A hyperspectral biomimetic thin film material simulating green vegetation leaves and its preparation method

Abstract

This invention discloses a hyperspectral biomimetic thin film material simulating green vegetation leaves and its preparation method, comprising the following components: water, a hydrophilic polymer, a high near-infrared reflectance pigment, a hygroscopic material, an inorganic hydrated salt, superabsorbent fibers, and an organosilicon modifier. The biomimetic thin film material provided by this invention not only possesses spectral characteristics highly similar to green vegetation but also exhibits excellent conventional properties, including water resistance, air permeability, wide applicability, and long service life. In its preparation, this invention involves simple casting and curing to form a film, which, after drying, yields coating materials of various shapes and thicknesses.

Description

Technical Field

[0001] This invention belongs to the field of biomimetic materials, and mainly relates to a thin film material that can simulate the visible light and near-infrared spectrum of green vegetation leaves and its preparation method. Background Technology

[0002] Camouflage materials simulating natural vegetation backgrounds have always been a key focus and challenge in optical camouflage material research. With the rapid development of hyperspectral detection technology, higher requirements are being placed on camouflage materials to maintain the same color and spectrum (380nm-2500nm). Green vegetation, as one of the most typical surface backgrounds, makes simulated green vegetation materials based on hyperspectral camouflage a key research focus for researchers. Existing artificial camouflage material technologies mostly utilize camouflage pigments to simulate the visible light spectrum, combined with water-retaining materials or special structural designs to simulate the characteristic absorption bands of leaf moisture, thus achieving hyperspectral camouflage functionality. However, fresh leaves not only contain abundant water but also experience transpiration, leading to significant shortcomings in the applicability and camouflage lifespan of existing biomimetic material technologies. Furthermore, the complex preparation process and high cost of camouflage pigments or compositions limit their application.

[0003] Patent CN202011537568.9 describes a coating with visible light and near-infrared camouflage function prepared using water-based resin, pigment, and hydrophilic fibers. However, the coating system requires immersion in water to achieve the camouflage function, which limits its application scenarios and camouflage lifespan.

[0004] Patent CN202210806494.7 discloses a coating material that mimics green plant leaves, using polyvinyl alcohol as a film-forming agent and combining camouflage pigments and water-absorbing material lithium chloride to achieve hyperspectral camouflage. This material has high spectral similarity, but the film-forming agent is not water-resistant and easily loses water at high temperatures, thus losing its camouflage function.

[0005] The urgent problem to be solved is how to prepare a material that can both mimic the transpiration of vegetation and withstand high temperatures to maintain the absorption band of moisture in the near-infrared band for a long time; and can simulate the spectral characteristics of various vegetation types. The preparation process should be simple and have a wide range of applications. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art.

[0007] The technical solution adopted in this invention is as follows: A hyperspectral biomimetic thin film material simulating green vegetation leaves, comprising the following components by mass percentage:

[0008] Water content 67%-72.5%

[0009] Hydrophilic polymers 10%-20%

[0010] High near-infrared reflectance pigments 3%-4%

[0011] Hygroscopic material 1%-1.5%

[0012] Inorganic hydrated salts 1.5%-3%

[0013] Super absorbent fiber 0.5%-1%

[0014] Organosilicon modifier 5%-10%.

[0015] The hydrophilic polymer is low-viscosity polyvinyl alcohol 1788 or polyvinyl alcohol 0588.

[0016] The high near-infrared reflectance pigment is G10241 and / or Fine Green from Schott Pigment Company, which contains chromium oxide.

[0017] The moisture-absorbing material is anhydrous lithium chloride.

[0018] The inorganic hydrated salt is: zinc sulfate heptahydrate and / or sodium sulfate decahydrate.

[0019] The superabsorbent fiber is calcium alginate fiber.

[0020] The organosilicon modifier is a polydimethylsiloxane emulsion containing aminoalkyl groups.

[0021] A method for preparing a hyperspectral biomimetic thin film material simulating green vegetation leaves includes the following steps:

[0022] First, the hydrophilic polymer powder is dissolved in water to prepare a solution component A with a content of 20%-30%.

