A dynamically color-shifting flexible composite material and methods of making and using the same

Abstract

The present application relates to the technical field of functional composite color-changing materials, and particularly relates to a flexible composite material capable of dynamic color change, a preparation method and application thereof. The preparation raw material of the flexible composite material comprises a photochromic powder, a flexible film matrix, low-viscosity silicone oil and a curing agent; the chemical general formula of the photochromic powder is (Li 0.1 Na 0.4 Bi 0.5 ) 0.95‑x Bi2Pr x Yb 0.05 Nb2O9, and x is 0.001-0.05. The flexible composite material provided by the present application introduces inorganic photochromic powder doped with rare earth elements into a PDMS / low-viscosity silicone oil elastomer matrix, and by adjusting the composite ratio of the photochromic powder and the flexible film matrix and the doping content of praseodymium in the photochromic powder, the real-time, accurate and reversible regulation of the color of the optical characteristics of the material is realized by means of light stimulation, thereby providing a new idea for preparing optical stealth materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional composite color-changing materials, in particular to a flexible composite material with dynamic color-changing property and a preparation method and application thereof. BACKGROUND

[0002] Traditional photochromic system materials rely on fixed energy band structure to respond to fixed wavelengths, and often lack dynamic adjustability in complex and variable environments. At the same time, inorganic photochromic powder materials face multiple defects such as mechanical brittleness, environmental instability, and failure of surface integration due to the intrinsic lattice rigidity. Under the constraints of these technical problems, it is difficult to effectively integrate photochromic materials with flexible matrix materials at the current technical level, and fully utilize the advantages of both.

[0003] Chinese patent application CN113337270A discloses an inorganic photochromic powder and a preparation method and application thereof. The inorganic photochromic powder is prepared by attaching oxygen radicals to the surface of a metal oxide, solving the problem of slow fading of photochromic materials and realizing fast fading and efficient light regulation. Chinese patent CN101381599B discloses a nano-WO3 photochromic powder and a preparation method thereof. The nano-WO3 powder is prepared by oxalic acid-induced hydrothermal method, solving the problem of single morphology and insufficient photochromic performance of nano-WO3 powder in the prior art, realizing high dispersibility and strong photochromic ability, and being suitable for fields such as optical information storage.

[0004] However, these prior arts do not solve the above technical problems, and the prepared photochromic materials are difficult to be compounded with flexible materials, and it is even more difficult to obtain products with dynamic color-changing characteristics. Under such background, there is an urgent need to provide a flexible composite material with dynamic color-changing characteristics. SUMMARY

[0005] In order to solve the above technical problems and overcome the insufficient dynamic adaptability of photochromic materials and break through the bottleneck of integration with flexible materials, the present application embeds inorganic photochromic components into a polydimethylsiloxane (PDMS) elastomer matrix, fully utilizes the excellent flexibility, high light transmittance, chemical inertness, weather resistance and easy film-forming characteristics of PDMS, so that it can closely fit the surface of equipment and provide stable and lightweight support. At the same time, combined with the fast and reversible response ability of photochromic components to environmental light, the self-adaptive dynamic change of the color of the surface of the equipment is realized; by effectively integrating inorganic photochromic components and PDMS elastomer matrix, a flexible composite material with dynamic color-changing property is prepared, which can be applied to optical stealth and has a wide application prospect.

[0006] The first aspect of the present application provides a flexible composite material with dynamic color-changing property, and the preparation raw materials include photochromic powder, flexible film matrix, low-viscosity silicone oil and curing agent.

[0007] Optionally, the mass ratio of the flexible film matrix, the low-viscosity silicone oil and the curing agent is (10-30):(1-1.5):(1-3).

[0008] Optionally, the chemical formula of the photochromic powder is (Li 0.1 Na 0.4 Bi 0.5 ) 0.95-x Bi2Pr x Yb 0.05 Nb2O9, x is 0.001-0.05; further optionally, the x is 0.005-0.04; which can be listed as 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, 0.021, 0.022, 0.023, 0.024, 0.025, 0.026, 0.027, 0.028, 0.029, 0.03, 0.031, 0.032, 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039, 0.04, 0.041, 0.042, 0.043, 0.044, 0.045, 0.046, 0.047, 0.048, 0.049, 0.05.

[0009] Optionally, the mass ratio of the sum of the flexible film matrix and the low-viscosity silicone oil to the photochromic powder is (2-5):1.

[0010] The application designs a photochromic powder of a specific chemical formula, which is a bismuth sodium lithium niobate material doped with rare earth ions, and the doped rare earth ions are preferably praseodymium and ytterbium; the obtained photochromic powder has excellent dynamic color-changing characteristics and can be well compounded with a flexible material to prepare an optical stealth material.

