Structural color thin film and method of making the same

Abstract

The present application belongs to the technical field of structural color materials, and particularly relates to a structural color film and a preparation method thereof. The structural color film comprises hollow SiO2 photonic crystal templates and high-strength flame-retardant polymers filled in the gaps of the hollow SiO2 photonic crystal templates. The hollow SiO2 photonic crystal templates are modified by a silane coupling agent and then filled with the high-strength flame-retardant polymers. The structural color film of the present application uses the polymer with flame retardation and high mechanical strength as the target filling material, uses the modified hollow SiO2 photonic crystal templates as the templates, fills the polymer into the gaps of the templates, and obtains the structural color film with harsh environment resistance. The structural color film exhibits excellent flame retardation, structural stability, and strong acid and strong base resistance in harsh environments.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of structural color materials, and particularly relates to a structural color film and a preparation method thereof. BACKGROUND

[0002] Structural color materials have high saturation, high brightness, and no fading, and have important application value in the field of color display. Common photonic crystal structural color materials formed by point contact between microspheres have poor mechanical stability, which seriously limits their application. In addition, the application range of current structural color materials is difficult to expand to harsh environments, such as high temperature, strong acid and alkaline environments. Combining special polymers with photonic crystal structural color materials can endow structural color materials with high mechanical strength and functionality, which provides an effective way to expand the application range of structural color materials. However, common polymers are flammable, which limits the application of polymer-based structural color materials in high-temperature flammable places.

[0003] Therefore, there is an urgent need in the art to develop structural color materials with excellent flame retardance, high strength, high temperature resistance and corrosion resistance. SUMMARY

[0004] Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the purposes of the present application is to at least solve one or more of the above-mentioned problems in the prior art, in other words, one of the purposes of the present application is to provide a structural color film and a preparation method thereof which meet one or more of the aforementioned needs.

[0005] In order to achieve the above-mentioned purposes of the application, the following technical solutions are adopted in the present application:

[0006] A structural color film, comprising hollow SiO2 photonic crystal templates and high-strength flame-retardant polymers filled in the gaps of the hollow SiO2 photonic crystal templates; wherein the hollow SiO2 photonic crystal templates are modified by a silane coupling agent before being filled with the high-strength flame-retardant polymers.

[0007] As a preferred solution, the high-strength flame-retardant polymer is one or a combination of poly-m-phenylene isophthalamide (PMIA), poly-p-phenylene terephthalamide (PPTA) and polybenzimidazole (PBI).

[0008] As a preferred solution, the silane coupling agent is one or a combination of aminopropyl triethoxysilane (APTES), methacryloyloxypropyl trimethoxysilane (MPS) and methyltrimethoxysilane (MTMS).

[0009] The present application also provides a preparation method of the structural color film according to any one of the above solutions, comprising the following steps:

[0010] (1) Preparation of hollow SiO2 photonic crystal templates;

[0011] (2) modifying the hollow SiO2 photonic crystal template by using a silane coupling agent;

[0012] (3) filling a high-strength flame-retardant polymer into the gap of the modified hollow SiO2 photonic crystal template, and vacuum drying to obtain a structural color film.

[0013] The present application uses an emulsion polymerization method to prepare monodisperse polymer nanospheres with uniform particle size, a layer of SiO2 is coated on the surface of the polymer nanospheres by hydrolysis of tetraethyl silicate TEOS to prepare core-shell microspheres, and a core-shell microsphere assembly liquid is obtained after dispersion; a photonic crystal template is formed by self-assembly of the core-shell microspheres, and a hollow SiO2 photonic crystal template, referred to as H-SiO2 PCs template, is formed by calcination; the H-SiO2 PCs template is placed in a mixed solution of a silane coupling agent, ethanol and water in a certain volume ratio, heated at a certain temperature for a period of time, and a modified H-SiO2 PCs template is obtained; an organic solvent and a cosolvent are added to a polymer with flame retardation and high mechanical strength, heated and stirred until the polymer is completely dissolved, and a transparent polymer solution is obtained, which is added dropwise to the modified H-SiO2 PCs template, and the solvent is completely volatilized by high-temperature vacuum drying to obtain a structural color film for harsh environments.

[0014] As a preferred solution, the step (2) specifically comprises:

[0015] The hollow SiO2 photonic crystal template is placed in a mixed solution of a silane coupling agent, ethanol and water for hydrothermal reaction, and a modified hollow SiO2 photonic crystal template is obtained.

