Intelligent stealth material based on photo-thermal expansion-electrochromism coupling and preparation method thereof

Abstract

The invention discloses an intelligent stealth material based on photo-thermal expansion-electrochromism coupling and a preparation method of the intelligent stealth material. The material is composed of a transparent conductive substrate, a WO3 nanosheet array and a ternary composite hydrogel (PNIPAM-Cu7S4-VO2). The hydrogel is induced to shrink through a photothermal effect, the space between the WO3 nanosheets is dynamically regulated and controlled to 200-300nm, and the 1.06 mu m laser absorptivity gt is realized; 90%; vO2 phase change and WO3 electrochemical behaviors cooperatively control the emissivity fluctuation at the wave band of 8-14 microns to be smaller than or equal to 0.05. The problem of multi-band independent precise regulation and control is solved, the response speed reaches the millisecond level, zero energy consumption is maintained, and the method is suitable for the military fields of unmanned aerial vehicle skin, ship-borne stealth systems and the like.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, specifically to a smart stealth material that modulates electrochromic behavior through photothermal expansion, suitable for multi-band adaptive camouflage of military equipment. Background Technology

[0002] The rapid development of multi-spectral detection technology on modern battlefields has placed unprecedentedly stringent demands on intelligent stealth materials for military equipment. Ideal materials need to achieve active environmental adaptive color change in the visible light band (400-700nm), possess millisecond-level dynamic high absorption capability for near-infrared laser ranging signals (e.g., 1.06μm, 1.55μm), maintain low emissivity in the mid-to-far-infrared atmospheric window (8-14μm) to suppress thermal radiation characteristics, and maintain stable performance in harsh environments such as extreme temperature ranges from -40℃ to 120℃, high humidity, and dust storms. However, current mainstream technologies all have inherent, irreconcilable flaws that fail to meet these comprehensive requirements.

[0003] While electrochromic materials (such as WO3 and NiO) can achieve optical control through ion insertion / extraction, their response speed is limited by slow ion diffusion kinetics. The coloring / fading process typically takes more than 3 seconds, making it difficult to meet the millisecond-level stealth requirements of sudden laser detection. More importantly, the electrochemical process has weak control over the infrared emissivity in the 8-14μm band, failing to effectively suppress equipment thermal signals. Furthermore, a voltage of 2V or higher must be continuously applied to maintain the colored state, significantly shortening the battery life of individual soldier systems. Thermochromic materials (such as VO2 films) serve as a supplementary solution. Although they can control infrared emissivity through insulator-metal phase transitions, their passive response characteristics depend on changes in ambient temperature, exhibiting a phase transition hysteresis exceeding 5°C. High carrier concentrations further reduce visible light transmittance to below 40%, compromising visible light camouflage. Moreover, when integrated with electrochromic layers, the mismatch in thermal expansion coefficients causes interfacial delamination, with over 30% of the area peeling off after 50 thermal cycles.

[0004] Emerging plasma metamaterials (such as Au / Ag nanoarrays) achieve rapid optical response in specific wavelength bands by modulating local surface plasmon resonance (LSPR) through structural deformation. However, their high cost is due to the use of precious metal materials and electron beam lithography processes. Furthermore, their designs cannot simultaneously cover the dual-band laser threats of 1.06 μm and 1.55 μm, and they lack a synergistic control mechanism for the mid- and far-infrared regions.

[0005] Current intelligent stealth materials face three major unsolvable contradictions: First, millisecond-level response requires a high driving voltage of over 5V, while low-energy solutions have response times exceeding 3 seconds; second, improving near-infrared absorptivity and suppressing infrared emissivity are physically mutually exclusive (positive correlation reaches 0.92); third, the requirements for flexible weather resistance are incompatible with the complexity of multi-layered structures. These fundamental defects severely restrict the engineering application of next-generation adaptive stealth equipment.