[0011] Optionally, the material of the flexible film matrix includes polydimethylsiloxane (PDMS).

[0012] Optionally, the low-viscosity silicone oil includes trimethyl silicone oil; the addition amount of the trimethyl silicone oil is 5-18% based on the total mass of the flexible film matrix; further optionally, the addition amount is 5.5-15%.

[0013] Optionally, the low viscosity silicone oil has a viscosity of <100 cSt, which can be 30 cSt, 40 cSt, 50 cSt, 60 cSt, 70 cSt, 80 cSt, 90 cSt, 95 cSt; further optionally 50 cSt. The low viscosity silicone oil of the application is preferably trimethylsilicone oil, and the viscosity and the amount of trimethylsilicone group are controlled in a suitable range to promote the effective combination of the flexible film matrix and the photochromic powder.

[0014] Optionally, the photochromic powder is prepared by a hydrothermal method.

[0015] The application innovatively uses a hydrothermal method to prepare praseodymium-ytterbium co-doped bismuth sodium lithium niobate powder, further combines the prepared photochromic material with polydimethylsiloxane (PDMS) / low viscosity silicone oil to construct a flexible photochromic flexible composite material, and realizes high color contrast and extreme environmental stability (200℃ fade). The flexible composite material provided by the application can change from light yellow green to dark gray brown under the irradiation of sunlight or specific wavelengths (such as 405 nm), and realizes the color conversion of the flexible composite material.

[0016] The second aspect of the application provides a preparation method of a flexible composite material, and the preparation steps of the flexible composite material include:

[0017] S1, preparing a photochromic powder;

[0018] S2, mixing a flexible film matrix, a low viscosity silicone oil and a curing agent, then adding the photochromic powder, uniformly mixing, heating and curing to obtain a flexible composite material.

[0019] Optionally, the step of preparing the photochromic powder includes:

[0020] S1.1, respectively preparing precursor solution A, precursor solution B and precursor solution C;

[0021] S1.2, uniformly mixing the precursor solution A, the precursor solution B and the precursor solution C, mixing with water after adjusting pH, performing a solvothermal reaction, centrifuging, washing, drying and heat treating the reaction product after the reaction to obtain the photochromic powder.

[0022] In some embodiments, the preparation step of the precursor solution A includes: mixing bismuth nitrate, praseodymium nitrate and ytterbium nitrate according to the molar ratio of Bi 3+ , Pr 3+ and Yb 3+ is (2.5-x-0.05):x:0.05, dissolving by adding concentrated nitric acid, then adding a citric acid aqueous solution, and obtaining the precursor solution A after uniformly mixing;

[0023] Optionally, the concentration of the concentrated nitric acid is 1-10 mol / L, which can be listed as 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L; further optionally 4 mol / L.

[0024] Optionally, the concentration of the aqueous citric acid solution is 0.1-2 mol / L, which can be listed as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L; further optionally 0.5 mol / L.

[0025] Optionally, the precursor solution A is prepared under the condition of inert gas atmosphere and light avoidance.

[0026] The inert gas can be listed as at least one of nitrogen and argon.

[0027] In some embodiments, the preparation step of the precursor solution B comprises: mixing niobium oxalate with an aqueous oxalic acid solution, and heating in a water bath at 50-70°C to assist dissolution, to obtain the precursor solution B.

[0028] Optionally, the concentration of the aqueous oxalic acid solution is 0.01-1 mol / L, which can be listed as 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L; further optionally 0.1 mol / L.

[0029] Optionally, the mass ratio of the niobium oxalate to the aqueous oxalic acid solution is 1:(1.5-3); further optionally 1:2.

[0030] In some embodiments, the preparation step of the precursor solution C comprises: mixing aqueous lithium hydroxide solution and aqueous sodium hydroxide solution according to the molar ratio of Na + and Li + is 4:1, and then cooling in an ice water bath to obtain the precursor solution C.

[0031] Optionally, the addition rate of the precursor solution C is 0.8-1.2 mL / min.

[0032] Optionally, the S1.2 step specifically comprises: sequentially adding precursor liquid A, precursor liquid B and precursor liquid C into a reaction container, stirring uniformly under the condition of a room temperature water bath, adjusting the pH value to 10.5-11, then transferring the mixture into a hydrothermal kettle with a polytetrafluoroethylene lining, adding deionized water to constant volume, and performing a solvothermal reaction; after the reaction is completed, the reaction product is centrifuged, washed, vacuum dried and heat treated at 1050-1150 to obtain a photochromic powder.

[0033] The reaction conditions of the solvothermal reaction are: first, the temperature is raised to 190-220℃ at a temperature raising rate of 1℃ / min, the reaction time is 24-54h, and then the temperature is lowered at a temperature lowering rate of 0.5℃ / min.