[0023] Next, moisture-absorbing material and inorganic hydrated salt were added to water in sequence according to mass percentage. After being dispersed evenly, super absorbent fiber was added to the solution according to mass percentage. After it was completely swollen into a hydrogel, high near-infrared reflective pigment was added and dispersed evenly to obtain component B.

[0024] Then, components A and B are mixed according to mass percentage, dispersed evenly, and then organosilicon modifier is added according to mass percentage; the mixture is then magnetically dispersed at room temperature to obtain a uniformly mixed solution.

[0025] Finally, the composition solution is poured into a mold and dried to form a high-spectral biomimetic thin film material.

[0026] In this invention, a high near-infrared reflectance pigment with the characteristics of simulating the "red edge" and "near-infrared plateau" of green plants is selected to realize the spectral characteristics of visible light and near-infrared plateau, and it has a high infrared reflectance in the range of 800nm-2500nm, without affecting the simulation of the absorption peak of moisture characteristics.

[0027] Targeting the characteristic absorption peaks of water molecules at 1490nm and 1950nm, we selected hygroscopic inorganic salts and high-temperature stable inorganic hydrated salts as carriers, and used superabsorbent fibers as carriers to simulate the mesh structure of green leaves to prepare biomimetic water-containing materials. Combined with hydrophilic film-forming materials, we imitated the transpiration of vegetation water and were able to absorb water from the air.

[0028] By using an aminoalkyl-containing polydimethylsiloxane emulsion and a hydroxyl-containing hydrophilic film-forming material, polyvinyl alcohol, through chemical bonding, the combined solution self-assembles on the surface during the drying process to form a waterproof layer that is breathable and functions like the waxy layer of vegetation.

[0029] In the preparation of this invention, a coating material of various shapes and thicknesses can be obtained by simply casting and curing it into a film, and then drying it.

[0030] The biomimetic leaf prepared by this invention has a high spectral similarity to natural leaves, and the preparation method is simple and efficient. Attached Figure Description

[0031] Figure 1 The graph shows the UV-Vis and near-infrared reflectance of a polyvinyl alcohol film.

[0032] Figure 2 The reflectance curve of a high near-infrared reflectance pigment;

[0033] Figure 3 Reflectance curves of mixed pigments (including pigment G10241, zinc sulfate heptahydrate, and sodium sulfate decahydrate);

[0034] Figure 4 Image showing pigment loading on superabsorbent fibers;

[0035] Figure 5 A comparison of the reflectance curves before and after the film is dried;

[0036] Figure 6 This is a comparison of the spectral reflectance curves of the biomimetic thin film material and the leaf of Buxus macrocarpa in Example 1.

[0037] Figure 7 Diagram of the molded blade;

[0038] Figure 8 This is a comparison of the spectral reflectance curves of the biomimetic thin film material and the leaf of Buxus macrocarpa in Example 2.

[0039] Figure 9 This is a comparison of the spectral reflectance curves of the biomimetic thin film material and the leaf of Buxus macrocarpa in Example 3;

[0040] Figure 10 This is a comparison of infrared curves before and after the addition of the organosilicon modifier. Detailed Implementation

[0041] The hyperspectral biomimetic thin film material simulating green vegetation leaves in this invention comprises the following components by mass percentage:

[0042] Water content 67%-72.5%

[0043] Hydrophilic polymers 10%-20%

[0044] High near-infrared reflectance pigments 3%-4%

[0045] Hygroscopic material 1%-1.5%

[0046] Inorganic hydrated salts 1.5%-3%

[0047] Super absorbent fiber 0.5%-1%

[0048] Organosilicon modifier 5%-10%.

[0049] In this invention, the hydrophilic polymer is low-viscosity polyvinyl alcohol 1788 or polyvinyl alcohol 0588. This type of polymer can be dissolved in water by stirring at room temperature, or dispersed by stirring at 60°C to prepare an aqueous solution, thus improving preparation efficiency. After curing into a film, the polyvinyl alcohol exhibits certain water retention. Measurements of its thermal reflectance at approximately 50% RH at room temperature show multiple absorption valleys in the 1300-2500 nm wavelength range that coincide with the water molecule peaks in leaves (see appendix). Figure 1 Its preferred ratio is 10%.