[0016] As a preferred solution, the volume ratio of the silane coupling agent, ethanol and water in the mixed solution is (0.05-0.2):20:(0.5-1.5).

[0017] As a preferred solution, the temperature of the hydrothermal reaction is 75-85℃, and the time length is 1-3h.

[0018] As a preferred solution, the step (3) specifically comprises:

[0019] The high-strength flame-retardant polymer is added to an organic solvent and a cosolvent, stirred at 70-100℃ for 10-20h to completely dissolve, and a transparent polymer solution with a mass fraction of 8-10% is obtained, and then the gap of the modified hollow SiO2 photonic crystal template is filled;

[0020] The organic solvent is one or a combination of several of N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N-methyl pyrrolidone (NMP), N,N-dimethylformamide (DMF), and hexamethylphosphoramide (HMPA); and the co-solvent is one or a combination of several of lithium chloride, calcium chloride, sodium hydroxide, and potassium hydroxide.

[0021] As a preferred solution, the mass ratio of the organic solvent and the co-solvent is (20-30):1.

[0022] As a preferred solution, the amount of the transparent polymer solution is determined according to the surface area of the hollow SiO2 photonic crystal template, and is 0.1-0.3 mL / cm2. 2 .

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] The structural color thin film of the present application uses a polymer with flame retardation and high mechanical strength as a target filling material, uses the modified H-SiO2 PCs as a template, fills the polymer into the gap of the template, and obtains a structural color thin film with harsh environment resistance. The structural color thin film exhibits excellent flame retardation, structural stability, and strong acid and strong base resistance in harsh environments. The structural color of the thin film remains bright before and after tests such as large tensile stress and friction; at the same time, the limiting oxygen index of the thin film is more than 33%, the flame retardation grade is V-0, and excellent flame retardation is exhibited. Based on the excellent performance exhibited in the harsh environment, the structural color thin film of the present application has broad application prospects in color display in the fields of high-temperature resistance, flame retardation protection, and fire passage identification. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 In the figure, a is a preparation flowchart of the PMIA / H-SiO2 PCs structural color thin film; b is an optical photo of the PS@SiO2 PCs template, the modified H-SiO2 PCs template, and the PMIA / H-SiO2 PCs structural color thin film; c is a reflection spectrum diagram of the PS@SiO2 PCs template, the modified H-SiO2 PCs template, and the PMIA / H-SiO2 PCs structural color thin film; and d is a CIE chromaticity diagram of the PS@SiO2 PCs template, the modified H-SiO2 PCs template, and the PMIA / H-SiO2 PCs structural color thin film.

[0026] Figure 2 The figure is a contact angle image photo of the polymer solution of Example 1 of the present application before and after modification of the H-SiO2 PCs template;

[0027] Figure 3Fig. 6 shows the optical photographs of three PMIA / H-SiO2 PCs structural color films with a shell thickness of 32 nm prepared using PS microspheres with particle sizes of 206 nm, 242 nm, and 266 nm, respectively, from left to right; Fig. 6d shows the reflectance spectra of the three PMIA / H-SiO2 PCs structural color films; Fig. 6e shows the CIE chromaticity diagram of the three PMIA / H-SiO2 PCs structural color films; Fig. 6f shows the photographs and reflectance spectra of the PMIA / H-SiO2 PCs structural color film with a shell thickness of 32 nm prepared using PS microspheres with a particle size of 266 nm at different incident angles;

[0028] Figure 4 Fig. 8 shows the tensile test schematic of the PMIA / H-SiO2 PCs structural color film (a), the stress-strain curves of the PMIA / H-SiO2 PCs structural color film and the pure PMIA film (b), the photographs of the PMIA / H-SiO2 PCs structural color film under 0.5 kg and 1 kg loads (c), and the reflectance spectra of the PMIA / H-SiO2 PCs structural color film under different tensile stresses and the comparison between the position of the reflectance spectrum peak and the reflectance (d and e);

[0029] Figure 5 Fig. 9 shows the optical photographs of the PMIA / H-SiO2 PCs structural color film in the strong acid and strong base resistance tests (a and b), and the reflectance spectra of the PMIA / H-SiO2 PCs structural color film after the strong acid and strong base resistance tests (c and d);