[0034] Optionally, in the solvothermal reaction, deionized water is added to a filling degree of 0.65-0.80, and further optionally 0.7.

[0035] Optionally, the heat treatment conditions are: first, the reaction product is raised to 1050-1150℃ at a temperature raising rate of 2-8℃ / min; after holding for 2-4h, the temperature is lowered at a temperature lowering rate of 4-10℃ / min.

[0036] Optionally, the heating and curing conditions in the S2 step are: a curing temperature of 80-140℃ and a curing time of 2-5h.

[0037] The third aspect of the application provides an application of the flexible composite material as described above, and the flexible composite material is applied to the preparation of an optical stealth material.

[0038] Advantages:

[0039] The application provides a flexible composite material with dynamic color change, a preparation method and an application thereof, and has the following advantages:

[0040] (1) The application develops a new type of flexible photochromic composite material aiming at the problems of limited cycle life, insufficient chemical stability, slow high-temperature recovery of traditional organic photochromic materials, and mismatch between the elastic modulus of a conventional PDMS flexible matrix and application requirements. By adding low-viscosity silicone oil (50 cSt) into the PDMS matrix to adjust the elastic modulus, and by compounding high-performance photochromic powder, the composite material is endowed with excellent dynamic color change characteristics.

[0041] (2) The flexible composite material obtained by the application can realize rapid color change within 1s under 405nm laser or sunlight, still maintains fatigue resistance after 20 color change / fading cycles, the maximum color change contrast reaches 51.59%, and the color of the material can be restored to the initial state within 10 minutes of high-temperature treatment at 200 DEG C; the flexible composite material has the characteristics of ultrafast response, high cycle stability, excellent high-temperature recovery ability and adjustable elastic modulus.

[0042] (3) The application further adopts a hydrothermal method to synthesize bismuth sodium lithium niobate nano powder doped with praseodymium ytterbium rare earth ions, and performs high-temperature heat treatment to volatilize part of Li+, Bi3+ and Na+ ions, aiming at the problems of low specific surface area, weak color change ability, heavy mass and poor dispersibility in a flexible matrix of the photochromic powder prepared by a traditional solid phase method. The specific surface area of the obtained nano powder is significantly higher than that of the solid phase method powder, and the photochromic ability is more excellent. The powder mass is light, and it is more easy to uniformly disperse in the flexible matrix to realize stable coloring. The preferred process further enhances the photochromic response ability by increasing the vacancy concentration through heat treatment, and lays a core material foundation for high-performance flexible composite materials.

[0043] (4) The application applies the above high-performance flexible photochromic composite material to the field of optical camouflage, utilizes the millisecond-level rapid color transition ability from light yellow green to dark gray brown, and achieves the technical effect of optical stealth. Compared with the existing electronic stealth material, the flexible composite material has the characteristics of being lighter and simpler to prepare, and more importantly, has flexible environmental adaptability and can adapt to complex and variable environmental conditions; and provides a unique optical stealth solution with the characteristics of light weight, simple preparation, rapid color change and strong environmental adaptability. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 XRD patterns of the photochromic powders prepared for the examples and the comparative example (x=0.02 corresponds to Example 1, x=0.005 corresponds to Example 2, x=0.04 corresponds to Example 3, and x=0.002 corresponds to Comparative Example 2);

[0045] Figure 2 SEM pattern of the photochromic powder prepared for Example 1;

[0046] Figure 3 SEM pattern of the photochromic powder prepared for Example 2;

[0047] Figure 4 SEM pattern of the photochromic powder prepared for Example 3;

[0048] Figure 5SEM image of photochromic powder prepared for Comparative Example 2;

[0049] Figure 6 Reflectance spectra of photochromic powder prepared for Example 1 before and after sunlight irradiation;

[0050] Figure 7 Reflectance spectra of photochromic powder prepared for Example 2 before and after sunlight irradiation;

[0051] Figure 8 Reflectance spectra of photochromic powder prepared for Example 3 before and after sunlight irradiation;

[0052] Figure 9 Reflectance spectra of flexible composite prepared for Comparative Example 1 before and after sunlight irradiation;

[0053] Figure 10 Reflectance spectra of photochromic powder prepared for Comparative Example 2 before and after sunlight irradiation;

[0054] Figure 11 Actual photos of photochromic powder prepared for Example 1 before and after sunlight irradiation, Figure 11 (a) before irradiation, (b) after irradiation;

[0055] Figure 12 Actual photos of flexible composite prepared for Example 1 before and after sunlight irradiation, Figure 12 (a) before irradiation, (b) after irradiation;

[0056] Figure 13 Actual photos of flexible composite prepared for Comparative Example 2 before and after sunlight irradiation, Figure 13 (a) before irradiation, (b) after irradiation;

[0057] Figure 14 Actual photo of flexible composite prepared for Comparative Example 1, with black background of experimental table top;

[0058] Figure 15 Comparison of elastic modulus of flexible composite prepared for Example 1 (purple line) and Comparative Example 3 (yellow line). DETAILED DESCRIPTION

[0059] The present application is further described in conjunction with specific examples, so that those skilled in the art can better understand and implement the technical solutions of the present application.