[0050] The high near-infrared reflectance pigment (i.e., green pigment) in this invention is G10241 containing chromium oxide and / or art green.

[0051] G10241 is an inorganic composite pigment containing chromium oxide produced by Schott Pigment Company. It has a high near-infrared reflectance and does not contain hexavalent chromium, making it non-toxic to the environment.

[0052] Artistic green is not a single pigment, but a mixed color pigment composed of chrome yellow and iron blue or phthalocyanine blue. The percentage of iron blue in artistic green can range from 2% to 3% (resulting in a light green) to 60% to 65% (resulting in a dark green). The higher the percentage of blue pigment, the deeper the color. Different proportions of iron blue can be selected according to different leaf types and colors.

[0053] The art green pigment selected in this invention has a green reflection peak around 525nm and high near-infrared reflectance. The pigment reflectance curve is attached. Figure 2In the visible light band, the main spectral characteristics of plant leaves are blue light absorption before 450 nm, green light reflection around 550 nm, and red light absorption around 670 nm. These spectral characteristics are due to the unique spectral properties of the abundant chloroplast pigments in the chloroplasts of plant leaves. In the near-infrared band, the main characteristics are a red edge around 800 nm and an infrared plateau between 800 nm and 1300 nm. Controlling the pigment content and aggregation state can regulate the reflectance value without affecting the reflectance characteristics and the position of the characteristic peaks. G10241 is preferred, with a preferred proportion of 4%.

[0054] This invention adjusts the near-infrared plateau reflectance (800nm-1300nm) by adjusting the particle size and content of biomimetic pigments to achieve hyperspectral camouflage of various types of leaves.

[0055] The moisture-absorbing material in this invention is anhydrous lithium chloride. Lithium chloride can form various hydrates after absorbing water; the amount of water of crystallization depends on the crystallization temperature, with lower temperatures resulting in higher hydration. Lithium chloride and its dihydrate readily absorb moisture from the air. When combined with superabsorbent fibers and PVA, it can increase the water content of the composite film. The presence of the absorbent fibers provides a unidirectional absorption path, increasing the moisture absorption rate, and it continuously absorbs water vapor from the environment even in environments with a relative humidity higher than 13% RH. Preferably, the proportion of lithium chloride is 1.5%.

[0056] The inorganic hydrated salts in this invention are zinc sulfate heptahydrate and / or sodium sulfate decahydrate. Zinc sulfate heptahydrate is a stable hydrate in equilibrium with the aqueous phase within the temperature range of 0-39°C, zinc sulfate hexahydrate within 39-60°C, and zinc sulfate monohydrate within 60-100°C, with a pH of 3-6 (50 g / L H₂O, 20°C). Sodium sulfate decahydrate loses 3 molecules of water of crystallization at room temperature, 5 molecules at 50°C, and 8 molecules at 90°C, with a pH of 5.5-7.5 (50 g / L H₂O, 20°C). The preferred ratio is 1.5%.

[0057] This inorganic hydrated salt can retain a certain amount of water of crystallization even at relatively high temperatures. When combined with green pigments, it can simulate the spectral characteristics of free water contained in plant leaves in the near-infrared region. Its spectral curve is attached. Figure 3 .

[0058] The superabsorbent fiber in this invention is calcium alginate fiber with a linear dimension range of 1.24-4.367 dtex, preferably 1.5 dtex; a breaking strength greater than 2.6 cN / dtex, a strength variation coefficient ≤12.5%, a moisture regain of 15%, and a mildew resistance rating of 0. It also exhibits antibacterial activity against Escherichia coli and Staphylococcus aureus with an antibacterial rate exceeding 99%, thus mitigating the negative feedback of polyvinyl alcohol materials' susceptibility to mold. The fiber length is 2-8 mm, and after swelling, it more easily and evenly disperses the adsorbed pigments and inorganic hydrated salt solutions. This absorbent fiber can absorb 100 times its own weight in water.

