Infrared stealth material based on thermal insulation and low emissivity collaborative strategy regulation and preparation method thereof

Abstract

The invention relates to an infrared stealth material based on thermal insulation and low emissivity collaborative strategy regulation and a preparation method thereof. The infrared stealth material based on heat insulation and low emissivity synergistic strategy regulation and control comprises a polyimide PI aerogel fiber braided fabric, a styrene-acrylic emulsion SA or polyvinyl alcohol transition layer attached to the surface of the polyimide PI aerogel fiber braided fabric, and a Ti < 3 > C < 2 > T < x > MXene / tannic acid TM composite low infrared emission layer attached to the surface of the transition layer.

Description

Technical Field

[0001] This invention belongs to the field of infrared stealth material preparation technology, specifically relating to an infrared stealth material and its preparation method based on a synergistic strategy of heat insulation and low emissivity. Background Technology

[0002] With the rapid development of modern military and weaponry, infrared detection technology has become an important means of information acquisition. To reduce the infrared radiation signature of military weapons and equipment and avoid detection, identification, or tracking by enemy infrared detection equipment, infrared stealth technology has been widely used in the military field. According to the Stefan-Boltzmann law (W=AσεT...),... 4 Where W is the total radiant energy, A is the radiant surface area, σ is the Boltzmann constant, ε is the infrared emissivity, and T is the absolute temperature), the infrared stealth design strategy mainly focuses on two aspects: controlling the temperature or reducing the emissivity of the object's surface.

[0003] Thermal insulation materials are the most readily available method for regulating the temperature of objects. Aerogels, as typical thermal insulation materials, significantly reduce heat convection due to their high porosity and nanopore size. Their high specific surface area and loose skeleton also limit solid-state heat conduction, resulting in ultra-low thermal conductivity and effectively blocking heat transfer. However, most aerogels currently studied are in block form, exhibiting shortcomings such as poor flexibility and shape fidelity. In contrast, polymer aerogel fibers possess excellent flexibility, weavability, and ease of integration, enabling them to be fabricated into flexible fabrics or integrated into complex systems through weaving processes. This overcomes the limitations of traditional block aerogels in applying to complex surfaces, demonstrating a broader application prospect than traditional aerogel materials. Among them, polyimide aerogel fibers, due to their excellent thermal stability and mechanical properties, have proven to be a promising flexible thermal insulation material.

[0004] Ti3C2T x MXene, as a novel low-infrared emissivity material, possesses a unique layered stacked structure and excellent conductivity, enabling it to reflect a large amount of infrared waves while reducing the absorption probability of infrared waves due to scattering behavior. It has been widely studied in the field of infrared stealth. Furthermore, after modification with tannic acid composites, it not only maintains the properties of Ti3C2T... x MXene's inherent low infrared emission significantly improves its susceptibility to oxidation, extending its lifespan. Furthermore, Ti3C2T... x MXene / tannic acid can be prepared in large areas at low cost through solution methods (such as spraying and spin coating), without the need for complex processes such as vacuum coating or magnetron sputtering required by traditional metal coatings. It can also be flexibly combined with polymers, fibers and other materials through simple surface modification or composite modification to adapt to different application scenarios. It shows more balanced comprehensive performance and broader application potential in the requirements of lightweight and flexible military equipment infrared stealth coatings.

[0005] However, in modern infrared stealth technology, both single thermal insulation materials and low emissivity materials have inherent limitations and cannot meet the stealth requirements in complex detection environments. While thermal insulation materials can suppress heat conduction through low thermal conductivity, their surface still forms a high-temperature radiation source due to heat accumulation. Conversely, while low emissivity materials can reduce surface infrared radiation intensity, they cannot effectively block the heat diffusion from internal heat sources. Therefore, combining the advantages of both, and using a composite material of thermal insulation and low emissivity materials, is an effective strategy for achieving efficient infrared stealth. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an infrared stealth multilayer material—polyimide / transition layer / Ti3C2T—based on a synergistic strategy of thermal insulation and low emissivity control. x MXene@tannic acid, its preparation method and application, the multilayer material has excellent infrared stealth properties.

[0007] In a first aspect, the present invention provides an infrared stealth material based on a synergistic strategy of thermal insulation and low emissivity. The infrared stealth material comprises: a polyimide (PI) aerogel fiber woven fabric, a styrene-acrylic emulsion (SA) or polyvinyl alcohol transition layer attached to the surface of the polyimide (PI) aerogel fiber woven fabric, and a Ti3C2T layer attached to the surface of the transition layer. x MXene / tannic acid™ composite low infrared emission layer.

[0008] Preferably, the polyimide aerogel fibers in the polyimide aerogel fiber woven fabric have a diameter of 200-700 μm and a length of 1-10 m.