[0030] Figure 6 Fig. 10 shows the photographs of the PMIA / H-SiO2 PCs structural color film in the liquid nitrogen resistance test (a) and the liquid nitrogen brittle fracture resistance test (b), and the reflectance spectra of the PMIA / H-SiO2 PCs structural color film in the liquid nitrogen resistance test and the liquid nitrogen brittle fracture resistance test (c and d);

[0031] Figure 7 Fig. 11 shows the vertical burning test schematic of the PMIA / H-SiO2 PCs structural color film (a), the comparison between the limiting oxygen indices of different structural color PMIA / H-SiO2 PCs structural color films and the pure PMIA film (b), and the photographs of the vertical burning test of the PMIA / H-SiO2 PCs structural color film (c). DETAILED DESCRIPTION

[0032] In order to more clearly illustrate the embodiments of the present application, the specific embodiments of the present application will be described below with reference to the drawings. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained according to these drawings, and other embodiments can also be obtained without creative labor for those skilled in the art.

[0033] Embodiment 1:

[0034] In this embodiment, PS monodisperse nanospheres with uniform particle size are prepared by emulsion polymerization. The PS nanospheres are uniformly dispersed in a mixed solution of anhydrous ethanol, deionized water and ammonia water. Tetraethyl silicate (TEOS) is quickly added to the above solution under magnetic stirring, and the PS@SiO2 core-shell microspheres are obtained by continuously stirring at room temperature for a period of time. The concentration of the PS@SiO2 dispersion is adjusted to 2.4%, and the PS@SiO2 core-shell microspheres are self-assembled for 8h under constant temperature conditions to form a PS@SiO2 PCs template on a hydrophilic treated substrate. The PS@SiO2 PCs template is placed in a muffle furnace and heated to 500°C, and after cooling to room temperature, an H-SiO2 PCs template is obtained. The specific preparation process of the H-SiO2 PCs template is prior art and will not be described here.

[0035] The H-SiO2 PCs template is placed in a hydrothermal kettle containing a mixed solution of methylacryloxypropyltrimethoxysilane (MPS), ethanol and water in a volume ratio of 0.1:20:1. After heating at 80°C for 2h, a modified H-SiO2 PCs template is obtained.

[0036] Poly-m-phenylene isophthalamide (PMIA) is added to N,N-dimethylacetamide (DMAc) and LiCl, and stirred at 90°C for 10h to completely dissolve, obtaining a transparent polymer solution with a mass fraction of 10%; wherein the mass ratio of N,N-dimethylacetamide (DMAc) to LiCl is 30:1;

[0037] The polymer solution is added dropwise to the surface of the modified H-SiO2 PCs template, and after the polymer solution is uniformly leveled, it is quickly moved into a vacuum drying oven, vacuumed to 0.003MPa, slowly heated to 100°C and continuously heated for 2h to completely volatilize the solvent, obtaining a PMIA / H-SiO2 PCs structural color thin film.

[0038] The amount of polymer solution is determined according to the surface area of the hollow SiO2 photonic crystal template, which is 0.2mL / cm 2 .

[0039] In this embodiment, PS microspheres with a particle size of 266 nm were used as the core material, and PS@SiO2 core-shell microspheres with a shell thickness of 32 nm were used as the composition unit of the PS@SiO2 PCs template. PMIA was infiltrated into the gap of the modified H-SiO2 PCs template to prepare a PMIA / H-SiO2 PCs high-strength flame-retardant structural color film. Figure 1 a is the preparation process of the PMIA / H-SiO2 PCs high-strength flame-retardant structural color film. PS@SiO2 core-shell microspheres are self-assembled to form a PS@SiO2 PCs template, which is calcined and modified to form an H-SiO2 PCs template. PMIA polymer is filled into the gap of the modified template to obtain a PMIA / H-SiO2 PCs high-strength flame-retardant structural color film. Figure 1 b is the optical photo of the PS@SiO2 PCs template, the modified H-SiO2 PCs template, and the PMIA / H-SiO2 PCs high-strength flame-retardant film, and their colors are green, blue, and cyan, respectively. Figure 1 Figure 1 b is the reflection spectrum of the corresponding sample. The PS core of the PS@SiO2 PCs template is removed by calcination, the average refractive index of the template decreases, which causes the reflection peak to blue shift from 513 nm (green) of the PS@SiO2 PCs template to 390 nm (blue) of the H-SiO2 PCs template. When PMIA is filled into the gap of the H-SiO2 PCs template to form a PMIA / H-SiO2 PCs film, the average refractive index increases significantly, and the reflection peak red shifts to 488 nm (cyan). Figure 1 d is the CIE chromaticity diagram of the three samples, and the color of the chromaticity point of each sample and Figure 1 The colors of the optical photos of b are basically consistent.