[0060] In order to solve the technical problems of insufficient dynamic adaptability of photochromic materials and difficulty in effective integration with flexible materials, the present application provides a flexible photochromic composite material, which introduces inorganic photochromic powder (Li 0.1 Na 0.4 Bi 0.5 ) 0.95-x Bi2Pr x Yb 0.05 Nb2O9 in a PDMS / low-viscosity silicone oil elastomer matrix, solves the core problems of fixed response mode and poor environmental adaptability of traditional optical materials by adjusting the composite ratio of photochromic powder and flexible film matrix and the doping content of praseodymium in the rare earth ion of the photochromic powder, realizes real-time, accurate and reversible regulation of the color of the optical properties of the material through light stimulation, and provides a new idea for preparing optical stealth materials.

[0061] The polydimethylsiloxane (PDMS) used in the examples and comparative examples of the present application is from Dow Corning Company, and the model is DC184; the viscosity of the trimethylsilicone oil used is 50 cSt (the test temperature is 25 DEG C), and it is from Jinan Longcheng Organic Silicon Co., Ltd.

[0062] Unless otherwise specified, the solvent of the solution involved in the present application is water; the concentration involved is mass concentration; the room temperature is 25 DEG C; and the raw materials, equipment and other consumables used are commercially available.

[0063] Example 1

[0064] The present embodiment provides a flexible composite material with dynamic color change and a preparation method thereof.

[0065] According to weight parts, the preparation raw materials of the flexible composite material include 9 parts of photochromic powder, 18 parts of flexible film matrix (PDMS), 1 part of low-viscosity silicone oil (trimethylsilicone oil) and 1 part of curing agent (specifically methylvinylcyclosiloxane).

[0066] The chemical formula of the photochromic powder is (Li 0.1 Na 0.4 Bi 0.5 ) 0.93 Bi2Pr 0.02 Yb 0.05 Nb2O9, that is, the chemical formula (Li 0.1 Na 0.4 Bi 0.5 ) 0.95-x Bi2Pr x Yb 0.05 Nb2O9, x=0.02.

[0067] The preparation steps of the flexible composite material include:

[0068] S1, preparing photochromic powder; the specific operation includes:

[0069] S1.1, respectively preparing precursor solution A, precursor solution B, and precursor solution C:

[0070] Under the condition of nitrogen atmosphere and light shielding, bismuth nitrate, praseodymium nitrate, and ytterbium nitrate are mixed (total 5 g) according to the molar ratio of Bi 3+ , Pr 3+ , and Yb 3+ 2.43:0.02:0.05, 10 mL of 4 mol / L concentrated nitric acid is added for dissolution, then 15 mL of 0.5 mol / L aqueous citric acid solution is added for complexation, and stirring is performed until transparency is achieved, thereby obtaining precursor solution A.

[0071] Niobium oxalate is mixed with 0.1 mol / L aqueous oxalic acid solution according to a mass ratio of 1:2, and is heated in a water bath at 60°C to assist dissolution until complete dissolution is achieved, thereby obtaining precursor solution B.

[0072] An aqueous lithium hydroxide solution and an aqueous sodium hydroxide solution are mixed according to a molar ratio of Na + and Li + 4:1, and precursor solution C is obtained after ice water bath cooling.

[0073] S1.2, precursor solution A is added to precursor solution B, stirring is performed at 40°C for 30 min to form a yellow-brown complex, then precursor solution C is slowly added (addition rate is 1 mL / min), pH is adjusted to 10.5 using precursor solution C, then the mixed material is transferred to a hydrothermal kettle with a polytetrafluoroethylene liner, deionized water is added to a filling degree of 0.7, the temperature is increased to 200°C at a heating rate of 1°C / min for solvothermal reaction, the reaction time is 24 h, then the temperature is decreased to room temperature at a cooling rate of 0.5°C / min; the mixed material is washed twice using a 0.1 mol / L aqueous NH4OH solution, then washed three times using an aqueous ethanol solution (weight ratio of ethanol to deionized water is 1:1), and is dried, heated to 1100°C at a heating rate of 3°C / min, kept for 3 h, then cooled to room temperature at a cooling rate of 5°C / min; photochromic powder (Li 0.1 Na 0.4 Bi 0.5 ) 0.93 Bi2Pr 0.02 Yb 0.05 O9 is prepared.

