly cooled by liquid nitrogen). Due to the temperature difference in space, ice crystals grow directionally from bottom to top, and the mixed colloidal solution changes from liquid to solid. Then, take out the mold and freeze-dry it in a vacuum environment below -60℃ for 24~72h.

[0047] (4) The freeze-dried aerogel is placed in a vacuum drying oven, and after vacuuming, it is heated at 100~120°C for 100~150 min for thermal polymerization, and then cooled naturally to obtain the microwave absorption-infrared stealth material.

[0048] Secondly, the present invention provides a microwave-absorbing infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel prepared by the preparation method described in the first aspect.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] This invention selects MXene, which has high conductivity, as the dielectric loss component. MXene has a large specific surface area, good dielectric properties, and low infrared emissivity, making it suitable for infrared stealth. Compared with other conductive materials such as graphene and carbon nanotubes, the aerogel materials prepared using the raw materials provided in this invention can achieve microwave absorption-infrared stealth compatibility, endowing the aerogel with multi-band stealth performance. ZIF-8@ZIF-67 core-shell MOF-derived CoZn-NC magnetic nanoparticles are selected as the magnetic loss component. The magnetic ZIF derivative significantly enhances the magnetic response and generates abundant carbon nanotubes in the shell after high-temperature carbonization, thereby improving interfacial polarization.

[0051] This invention constructs a multi-electromagnetic loss mechanism by dielectric coupling MXene with CoZn-NC magnetic nanoparticles. The magnetic loss introduced by CoZn-NC magnetic nanoparticles and the dielectric loss of MXene generate a synergistic enhancement effect. Anisotropic hierarchical channel structures are formed by directional freezing-induced formation of nanocellulose. At the same time, the interaction between MXene and nanocellulose and other components is achieved by using a silane coupling agent to realize the stable cross-linking of the three-dimensional network. This achieves synergistic optimization of electromagnetic parameters and impedance matching, resulting in a high-performance, lightweight, and efficient microwave absorbing material.

[0052] The preparation method provided by this invention constructs a directional multi-level pore structure, resulting in a microwave absorbing material with excellent absorption performance and good impedance matching. It exhibits a superior effective absorption bandwidth (EAB) of 6.25 GHz at a thickness of only 1.5 mm, covering 100% of the Ku band (12.4-18 GHz), with a minimum reflection loss below -30 dB. Furthermore, it possesses infrared stealth capabilities, remaining invisible to infrared detectors, achieving multi-band compatible stealth capabilities combining microwave absorption and infrared stealth. Secondly, the microwave absorption-infrared stealth material prepared by this invention exhibits excellent environmental adaptability, with a water contact angle as high as 150.6°, excellent reversible compressibility under strain conditions of 20-80%, and is difficult to ignite in air. Thirdly, the aerogel material prepared by this invention has a low density of only 0.0195 g / cm³. 3 Around 1.0 g / cm³, compared to traditional coating-type microwave absorbing materials (with a density of 1.0 g / cm³ after using paraffin binder). 3 Its density is significantly reduced. Attached Figure Description

[0053] Figure 1 This is a scanning electron microscope image of the cross-section of the microwave absorbing infrared stealth material prepared in Example 1 of the present invention;

[0054] Figure 2 This is a scanning electron microscope image of the longitudinal section of the microwave absorbing infrared stealth material prepared in Example 1 of the present invention;

[0055] Figure 3 This is a scanning electron microscope image of the internal structure of the microwave absorbing infrared stealth material prepared in Example 1 of the present invention;

[0056] Figure 4 This is a schematic diagram of the structure of the microwave absorption-infrared stealth material absorption performance testing device prepared according to an embodiment of the present invention;

[0057] Figure 5 The microwave absorption-infrared stealth material prepared in Example 1 of this invention exhibits microwave absorption properties.