[0040] Figure 2 To add PMIA solution to the H-SiO2 PCs template before and after modification, respectively, the contact angle image after 10 minutes. The contact angle of the PMIA solution on the modified template is smaller, which indicates that its wettability on the template is better, which is beneficial to the smoother infiltration of the PMIA solution into the template gap.

[0041] Figure 3 a, Figure 3 b and Figure 3 c are the optical photos of three PMIA / H-SiO2 PCs high-strength flame-retardant films with a shell thickness of 32 nm prepared by using PS microspheres with particle sizes of 206 nm, 242 nm, and 266 nm, respectively, in Example 1. Figure 3 ​d are the reflection spectra of the three films, and the reflection peak positions are 514 nm, 617 nm and 660 nm, respectively. The larger the particle size of H-SiO2 in the film, the larger the interplanar spacing of the crystal, and according to Bragg's law, the wavelength position of the film reflection peak will also increase accordingly. Figure 3 e are the CIE chromaticity diagrams of the three films, and the corresponding chromaticity points of the films are basically consistent with their optical photographs. Figure 3 f are Figure 3 c are the photographs and reflection spectra of the film at different incident angles. According to Bragg's law, as the incident angle of light increases, the position of the film reflection peak will gradually blue shift. The structural color of the film also gradually changes from red to a smaller wavelength color.

[0042] Figure 4 a is the tensile test schematic diagram of the PMIA / H-SiO2 PCs high-strength flame-retardant structural color film of the present embodiment, Figure 4 b are the stress-strain curves of the PMIA / H-SiO2 PCs film and the pure PMIA film. The breaking strength and breaking strain of the PMIA / H-SiO2 PCs film are 66 MPa and 12%, respectively, which are higher than those of the pure PMIA film, 57 MPa and 6%, respectively, which indicates that the PMIA / H-SiO2 PCs film has excellent mechanical properties. Figure 4 c are photographs of the PMIA / H-SiO2 PCs film under 0.5 kg and 1 kg loads, respectively. From the photographs, it can be seen that the structural color of the film does not change significantly. Figure 4 d and Figure 4 e are the reflection spectra of the PMIA / H-SiO2 PCs film under different tensile stresses, as well as the position of the reflection spectrum peak and the reflectivity. The above optical property data of the film do not change significantly under different tensile stresses, indicating that the structural color of the film has excellent stability under the action of stretching.

[0043] Figure 5 a and Figure 5 b are optical photographs of the PMIA / H-SiO2 PCs high-strength flame-retardant structural color film of the present embodiment in strong acid and strong base resistance tests. The film was immersed in a sulfuric acid solution with pH = 1 for 7 days and in a sodium hydroxide solution with pH = 14 for 7 days, and the film remained intact and the structural color did not change significantly. Figure 5 c, 5d are the reflection spectra of the film after the strong acid and strong base resistance tests. After the film has experienced long-term acid and alkali resistance tests, the structural color and the reflection spectrum of the film do not change significantly, which verifies the excellent acid and alkali resistance of the film.

[0044] The film was subjected to low-temperature brittle fracture resistance test in liquid nitrogen, Figure 6a is the liquid nitrogen resistance test photo of the PMIA / H-SiO2 PCs high-strength flame-retardant structural color film of the present embodiment, Figure 6 b is the liquid nitrogen brittle fracture resistance test photo of the film, Figure 6 c and Figure 6 d are the reflection spectrum diagrams of the film in the liquid nitrogen resistance test and the liquid nitrogen brittle fracture resistance test, respectively. The test results of the photos and the spectrum show that the structural color and the reflection spectrum of the film do not change significantly, which verifies that the structural color has excellent stability at low temperature. Figure 6 e is the stress-strain curve diagram of the film before and after the low-temperature resistance test, and the mechanical properties of the film only decrease to a small extent after being immersed in liquid nitrogen for 6h.