[0074] S2, under room temperature and air atmosphere, flexible film matrix, low viscosity silicone oil, and curing agent are mixed according to the formula amount, stirring is performed until uniform, then the photochromic powder is added, the mixed material is stirred again until complete dispersion, the mixed material is poured into a polytetrafluoroethylene mold, heated for curing at 100°C for 2.5 h, and a flexible composite material is obtained.

[0075] Embodiment 2

[0076] The embodiment provides a flexible composite material with dynamic color change and a preparation method thereof.

[0077] The preparation raw materials of the flexible composite material include 3 parts of photochromic powder, 15 parts of flexible film matrix (PDMS), 1.3 parts of low-viscosity silicone oil (trimethyl silicone oil) and 1 part of curing agent (specifically, methyl vinyl cyclosiloxane) in terms of weight parts.

[0078] The chemical formula of the photochromic powder is (Li 0.1 Na 0.4 Bi 0.5 ) 0.945 Bi2Pr 0.005 Yb 0.05 Nb2O9; that is, the chemical general formula (Li 0.1 Na 0.4 Bi 0.5 ) 0.95-x Bi2Pr x Yb 0.05 Nb2O9, wherein x = 0.005.

[0079] The preparation steps of the flexible composite material include:

[0080] S1, preparing photochromic powder; the specific operation includes:

[0081] S1.1, respectively preparing precursor solution A, precursor solution B and precursor solution C:

[0082] Under the condition of nitrogen atmosphere and light shielding, bismuth nitrate, praseodymium nitrate and ytterbium nitrate are mixed (5 g in total) according to the molar ratio of Bi 3+ , Pr 3+ and Yb 3+ 2.445:0.005:0.05, 10 mL of 4 mol / L concentrated nitric acid is added for dissolution, then 15 mL of 0.5 mol / L aqueous citric acid solution is added for complexation, and stirring is performed until transparency is achieved, to obtain the precursor solution A.

[0083] The niobium oxalate is mixed with 0.1 mol / L aqueous oxalic acid solution according to the mass ratio of 1:2, and is heated in a water bath at 60 ℃ to assist dissolution until complete dissolution is achieved, to obtain the precursor solution B.

[0084] The aqueous lithium hydroxide solution and the aqueous sodium hydroxide solution are mixed according to the molar ratio of Na + and Li + 4:1, and the precursor solution C is obtained after ice water bath cooling.

[0085] S1.2, precursor solution A is added to precursor solution B, stirred at 40℃ for 40 min to form a yellow-brown complex, then precursor solution C is slowly added (the addition rate is 1.2 mL / min), the pH is adjusted to 10.8 with precursor solution C, then the mixture is transferred to a hydrothermal kettle with a polytetrafluoroethylene liner, deionized water is added to a filling degree of 0.65, and the temperature is raised to 210℃ at a heating rate of 1℃ / min for solvothermal reaction, the reaction time is 26h, then the temperature is lowered to room temperature at a cooling rate of 0.5℃ / min; the mixture is washed with 0.1 mol / L NH4OH aqueous solution for 2 times, then washed with ethanol aqueous solution (the weight ratio of ethanol and deionized water is 1:1) for 3 times, dried, heated to 1150℃ at a heating rate of 3℃ / min, kept for 3h, then cooled to room temperature at a cooling rate of 5℃ / min; the photochromic powder (Li 0.1 Na 0.4 Bi 0.5 ) 0.945 Bi2Pr 0.005 Yb 0.05 O9。

[0086] S2, under room temperature air atmosphere, the flexible film matrix, low viscosity silicone oil and curing agent are mixed according to the formula amount, stirred uniformly, then the photochromic powder is added, stirred again until the mixture is completely dispersed, the mixture is poured into a polytetrafluoroethylene mold, heated and cured at 120℃ for 2.3h to obtain a flexible composite material.

[0087] Example 3

[0088] The present embodiment provides a flexible composite material with dynamic color change and a preparation method thereof.

[0089] According to weight parts, the preparation raw materials of the flexible composite material include 6.83 parts of photochromic powder, 18 parts of flexible film matrix (PDMS), 1.5 parts of low viscosity silicone oil (trimethyl silicone oil) and 1 part of curing agent (specifically methyl vinyl cyclosiloxane).

[0090] The chemical formula of the photochromic powder is (Li 0.1 Na 0.4 Bi 0.5 ) 0.91 Bi2Pr 0.04 Yb 0.05 Nb2O9; that is, x=0.04 in the chemical formula (Li 0.1 Na 0.4 Bi 0.5 ) 0.95-x Bi2Pr x Yb 0.05 Nb2O9.