[0058] Figure 6 This is a test image of the infrared stealth capability of the microwave absorption-infrared stealth material prepared in Example 1 of the present invention;

[0059] Figure 7 This is a test image of the flame retardant properties of the microwave absorbing-infrared stealth material prepared in Example 1 of the present invention;

[0060] Figure 8 The water contact angle test diagrams are shown for the microwave absorbing-infrared stealth materials prepared in Example 1 and Comparative Example 2 of this invention.

[0061] Figure 9 This is a comparison diagram of the mechanical properties of the microwave absorbing-infrared stealth materials prepared in Example 1 and Comparative Example 2 of the present invention;

[0062] Figure 10 This is a typical cyclic compressive stress-strain curve of the microwave absorbing infrared stealth material prepared in Example 1 of the present invention. Detailed Implementation

[0063] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0064] Example 1

[0065] This embodiment provides a method for preparing a microwave-absorbing infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel, specifically including the following steps:

[0066] (1) Add 0.1 mL of MTMS / dilute hydrochloric acid mixed solution to 10 g of TEMPO oxidized cellulose nanofiber solution; wherein, the mass fraction of TEMPO oxidized cellulose nanofiber solution is 1.7 wt%, the mass fraction of MTMS in MTMS / dilute hydrochloric acid mixed solution is 50 wt%, and the pH of dilute hydrochloric acid is 3;

[0067] (2) Add 120 mg of MXene and 120 mg of CoZn-NC magnetic nanoparticles to the obtained mixed solution respectively, stir vigorously for 100 min to form a homogeneous and stable mixed colloidal solution;

[0068] (3) Pour the well-stirred mixed colloidal solution into a silicone-based mold and place the mold on a low-temperature freezing plate for freezing treatment (the low-temperature freezing plate is rapidly cooled by liquid nitrogen). Due to the temperature difference in space, ice crystals grow directionally from bottom to top, and the mixed colloidal solution changes from liquid to solid. Then, take out the mold and freeze-dry it in a vacuum environment at -70℃ for 48 hours.

[0069] (4) The freeze-dried aerogel is placed in a vacuum drying oven, and after vacuuming, it is heated at 110°C for 120 min for thermal polymerization. Then it is cooled naturally to obtain the dielectric-magnetic coupling aerogel microwave absorption-infrared stealth material.

[0070] After measurement, the density of the finally prepared dielectric-magnetic coupled aerogel microwave absorption-infrared stealth material was found to be 0.0193 g / cm³. 3 .

[0071] Figure 1 , Figure 2 and Figure 3 The microstructure of the dielectric-magnetic coupled aerogel microwave absorption-infrared stealth material prepared in this embodiment is shown. Figure 1 and Figure 2 It can be seen that directional freezing gives aerogels an anisotropic structure, such as... Figure 1 As shown, the aerogel exhibits a honeycomb-like square porous structure along its cross-section, with pore sizes ranging from 30 to 60 μm. Figure 2 As shown, the aerogel exhibits a vertical tubular structure along its longitudinal cross-section, with cell walls arranged along the direction of ice crystal growth. Figure 3 As shown, the CoZn-NC magnetic nanoparticles are uniformly anchored on the cell wall.

[0072] Figure 4 A testing device for the microwave absorption performance of flame-retardant structural microwave absorbing materials is shown, such as... Figure 4As shown, the microwave absorption performance testing device includes a vector network analyzer and a rectangular waveguide fixture. The dielectric constant of the material is tested using the waveguide method. The material is cut to a specified size and filled into a brass sample cell. The dielectric properties are tested in the X-band (8.2-12.4 GHz) and Ku-band (12.4-18 GHz).

[0073] Figure 5 The microwave absorption properties of the dielectric-magnetic coupled aerogel microwave-absorbing-infrared stealth material prepared in this embodiment are shown. Figure 4 The test device shown is used for testing, by Figure 5 It can be seen that with a thickness of 1.5mm, the effective absorption bandwidth EAB covers 100% of the Ku band, reaching 6.25GHz, and the minimum reflection loss RLmin with a thickness of 2mm is -31dB.