[0009] Preferably, the thickness of the styrene-acrylic emulsion SA or polyvinyl alcohol transition layer is 200-1000 μm; Preferably, the Ti3C2T x The thickness of the MXene / tannic acid composite low infrared emission layer is 1-100 μm.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned infrared stealth material based on a synergistic strategy of thermal insulation and low emissivity, the preparation method comprising the following steps: (1) A mixed solution of p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic dianhydride was stirred in an ice-water bath and under nitrogen conditions. Then, triethylamine catalyst was added and stirring was continued to obtain a polyamide salt solution. The polyamide salt was then loaded into a syringe and extruded into a coagulation bath in the form of fibers using an injection pump for amination reaction. The solution was then dried and woven to obtain a polyimide aerogel fiber woven fabric. (2) Ti3AlC2 was added to a mixed solution of hydrochloric acid A and lithium fluoride and reacted in a water bath. Then, it was washed with hydrochloric acid B and deionized water and centrifuged until the pH of the supernatant was neutral. The lower precipitate obtained after centrifugation was redispersed in deionized water, sonicated, and centrifuged again. The supernatant was collected as the mono / few-layer Ti3C2T obtained by peeling. x MXene nanosheet solution, then tannic acid dissolved in the mono / few-layer Ti3C2T x The MXene nanosheet solution was mixed and stirred to obtain Ti3C2T. x MXene / tannic acid composite solution; (3) Coat the surface of the polyimide aerogel fiber woven fabric with styrene-acrylic emulsion or polyvinyl alcohol solution and cure it, then continue to spray Ti3C2T. x The MXene / tannic acid composite solution was dried to obtain the infrared stealth material based on the synergistic strategy of thermal insulation and low emissivity.

[0011] Preferably, in step (1), the solvent for the mixed solution of p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic dianhydride includes N-methylpyrrolidone; Preferably, the ratio of N-methylpyrrolidone, p-phenylenediamine, 3,3',4,4'-biphenyltetracarboxylic dianhydride and triethylamine is (130-300) mL : (6.48-9.72) g : (17.76-26.64) g : (15.9-33.4) mL, more preferably (170-220) mL : (8.1-9.18) g : (22.2-25.16) g : (16.7-26.3) mL.

[0012] Preferably, in step (1), the coagulation bath is prepared by mixing acetone, acetic anhydride and triethylamine in a volume ratio of (15-22):(1-1.1):(1-1.05).

[0013] Preferably, in step (1), the amination reaction is carried out at a temperature of 20-40°C for 12-30 hours.

[0014] Preferably, in step (2), the concentration of hydrochloric acid A is 8-10M; more preferably, the ratio of lithium fluoride, hydrochloric acid A, and Ti3AlC2 is 1.6-7.5g: 16-70mL: 1-3g.

[0015] Preferably, in step (2), the Ti3C2T x In MXene / tannic acid composite solution, Ti3C2T x The concentration of MXene is 10-20 mg / mL, and the concentration of tannic acid is 2-150 mg / mL.

[0016] Preferably, in step (3), the coating method includes spin coating, drop coating, spray coating or scraping coating; the concentration of the polyvinyl alcohol solution is 7.5-15%, preferably 12.5%; the curing temperature after coating the styrene-acrylic emulsion is 20-80℃, and the curing temperature after coating the polyvinyl alcohol solution is -18 to 60℃.

[0017] Beneficial effects (1) This invention establishes a styrene-acrylic emulsion transition layer on the surface of fiber fabric prepared by wet spinning combined with freeze drying, which solves the drawback of the unevenness of the fabric surface affecting the infrared emission performance, and successfully integrates heat-insulating aerogel fiber and low infrared emissivity Ti3C2T x By combining MXene and tannic acid, an infrared stealth multilayer material PI / SA / TM with excellent infrared stealth performance was prepared. (2) The infrared stealth multilayer material prepared by this invention exhibits low thermal conductivity (0.084 W / (m·K)) and low infrared emissivity (0.17), which compensates for the high emissivity (0.91) on the surface of polyimide aerogel fibers caused by the heat accumulation effect, and at the same time compensates for the low emissivity of Ti3C2T x The MXene / tannic acid exhibits a relatively high thermal conductivity (0.251 W / (m·K)) due to its inability to effectively block the thermal diffusion of internal heat sources. After heating on a 200℃ hot stage for ten minutes, the surface radiation temperature of the PI / SA / TM multilayer material is 40.7℃, which is superior to that of aerogel fiber fabric (118.1℃) and Ti3C2T. x MXene / tannic acid composite membrane (65.8℃); (3) The low emissivity layer of the multilayer stealth material PI / SA / TM used in this invention is tannic acid modified Ti3C2T. x MXene material significantly improves the oxidation stability of the material. Even after 15 days of humid heat at 50℃ and 95% humidity, it still maintains a low infrared emissivity of 0.24, extending its service life as an infrared stealth material. Attached Figure Description