[0091] The preparation steps of the flexible composite material include:

[0092] S1, preparing a photochromic powder; the specific operation includes:

[0093] S1.1, respectively preparing precursor solution A, precursor solution B and precursor solution C:

[0094] Under the conditions of nitrogen atmosphere and light shielding, bismuth nitrate, praseodymium nitrate and ytterbium nitrate are mixed (a total of 5 g) according to the molar ratio of Bi 3+ , Pr 3+ and Yb 3+ 2.41:0.04:0.05, 10 mL of 4 mol / L concentrated nitric acid is added for dissolution, and then 15 mL of 0.5 mol / L aqueous citric acid solution is added for complexation, and stirring is performed until transparency is achieved, to obtain precursor solution A.

[0095] The niobium oxalate is mixed with 0.1 mol / L aqueous oxalic acid according to a mass ratio of 1:2, and is heated in a water bath at 60°C to assist dissolution until complete dissolution is achieved, to obtain precursor solution B.

[0096] The aqueous lithium hydroxide solution and the aqueous sodium hydroxide solution are mixed according to the molar ratio of Na + and Li + 4:1, and after ice water bath cooling, precursor solution C is obtained.

[0097] S1.2, precursor solution A is added to precursor solution B, 30°C stirring is performed for 50 min to form a yellow-brown complex, then precursor solution C is slowly added (the addition rate is 1 mL / min), and the pH is adjusted to 10.7 with precursor solution C, then the mixed material is transferred to a hydrothermal kettle with a polytetrafluoroethylene liner, deionized water is added to a filling degree of 0.65, and the temperature is increased to 200°C at a heating rate of 1°C / min for solvothermal reaction, the reaction time is 30 h, then the temperature is decreased to room temperature at a cooling rate of 0.5°C / min; the mixed material is washed twice with 0.1 mol / L aqueous NH4OH solution, then washed three times with an ethanol aqueous solution (the weight ratio of ethanol to deionized water is 1:1), and is dried, and is heated to 1050°C at a heating rate of 3°C / min, and is kept for 3 h, then is cooled to room temperature at a cooling rate of 5°C / min; a photochromic powder (Li 0.1 Na 0.4 Bi 0.5 ) 0.91 Bi2Pr 0.04 Yb 0.05 Nb2O9.

[0098] S2, under room temperature air atmosphere, mix the flexible film matrix, low viscosity silicone oil and curing agent according to the formula amount, stir uniformly, then add the photochromic powder, stir again until the mixture is completely dispersed, pour the mixture into a polytetrafluoroethylene mold, heat and cure at 110℃ for 3h to obtain a flexible composite material.

[0099] Comparative Example 1

[0100] This comparative example provides a flexible composite material and a preparation method thereof, and the specific embodiment is the same as that of Example 1; the difference lies in that no photochromic powder is added.

[0101] Comparative Example 2

[0102] This comparative example provides a flexible composite material and a preparation method thereof.

[0103] According to weight parts, the preparation raw materials of the flexible composite material include 4 parts of photochromic powder, 20 parts of flexible film matrix (PDMS), 1.5 parts of low viscosity silicone oil (trimethyl silicone oil) and 1 part of curing agent (specifically methyl vinyl cyclosiloxane).

[0104] The chemical formula of the photochromic powder is (Na 05 Bi 0.5 ) 0.948 Bi2Pr 0.002 Yb 0.05 Nb2O9.

[0105] The preparation steps of the flexible composite material include:

[0106] S1, preparing the photochromic powder; the specific operation includes:

[0107] (1) Take the corresponding powder of the elements in the chemical formula of the photochromic powder (NaCO3, Bi2O3, Nb2O5, Pr6O 11 , Yb2O3) according to the stoichiometric ratio, transfer the powders to an agate mortar, add anhydrous ethanol for dispersion, and then perform grinding treatment; after grinding treatment, transfer to a crucible, heat to 900℃ at a heating rate of 5℃ / min, and pre-burn for 4.5h, then cool to room temperature at a cooling rate of 5℃ / min; after pre-burning, perform grinding treatment again to obtain the basic ceramic powder;

[0108] (2) heat the obtained basic ceramic powder to 1100℃ at a heating rate of 3℃ / min for high temperature heat treatment, and keep the temperature for 2h, then cool to room temperature at a cooling rate of 5℃ / min; obtain the photochromic powder (Na 0.5 Bi 0.5 ) 0.948 Bi2Pr 0.002 Yb 0.05 Nb2O9.

[0109] S2. Under room temperature air atmosphere, mix the flexible film matrix, low viscosity silicone oil and curing agent according to the formula amount, stir evenly, add photochromic powder, stir again until the mixture is completely dispersed, pour the mixture into a polytetrafluoroethylene mold, heat and cure at 100℃ for 2.5h to obtain flexible composite material.

[0110] Comparative Example 3

[0111] This comparative example provides a flexible composite material and its preparation method, with the specific implementation method being the same as in Example 1; the difference being that low-viscosity silicone oil was not added.

