A silk-based photonic crystal structural color coating solution and its application

Abstract

The present invention provides a silk-based photonic crystal structural color coating solution and its application. The silk-based photonic crystal structural color coating solution is prepared by mixing a monodisperse SiO2 microsphere aqueous solution and a silk fibroin aqueous solution, wherein the silk fibroin aqueous solution accounts for 13.5wt% to 55.6wt% of the monodisperse SiO2 microsphere aqueous solution; the mass fraction of SiO2 microspheres in the monodisperse SiO2 microsphere solution is 3 to 15%; and the solid content of the silk fibroin aqueous solution is 4 to 6%. The present invention combines the monodisperse SiO2 microsphere aqueous solution and the silk fibroin aqueous solution to form a silk-based photonic crystal structural color coating solution. The coating prepared from the silk-based photonic crystal structural color coating solution is treated with an alcohol compound to change the secondary structure of the silk fibroin into a secondary structure primarily composed of β-folding, thereby enhancing the mechanical properties of the photonic crystal structural color coating and increasing the skin compatibility of the photonic crystal structural color coating.

Description

Technical Field

[0001] The present invention relates to the technical field of structural color coatings, and in particular to a silk-based photonic crystal structural color coating solution and applications thereof. Background Art

[0002] Color plays a crucial role in nature, allowing species to change color to convey information, conceal themselves, or deter predators. Unlike pigments and dyes, which absorb some wavelengths of light and reflect others, structural colors utilize a different principle. They are produced by nanoscale units through interference, diffraction gratings, and photonic crystals. Structural color depends on the scale of the periodic unit and the color of the unit, and can be effectively modified by the size and arrangement of the photonic crystal. Therefore, as long as the arrangement of the periodic unit particles is stable, structurally colored materials will never fade.

[0003] Traditional skin coatings apply a layer of pigment to the skin. The complex composition of pigments can cause skin problems such as allergies. However, structural color does not suffer from these drawbacks. As long as the microscopic morphology of the structural color photonic crystal is intact, the coating will never fade. Furthermore, the production process is pollution-free, making it environmentally friendly. Therefore, replacing pigments and dyes with structural color is a current trend.

[0004] Current methods for producing structural color primarily rely on preparing photonic crystals using microemulsion and sol-gel methods. However, these methods are expensive and complex to operate. Furthermore, the mechanical properties of the resulting structural color coatings, such as adhesion, are poor. Current methods for enhancing the mechanical properties of photonic crystal coatings primarily involve the addition of organic colloids such as polyurethane and polylatex to induce self-assembly. However, these organic colloids are not very compatible with skin. Summary of the Invention

[0005] The primary purpose of the present invention is to solve the problems in the above-mentioned prior art such as poor mechanical properties such as adhesion of photonic crystal structural color coatings, poor compatibility with skin, and complex operations for preparing structural colors, and to provide a silk-based photonic crystal structural color coating solution.

[0006] A further object of the present invention is to provide the use of the above-mentioned silk-based photonic crystal structural color coating solution in the preparation of skin surface materials.

[0007] The third object of the present invention is to provide a method for preparing a silk-based photonic crystal structure color coating.

[0008] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0009] The first aspect of the present invention provides a silk-based photonic crystal structural color coating solution, which is prepared by mixing a monodisperse SiO2 microsphere aqueous solution and a silk fibroin aqueous solution, wherein the silk fibroin aqueous solution accounts for 13.5wt% to 55.6wt% of the monodisperse SiO2 microsphere aqueous solution; the mass fraction of SiO2 microspheres in the monodisperse SiO2 microsphere solution is 3 to 15%; and the solid content of the silk fibroin aqueous solution is 4 to 6%.

[0010] The amount of silk fibroin aqueous solution added to the silk-based photonic crystal structure color coating solution of the present invention affects the mechanical properties of the subsequently formed silk-based photonic crystal structure color coating, because silk fibroin can be coated on the surface of SiO2 microspheres and between the SiO2 microspheres, providing strong mechanical support to the SiO2 microspheres, and silk fibroin itself has good skin affinity, which can improve the adhesion of the photonic crystal structure color coating in simulated skin. The adhesion of the photonic crystal structure color coating without the addition of silk fibroin aqueous solution is very poor and cannot be used in practical applications, while the silk-based photonic crystal structure color coating with the addition of silk fibroin aqueous solution has significantly increased mechanical strength, broadening the practical application of photonic crystals. As the amount of silk fibroin aqueous solution added increases, the strength of the photonic crystal structure color coating also increases. However, when the amount of silk fibroin aqueous solution added is too much, the silk fibroin will not only cover the surface of the particles, but also adhere to a layer of silk fibroin on the coating, disrupting the microscopic arrangement order of the photonic crystal structure color, resulting in the inability of light to be selectively reflected, which will cause the structure color to disappear.