[0018] Figure 1 The images show physical photos and SEM images of the PI fiber fabric and infrared stealth material PI / SA / TM prepared in Example 1. Figure 2 Fourier transform infrared spectra of the PI fiber fabric prepared in Example 1, the PI fiber fabric covered with styrene-acrylic emulsion, and the infrared stealth material PI / SA / TM. Figure 3 The high-resolution X-ray photoelectron spectroscopy (C1s) spectra of the PI fiber fabric prepared in Example 1, the PI fiber fabric covered with styrene-acrylic emulsion, and the infrared stealth material PI / SA / TM. Figure 4The PI / SA / TM prepared in Example 1 and the PI fiber fabric and Ti3C2T prepared in Comparative Examples 1-2 are examples of materials that can be compared with those prepared in Comparative Examples 1-2. x Thermal infrared images of the MXene / tannic acid composite membrane at ambient temperatures of 100°C and 200°C; Figure 5 This is a thermal infrared image of the infrared stealth material PI / SA / TM prepared in Example 1 applied to the surface of a weapon model. Figure 6 This is a thermal infrared imaging photograph of the infrared stealth material PI / SA / TM prepared in Example 1 applied to the field of human thermal camouflage. Detailed Implementation

[0019] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0020] First, this invention provides an infrared stealth material based on a synergistic strategy of thermal insulation and low emissivity. The infrared stealth material based on this synergistic strategy may include: a polyimide (PI) aerogel fiber woven fabric, a styrene-acrylic emulsion (SA) or polyvinyl alcohol transition layer attached to the surface of the polyimide (PI) aerogel fiber woven fabric, and a Ti3C2T layer attached to the surface of the transition layer. x MXene / tannic acid™ composite low infrared emission layer.

[0021] In some embodiments, the diameter of the polyimide aerogel fibers in the polyimide aerogel fiber woven fabric can be 200-700 μm, and the length can be 1-10 m.

[0022] The core reason for choosing polyimide (PI) for polymer aerogel fibers lies in the fact that PI's molecular characteristics and performance perfectly match the processing requirements and application needs of aerogel fibers: PI precursors (polyamide salts) have excellent spinning adaptability, and fibers can be continuously produced through processes such as wet spinning, while simultaneously constructing porous aerogel structures during the spinning process; finished PI aerogel fibers have high temperature resistance (far exceeding that of other polymers such as polyurethane), excellent mechanical toughness (can be bent and stretched, solving the brittleness problem of silica aerogel fibers) and low thermal conductivity; at the same time, it can be adapted to flexible thermal insulation scenarios such as aerospace thermal insulation fabrics and high-end protective clothing, and can also be extended with additional functions such as infrared stealth through composite modification, making it the best material for polymer aerogel fibers.

[0023] In some embodiments, the thickness of the styrene-acrylic emulsion (SA) or polyvinyl alcohol transition layer can be 200-1000 μm.

[0024] Among them, styrene-acrylic emulsion and polyvinyl alcohol, as material transition layers, both possess excellent interfacial adhesion capabilities, forming a continuous and smooth film. This effectively fills in the morphological undulations of the fiber fabric surface, achieving surface smoothing modification of the material, thereby facilitating the formation of Ti3C2T. x Uniform coating of MXene / tannic acid creates conditions to maximize its low infrared emission characteristics. Furthermore, both are aqueous systems, resulting in low energy consumption and ease of preparation. Insufficient transition layer thickness can lead to insufficient surface smoothness, affecting emission performance; excessive thickness, on the other hand, can compromise the flexibility of the multilayer material.

[0025] In some embodiments, the Ti3C2T x The thickness of the MXene / tannic acid composite low infrared emission layer can range from 1 to 100 μm. If the TM layer thickness is too small, the TM sheet may not be able to completely cover the material surface; if the thickness is too large, it will increase the surface roughness of the material. Both of these situations will cause a decrease in the emission performance of the material.

[0026] Furthermore, the low emissivity layer of the multilayer stealth material is made of tannic acid-modified Ti3C2T. x MXene material significantly improves the oxidation stability of the material. Even after 15 days of humid heat at 50℃ and 95% humidity, it still maintains a low infrared emissivity of 0.24, extending its service life as an infrared stealth material.

[0027] In some embodiments, the thermal conductivity of the infrared stealth material can be 0.07-0.1 W / (m·K), and the hemispherical infrared emissivity of 3-30 μm is ≤0.25, preferably 0.14-0.25. This compensates for the high emissivity (0.91) of the polyimide aerogel fiber surface caused by the heat accumulation effect, while also compensating for the low emissivity of Ti3C2T. x The MXene / tannic acid exhibits a relatively high thermal conductivity (0.251 W / (m·K)) due to its inability to effectively block the thermal diffusion of internal heat sources. After heating on a 200℃ hot stage for 30 minutes, the surface radiation temperature of the PI / SA / TM multilayer material is 40.7℃, which is superior to that of aerogel fiber fabric (118.1℃) and Ti3C2T. x MXene / tannic acid composite membrane (65.8℃).