[0074] Figure 6 This embodiment demonstrates the infrared stealth capability of the dielectric-magnetic coupling aerogel microwave absorption-infrared stealth material. The material was placed over a person's hand, and an infrared detector captured the covered portion, showing it blending seamlessly with the surrounding environment. However, the uncovered portion of the hand stood out. This indicates that the dielectric-magnetic coupling aerogel prepared in this embodiment achieves multi-band stealth capability through microwave absorption-infrared stealth, making it more practically applicable.

[0075] Figure 7 The flame retardant properties of the dielectric-magnetic coupled aerogel microwave absorption-infrared stealth material provided in this example are shown. When the dielectric-magnetic coupled aerogel microwave absorption-infrared stealth material prepared in this example is burned in air with an alcohol lamp, there is no obvious combustion phenomenon within 30 seconds, which shows that it has excellent flame retardant properties.

[0076] Example 2

[0077] This embodiment provides a method for preparing a microwave-absorbing infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel, specifically including the following steps:

[0078] (1) Add 0.3 mL of VTMS / dilute hydrochloric acid mixed solution to 11 g of TEMPO oxidized cellulose nanofiber solution; wherein, the mass fraction of TEMPO oxidized cellulose nanofiber solution is 1.5 wt%, the mass fraction of VTMS in VTMS / dilute hydrochloric acid mixed solution is 40 wt%, and the pH of dilute hydrochloric acid is 4;

[0079] (2) Add 130 mg of MXene and 130 mg of CoZn-NC magnetic nanoparticles to the obtained mixed solution respectively, stir vigorously for 120 min to form a homogeneous and stable mixed colloidal solution;

[0080] (3) Pour the well-stirred mixed colloidal solution into a silicone-based mold and place the mold on a low-temperature freezing plate for freezing treatment (the low-temperature freezing plate is rapidly cooled by liquid nitrogen). Due to the temperature difference in space, ice crystals grow directionally from bottom to top, and the mixed colloidal solution changes from liquid to solid. Then, take out the mold and freeze-dry it in a vacuum environment at -70℃ for 72 hours.

[0081] (4) The freeze-dried aerogel is placed in a vacuum drying oven, and after vacuuming, it is heated at 120°C for 100 min for thermal polymerization, and then cooled naturally to obtain the dielectric-magnetic coupling aerogel microwave absorption-infrared stealth material.

[0082] The flame-retardant structural microwave absorbing material prepared in this embodiment has basically the same macroscopic and microscopic morphology as the material obtained in Example 1. It effectively absorbs 100% of the Ku band in its EAB bandwidth and also possesses infrared stealth, waterproof, flame-retardant, and mechanical properties. The density and minimum reflection loss values ​​are shown in Table 1.

[0083] Example 3

[0084] This embodiment provides a method for preparing a microwave-absorbing infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel, specifically including the following steps:

[0085] (1) Add 0.5 mL of PTES / dilute hydrochloric acid mixed solution to 12 g of TEMPO oxidized cellulose nanofiber solution; wherein, the mass fraction of TEMPO oxidized cellulose nanofiber solution is 2.0 wt%, the mass fraction of PTMS in MTMS / dilute hydrochloric acid mixed solution is 30 wt%, and the pH of dilute hydrochloric acid is 4;

[0086] (2) Add 150 mg of MXene and 150 mg of CoZn-NC magnetic nanoparticles to the obtained mixed solution respectively, and stir vigorously for 90 min to form a homogeneous and stable mixed colloidal solution;

[0087] (3) Pour the well-stirred mixed colloidal solution into a silicone-based mold and place the mold on a low-temperature freezing plate for freezing treatment (the low-temperature freezing plate is rapidly cooled by liquid nitrogen). Due to the temperature difference in space, ice crystals grow directionally from bottom to top, and the mixed colloidal solution changes from liquid to solid. Then, take out the mold and freeze-dry it in a vacuum environment at -80℃ for 48 hours.