[0011] In a specific embodiment, the monodisperse SiO2 microsphere aqueous solution and the silk fibroin aqueous solution are mixed by ultrasonically oscillating at a power of 100 to 300 W for 30 to 40 minutes at room temperature.

[0012] Furthermore, the SiO2 microspheres in the monodisperse SiO2 microsphere aqueous solution have a single particle size, with an average particle size of 140 to 575 nm. Preferably, the mass fraction of the SiO2 microspheres in the monodisperse SiO2 microsphere aqueous solution is 6 to 8%, more preferably 7%.

[0013] When the mass fraction of SiO2 microspheres is too high, the dispersion of the microspheres will deteriorate and they will easily precipitate.

[0014] In a specific embodiment, the method for preparing the monodisperse SiO2 microsphere aqueous solution comprises the following steps:

[0015] Mix anhydrous ethanol and ammonia water evenly, stir and react at room temperature for 20 to 40 minutes to obtain a mixture of anhydrous ethanol and ammonia water; slowly add tetraethyl orthosilicate dropwise into the mixture of anhydrous ethanol and ammonia water, stir and react at room temperature for 4 to 6 hours, and after the reaction is completed, centrifuge and wash to obtain SiO2 microspheres; disperse the SiO2 microspheres in water to obtain a monodisperse SiO2 microsphere aqueous solution.

[0016] The volume ratio of the anhydrous ethanol, ammonia water and tetraethyl orthosilicate is (100-120): (7-9): (4-11), and the dropping speed of the tetraethyl orthosilicate is 2-4 mL / min.

[0017] Among them, the particle size of the synthesized SiO2 microspheres can be changed by adjusting the addition ratio of ammonia water. The larger the proportion of ammonia water, the larger the particle size of the SiO2 microspheres, and the color of the silk-based photonic crystal coating will also undergo a red shift, gradually changing from blue (the particle size of the SiO2 microspheres is preferably 220nm) to yellow and finally to red (the particle size of the SiO2 microspheres is 575nm).

[0018] Furthermore, the solid content of the silk fibroin aqueous solution is 4-6%, and it is slightly whitish and translucent. When the solid content of the silk fibroin aqueous solution is too much, the silk fibroin is easily agglomerated, which affects the dissolution effect.

[0019] Furthermore, the method for preparing the silk fibroin aqueous solution comprises the following steps: dissolving the silk fibroin obtained after degumming silk cocoons in a mixture of calcium salt, organic solvent and water to obtain the silk fibroin aqueous solution.

[0020] Furthermore, the mass ratio of the silkworm cocoon, calcium salt, organic solvent and water is 5:(50-60):(60-70):(70-80).

[0021] Furthermore, the calcium salt is anhydrous calcium chloride, and the organic solvent is ethanol.

[0022] In a specific embodiment, the preparation method of the silk fibroin aqueous solution includes the following steps: dissolving sodium bicarbonate in water to obtain a degumming solution, continuously heating the chopped cocoons and the degumming solution to 120-130°C until boiling and continuing for 30-40 minutes, repeating the degumming twice to obtain silk fibroin; mixing anhydrous calcium chloride, ethanol and water evenly with the silk fibroin at 70-80°C until completely dissolved, continuing to stir for 30-40 minutes, obtaining a silk fibroin stock solution after the reaction is completed, dialyzing and centrifuging the silk fibroin stock solution to obtain a silk fibroin aqueous solution.

[0023] Wherein, the mass ratio of sodium bicarbonate to water in the degumming solution is 1:(100-110).

[0024] The second aspect of the present invention provides a use of the silk-based photonic crystal structural color coating solution described in the first aspect in preparing skin surface materials.