[0028] The following is an exemplary description of the preparation method of infrared stealth material based on a synergistic strategy of heat insulation and low emissivity provided by the present invention. The preparation method includes the following steps: (1) A mixed solution of p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic dianhydride was stirred in an ice-water bath and under nitrogen conditions. Then, triethylamine catalyst was added and stirring was continued to obtain a polyamide salt solution. The polyamide salt was then loaded into a syringe and extruded into a coagulation bath in the form of fibers using an injection pump for amination reaction. The solution was then dried and woven to obtain a polyimide aerogel fiber woven fabric. (2) Ti3AlC2 was added to a mixed solution of hydrochloric acid A and lithium fluoride and reacted in a water bath. Then, it was washed with hydrochloric acid B and deionized water and centrifuged until the pH of the supernatant was neutral. The lower precipitate obtained after centrifugation was redispersed in deionized water, sonicated, and centrifuged again. The supernatant was collected as the mono / few-layer Ti3C2T obtained by peeling. x MXene nanosheet solution, then tannic acid dissolved in the mono / few-layer Ti3C2T x The MXene nanosheet solution was mixed and stirred to obtain Ti3C2T. x MXene / tannic acid composite solution; (3) Coat the surface of the polyimide aerogel fiber woven fabric with styrene-acrylic emulsion or polyvinyl alcohol solution and cure it, then continue to spray Ti3C2T. x The MXene / tannic acid composite solution was dried to obtain the infrared stealth material based on the synergistic strategy of thermal insulation and low emissivity.

[0029] In some embodiments, in step (1), the solvent for the mixed solution of p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic dianhydride may include N-methylpyrrolidone; preferably, the ratio of N-methylpyrrolidone, p-phenylenediamine, 3,3',4,4'-biphenyltetracarboxylic dianhydride and triethylamine may be (130-300) mL: (6.48-9.72) g: (17.76-26.64) g: (15.9-33.4) mL, more preferably (170-220) mL: (8.1-9.18) g: (22.2-25.16) g: (16.7-26.3) mL.

[0030] Specifically, p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic dianhydride are preferably maintained in a 1:1 molar ratio as polymerization monomers; otherwise, the mechanical properties and thermal stability of the final polyimide will be affected. Excess N-methylpyrrolidone will reduce monomer concentration and slow down the polymerization rate, resulting in poor processability and high energy consumption for solvent removal. Insufficient N-methylpyrrolidone will easily cause monomer agglomeration, a sharp increase in system viscosity, and defects such as spinning blockage. Excess triethylamine will accelerate the hydrolysis of polyamic acid carboxyl groups and produce side reactions, reduce PI performance, and leave residual impurities. Insufficient triethylamine will fail to adequately neutralize carboxyl groups, leading to incomplete imidization of the solution and a comprehensive decline in the core mechanical and thermal properties of the polyimide product.

[0031] In some embodiments, in step (1), the coagulation bath can be prepared from acetone, acetic anhydride and triethylamine in a volume ratio of (15-22):(1-1.1):(1-1.05).

[0032] An imbalance in the ratio of acetone (coagulant), acetic anhydride (dehydrating agent), and triethylamine (iminolation catalyst) can directly lead to fiber forming defects and performance degradation: too little acetone results in a slow coagulation rate, making fibers prone to sticking and breaking; too much acetone leads to rapid curing, forming a dense skin layer, preventing the internal solvent from escaping and causing pores and cracks; insufficient acetic anhydride leads to incomplete iminolation, resulting in poor fiber heat resistance and structural stability; too much triethylamine leads to side reactions causing fiber embrittlement; too little triethylamine reduces catalytic efficiency and results in insufficient iminolation; too much triethylamine easily causes molecular chain hydrolysis and a decrease in fiber mechanical properties.

[0033] In some embodiments, in step (1), the injection pump can have a propulsion speed of 0.01-1 mL / min. If the propulsion speed is too slow, the fibers are prone to brittleness and breakage; if the propulsion speed is too fast, the coagulation rate of the original solution lags behind the extrusion rate, resulting in fiber adhesion and a significant decrease in tensile strength and elongation at break.

[0034] In some embodiments, in step (1), the amination reaction temperature can be 20-40°C and the time can be 12-30 hours. If the temperature is too low, the imidization reaction rate is slow and the degree is insufficient; if the temperature is too high, it is easy to cause local overheating, resulting in degradation of the polyimide molecular chain or excessive cross-linking, and fiber embrittlement.

[0035] In some embodiments, in step (2), the concentration of hydrochloric acid A can be 8-10M; preferably, the ratio of lithium fluoride, hydrochloric acid A, and Ti3AlC2 can be 1.6-7.5g: 16-70mL: 1-3g.

[0036] In some embodiments, in step (2), the temperature of the water bath heating reaction can be 35-50°C and the time can be 12-30h.

[0037] In some embodiments, in step (2), the concentration of hydrochloric acid B can be 0.5-2M.

[0038] In some implementations, in step (2), the Ti3C2T x In MXene / tannic acid composite solution, Ti3C2T x The concentration of MXene can be 10-20 mg / mL, and the concentration of tannic acid can be 2-150 mg / mL. Too low a concentration of tannic acid will result in insufficient antioxidant properties; too high a concentration will affect emission performance.