[0088] (4) The freeze-dried aerogel is placed in a vacuum drying oven, and after vacuuming, it is heated at 100°C for 150 min for thermal polymerization. Then it is cooled naturally to obtain the dielectric-magnetic coupling aerogel microwave absorption-infrared stealth material.

[0089] The flame-retardant structural microwave absorbing material prepared in this embodiment has basically the same macroscopic and microscopic morphology as the material obtained in Example 1. It effectively absorbs 100% of the Ku band in its EAB bandwidth and also possesses infrared stealth, waterproof, flame-retardant, and mechanical properties. The density and minimum reflection loss values ​​are shown in Table 1.

[0090] Example 4

[0091] This embodiment provides a method for preparing a microwave-absorbing infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel, specifically including the following steps:

[0092] (1) Add 0.8 mL of MTMS / dilute hydrochloric acid mixed solution to 13 g of TEMPO oxidized cellulose nanocrystal solution; wherein, the mass fraction of TEMPO oxidized cellulose nanocrystal solution is 1.5 wt%, the mass fraction of MTMS in MTMS / dilute hydrochloric acid mixed solution is 40 wt%, and the pH of dilute hydrochloric acid is 4.

[0093] (2) Add 100 mg of MXene and 100 mg of CoZn-NC magnetic nanoparticles to the obtained mixed solution respectively, and stir vigorously for 60 min to form a homogeneous and stable mixed colloidal solution;

[0094] (3) Pour the well-stirred mixed colloidal solution into a silicone-based mold and place the mold on a low-temperature freezing plate for freezing treatment (the low-temperature freezing plate is rapidly cooled by liquid nitrogen). Due to the temperature difference in space, ice crystals grow directionally from bottom to top, and the mixed colloidal solution changes from liquid to solid. Then, take out the mold and freeze-dry it in a vacuum environment at -60℃ for 72 hours.

[0095] (4) The freeze-dried aerogel is placed in a vacuum drying oven, and after vacuuming, it is heated at 110°C for 120 min for thermal polymerization. Then it is cooled naturally to obtain the dielectric-magnetic coupling aerogel microwave absorption-infrared stealth material.

[0096] The flame-retardant structural microwave absorbing material prepared in this embodiment has basically the same macroscopic and microscopic morphology as the material obtained in Example 1. It effectively absorbs 100% of the Ku band in its EAB bandwidth and also possesses infrared stealth, waterproof, flame-retardant, and mechanical properties. The density and minimum reflection loss values ​​are shown in Table 1.

[0097] Example 5

[0098] This embodiment provides a method for preparing a microwave-absorbing infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel, specifically including the following steps:

[0099] (1) Add 1 mL of VTMS / dilute hydrochloric acid mixed solution to 15 g of phosphorylated cellulose nanofiber solution; wherein, the mass fraction of phosphorylated cellulose nanofiber solution is 0.5 wt%, the mass fraction of MTMS in MTMS / dilute hydrochloric acid mixed solution is 50 wt%, and the pH of dilute hydrochloric acid is 5;

[0100] (2) Add 140 mg of MXene and 140 mg of CoZn-NC magnetic nanoparticles to the obtained mixed solution respectively, and stir vigorously for 100 min to form a homogeneous and stable mixed colloidal solution;

[0101] (3) Pour the well-stirred mixed colloidal solution into a silicone-based mold and place the mold on a low-temperature freezing plate for freezing treatment (the low-temperature freezing plate is rapidly cooled by liquid nitrogen). Due to the temperature difference in space, ice crystals grow directionally from bottom to top, and the mixed colloidal solution changes from liquid to solid. Then, take out the mold and freeze-dry it in a vacuum environment at -80℃ for 24 hours.

[0102] (4) The freeze-dried aerogel is placed in a vacuum drying oven, and after vacuuming, it is heated at 110°C for 150 min for thermal polymerization, and then cooled naturally to obtain the dielectric-magnetic coupling aerogel microwave absorption-infrared stealth material.