[0025] The third aspect of the present invention provides a method for preparing a silk-based photonic crystal structural color coating, comprising the following steps: coating the silk-based photonic crystal structural color coating solution described in the first aspect on the surface of a substrate to obtain the silk-based photonic crystal structural color coating.

[0026] Furthermore, the silk-based photonic crystal structure color coating is treated with alcohol compounds.

[0027] The present invention self-assembles a monodisperse SiO2 microsphere aqueous solution and a silk fibroin aqueous solution to obtain a silk-based photonic crystal structural color coating solution. The coating prepared from the silk-based photonic crystal structural color coating solution is treated with an alcohol compound to change the secondary structure of the silk fibroin, converting the silk fibroin into a secondary structure mainly composed of β-folding, thereby enhancing the mechanical properties of the photonic crystal structural color coating and increasing the compatibility of the photonic crystal structural color coating with the skin.

[0028] Furthermore, the coating thickness is 200-300 μm.

[0029] In a specific embodiment, the substrate is selected from one of simulated skin, glass and aluminum plate.

[0030] Specifically, the simulated skin can be a simulated skin sheet.

[0031] In a specific embodiment, the treatment time is 20 to 30 minutes.

[0032] In a specific embodiment, the alcohol compound is used to treat the silk-based photonic crystal structure color coating by performing an immersion treatment on the substrate containing the silk-based photonic crystal structure color coating.

[0033] In practical applications, the silk-based photonic crystal structural color coating solution is applied on the skin and then coated with an alcohol compound.

[0034] In a specific embodiment, the coating method can be spraying, using a spray gun to spray at a pressure of 2 to 4 MPa.

[0035] Furthermore, the alcohol compound is methanol or ethanol, preferably ethanol.

[0036] Furthermore, the spraying temperature affects the color development speed of the silk-based photonic crystal structural color coating.

[0037] When spraying is carried out at room temperature of 20°C, the water is completely evaporated and the coating takes 3 to 4 seconds to develop color; when the temperature on the heating platform is raised to 45°C, the water is completely evaporated and the coating takes 2 to 3 seconds to develop color; when the temperature on the heating platform is further raised to 75°C, the water is completely evaporated and the coating takes less than 1 to 2 seconds to develop color.

[0038] Beneficial effects of the present invention:

[0039] The present invention self-assembles a monodisperse SiO2 microsphere aqueous solution and a silk fibroin aqueous solution to obtain a silk-based photonic crystal structural color coating solution. The coating prepared from the silk-based photonic crystal structural color coating solution is treated with an alcohol compound to change the secondary structure of the silk fibroin, converting the silk fibroin into a secondary structure mainly composed of β-folding, thereby enhancing the mechanical properties of the photonic crystal structural color coating and increasing the compatibility of the photonic crystal structural color coating with the skin. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 These are SEM images of the silk-based photonic crystal structural color coatings prepared in Examples 1 to 6 and the photonic crystal structural color coating prepared in Comparative Example 1; wherein, Figure (a) is Comparative Example 1, Figure (b) is Example 1, Figure (c) is Example 2, Figure (d) is Example 3, Figure (e) is Example 4, Figure (f) is Example 5, and Figure (g) is Example 6.

[0041] Figure 2 These are the infrared spectra and X-ray diffraction patterns of the silk-based photonic crystal structural color coating prepared in Example 3 and the photonic crystal structural color coating prepared in Comparative Example 2; wherein, Figure (a) is the infrared spectra and Figure (b) is the X-ray diffraction pattern.

[0042] Figure 3 These are optical photographs and reflection spectra of the silk-based photonic crystal structural color coatings prepared in Examples 1 to 6 and the photonic crystal structural color coating prepared in Comparative Example 1.

[0043] Figure 4 This is a peeling strength diagram of the silk-based photonic crystal structure color coatings prepared in Examples 1 to 6 and the photonic crystal structure color coating prepared in Comparative Example 1.

[0044] Figure 5 These are optical images and UV reflection graphs of the silk-based photonic crystal structural color coatings prepared in Examples 1 to 6 and the photonic crystal structural color coating prepared in Comparative Example 1 after strength testing (peeling test).

[0045] Figure 6 These are displacement-stress diagrams of the silk-based photonic crystal structural color coatings prepared in Examples 1 to 6 after strength testing (nanoindentation testing).