[0039] In some embodiments, in step (3), the coating method may include spin coating, drop coating, spray coating or scraping coating; the concentration of the polyvinyl alcohol solution may be 7.5-15%, preferably 12.5%; the curing temperature after coating the styrene-acrylic emulsion may be 20-80℃, and the curing temperature after coating the polyvinyl alcohol solution may be -18 to 60℃.

[0040] By establishing a styrene-acrylic emulsion transition layer on the surface of fiber fabrics prepared by wet spinning combined with freeze-drying, the drawback of uneven fabric surface affecting infrared emission performance was solved, successfully integrating heat-insulating aerogel fibers and low infrared emissivity Ti3C2T. x By combining MXene and tannic acid, an infrared stealth multilayer material with excellent infrared stealth performance was prepared.

[0041] In some embodiments, in step (3), Ti3C2T is sprayed. x The spraying distance for MXene / tannic acid composite solution can be 10-30cm.

[0042] In summary, this invention combines polyimide aerogel fiber braids with Ti3C2T x The MXene / tannic acid composite combines the advantages of both thermal insulation and low infrared emissivity to prepare a multilayer material with excellent infrared stealth performance. Its stealth performance is superior to that of a single polyimide aerogel fiber woven fabric and a single Ti3C2T composite. x The MXene / tannic acid composite membrane also overcomes the bulk brittleness, lack of extensibility, and high thickness of traditional aerogel materials used in stealth applications, demonstrating great application potential.

[0043] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0044] Example 1 The method for preparing infrared stealth materials based on a synergistic strategy of thermal insulation and low emissivity provided in this embodiment includes the following steps: (1) Weigh 200 mL of N-methylpyrrolidone and 9.18 g of p-phenylenediamine crystals, stir thoroughly under ice-water bath and nitrogen conditions, and slowly add 24.99 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride after complete dissolution, and continue stirring for 12 h to form a polyamic acid (PAA) oligomer solution; finally add 24.31 mL of triethylamine, and continue mechanical stirring for 6 h to obtain a polyamide salt (PAAS) solution; after vacuum degassing of PAAS, load it into a syringe, and use an injection pump to squeeze the spinning solution into the coagulation bath at a rate of 0.05 mL / min; wherein, the coagulation bath is composed of acetone, acetic anhydride and triethylamine in a volume ratio of 20:1:1; allow the fiber to soak in the coagulation bath for 24 h for full amination, and then replace the wet fiber with water every 12 hours. The water was changed and circulated 3 times. Finally, the wet fibers were freeze-dried to collect polyimide (PI) aerogel fibers with a diameter of 440 μm, which were then woven into a mesh fabric. (2) 5g of lithium fluoride was placed in 40 mL of 9 M hydrochloric acid and magnetically stirred for 20 min. Then, a total of 2g of Ti3AlC2 was added in small amounts several times and reacted in a water bath at 45℃ for 24 h. Then, the supernatant was repeatedly centrifuged and washed with 1 M hydrochloric acid and deionized water until the pH of the supernatant was neutral. The centrifugation rate was 600 rpm. The lower precipitate after centrifugation was redispersed in deionized water and treated with sonication and centrifugation for 1 h each. The sonication power was 50 kHz and the centrifugation rate was 3500 rpm. The supernatant after centrifugation was collected as the mono / few-layer Ti3C2T obtained by stripping. x MXene nanosheets; finally, tannic acid was dissolved in Ti3C2T x The MXene solution was mixed and stirred to obtain a composite solution, wherein the tannic acid concentration was 10 mg / mL. (3) Apply styrene-acrylic emulsion to the surface of polyimide fiber fabric, cure at 70°C to obtain a styrene-acrylic emulsion transition layer, and then use a spray gun to apply Ti3C2T x MXene / tannic acid was uniformly sprayed onto its surface at a distance of 15 cm. After drying at room temperature, the heat-insulating, low-emission multilayer infrared stealth material PI / SA / TM was obtained.

[0045] Example 2 The preparation method of the infrared stealth multilayer material provided in this embodiment is the same as that in Embodiment 1, with the main difference being: In step (2), the concentration of tannic acid is 2 mg / mL.

[0046] Example 3 The preparation method of the infrared stealth multilayer material provided in this embodiment is the same as that in Embodiment 1, with the main difference being: In step (2), the concentration of tannic acid is 5 mg / mL.

[0047] Example 4 The preparation method of the infrared stealth multilayer material provided in this embodiment is the same as that in Embodiment 1, with the main difference being: In step (2), the concentration of tannic acid is 20 mg / mL.

[0048] Example 5 The preparation method of the infrared stealth multilayer material provided in this embodiment is the same as that in Embodiment 1, with the main difference being: In step (2), the concentration of tannic acid is 50 mg / mL.

[0049] Example 6 The preparation method of the infrared stealth multilayer material provided in this embodiment is the same as that in Embodiment 1, with the main difference being: In step (2), the concentration of tannic acid is 100 mg / mL.