[0059] This material is stable under neutral pH conditions. Its high water absorption rate allows it to act as a carrier for adsorbing pigments and inorganic hydrated salt solutions in the composition. During the drying process, the pigments aggregate on the inside and outside surface of the fibers, mimicking the network structure of plant leaves in a microstructure. By adjusting its content, the aggregation state of the pigments can be controlled, and the scattering coefficient of the pigment particles can be changed to regulate the reflectivity. The microstructure after pigment adsorption is shown in the appendix. Figure 4 . Figure 4 Specifically, the microscopic images are magnified 200 times in image a, 500 times in image b, 200 times in transmission image c, and 500 times in image d. The preferred content is 0.5%, and the preferred length is 3-4 mm.

[0060] The organosilicon modifier in this invention is a polydimethylsiloxane emulsion containing aminoalkyl groups, such as Wacker Chemie BS1306 and / or BS4004 emulsions. This functional organosilicon resin can automatically float to the liquid-liquid interface of the material surface during the drying process of the composition. Its hydrophobic alkyl groups automatically align on the coating surface, while the other aminoalkyl group reacts with the hydroxyl side chains of polyvinyl alcohol to form stable chemical bonds, providing a structure similar to the waxy layer of a leaf. Infrared curves comparing the results before and after adding the reactive organosilicon material are shown below. Figure 10 The material components exhibit excellent high and low temperature resistance, improving the high and low temperature resistance of the dried film. The silicone coating is hydrophobic and breathable. The film retains a certain moisture content even at high temperatures, and the unsealed micropores do not affect water vapor adsorption. After applying the silicone modifier and drying at 100℃ for 2 hours to constant weight, the film still showed consistent spectral characteristics with the leaf blade. Figure 5 The preferred ratio is BS1306:BS4004 = 1:1, with a preferred ratio of 10%.

[0061] Plant leaves are fragile yet able to withstand damage from environmental and climatic factors because their cuticle structure provides waterproofing and breathability. This invention utilizes a chemically bonded solution of an aminoalkyl-containing polydimethylsiloxane emulsion and a hydroxyl-containing hydrophilic film-forming material, polyvinyl alcohol, to achieve self-assembly on the surface during drying, forming a waterproof and breathable layer that mimics the waxy layer function of vegetation.

[0062] from Figure 10 As can be seen, in Figure a, 1#-1 is the infrared curve without the addition of organosilicon material, and the main component is polyvinyl alcohol (the lower curve in a is the infrared spectrum of PVA in the spectral library). In Figure b, 1#-1-2 is the infrared curve after the addition of organosilicon material (the lower curve in b is the infrared curve of similar components in the spectral library), and the obvious characteristics of organosilicon polymers can be clearly seen. 1000-1300cm -1 The peak value for carbon-silicon bond stretching vibration is within the wavenumber range. 1260 cm⁻¹ -1 The wavenumber is the absorption peak of the CH3 symmetric deformation vibration, 800 cm⁻¹. -1 The wavenumbers are absorption peaks for the CH3 planar rocking vibration and the Si-C stretching vibration. 1080, 1025 cm⁻¹ -1 The absorption peak is due to the Si-O stretching vibration.

[0063] A method for preparing a hyperspectral biomimetic thin film material simulating green vegetation leaves includes the following steps:

[0064] First, the hydrophilic polymer powder is dissolved in water to prepare a solution component A with a content of 20%-30%.

[0065] Secondly, add the hygroscopic material and inorganic hydrated salt to the water in sequence according to their mass percentages. After dispersing evenly, add the superabsorbent fiber to the solution in the same mass percentage. Wait until it completely swells into a hydrogel, then add the high near-infrared reflective pigment and disperse it evenly to obtain component B. The order of addition cannot be changed. Adding them out of order will affect the solubility of the hygroscopic material and inorganic hydrated salt. Only after the inorganic hydrated salt and hygroscopic material are completely dissolved can the addition of hydrophilic fiber ensure that the fiber forms a gel state. Then, adding the green pigment can make the pigment evenly adsorbed in the fiber gel. Changing the order will cause the pigment particles to compete with other supersaturated salt materials for adsorption after water evaporates, affecting the dispersion effect of the green pigment.