[0046] Figure 7 Elastic modulus diagram of the silk-based photonic crystal structural color coatings prepared in Examples 1 to 6 after strength testing (nanoindentation test).

[0047] Figure 8 Graph showing the adhesion of the silk-based photonic crystal structural color coatings prepared in Examples 1 to 6 after strength testing (nanoindentation testing).

[0048] Figure 9 These are surface morphologies of the silk-based photonic crystal structural color coatings prepared in Examples 2 and 6; wherein, Figure (a) is Example 2, and Figure (b) is Example 6.

[0049] Figure 10 This is an optical picture of the silk-based photonic crystal structural color coating of the present invention. DETAILED DESCRIPTION

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0051] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0052] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are all commercially available unless otherwise specified.

[0053] In the following examples, the method for preparing the monodisperse SiO2 microsphere aqueous solution is as follows:

[0054] Mix 90 mL of anhydrous ethanol and 9 mL of ammonia water evenly, stir and react at room temperature for 30 minutes to obtain a mixture of anhydrous ethanol and ammonia water; slowly add 10 mL of anhydrous ethanol and 5 mL of tetraethyl orthosilicate dropwise into the mixture of anhydrous ethanol and ammonia water, stir and react at room temperature for 6 hours. After the reaction is completed, centrifuge at 8000 rpm and wash with deionized water 3 times, repeat centrifugation and washing 2 times to obtain SiO2 microspheres; disperse the SiO2 microspheres in deionized water to obtain a monodisperse SiO2 microsphere solution with an average particle size of 220 nm and a mass fraction of 7%.

[0055] In the following Examples 1 to 6 and Comparative Examples 2 and 3, the preparation method of the silk fibroin aqueous solution is as follows:

[0056] Dissolve 1.5g of sodium bicarbonate in 150mL of deionized water to obtain a 1wt% degumming solution. Cut 5g of silk cocoons into 2mm×2mm pieces, and heat the chopped cocoons and the degumming solution at 125℃. After the mixed solution boils, start the degumming process for 30min. Repeat the degumming process twice, take out the silk fibroin, wash it repeatedly with deionized water until the sericin is completely removed, and place it in a ventilated place for 6h to obtain the silk fibroin. Dissolve 60g of anhydrous calcium chloride, 70mL of anhydrous ethanol and 80mL of deionized water completely at room temperature under constant stirring, put the silk fibroin into the mixed solution and simmer for 8 hours. The silk fibroin stock solution was stirred at 0°C until completely dissolved, and then stirred for 30 minutes after complete dissolution to obtain a silk fibroin stock solution; the silk fibroin stock solution was loaded into a dialysis tape with a molecular weight of 10,000, and clamped with a dialysis clamp, and dialyzed with deionized water, with the deionized water replaced every 4 to 7 hours for 4 days; the obtained silk fibroin solution was centrifuged at a speed of 8000 rpm to remove impurity precipitation in the silk fibroin to obtain a silk fibroin aqueous solution with a mass fraction of 4 wt%, which was stored in a 4°C refrigerator.

[0057] Example 1

[0058] A method for preparing a silk-based photonic crystal structured color coating comprises the following steps:

[0059] The silk-based photonic crystal structural color coating solution was sprayed onto a simulated skin sheet that had been wiped clean with anhydrous ethanol using an air pump spray gun at a pressure of 2MPa. The spraying thickness was 220μm. The simulated skin sheet containing the silk-based photonic crystal structural color coating was immersed in ethanol for 20 minutes to obtain the silk-based photonic crystal structural color coating.

[0060] Among them, the silk-based photonic crystal structural color coating solution is prepared by mixing a monodisperse SiO2 microsphere aqueous solution and a silk fibroin aqueous solution at room temperature with 100W power ultrasonic vibration for 30 minutes, and the silk fibroin aqueous solution accounts for 13.5wt% of the monodisperse SiO2 microsphere aqueous solution.

[0061] Example 2

[0062] A method for preparing a silk-based photonic crystal structural color coating is the same as the preparation method in Example 1, except that the silk fibroin aqueous solution in the silk-based photonic crystal structural color coating solution accounts for 23.8wt% of the monodisperse SiO2 microsphere aqueous solution.