[0050] Example 7 The preparation method of the infrared stealth multilayer material provided in this embodiment is the same as that in Embodiment 1, with the main difference being: In step (2), the concentration of tannic acid is 150 mg / mL.

[0051] Example 8 The preparation method of the infrared stealth multilayer material provided in this embodiment is the same as that in Embodiment 1, with the main difference being: In step (3), the curing temperature of the styrene-acrylic emulsion is 25°C.

[0052] Example 9 The preparation method of the infrared stealth multilayer material provided in this embodiment is the same as that in Example 1, with the main difference being: In step (3), the transition layer is coated with polyvinyl alcohol, and the polyvinyl alcohol aqueous solution is formed into a stable hydrogel by alternating cycles of freezing at -18°C and thawing at room temperature (3 times).

[0053] Example 10 The preparation method of the infrared stealth multilayer material provided in this embodiment is the same as that in Embodiment 1, with the main difference being: In step (3), the transition layer is coated with polyvinyl alcohol, and the curing temperature is 25°C.

[0054] Example 11 The preparation method of the infrared stealth multilayer material provided in this embodiment is the same as that in Embodiment 1, with the main difference being: In step (3), the transition layer is coated with polyvinyl alcohol and the curing temperature is 50°C.

[0055] Comparative Example 1 Weigh 200 mL of N-methylpyrrolidone and 9.18 g of p-phenylenediamine crystals, and stir thoroughly under ice-water bath and nitrogen conditions. After complete dissolution, slowly add 24.99 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride, and continue stirring for 12 h to form a polyamic acid (PAA) oligomer solution. Finally, add 24.31 mL of triethylamine, and continue mechanical stirring for 6 h to obtain a polyamide salt (PAAS) solution. After vacuum degassing of the PAAS, load it into a syringe and use an injection pump to expel the spinning solution into a coagulation bath at a rate of 0.05 mL / min. The coagulation bath consists of acetone, acetic anhydride, and TEA in a volume ratio of 20:1:1. Soak the fibers in the coagulation bath for 24 h for full amination, and then replace the wet fibers with water every 12 hours. The water was changed and circulated 3 times. Finally, the wet fibers were freeze-dried to collect polyimide (PI) aerogel fibers with a diameter of 440 μm, which were then woven into a mesh fabric.

[0056] Comparative Example 2 5 g of lithium fluoride was placed in 40 mL of 9 M hydrochloric acid and magnetically stirred for 20 min. Then, 2 g of Ti3AlC2 was added in small batches, and the mixture was reacted in a 45 °C water bath for 24 h. The supernatant was then repeatedly washed by centrifugation with 1 M hydrochloric acid and deionized water until the pH of the supernatant was neutral (centrifugation speed: 600 rpm). The lower precipitate after centrifugation was redispersed in deionized water and subjected to ultrasonic and centrifugation treatments for 1 h each (ultrasonic power: 50 kHz, centrifugation speed: 3500 rpm). The supernatant after centrifugation was collected as the monolayer / few-layer Ti3C2T obtained by exfoliation. x MXene nanosheets; finally, tannic acid was dissolved in Ti3C2T x The MXene solution was mixed and stirred to obtain a composite solution, which was then vacuum filtered to obtain Ti3C2T. x MXene / tannic acid composite membrane, wherein the tannic acid concentration is 10 mg / mL.

[0057] Comparative Example 3 The TM solution prepared in Comparative Example 2 was directly sprayed onto the surface of the PI fabric prepared in Comparative Example 1, i.e. no intermediate transition layer was prepared. The sample obtained after drying at room temperature was denoted as PI / TM.

[0058] Comparative Example 4 Other conditions are the same as in Example 1, the main difference being that the thickness of the styrene-acrylic emulsion transition layer is 100 μm.

[0059] Comparative Example 5 Other conditions are the same as in Example 1, the main difference being that the thickness of the styrene-acrylic emulsion transition layer is 1500 μm.

[0060] Comparative Example 6 Other conditions are the same as in Example 1, the main difference being that the tannic acid concentration is 1 mg / mL.

[0061] Comparative Example 7 Other conditions are the same as in Example 1, the main difference being that the tannic acid concentration is 200 mg / mL.

[0062] In this experiment, PI / SA / TM must simultaneously meet the requirements of low emissivity (≤0.25), oxidation resistance (emissivity change before and after damp heat ≤0.05) and low thermal conductivity (≤0.1 W / (m·K)).

[0063] Table 1 below shows the reaction parameters of Examples 1-7 and Comparative Examples 6-7, and the performance parameters of the multilayer stealth materials prepared therefrom: .

[0064] The damp heat experiment simulated an easily oxidizing environment. Antioxidant performance was evaluated by comparing the change in infrared emissivity before and after three days of damp heat; the smaller the change in emissivity, the better the antioxidant performance. The optimal balance between infrared emissivity and antioxidant performance was achieved when the tannic acid concentration was 10 mg / mL.

[0065] Table 2 below shows the reaction parameters of Examples 1 and 8-11 and the performance parameters of the multilayer stealth materials prepared therefrom: .