[0006] Therefore, there is an urgent need for a new type of intelligent stealth material with fast response speed, multi-band control, and good environmental adaptability. Summary of the Invention

[0007] The purpose of this invention is to provide a smart stealth material based on a photothermal expansion-electrochromic coupling mechanism and its preparation method. Multi-field coupling functionality is achieved through a "sandwich" structure design.

[0008] The specific technical solution adopted by this invention is as follows:

[0009] A smart stealth material based on a photothermal expansion-electrochromic coupling mechanism comprises a three-layer structure from bottom to top: a bottom layer is a transparent conductive substrate, a middle layer is a vertical array of WO3 nanosheets, and a top layer is a ternary composite hydrogel layer. The nanosheets have specific spacing to form plasmon resonance units; the hydrogel layer contains a temperature-sensitive polymer, photothermal conversion nanoparticles, and phase change material nanoparticles.

[0010] Preferably, the transparent conductive substrate is FTO glass or ITO-PET flexible film.

[0011] Preferably, in the vertical array layer of WO3 nanosheets, the thickness of the nanosheets is 40-60 nm, the initial spacing is 70-90 nm, and the spacing can be expanded to 200-300 nm under the deformation of the hydrogel layer.

[0012] Preferably, the temperature-sensitive polymer in the ternary composite hydrogel layer is poly(N-isopropylacrylamide) (PNIPAM);

[0013] Preferably, the photothermal conversion nanoparticles are Cu7S4 hollow spheres with a diameter of 180-220 nm, a shell thickness of 25-35 nm, and a mass percentage of 12-18% in the hydrogel layer.

[0014] Preferably, the phase change material nanoparticles are VO2 nanoparticles with a particle size of less than 100 nm, a phase change temperature of 33-37 °C, and a mass percentage of 3-8% in the hydrogel layer.

[0015] The second aspect of this invention provides a method for preparing the above-mentioned intelligent stealth material, the specific steps of which include:

[0016] a) Hydrothermal growth of WO3 nanosheet arrays on a transparent conductive substrate;

[0017] b) Synthesis of VO2 nanoparticles: using V2O5 and oxalic acid as precursors, followed by hydrothermal reaction and nitrogen annealing at 300-400℃; c) dispersing VO2 nanoparticles and Cu7S4 hollow spheres in a prepolymer solution containing NIPAM monomer and crosslinking agent, and then ultrasonically mixing.

[0018] d) A prepolymer liquid is coated on the surface of the WO3 layer, covered with a micropillar template, and then cured under ultraviolet light to form a ternary composite hydrogel layer with a microstructure.

[0019] Preferably, the specific steps of growing the vertical array of WO3 nanosheets by hydrothermal method in step a) include: using a precursor solution containing 0.03-0.07M Na2WO4 and 0.05-0.15M oxalic acid, and adjusting the pH value to 2.0-3.0, reacting in a reactor at 160-200℃ for 2-4 hours, followed by annealing.

[0020] Preferably, the VO2 nanoparticles in step b) are prepared by the following steps: using V2O5 and oxalic acid as precursors, after hydrothermal reaction, annealing is carried out in an inert atmosphere at 300-400℃ to obtain monoclinic VO2 nanoparticles.

[0021] Preferably, in the mixed prepolymer liquid of step c), the mass ratio of the photothermal conversion nanoparticles (Cu7S4) to the phase change material nanoparticles (VO2) is (1.5:1) to (2.5:1).

[0022] The technical effects achieved by this invention are as follows:

[0023] The intelligent stealth material of this invention achieves rapid, efficient, and decoupled synergistic control of multi-band optical performance. Through a novel photothermal deformation-regulated plasmon resonance (PDMPR) mechanism, the material's absorptivity in the near-infrared band (1.06 μm) can be instantaneously increased to over 93% (response time 120 ms), while simultaneously maintaining emissivity fluctuations within ±0.05 in the mid-far-infrared band (8-14 μm), and possessing a modulation amplitude exceeding 60% in the visible light band, thus completely resolving the technical contradictions of multi-spectral stealth.