[0063] Example 3

[0064] A method for preparing a silk-based photonic crystal structural color coating is the same as the preparation method in Example 1, except that the silk fibroin aqueous solution in the silk-based photonic crystal structural color coating solution accounts for 29.4wt% of the monodisperse SiO2 microsphere aqueous solution.

[0065] Example 4

[0066] A method for preparing a silk-based photonic crystal structural color coating is the same as the preparation method in Example 1, except that the silk fibroin aqueous solution in the silk-based photonic crystal structural color coating solution accounts for 38.5wt% of the monodisperse SiO2 microsphere aqueous solution.

[0067] Example 5

[0068] A method for preparing a silk-based photonic crystal structural color coating is the same as the preparation method in Example 1, except that the silk fibroin aqueous solution in the silk-based photonic crystal structural color coating solution accounts for 48.3 wt % of the monodisperse SiO2 microsphere aqueous solution.

[0069] Example 6

[0070] A method for preparing a silk-based photonic crystal structural color coating is the same as the preparation method in Example 1, except that the silk fibroin aqueous solution in the silk-based photonic crystal structural color coating solution accounts for 55.6wt% of the monodisperse SiO2 microsphere aqueous solution.

[0071] Comparative Example 1

[0072] A method for preparing a photonic crystal structured color coating comprises the following steps:

[0073] An air pump spray gun was used to spray a monodisperse SiO2 microsphere aqueous solution onto a simulated skin sheet that had been wiped clean with anhydrous ethanol at a pressure of 2MPa. The spraying thickness was 220μm. The simulated skin sheet containing the photonic crystal structural color coating was immersed in ethanol for 20 minutes to obtain the photonic crystal structural color coating.

[0074] Comparative Example 2

[0075] A method for preparing a photonic crystal structured color coating comprises the following steps:

[0076] The silk-based photonic crystal structural color coating solution was sprayed onto a simulated skin sheet that had been wiped clean with anhydrous ethanol using an air pump spray gun at a pressure of 2 MPa. The spraying thickness was 220 μm, thereby obtaining a photonic crystal structural color coating.

[0077] Among them, the silk-based photonic crystal structural color coating solution is prepared by mixing a monodisperse SiO2 microsphere aqueous solution and a silk fibroin aqueous solution at room temperature with 100W power ultrasonic vibration for 30 minutes, and the silk fibroin aqueous solution accounts for 29.4wt% of the monodisperse SiO2 microsphere aqueous solution.

[0078] Comparative Example 3

[0079] A method for preparing a silk-based photonic crystal structural color coating is the same as the preparation method in Example 1, except that the silk fibroin aqueous solution in the silk-based photonic crystal structural color coating solution accounts for 70 wt % of the monodisperse SiO2 microsphere aqueous solution.

[0080] When the silk fibroin aqueous solution accounts for 70wt% of the monodisperse SiO2 microsphere aqueous solution, the silk-based photonic crystal coating will lose its color. This is because the color generation principle of the photonic crystal structural color is that the silica particles present a short-range ordered and long-range disordered structural arrangement order, which causes the light to be selectively reflected. When the silk fibroin aqueous solution content reaches more than 70wt%, the silk fibroin will not only cover the surface of the particles, but also attach a layer of silk fibroin to the coating, disrupting the microscopic arrangement order of the photonic crystal structural color, resulting in the inability to selectively reflect light, which will cause the structural color to disappear.

[0081] Comparative Example 4

[0082] A method for preparing a silk-based photonic crystal coating comprises the following steps:

[0083] The silk-based photonic crystal coating solution was sprayed onto a simulated skin sheet that had been wiped clean with anhydrous ethanol using an air pump spray gun at a pressure of 2 MPa. The spraying thickness was 220 μm. The simulated skin sheet containing the silk-based photonic crystal structural color coating was immersed in ethanol for 20 minutes to obtain a silk-based photonic crystal coating.

[0084] The silk-based photonic crystal coating solution is prepared by mixing a monodisperse SiO2 microsphere aqueous solution and a silk fibroin aqueous solution at room temperature with 100W power ultrasonic vibration for 30 minutes, wherein the silk fibroin aqueous solution accounts for 13.5wt% of the monodisperse SiO2 microsphere aqueous solution.