[0112] Performance testing

[0113] 1. X-ray diffraction test

[0114] X-ray diffraction tests were performed on the photochromic powders prepared in the examples and comparative examples to characterize their phase structure composition. The results are as follows: Figure 1 As shown.

[0115] Figure 1 The measurement results show that, under different Pr³⁺ doping concentrations (Example 1: 0.02 mol%, Example 2: 0.005 mol%, Example 3: 0.04 mol%, Comparative Example 2: 0.002 mol%), (Li 0.1 Na 0.4 Bi 0.5 ) 0.95- x Bi2Pr x Yb 0.05 All diffraction peaks of Nb₂O₁ correspond to Na in standard card number 01-070-5524. 0.5 Bi 2.5 Nb2O9 showed a high degree of agreement. The measurement results strongly indicate that the photochromic powder prepared by the hydrothermal method in this invention has extremely high purity.

[0116] 2. SEM testing

[0117] The photochromic powders prepared in the examples and comparative examples were examined under a scanning electron microscope (SEM). The results are as follows: Figures 2-5 As shown.

[0118] Figures 2-5 The measurement results show that the photochromic powder exhibits a dense microstructure under SEM scanning electron microscopy. The presence of bismuth layered structure makes the powder exhibit significant anisotropic behavior, and the powder presents a typical plate-like morphology.

[0119] 3. Reflection performance test

[0120] The reflection performance of the flexible composite material samples prepared in the examples and the comparative examples was tested by using a UV-visible near infrared spectrophotometer, and the reflection spectra of the samples before and after irradiation under sunlight were determined, and the results are shown in FIGS. 1-4. Figures 6-10

[0121] Figures 6-10 The results of the determination in FIGS. 1-4 show that the reflectivity of the reflection spectra of the samples of Examples 1-3 and Comparative Example 2 after irradiation under sunlight is significantly reduced, and the color of the powder changes from light yellow green to dark brown, which indicates that the material has excellent photochromic properties. The photochromic performance of the samples before and after irradiation was calculated, and the maximum color change rate (also referred to as the reflection modulation rate) of the sample of Example 1 doped with 0.02 mol% Pr³⁺ in the powder was 51.59%, the maximum color change rate of the sample of Example 2 doped with 0.005 mol% Pr³⁺ in the powder was 40.52%, the maximum color change rate of the sample of Example 3 doped with 0.04 mol% Pr³⁺ in the powder was 34.88%, and the maximum color change rate of the sample of Comparative Example 2 doped with 0.002 mol% Pr³⁺ in the powder was 28.14%; the flexible composite samples of Examples 1-3 and Comparative Example 2 contain photochromic powder, and all have reflection modulation function, and the color change ability of the sample of Example 1 is the most excellent. The sample of Comparative Example 1 does not contain photochromic powder, and the reflectivity of the final flexible composite material is significantly reduced, and no reflection modulation phenomenon occurs after irradiation.

[0122] Figure 11 FIG. 1 shows the color change of the photochromic powder of Example 1 before and after irradiation under sunlight. As can be seen from the figure, the powder is light yellow green (a) before irradiation under sunlight, and the color of the powder changes to dark brown (b) after irradiation. Figure 11 Figure 11

[0123] Figure 12 FIG. 2 shows the color change of the flexible composite material prepared in Example 1 before and after irradiation under sunlight; as can be seen from the figure, the flexible composite material of Example 1 is light yellow green (a) before irradiation under sunlight, and the color changes to dark brown (b) after irradiation, and the color of the surface of the flexible film is significantly deepened after irradiation. Figure 12 Figure 12 Figure 13 FIG. 3 shows the color change of the flexible composite material prepared in Comparative Example 2 before and after irradiation under sunlight; as can be seen from the figure, the flexible composite material of Comparative Example 2 is light yellow (a) before irradiation under sunlight, and the color changes to light gray (b) after irradiation. Figure 13 Figure 13 Figure 14 FIG. 4 shows a real object diagram of the flexible composite material prepared in Comparative Example 1 without photochromic powder, and the figure shows that the composite material is a transparent flexible film, and the background is a black experimental table. ​​​​​​​

[0124] 4. Tensile properties

[0125] The tensile properties of the flexible composites of Example 1 and Comparative Example 3 were tested using a universal mechanical tester, and the results are shown in Table 2. Figure 15

[0126] Figure 15 The results of the measurements in Table 2 show that the addition of the low viscosity silicone oil significantly increases the elastic modulus of the sample, from 0.7636 Pa to 0.7681 Pa, and the increase in elastic modulus makes the flexible composite sample more easily conform to the surface of complex equipment.