[0024] This invention successfully overcomes the bottleneck of high energy consumption in traditional electrochromic technology. By using physical deformation to lock the optical state, the material can maintain a high absorption or low emission state for a long time without continuous power supply after the light-triggered response, achieving "zero energy consumption maintenance after triggering" and significantly reducing the energy demand of stealth equipment.

[0025] This invention employs a fully low-temperature preparation process. The application of mature industrial technologies such as hydrothermal method, ultrasonic dispersion, and ultraviolet curing avoids complex and expensive processes such as electron beam lithography and magnetron sputtering, making it economically feasible for large-scale production and application.

[0026] This intelligent stealth material has broad application prospects, especially suitable for various military equipment platforms. It can be made into rigid or flexible devices according to requirements, making it an ideal choice for adaptive skin of UAVs, infrared stealth coatings for ships, and intelligent camouflage clothing for individual soldiers, providing a brand-new solution for the stealth technology upgrade of next-generation main battle equipment.

[0027] In summary, this invention, through triple innovation in materials, structure, and mechanism, successfully overcomes the long-standing technical challenge in the field of intelligent stealth that makes it impossible to simultaneously achieve high response speed, multi-band coordination, and energy consumption, and provides a practical technical path that is high-performance, highly reliable, and low-cost. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the present invention;

[0029] Figure 2 This is a schematic diagram of the working principle of the present invention;

[0030] Figure 3 These are performance test diagrams for the embodiments and comparative examples;

[0031] Figure 4 This is a comparison chart of the response times of the embodiments and comparative examples; Detailed Implementation

[0032] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0033] Example 1: Preparation of Smart Stealth Materials

[0034] Step 1: Fabrication of a vertical array of WO3 nanosheets

[0035] 1. Substrate treatment: The FTO conductive glass was ultrasonically cleaned in acetone, ethanol and deionized water for 15 minutes each, and then dried with nitrogen.

[0036] 2. Hydrothermal Growth: Prepare a 100 mL precursor solution containing 0.05 mol / L Na₂WO₄ and 0.1 mol / L oxalic acid, and adjust the pH to 2.5 with hydrochloric acid. Place the cleaned FTO glass container obliquely in a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE), and pour in the precursor solution. Place the reactor in a 180°C drying oven and react for 3 hours.

[0037] 3. Post-treatment: After the reaction, the sample was allowed to cool naturally to room temperature, rinsed with deionized water, and annealed in a 120℃ oven for 2 hours. A vertical array of WO3 nanosheets was obtained. SEM characterization showed that the nanosheet thickness was 50±5nm and the initial spacing was 80±10nm.

[0038] Step 2: Synthesis of VO2 nanoparticles

[0039] 1. Hydrothermal reaction: Dissolve 0.1 mol V₂O₅ and 0.3 mol oxalic acid in 100 mL of deionized water and stir magnetically for 30 minutes to form an orange-red solution. Transfer the solution to a 200 mL reaction vessel and react at 200 °C for 24 hours.

[0040] 2. Annealing treatment: After the reaction, the blue VO2(B) precursor was collected by centrifugation and washed three times each with deionized water and ethanol. The precursor was placed in a tube furnace and annealed at 350℃ for 2 hours under a N2 atmosphere. After natural cooling, monoclinic VO2 nanoparticles were obtained. TEM characterization showed a particle size of 80±20 nm, and DSC analysis showed a phase transition temperature of 35℃.

[0041] Step 3: Preparation of ternary composite hydrogel layer

[0042] 1. Preparation of prepolymer solution: Weigh 1.6g of NIPAM monomer and 0.032g of crosslinking agent N,N'-methylenebisacrylamide.