[0066] Then, components A and B are mixed according to mass percentage, dispersed evenly, and then organosilicon modifier is added according to mass percentage; the mixture is then magnetically dispersed at room temperature to obtain a uniformly mixed solution.

[0067] Finally, the composition solution is poured into a mold and dried to obtain the hyperspectral biomimetic thin film material. See the mold and finished product for details. Figure 7 .

[0068] In practical applications

[0069] Example 1:

[0070] First, prepare the PVA solution (i.e., polyvinyl alcohol solution): Dissolve 20g of PVA1788 in 80g of cold water or magnetically disperse it at 60℃ for 30min on an electromagnetic stirrer with heating function to prepare a 20% mass fraction PVA solution A for later use.

[0071] Preparation of the water-retaining composition: Dissolve 0.6g of anhydrous lithium chloride and 0.6g of zinc sulfate heptahydrate in 13g of cold water, disperse magnetically for 5min, add 0.2g of superabsorbent fiber, disperse for 5min, add 1.6g of green pigment G10241 and stir evenly. The gel-like water-retaining component B is ready for use.

[0072] After mixing 20g of component A and component B thoroughly, add 4g of BS1306 emulsion and disperse for 10 minutes to complete the composition preparation. Pour the composition solution into a mold to form the material, and dry at room temperature for 12 hours or at 60 degrees Celsius for 4 hours to obtain the biomimetic thin film material.

[0073] The calculation of spectral data similarity was based on the article "Matching Classification Based on Overall Similarity Measure of Spectral Curves" published in Volume 26, Issue 2 of the Journal of Surveying and Mapping Science and Technology in April 2009, and was performed using the calculation formula of spectral correlation coefficient in Section 1.2.1 of the Probability Space Measure.

[0074] Calculations using the formula show that the spectral similarity coefficient between the thin film and the leaves of natural Buxus macrocarpa in the visible-near infrared band is 0.9612. The closer this coefficient is to 1, the higher the spectral simulation effect.

[0075] Meanwhile, the calculation is performed using the formula in 1.1.2 spectral angle quantity in the geometric space measurement section 1.1;

[0076] The cosine value of the spectral similarity angle, calculated using the formula, is 0.9891. A cosine value close to 1 indicates high spectral similarity.

[0077] Spectral curves are shown below Figure 6 The coating has a contact angle of 110°, and the film shows no abnormalities after being immersed in water for 24 hours, indicating excellent water resistance.

[0078] Example 2

[0079] First, prepare the PVA solution: Dissolve 20g of PVA1788 in 80g of cold water or magnetically disperse it at 60℃ for 30min on an electromagnetic stirrer with heating function to prepare a 20% mass fraction PVA solution A for later use.

[0080] Preparation of the water-retaining composition: Dissolve 0.6g of anhydrous lithium chloride and 0.6g of sodium sulfate decahydrate in 13g of cold water, disperse magnetically for 5min, add 0.2g of superabsorbent fiber, disperse for 5min, add 0.8g of green pigment G10241 and 0.8g of art green PG550 and stir evenly. The gel-like water-retaining component B is ready for use.

[0081] After mixing 20g of component A with component B and stirring evenly, add 2g of BS4004 and 2g of BS1306 emulsion, and disperse for 10 minutes to complete the composition preparation. Pour the composition solution into a mold to form the material, and dry at room temperature for 12 hours or at 60 degrees Celsius for 4 hours to obtain the biomimetic thin film material.

[0082] The calculated spectral similarity coefficient of the coating is 0.9549, and the cosine of the spectral similarity angle is 0.9862. The spectral similarity between the film and the natural leaf is greater than 96%. (See the spectral curve for details.) Figure 8 The coating has a contact angle of 110°, and the film shows no abnormalities after being immersed in water for 24 hours, indicating excellent water resistance.