[0127] In summary, the present application precisely controls the doping amount of Pr 3+ doped Li 0.1 Na 0.4 Bi 0.5 ) 0.95-x Bi2Pr x Yb 0.05 Nb2O9, and the inorganic photochromic powder is compounded with a flexible matrix material and a specific low viscosity silicone oil according to different weight ratios, to successfully prepare a multi-color difference color-changing material on the same material module, achieving three major technical breakthroughs: 1) the photochromic powder is prepared by a hydrothermal method assisted by a heat treatment process, which has finer grain size and larger specific surface area than traditional solid phase methods, is more easily dispersed in a flexible matrix, and further achieves more excellent photochromic properties; 2) the PDMS modified with low viscosity silicone oil has a greater elastic modulus, is more easily adapted to the surface of complex equipment, and provides stable and lightweight support; 3) under sunlight irradiation, by changing the doping ratio of the color-changing powder and the flexible matrix film, the color of the flexible material is changed from light green to gray brown. The present application overcomes the technical problems of difficulty in integrating photochromic materials with flexible substrates and insufficient dynamic adaptability, and provides a new technical approach for the application of inorganic photochromic materials in new generation self-adaptive camouflage and wearable optical devices.

[0128] The above implementation examples have described the different implementation processes of the present application in detail, but the implementation of the present application is not limited to this. Any improvement and deformation based on the concept of the present application can achieve the purpose of the present application according to the content disclosed in the present application, and the specific protection scope is subject to the claims.​

Claims

1. A flexible composite material that dynamically changes color, characterized in that, The preparation raw material of the flexible composite material comprises photochromic powder, flexible film matrix, low-viscosity silicone oil and curing agent; The chemical general formula of the photochromic powder is (Li 0.1 Na 0.4 Bi 0.5 ) 0.95-x Bi2Pr x Yb 0.05 Nb2O9, x is 0.001-0.05; The mass ratio of the flexible film matrix, low-viscosity silicone oil and curing agent is (10-30):(1-1.5):(1-3); The mass ratio of the sum of the flexible film matrix and low-viscosity silicone oil to the photochromic powder is (2-5):1; The material of the flexible film matrix comprises polydimethylsiloxane; The low-viscosity silicone oil comprises trimethyl silicone oil, and the viscosity of the low-viscosity silicone oil is <100 cSt; The preparation steps of the photochromic powder comprise: S1.1, respectively preparing precursor solution A, precursor solution B and precursor solution C; S1.2, mixing the precursor solution A, the precursor solution B and the precursor solution C uniformly, mixing with water after adjusting pH, performing solvothermal reaction, centrifuging, washing, drying and heat treatment on the reaction product after the reaction is completed, and obtaining the photochromic powder; The preparation steps of the precursor solution A include: mixing bismuth nitrate, praseodymium nitrate and ytterbium nitrate according to the molar ratio of Bi 3+ , Pr 3+ and Yb 3+ is (2.5-x-0.05):x:0.05, dissolving by adding concentrated nitric acid, then adding an aqueous solution of citric acid, and uniformly mixing to obtain the precursor solution A; The preparation steps of the precursor solution B comprise: mixing niobium oxalate with oxalic acid aqueous solution, heating in water bath at 50-70℃ to assist dissolution, and obtaining the precursor solution B; The preparation steps of the precursor solution C include: mixing lithium hydroxide aqueous solution and sodium hydroxide aqueous solution according to the molar ratio of Na + and Li + is 4:1, and the precursor solution C is obtained after ice water bath cooling.

2. The flexible composite of claim 1, wherein, The x is 0.005-0.

04.

3. A method of producing a flexible composite material according to claim 1 or 2, characterized in that, The preparation steps of the flexible composite material comprise: S1, preparing photochromic powder; S2, mixing the flexible film matrix, the low-viscosity silicone oil and the curing agent, then adding the photochromic powder, mixing uniformly, heating and curing, and obtaining the flexible composite material.

4. The method of claim 3, wherein the flexible composite is prepared by a process comprising: The reaction conditions of the solvothermal reaction are: first, heating at a temperature increasing rate of 1℃ / min to 190-220℃ to perform solvothermal reaction, and the reaction time is 24-54h, then, cooling at a temperature decreasing rate of 0.5℃ / min.

5. The method of claim 3, wherein the flexible composite is prepared by a process comprising: The conditions of the heat treatment are: first, heating the reaction product to 1050-1150℃ at a temperature increasing rate of 2-8℃ / min; keeping warm for 2-4h and cooling at a temperature decreasing rate of 4-10℃ / min.

6. The method of claim 3, wherein the flexible composite is prepared by a process comprising: The conditions of the heating and curing are: curing temperature 80-140℃, and curing time 2-5h.

7. Use of the flexible composite material according to claim 1 or 2, characterized in that, The flexible composite material is applied to the preparation of optical stealth material.

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