[0043] (MBA) and 0.015g of photoinitiator TPO were dissolved in 10mL of deionized water. 0.2g of Cu7S4 hollow spheres were added.

[0044] (200nm in diameter, 30nm in shell thickness) and 0.1g of VO2 nanoparticles were ultrasonically treated (300W, 30 minutes) to form a uniformly dispersed prepolymer.

[0045] 2. UV Curing: 100 μL of prepolymer was drop-coated onto the surface of a WO3 nanosheet array, and then covered with a PDMS template containing a micropillar array (micropillar diameter 10 μm, height 20 μm, spacing 25 μm). The hydrogel was polymerized and cured by irradiation under 365 nm UV light for 10 minutes. The PDMS template was carefully removed, revealing the corresponding microcavity structure within the hydrogel layer. The final result is a three-layered smart stealth material.

[0046] Example 2: Preparation of Flexible Smart Stealth Materials

[0047] The basic steps are the same as in Example 1, with only the following changes:

[0048] Substrate replacement: Use ITO-PET flexible film to replace FTO glass.

[0049] Hydrothermal growth temperature adjustment: To prevent deformation of the PET substrate, the temperature for hydrothermal growth of the WO3 nanosheet array was adjusted to 160℃, and the reaction time was extended to 4 hours. This ultimately yielded a flexible smart stealth material.

[0050] Comparative Example 1: Traditional Electrochromic Materials

[0051] Dissolve 1.0g of tungsten powder in 30mL of 30% H2O2 and stir magnetically for 24 hours to obtain peroxytungstic acid sol.

[0052] 1. The sol was coated onto the FTO glass using a spin coating method (3000 rpm, 30 s).

[0053] 2. Annealing in a muffle furnace at 500℃ for 2 hours yielded a dense WO3 electrochromic film.

[0054] Comparative Example 2: Thermochromic VO2 Thin Film

[0055] 1. VO2 thin film was deposited on FTO glass by magnetron sputtering: substrate temperature 500℃, O2 / Ar flow ratio 1:20, sputtering power 200W, time 40 minutes, and a VO2 thin film with a thickness of about 150nm was obtained.

[0056] Performance Testing and Result Analysis

[0057] A series of performance tests were performed on the samples prepared above.

[0058] Near-infrared absorption (ASTM E903, G173) 1.06μm reflectance

[0059] Infrared emissivity ASTM E1933, GJB 2038A: ε value and fluctuation in the 8-14μm band.

[0060] Response time (ISO 18510, IEC 62341) 10%–90% switchover time

[0061] High and low temperature cycling MIL-STD-810H, IEC 60068-2-1 / 2-40℃ 60℃, 100 cycles

[0062] Damp heat aging MIL-STD-810H, IEC 60068-2-78 85℃ / 85%RH, 500h

[0063] Dust erosion MIL-STD-810H, Method 510.7 15m / s, A2 sand.

[0064] The results are shown in the table below:

[0065] Table 1: Comparison of optical properties of each sample

[0066]

[0067] Table 2: Environmental Adaptability Test Results (Performance Degradation Rate After Test)

[0068]

[0069] Results analysis:

[0070] 1. Optical performance: Samples S1 and S2 significantly outperformed comparative samples 1 and 2 in terms of near-infrared absorptivity, response speed, and infrared stability. This demonstrates the effectiveness of the novel mechanism of "photothermal deformation-induced plasmonic resonance".

[0071] 2. Environmental adaptability: The performance degradation of the sample of this invention was less than 5% after high and low temperature alternation, damp heat aging and sand and dust erosion tests, which was much lower than that of the comparative sample, proving its excellent environmental stability and durability.

[0072] In summary, this invention, through innovative material system design and ingenious "light-heat-mechanical-electric" multi-field coupling mechanism, successfully prepared an intelligent stealth material with rapid response, multi-band coordinated control, zero energy consumption maintenance, and excellent environmental adaptability. Its comprehensive performance far exceeds that of existing technologies, demonstrating high innovation and broad practical prospects.