[0066] Table 3 below shows the performance parameters of Example 1 and Comparative Examples 1-5: .

[0067] Figure 1 The images show physical photos and SEM images of the PI fiber fabric and infrared stealth material PI / SA / TM prepared in Example 1. As can be seen from the images, the PI fibers exhibit a typical porous structure. Numerous closed or semi-closed micropores within the material contain a large amount of air, significantly reducing heat conduction efficiency. Furthermore, the air trapped within these micropores inhibits thermal convection between the inside and outside of the pores, further improving the material's thermal insulation performance. By composited with a low-emissivity material on the surface of the thermally insulating PI aerogel fibers, a more complete infrared stealth system is formed. The optical and cross-sectional SEM images of the prepared PI / SA / TM clearly reveal the three-layer composite material: the bottom PI layer is used for thermal insulation; the middle transition layer improves the surface smoothness of the fiber fabric, promoting bonding with the top TM layer and allowing the low-emissivity performance of the TM layer to be fully utilized; and the top TM layer exhibits a clear layered structure, which is beneficial for the reflection of infrared waves from the surface and between layers, reducing emissivity.

[0068] Figure 2The images show the Fourier transform infrared (FTIR) spectra of the PI fiber fabric prepared in Example 1, the PI fiber fabric coated with styrene-acrylic emulsion, and the infrared stealth material PI / SA / TM. As can be seen from the figures, the PI sample has a diameter of 1774 cm⁻¹. -1 An absorption peak appeared at 1707 cm⁻¹, which is attributed to the asymmetric stretching vibration of C=O in aromatic imides. -1 The absorption peak at 1345 cm⁻¹ originates from the C=O symmetric stretching vibration in aromatic imides. -1 and 732 cm -1 The four absorption peaks originate from the CN stretching and C=O bending vibrations in the aromatic imide, respectively. These four absorption peaks are characteristic absorption peaks of the aromatic imide structure, indicating the successful preparation of polyimide fibers; the 1727 cm⁻¹ peak in the PI / SA sample... -1 and 1159 cm -1 The absorption peaks at 1623 cm⁻¹ originate from the C=O and COC stretching vibrations in the ester group, respectively; the absorption peaks at 1623 cm⁻¹ in the PI / SA / TM sample... -1 The absorption peak at this point originates from Ti3C2T x C=O vibration in MXene, 552 cm -1 The peak corresponds to the Ti-O vibration; it is located at 1318 cm⁻¹. -1 The peak corresponds to the stretching vibration of the CO bond in TA; 1185 cm⁻¹ -1 and 1034 cm -1 The peaks at these locations correspond to the bending vibrations of the -OH and CH bonds in TA, respectively, indicating that Ti3C2T x Successful composite of MXene / TA on the material surface.

[0069] Figure 3 The images show the high-resolution X-ray photoelectron spectroscopy (C1s) spectra of the PI fiber fabric prepared in Example 1, the PI fiber fabric coated with styrene-acrylic emulsion, and the infrared stealth material PI / SA / TM. The figures show that the C1s phase in the PI fiber contains three bonds: CC, CN, and C=O. A CO peak appeared in the PI / SA sample after the addition of the styrene-acrylic emulsion. Furthermore, a Ti3C2T coating on the surface... x After MXene / TA, a C-Ti peak appeared in the PI / SA / TM sample, which is consistent with the results of infrared spectroscopy, indicating that the sample was successfully prepared.

[0070] Figure 4 The PI / SA / TM prepared in Example 1 and the PI fiber fabric and Ti3C2T prepared in Comparative Examples 1-2 are examples of materials that can be compared with those prepared in Comparative Examples 1-2. xThermal infrared images of the MXene / tannic acid composite membrane at ambient temperatures of 100℃ and 200℃. The images show that the radiation temperatures of the PI fiber mesh surface on the hot stage at 100℃ and 200℃ are 66.5℃ and 118.1℃, respectively. This indicates that the fiber mesh has thermal insulation properties, especially at 200℃, reducing the surface temperature by ~80℃. For the TM film, due to its low emissivity, the film's radiation temperature is only 44.1℃ at a background temperature of 100℃. However, as the temperature further increases to 200℃, the film begins to curl due to heat, exhibiting temperature unevenness with a temperature difference reaching ~14℃. Thanks to the thermal insulation properties of the PI fiber mesh and the low emissivity of TM, the PI / SA / TM exhibits excellent infrared stealth performance. At ambient temperatures of 100℃ and 200℃, the radiation temperatures of the sample surface are 31.5℃ and 40.7℃, respectively, reducing the temperature by ~68℃ and ~160℃.

[0071] Figure 5 The image shows a thermal infrared image of the infrared stealth material PI / SA / TM prepared in Example 1 applied to the surface of a weapon model. As can be seen from the image, after covering the aircraft and tank models with PI / SA / TM for 20 minutes, the temperatures were 35.8 and 34.9°C, respectively, significantly lower than the temperatures of the uncovered areas (78.1 and 76.1°C).