[0083] Example 3

[0084] First, prepare the PVA solution: Dissolve 30g of PVA0588 in 70g of cold water or magnetically disperse it at 60℃ for 30min on an electromagnetic stirrer with heating function to prepare a 30% mass fraction PVA solution A for later use.

[0085] Preparation of the water-retaining composition: Dissolve 0.4g of anhydrous lithium chloride and 1.2g of zinc sulfate heptahydrate in 8g of cold water, disperse magnetically for 5min, add 0.4g of superabsorbent fiber, disperse for 5min, add 1.2g of G10241 green pigment and stir evenly. The gel-like water-retaining component B is ready for use.

[0086] After mixing 26.8g of component A with component B and stirring until homogeneous, 2g of BS1306 emulsion was added and dispersed for 10 minutes to complete the composition preparation. The composition solution was then poured into a mold for molding and dried at room temperature for 12 hours or at 60 degrees Celsius for 4 hours to obtain the hyperspectral biomimetic thin film material.

[0087] The calculated spectral similarity coefficient of the coating is 0.9319, and the cosine of the spectral similarity angle is 0.9712. The spectral similarity between the film and the natural leaf is greater than 93%. (See the spectral curve for details.) Figure 9 The coating has a contact angle of 120°, and the film shows no abnormalities after being immersed in water for 24 hours, indicating excellent water resistance.

[0088] Specific configuration examples for each embodiment are shown in Table 1:

[0089] Example 1 Example 2 Example 3 water 72.5% 72.5% 67% hydrophilic polymers 10% 10% 20% hygroscopic material 1.5% 1.5% 1% Inorganic hydrated salts 1.5% 1.5% 3% super absorbent fiber 0.5% 0.5% 1% Organosilicon modifier 10% 5%+5% 5% High near-infrared reflectance pigments 4% 2%+2% 3% total 100% 100% 100%

[0090] Table 1

[0091] This invention simulates the microstructure and composition of green leaves to biomimetically achieve plant-like transpiration and highly consistent spectral characteristics, resulting in uniform color and spectrum with a long lifespan. This material can be molded into thin films of various thicknesses and shapes, and its applications are not limited to camouflage of military equipment and facilities.

Claims

1. A hyperspectral biomimetic thin film material simulating green vegetation leaves, characterized in that, It includes the following components by mass percentage: Water content 67%-72.5% Hydrophilic polymers 10%-20% High near-infrared reflectance pigments 3%-4% Hygroscopic material 1%-1.5% Inorganic hydrated salts 1.5%-3% Super absorbent fiber 0.5%-1% Organosilicon modifier 5%-10%; The hydrophilic polymer is low-viscosity polyvinyl alcohol 1788 or polyvinyl alcohol 0588; The high near-infrared reflectance pigment is G10241 and / or Fine Green containing chromium oxide from Xuete Pigment Company; The moisture-absorbing material is anhydrous lithium chloride; The inorganic hydrated salt is: zinc sulfate heptahydrate and / or sodium sulfate decahydrate; The superabsorbent fiber is calcium alginate fiber; The organosilicon modifier is a polydimethylsiloxane emulsion containing aminoalkyl groups; The thin film material is prepared by casting and solidifying it into a film, followed by drying.

2. A method for preparing a hyperspectral biomimetic thin film material simulating green vegetation leaves as described in claim 1, characterized in that, Includes the following steps: First, the hydrophilic polymer powder is dissolved in water to prepare a solution component A with a content of 20%-30%. Next, moisture-absorbing material and inorganic hydrated salt are added to water in sequence according to mass percentage. After being dispersed evenly, super absorbent fiber is added to the solution according to mass percentage. After it is completely swollen into a hydrogel, high near-infrared reflective pigment is added and dispersed evenly to obtain component B. Then, components A and B are mixed according to mass percentage, dispersed evenly, and then organosilicon modifier is added according to mass percentage; the mixture is then magnetically dispersed at room temperature to obtain a uniformly mixed solution. Finally, the composition solution is poured into a mold and dried to form a high-spectral biomimetic thin film material.

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