[0073] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A smart stealth material coupled with photothermal expansion and electrochromic properties, characterized in that, include: The material comprises a transparent conductive substrate, a vertical array layer of WO3 nanosheets, and a ternary composite hydrogel layer; the nanosheets have a specific spacing to form a plasmonic resonant unit; the hydrogel layer contains a thermosensitive polymer, photothermal conversion nanoparticles, and phase change material nanoparticles.

2. The intelligent stealth material as described in claim 1, characterized in that, In the vertical array layer of WO3 nanosheets, the thickness of the nanosheets is 40-60 nm and the initial spacing is 70-90 nm. Driven by the deformation of the hydrogel layer, the spacing can be expanded to 200-300 nm.

3. The intelligent stealth material as described in claim 1 or 2, characterized in that, The thermosensitive polymer in the ternary composite hydrogel layer is poly(N-isopropylacrylamide) (PNIPAM); the photothermal conversion nanoparticles are Cu7S4 hollow spheres with a diameter of 180-220 nm, a shell thickness of 25-35 nm, and a mass percentage of 12-18% in the hydrogel layer. The phase change material nanoparticles are VO2 nanoparticles with a particle size of less than 100 nm, a phase change temperature of 33-37℃, and a mass percentage of 3-8% in the hydrogel layer.

4. The intelligent stealth material as described in claim 1, characterized in that, The ternary composite hydrogel layer has a predefined microcavity structure, which is used to transfer the thermal deformation generated by the photothermal conversion nanoparticles under light excitation to the vertical array layer of WO3 nanosheets, thereby dynamically controlling the spacing between the nanosheets and realizing active modulation of optical performance.

5. The intelligent stealth material as described in claim 1, characterized in that, The transparent conductive substrate is FTO conductive glass or ITO-PET flexible film.

6. A method for preparing the smart stealth material as described in any one of claims 1-5, characterized in that, Includes the following steps: a) Hydrothermal growth of WO3 nanosheet arrays on a transparent conductive substrate; b) Synthesis of VO2 nanoparticles: using V2O5 and oxalic acid as precursors, followed by hydrothermal reaction and nitrogen annealing at 300-400℃; c) Disperse VO2 nanoparticles and Cu7S4 hollow spheres in a prepolymer solution containing NIPAM monomer and crosslinking agent, and mix ultrasonically; d) A prepolymer liquid is coated on the surface of the WO3 layer, covered with a micropillar template, and then cured under ultraviolet light to form a ternary composite hydrogel layer with a microstructure.

7. The method as described in claim 6, characterized in that, The specific steps of growing the vertical array of WO3 nanosheets by hydrothermal method in step a) include: using a precursor solution containing 0.03-0.07M Na2WO4 and 0.05-0.15M oxalic acid, and with the pH value adjusted to 2.0-3.0, reacting in a reactor at 160-200℃ for 2-4 hours, followed by annealing.

8. The method as described in claim 6, characterized in that, Step b) The VO2 nanoparticles are prepared by the following steps: using V2O5 and oxalic acid as precursors, after hydrothermal reaction, annealing is carried out in an inert atmosphere at 300-400℃ to obtain monoclinic VO2 nanoparticles.

9. The method as described in claim 6, characterized in that, In step c), the mass ratio of the photothermal conversion nanoparticles (Cu7S4) to the phase change material nanoparticles (VO2) in the mixed prepolymer liquid is (1.5:1) to (2.5:1).

10. An application of the intelligent stealth material as described in any one of claims 1-5 in adaptive camouflage of military equipment, characterized in that, The material is used to prepare drone skin, ship infrared stealth coating, or individual soldier smart camouflage clothing. By receiving light signal stimulation, it achieves high absorption of near-infrared laser and stable control of low emissivity of mid- and far-infrared thermal radiation.

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