[0045] The film was subjected to limiting oxygen index test and vertical combustion test, Figure 7 a is the vertical combustion test schematic diagram of the PMIA / H-SiO2 PCs high-strength flame-retardant structural color film of the present embodiment, Figure 7 b is the limiting oxygen index of different structural color PMIA / H-SiO2 PCs films and pure PMIA film, and the limiting oxygen index of different structural color PMIA / H-SiO2 PCs films is higher than 33% (difficult material level), and higher than that of pure PMIA (29.1%). This shows that the addition of H-SiO2 PCs template in the composition is beneficial to achieve higher flame retardant performance. As shown in c, the photo shows that the film is self-extinguished quickly after being ignited for many times, and no molten droplets are generated, and the flame retardant level reaches the highest V-0 level, indicating that the film has excellent flame retardant performance. Figure 7

[0046] Example 2:

[0047] In the present embodiment, monodisperse PS nanospheres with uniform particle size are prepared by emulsion polymerization. The PS nanospheres are uniformly dispersed in a mixed solution of anhydrous ethanol, deionized water and ammonia water, and then TEOS is quickly added to the above-mentioned solution under magnetic stirring, and the PS@SiO2 core-shell microspheres are obtained after continuous stirring at room temperature for a period of time. The concentration of the PS@SiO2 dispersion liquid is configured to be 2.4%, and the PS@SiO2 core-shell microspheres are self-assembled for 8h under constant temperature conditions to form PS@SiO2 PCs templates on the base surface after hydrophilic treatment. The PS@SiO2 PCs template is placed in a muffle furnace and heated to 500℃, and after cooling to room temperature, the H-SiO2 PCs template is obtained. The H-SiO2 PCs template is placed in a hydrothermal kettle containing a mixed solution of MPS, ethanol and water in a volume ratio of 0.05:20:1.5, and heated at 75℃ for 3h to obtain the modified H-SiO2 PCs template.

[0048] ​Poly (p-phenylene terephthamide) PPTA is added into dimethyl sulfoxide DMSO and NaOH, and stirred at 100℃ for 15h to make it completely dissolved, to obtain a transparent polymer solution with a mass fraction of 8%; wherein the mass ratio of dimethyl sulfoxide DMSO to NaOH is 25:1;

[0049] The polymer solution is added dropwise to the surface of the modified template, and after the polymer solution is uniformly leveled, it is quickly moved into a vacuum drying oven, vacuumed to 0.003MPa, slowly heated to 100℃ and continuously heated for 2h to make the solvent completely volatilize, to obtain a PPTA / H-SiO2 PC structural formula film.

[0050] The amount of the polymer solution is determined according to the surface area of the hollow SiO2 photonic crystal template, and is 0.3mL / cm 2 .

[0051] Example 3:

[0052] The PS monodisperse nanospheres with uniform particle size are prepared by an emulsion polymerization method, the PS microspheres are uniformly dispersed into a mixed solution of anhydrous ethanol, deionized water and ammonia water, TEOS is quickly added into the above solution under magnetic stirring, and the PS@SiO2 core-shell microspheres can be obtained after stirring at room temperature for a period of time. The PS@SiO2 PCs template is formed on the hydrophilic treated base surface by self-assembly of the PS@SiO2 core-shell microspheres under constant temperature conditions for 8h. The PS@SiO2 PCs template is placed in a muffle furnace and heated to 500℃, and after cooling to room temperature, the H-SiO2 PCs template is obtained. The H-SiO2 PCs template is placed in a hydrothermal kettle containing a mixed solution of MPS, ethanol and water with a volume ratio of 0.2:20:0.5, heated at 85℃ for 1h, and the modified H-SiO2 PCs template is obtained.

[0053] Polybenzimidazole PBI is added into N-methyl pyrrolidone NMP and CaCl2, and stirred at 70℃ for 20h to make it completely dissolved, to obtain a transparent polymer solution with a mass fraction of 9%; wherein the mass ratio of N-methyl pyrrolidone NMP to CaCl2 is 20:1;

[0054] The polymer solution is added dropwise to the surface of the modified template, and after the polymer solution is uniformly leveled, it is quickly moved into a vacuum drying oven, vacuumed to 0.003MPa, slowly heated to 100℃ and continuously heated for 2h to make the solvent completely volatilize, to obtain a PBI / H-SiO2 PC film.

[0055] The amount of the polymer solution is determined according to the surface area of the hollow SiO2 photonic crystal template, and is 0.1mL / cm 2 .