[0072] Figure 6 The image shows a thermal infrared imaging photograph of the infrared stealth material PI / SA / TM prepared in Example 1 applied to the field of human thermal camouflage. As can be seen from the image, thanks to the lightweight and flexible properties of the PI / SA / TM composite material, it can be directly applied to the surface of clothing, thereby reducing the human body's radiation temperature (29.3℃) to near the ambient temperature (28.7℃), achieving a thermal camouflage effect. Furthermore, the material's high flexibility allows it to be processed into a flexible wristband, effectively achieving thermal camouflage capabilities by reducing the local radiation temperature of the human body (from 32.8℃ to 27℃).

[0073] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. An infrared stealth material based on a synergistic strategy of thermal insulation and low emissivity, characterized in that, The infrared stealth material based on a synergistic strategy of thermal insulation and low emissivity includes: a polyimide (PI) aerogel fiber woven fabric, a styrene-acrylic emulsion (SA) or polyvinyl alcohol transition layer attached to the surface of the polyimide (PI) aerogel fiber woven fabric, and a Ti3C2T layer attached to the surface of the transition layer. x MXene / tannic acid™ composite low infrared emission layer.

2. The infrared stealth material based on a synergistic strategy of heat insulation and low emissivity as described in claim 1, characterized in that, The polyimide aerogel fiber woven fabric has a diameter of 200-700 μm and a length of 1-10 m.

3. The infrared stealth material based on a synergistic strategy of heat insulation and low emissivity as described in claim 1 or 2, characterized in that, The thickness of the styrene-acrylic emulsion (SA) or polyvinyl alcohol transition layer is 200-1000 μm; Preferably, the Ti3C2T x The thickness of the MXene / tannic acid composite low infrared emission layer is 1-100 μm.

4. A method for preparing an infrared stealth material based on a synergistic strategy of heat insulation and low emissivity as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: (1) A mixed solution of p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic dianhydride was stirred in an ice-water bath and under nitrogen conditions. Then, triethylamine catalyst was added and stirring was continued to obtain a polyamide salt solution. The polyamide salt was then loaded into a syringe and extruded into a coagulation bath in the form of fibers using an injection pump for amination reaction. The solution was then dried and woven to obtain a polyimide aerogel fiber woven fabric. (2) Ti3AlC2 was added to a mixed solution of hydrochloric acid A and lithium fluoride and reacted in a water bath. Then, it was washed with hydrochloric acid B and deionized water and centrifuged until the pH of the supernatant was neutral. The lower precipitate obtained after centrifugation was redispersed in deionized water, sonicated, and centrifuged again. The supernatant was collected as the mono / few-layer Ti3C2T obtained by peeling. x MXene nanosheet solution, then tannic acid dissolved in the mono / few-layer Ti3C2T x The MXene nanosheet solution was mixed and stirred to obtain Ti3C2T. x MXene / tannic acid composite solution; (3) Coat the surface of the polyimide aerogel fiber woven fabric with styrene-acrylic emulsion or polyvinyl alcohol solution and cure it, then continue to spray Ti3C2T. x The MXene / tannic acid composite solution was dried to obtain the infrared stealth material based on the synergistic strategy of thermal insulation and low emissivity.

5. The preparation method according to claim 4, characterized in that, In step (1), the solvent for the mixed solution of p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic dianhydride includes N-methylpyrrolidone; Preferably, the ratio of N-methylpyrrolidone, p-phenylenediamine, 3,3',4,4'-biphenyltetracarboxylic dianhydride and triethylamine is (130-300) mL : (6.48-9.72) g : (17.76-26.64) g : (15.9-33.4) mL, more preferably (170-220) mL : (8.1-9.18) g : (22.2-25.16) g : (16.7-26.3) mL.

6. The preparation method according to claim 4 or 5, characterized in that, In step (1), the coagulation bath is prepared by mixing acetone, acetic anhydride and triethylamine in a volume ratio of (15-22):(1-1.1):(1-1.05).

7. The preparation method according to any one of claims 4-6, characterized in that, In step (1), the amination reaction is carried out at a temperature of 20-40°C for 12-30 hours.

8. The preparation method according to any one of claims 4-7, characterized in that, In step (2), the concentration of hydrochloric acid A is 8-10M; preferably, the ratio of lithium fluoride, hydrochloric acid A, and Ti3AlC2 is 1.6-7.5g: 16-70mL: 1-3g.

9. The preparation method according to any one of claims 4-8, characterized in that, In step (2), the Ti3C2T x In MXene / tannic acid composite solution, Ti3C2T x The concentration of MXene is 10-20 mg / mL, and the concentration of tannic acid is 2-150 mg / mL.

10. The preparation method according to any one of claims 4-9, characterized in that, In step (3), the coating method includes spin coating, drop coating, spray coating or scraping coating; the concentration of the polyvinyl alcohol solution is 7.5-15%, preferably 12.5%; the curing temperature after coating the styrene-acrylic emulsion is 20-80℃, and the curing temperature after coating the polyvinyl alcohol solution is -18~60℃.

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