[0103] The flame-retardant structural microwave absorbing material prepared in this embodiment has basically the same macroscopic and microscopic morphology as the material obtained in Example 1. It effectively absorbs 100% of the Ku band in its EAB bandwidth and also possesses infrared stealth, waterproof, flame-retardant, and mechanical properties. The density and minimum reflection loss values ​​are shown in Table 1.

[0104] Example 6

[0105] This embodiment provides a method for preparing microwave absorption-infrared stealth material based on dielectric-magnetic coupling aerogel. The difference from Embodiment 1 is that in step (2), the amount of MXene added is adjusted to 10 mg, while other process parameters and operation steps are exactly the same as in Embodiment 1.

[0106] The flame-retardant structural microwave absorbing material prepared in this embodiment has basically the same macroscopic and microscopic morphology as the material obtained in Example 1, and its effective absorption bandwidth EAB covers 10% of the Ku band, and it also has flame-retardant properties. The density and minimum reflection loss values ​​are shown in Table 1.

[0107] Example 7

[0108] This embodiment provides a method for preparing microwave absorption-infrared stealth material based on dielectric-magnetic coupling aerogel. The difference from Embodiment 1 is that in step (2), the amount of MXene added is adjusted to 300mg, while other process parameters and operation steps are exactly the same as in Embodiment 1.

[0109] The flame-retardant structural microwave absorbing material prepared in this embodiment has basically the same macroscopic and microscopic morphology as the material obtained in Example 1. Its effective absorption bandwidth EAB covers 60% of the Ku band, and it also possesses the same infrared stealth, waterproof, flame-retardant, and mechanical properties. The density and minimum reflection loss values ​​are shown in Table 1.

[0110] Example 8

[0111] This embodiment provides a method for preparing microwave absorption-infrared stealth material based on dielectric-magnetic coupling aerogel. The difference from Embodiment 1 is that in step (2), the amount of CoZn-NC magnetic nanoparticles added is adjusted to 20mg, while other process parameters and operation steps are exactly the same as in Embodiment 1.

[0112] The flame-retardant structural microwave absorbing material prepared in this embodiment has basically the same macroscopic and microscopic morphology as the material obtained in Example 1. Its effective absorption bandwidth EAB covers 50% of the Ku band, and it also possesses the same infrared stealth, waterproof, flame-retardant, and mechanical properties. The density and minimum reflection loss values ​​are shown in Table 1.

[0113] Example 9

[0114] This embodiment provides a method for preparing microwave absorption-infrared stealth material based on dielectric-magnetic coupling aerogel. The difference from Embodiment 1 is that in step (2), the amount of CoZn-NC magnetic nanoparticles added is adjusted to 250mg, while other process parameters and operation steps are exactly the same as in Embodiment 1.

[0115] The flame-retardant structural microwave absorbing material prepared in this embodiment has basically the same macroscopic and microscopic morphology as the material obtained in Example 1. Its effective absorption bandwidth EAB covers 60% of the Ku band, and it also possesses the same infrared stealth, waterproof, flame-retardant, and mechanical properties. The density and minimum reflection loss values ​​are shown in Table 1.

[0116] Comparative Example 1

[0117] This comparative example provides a method for preparing a dielectric-magnetic coupled aerogel microwave absorption-infrared stealth material. The difference from Example 1 is that the addition of MTMS / dilute hydrochloric acid mixed solution in step (1) is omitted. Instead, TEMPO oxidized cellulose nanofiber solution, MXene and CoZn-NC magnetic nanoparticles are directly stirred. At the same time, the thermal polymerization operation in step (4) is omitted. Other process parameters and operation steps are exactly the same as in Example 1.

[0118] The dielectric-magnetically coupled aerogel microwave-absorbing infrared stealth material prepared in this comparative example has a volume that is 90% of the original material, an effective absorption bandwidth (EAB) covering 90% of the Ku band, and is not waterproof. Density and minimum reflection loss values ​​are shown in Table 1.