[0056] Example 4:

[0057] The difference between this embodiment and Example 1 or Example 2 or Example 3 is that:

[0058] PMMA@SiO2 core-shell microspheres, PS@TiO2 core-shell microspheres, and PMMA@TiO2 core-shell microspheres are used instead of PS@SiO2 core-shell microspheres in Example 1 as the nanometer microspheres for assembling the template, and other conditions are consistent with those in Example 1.

[0059] The present application uses polymer microspheres as the core material, and a layer of SiO2 is coated on the surface of the polymer microspheres by hydrolysis of tetraethyl silicate (TEOS) to prepare core-shell microspheres. Photonic crystal templates are formed by self-assembly of the core-shell microspheres, and hollow SiO2 photonic crystal (H-SiO2 PCs) templates are formed by calcination to remove the polymer ball core. After modification of the H-SiO2 PCs template with a silane coupling agent, a polymer with flame retardant and high mechanical strength is filled into the gap, and a structural color film for harsh environments is obtained. The film's flame retardant, tensile resistance, high and low temperature resistance, friction resistance, and strong acid and alkali resistance tests show that it has excellent flame retardancy, structural color stability, and strong acid and alkali resistance. Based on the above-mentioned excellent performance in harsh environments, this structural color film has broad application prospects in color display in the fields of high temperature resistance, flame retardant protection, and fire passage identification.

[0060] Since there are many embodiments of the present application, the raw materials and amounts involved can be selected according to actual needs within the limited range, and the experimental data of each embodiment are numerous and not suitable for enumeration here. However, the content to be verified and the final conclusion obtained by each embodiment are similar. Therefore, the verification content of each embodiment is not described one by one here.

[0061] The above only describes the preferred embodiments and principles of the present application in detail. For ordinary skilled persons in the art, the specific implementation methods provided by the present application will change according to the ideas provided by the present application, and these changes should also be considered as the protection scope of the present application.

Claims

1. A structural color thin film, characterized by, The hollow SiO2 photonic crystal template and high-strength flame-retardant polymer filled in the gap of the hollow SiO2 photonic crystal template are included; wherein the hollow SiO2 photonic crystal template is modified by a silane coupling agent and then filled with the high-strength flame-retardant polymer. The high-strength flame-retardant polymer is one or a combination of poly-m-phenylene isophthalamide, poly-p-phenylene terephthalamide and polybenzimidazole.

2. The structural color thin film according to claim 1, characterized by The silane coupling agent is one or a combination of aminopropyl triethoxysilane, methacryloxypropyl trimethoxysilane and methyl trimethoxysilane.

3. The method of producing a structural color thin film according to any one of claims 1 to 2, characterized by, The method comprises the following steps: (1) preparation of the hollow SiO2 photonic crystal template; (2) modification of the hollow SiO2 photonic crystal template by a silane coupling agent; (3) filling of the high-strength flame-retardant polymer into the gap of the modified hollow SiO2 photonic crystal template and vacuum drying to obtain a structural color film.

4. The production method according to claim 3, characterized by, The step (2) specifically comprises: The hollow SiO2 photonic crystal template is placed in a mixed solution of the silane coupling agent, ethanol and water for hydrothermal reaction to obtain the modified hollow SiO2 photonic crystal template.

5. The preparation method according to claim 4, characterized in that, The volume ratio of the silane coupling agent, ethanol and water in the mixed solution is (0.05-0.2):20:(0.5-1.5).

6. The preparation method according to claim 4, characterized in that, The hydrothermal reaction is carried out at a temperature of 75-85℃ for 1-3h.

7. The preparation method according to claim 3, characterized in that, The step (3) specifically comprises: The high-strength flame-retardant polymer is added into an organic solvent and a cosolvent, stirred at 70-100℃ for 10-20h to completely dissolve the polymer and obtain a transparent polymer solution with a mass fraction of 8-10%, and then the gap of the modified hollow SiO2 photonic crystal template is filled; The organic solvent is one or a combination of N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl pyrrolidone, N,N-dimethylformamide and hexamethylphosphoramide; and the cosolvent is one or a combination of lithium chloride, calcium chloride, sodium hydroxide and potassium hydroxide.

8. The preparation method according to claim 7, characterized in that, The mass ratio of the organic solvent to the cosolvent is (20-30):

1.

9. The preparation method according to claim 7, characterized in that, The amount of the transparent polymer solution is determined according to the surface area of the hollow SiO2 photonic crystal template, and is 0.1-0.3 mL / cm 2 .

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