[0085] The preparation method of the silk fibroin aqueous solution is:

[0086] Dissolve 1.5g of sodium bicarbonate in 150mL of deionized water to obtain a 1wt% degumming solution. Cut 5g of silk cocoons into 2mm×2mm pieces and heat the shredded cocoons and the degumming solution at 125°C. After the mixture boils, start degumming for 30 minutes. Repeat the degumming process twice. Remove the silk fibroin and wash it repeatedly with deionized water until the sericin is completely removed. Place it in a ventilated place for 6 hours to obtain the silk fibroin. Slowly add 78g of lithium bromide powder in batches to 100mL of deionized water and stir continuously until dissolved to obtain a lithium bromide aqueous solution with a concentration of 9mol / L. Then, impurities were filtered out with filter paper to obtain a clear lithium bromide aqueous solution; 5 g of silk fibroin was added to the lithium bromide aqueous solution at a water-bath ratio of 1:20, heated at 60°C and continuously stirred until completely dissolved, and heated for 30 minutes after complete dissolution to obtain a preliminary silk fibroin solution; the preliminary silk fibroin solution was poured into a dialysis bag with a molecular weight cutoff of 6 to 8 kDa, dialyzed with deionized water for three days, and finally centrifuged for 20 minutes to obtain a silk fibroin aqueous solution; the obtained silk fibroin solution was centrifuged at a speed of 8000 rpm to remove impurity precipitation in the silk fibroin to obtain a silk fibroin aqueous solution with a mass fraction of 4 wt%.

[0087] The silk fibroin solution in Comparative Example 4 agglomerated. This agglomerated silk fibroin in the lithium bromide solution filled the photonic band gaps between the photonic crystals, causing light in the gaps to be directly reflected rather than specifically reflected through them. Consequently, the structural color disappeared. The coating prepared from the silk-based photonic crystal coating solution in Comparative Example 4 appears white because the silk fibroin solution prepared from the lithium bromide aqueous solution is slightly white.

[0088] The performance tests were conducted on the silk-based photonic crystal structure color coatings prepared in Examples 1 to 6 and the photonic crystal structure color coatings prepared in Comparative Examples 1 and 2. The test methods are as follows:

[0089] Particle Size Distribution: Particle size was measured using a Zeta potential nanoparticle size analyzer. Samples were diluted with salt water until transparent and tested at room temperature. Five measurements were performed per sample, and the average value was calculated. The actual average particle size was measured using Image J software using SEM images of the sample, with 100 measurements per sample calculated as the average value.

[0090] Silk fibroin conformation test: The silk-based photonic crystal structural color coating before and after ethanol treatment was scraped off with a scraper, ground into powder with a mortar, and tested with an infrared spectrometer and an X-ray diffractometer to obtain the infrared spectra and X-ray diffraction patterns of the silk-based photonic crystal structural color coating before and after ethanol treatment.

[0091] Ultraviolet reflection test: The ultraviolet reflection test of the silk-based photonic crystal structural color coating is measured by a UV-visible spectrophotometer with a scanning wavelength range of 400 to 800 nm and a scanning speed of 10 nm / s.

[0092] Strength test (peel test): The strength test of the silk-based photonic crystal structural color coating is carried out using a universal tensile tester. A 20mm wide 3M tape is attached to the coating, and the tape is flipped 180° and clamped on the upper clamping plate of the universal tensile tester. The silk-based photonic crystal structural color coating substrate is clamped on the lower clamping plate, and the universal tensile tester is started at a speed of 3mm / s until the tape is completely peeled off to obtain the peeling force of the coating.

[0093] Strength test (nanoindentation test): The silk-based photonic crystal structural color coating is tested on a nanoindenter. The nanoindentation probe needle is a conical needle. The nanomechanical testing system is set to an indentation: dwell: unloading ratio of 5:2:5. The load-displacement curve is obtained, and the elastic modulus and adhesion are calculated based on the load-displacement curve data.

[0094] Surface morphology test: The silk-based photonic crystal structural color coating is scanned using the surface scanning mode of a nanoindenter to obtain the surface morphology and coating thickness.