[0119] Comparative Example 2

[0120] This comparative example provides a method for preparing a dielectric-magnetic coupled aerogel microwave absorption-infrared stealth material. The difference from Example 1 is that the addition of MTMS / dilute hydrochloric acid mixed solution and MXene in steps (1) and (2) is omitted. Instead, TEMPO oxidized cellulose nanofiber solution is directly stirred with CoZn-NC magnetic nanoparticles. At the same time, the thermal polymerization operation in step (4) is omitted. Other process parameters and operation steps are exactly the same as in Example 1.

[0121] The volume of the dielectric-magnetic coupled aerogel microwave-absorbing infrared stealth material prepared in this comparative example is 86% of that of the raw material. It lacks microwave absorption, waterproofing, and mechanical properties. The density and minimum reflection loss values ​​are shown in Table 1.

[0122] The waterproof and mechanical properties of the microwave-absorbing infrared stealth materials prepared in Example 1 and Comparative Example 2 were compared and tested.

[0123] (1) Waterproofing test: Figure 8 The water contact angle test results of the microwave absorbing-infrared stealth materials prepared in Example 1 and Comparative Example 2 are shown. The microwave absorbing-infrared stealth material prepared in Example 1 can support water droplets and form a water contact angle of 150.5°, exhibiting significant superhydrophobicity (e.g., Figure 8 (a) shows that the microwave-absorbing infrared stealth material prepared in Comparative Example 2 immediately collapses on the surface and leaves holes when a water droplet falls, making it unable to support the droplet's residence (as shown in Figure 2). Figure 8 (b) shown).

[0124] (2) Mechanical performance testing: Figure 9 The mechanical properties of the microwave-absorbing infrared stealth materials prepared in Example 1 and Comparative Example 2 are compared. Figure 9 As can be seen in (a), the microwave absorbing-infrared stealth material prepared in Comparative Example 2, under 50% strain, cannot recover its shape after compression, while the microwave absorbing-infrared stealth material prepared in Example 1 exhibits excellent compression recovery ability under 50% strain (e.g., Figure 9 (b) shown).

[0125] Figure 10Typical cyclic compressive stress-strain curves of the microwave absorbing infrared stealth material prepared in Example 1 are shown. The aerogel exhibits excellent compression recovery ability at compression ratios of 20-80%, and does not undergo geometric deformation even at high strains of up to 80%. The maximum stress of the aerogel reaches 13.6 kPa at 80% strain.

[0126] Table 1

[0127] As can be seen from the test data provided in Table 1, the microwave absorption, infrared stealth, waterproof, flame retardant, and mechanical properties of the dielectric-magnetic coupled aerogel microwave absorption-infrared stealth materials prepared in Examples 1-5 of this invention all meet the requirements for use. However, compared with Examples 6-9, the overall performance of the microwave absorption materials prepared in Examples 1-5 is even better.

[0128] The test results of Examples 1, 6 and 7 show that the microwave absorption performance of the dielectric-magnetic coupled aerogel microwave absorption-infrared stealth materials prepared in Examples 6 and 7 has decreased. This is because the amount of MXene added in Example 6 is too low, which cannot form a complete conductive path, weakens the carrier migration ability, and makes it difficult to generate effective dielectric loss for electromagnetic waves. In contrast, the amount of MXene added in Example 7 is too high, which leads to a sharp increase in the conductivity of the aerogel, causing a serious impedance mismatch, which causes most of the electromagnetic waves to be reflected on the material surface and unable to enter the interior.

[0129] The test results of Examples 1, 8, and 9 show that the microwave absorption performance of the dielectric-magnetic coupled aerogel microwave absorption-infrared stealth materials prepared in Examples 8 and 9 has decreased. This is because the amount of CoZn-NC magnetic nanoparticles added in Example 8 is too low, which cannot form enough magnetic loss centers in the matrix, resulting in insufficient magnetic loss capacity of the material and failure to match the dielectric properties. In contrast, the amount of CoZn-NC magnetic nanoparticles added in Example 9 is too high, which causes the magnetic particles to easily agglomerate, leading to impedance mismatch and weakening the loss mechanism, thus causing its performance to degrade.

[0130] The test results of Example 1, Comparative Example 1 and Comparative Example 2 show that the absence of MTMS in Comparative Example 1 caused the material to change from superhydrophobic to hydrophilic, resulting in a significant decrease in waterproof performance. The absence of both MTEM and MXene in Comparative Example 2 caused severe deterioration of the material's mechanical properties, loss of compression resilience, and complete failure of its wave absorption performance.

[0131] The above results demonstrate that the present invention effectively constructs a stable superhydrophobic structure by introducing MTMS, significantly improving the water resistance of the material. Simultaneously, through the synergistic effect of MXene, TOCNF, CoZn-NC magnetic nanoparticles, and other components, a continuous conductive network and a stable framework are constructed in the hierarchical porous aerogel formed by directional freezing. This not only endows the material with excellent compressive resilience but also synergistically enhances dielectric loss and electromagnetic wave absorption performance, thereby obtaining a multifunctional dielectric-magnetic coupled aerogel microwave absorption-infrared stealth material with excellent comprehensive performance.

[0132] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a microwave-absorbing infrared stealth material based on nanocellulose dielectric-magnetically coupled aerogel, characterized in that, The preparation method includes: MXene, a silane coupling agent / dilute hydrochloric acid mixed solution, CoZn-NC magnetic nanoparticles, and nanocellulose solution were mixed evenly to obtain a mixed colloidal solution. The mixed colloidal solution was injected into a mold for directional freezing, followed by drying and thermal polymerization to obtain the microwave absorbing-infrared stealth material.

2. The preparation method according to claim 1, characterized in that, The ratio of MXene, the silane coupling agent / dilute hydrochloric acid mixed solution, the CoZn-NC magnetic nanoparticles and the nanocellulose solution is (100~150)mg:(0.1~1)mL:(100~150)mg:(10~15)g.

3. The preparation method according to claim 1, characterized in that, The MXene is titanium carbide.

4. The preparation method according to claim 1, characterized in that, The silane coupling agent / dilute hydrochloric acid mixed solution is composed of a silane coupling agent and a dilute hydrochloric acid solution; The silane coupling agent includes any one or a combination of at least two of vinyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, n-propyltrimethoxysilane, n-octyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or γ-aminopropyltriethoxysilane. The mass fraction of the silane coupling agent in the silane coupling agent / dilute hydrochloric acid mixed solution is 30~50 wt%. The pH of the dilute hydrochloric acid solution is 3-5.

5. The preparation method according to claim 1, characterized in that, The nanocellulose in the nanocellulose solution includes any one or a combination of at least two of the following: TEMPO oxidized cellulose nanofibers, TEMPO oxidized cellulose nanocrystals, carboxylated cellulose nanofibers, phosphorylated cellulose nanofibers, carboxylated cellulose nanocrystals, or phosphorylated cellulose nanocrystals. The mass fraction of the nanocellulose solution is 0.5~2wt%.

6. The preparation method according to claim 1, characterized in that, The stirring time for the mixed colloidal solution is 60-120 minutes.

7. The preparation method according to claim 1, characterized in that, The directional freezing process includes: A mold containing a mixed colloidal solution is placed on a cryogenic freezing plate, and ice crystals grow from bottom to top, transforming the mixed colloidal solution from a liquid to a solid.

8. The preparation method according to claim 1, characterized in that, The drying method is freeze drying; The freeze-drying temperature is ≤-60℃; The freeze-drying time is 24~72h.

9. The preparation method according to claim 1, characterized in that, The thermal polymerization is carried out in a vacuum environment; The temperature of the thermal polymerization is 100~120℃; The thermal polymerization time is 100~150 min.

10. A microwave-absorbing infrared stealth material based on nanocellulose dielectric-magnetic coupling aerogel, prepared by the preparation method according to any one of claims 1 to 9.

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