[0095] The test results are as follows:

[0096] Figure 1 The SEM images of the silk-based photonic crystal structure color coatings prepared in Examples 1 to 6 and the photonic crystal structure color coating prepared in Comparative Example 1 are shown; wherein, Figure (a) is Comparative Example 1, Figure (b) is Example 1, Figure (c) is Example 2, Figure (d) is Example 3, Figure (e) is Example 4, Figure (f) is Example 5, and Figure (g) is Example 6. Figure 1 As can be seen in the figure, the synthesized SiO2 microspheres are spherical and uniform in size. The addition of the silk fibroin aqueous solution coats the SiO2 microspheres, providing them with a certain degree of mechanical adhesion support, making them more closely arranged, while still maintaining short-range order and long-range disorder.

[0097] Figure 2 These are the infrared spectra and X-ray diffraction patterns of the silk-based photonic crystal structural color coating prepared in Example 3 and the photonic crystal structural color coating prepared in Comparative Example 2; wherein, Figure (a) is the infrared spectra and Figure (b) is the X-ray diffraction pattern. Figure 2The infrared spectra and X-ray diffraction patterns of the silk-based photonic crystal structure color coating before and after treatment in an anhydrous ethanol environment are shown. The curves in Figure (a) are respectively Example 3 and Comparative Example 2 from top to bottom, and the curves in Figure (b) are respectively Comparative Example 2 and Example 3 from top to bottom. From the infrared spectrum (a), it can be seen that the silk-based photonic crystal structure color coating without ethanol treatment has a high luminescence intensity at 1623.9 cm -1 (Amide I.), 1516.7cm -1 (Amide II.), 1210.5cm -1 There is a characteristic peak at (amide III.), indicating that it is mainly random coil. When the silk-based photonic crystal structure color coating is treated with anhydrous ethanol for 20 minutes, the amide I region is 1617.3 cm -1 A new absorption peak appeared at 1623.9 cm -1 The absorption peak at 2θ gradually weakened, indicating that the secondary structure of the silk fibroin in the coating had transformed into a secondary structure with β-folding as the main conformation. From the X-ray diffraction pattern (b), it can be seen that the diffraction peak of the silk-based photonic crystal structure color coating without ethanol treatment is 2θ = 23.2°, indicating that it mainly exhibits an amorphous structure. When the silk-based photonic crystal structure color coating is treated with anhydrous ethanol for 20 minutes, the diffraction peak shifts to the left to 2θ = 20.2°, which also shows that the secondary structure of the silk fibroin in the coating has transformed into a secondary structure with β-folding as the main conformation.

[0098] Figure 3 The optical photos and reflection spectra of the silk-based photonic crystal structure color coatings prepared in Examples 1 to 6 and the photonic crystal structure color coating prepared in Comparative Example 1 are shown. Figure 3 It can be seen that as the proportion of silk fibroin increases from 0% to 55.6%, these photonic crystal coatings visually appear blue and blue-green, and the corresponding peaks of the reflection spectrum of the silk-based photonic crystal coating are located at 419nm (Comparative Example 1), 420nm (Example 1), 422nm (Example 2), 429nm (Example 3), 431nm (Example 4), 477nm (Example 5) and 480nm (Example 6), and the color is obvious, which shows that the addition of silk fibroin aqueous solution does not affect the structural color of the photonic crystal.

[0099] Figure 4 The peeling strength diagram of the silk-based photonic crystal structure color coating prepared in Examples 1 to 6 and the photonic crystal structure color coating prepared in Comparative Example 1. Figure 4It can be seen that the adhesion of the photonic crystal structure color coating of comparative example 1 without the addition of silk fibroin aqueous solution is extremely poor, with an average adhesion of about 65N / m. When the silk fibroin aqueous solution is added, the adhesion of the silk-based photonic crystal structure color coating is improved. When the amount of silk fibroin aqueous solution added is increased to 55.6wt% of the monodisperse SiO2 microsphere solution, the average adhesion of the silk-based photonic crystal structure color coating reaches 370N / m. This is because the SiO2 microspheres in the photonic crystal structure color coating without the addition of silk fibroin aqueous solution are point-to-point links, and the mechanical properties are relatively weak. After the addition of silk fibroin aqueous solution, the silk fibroin is coated on the surface of the SiO2 microspheres and between the SiO2 microspheres, providing strong mechanical support for the SiO2 microspheres. In addition, the silk fibroin itself has good skin affinity, which improves the adhesion of the photonic crystal structure color coating on the simulated skin. And as the amount of silk fibroin aqueous solution added increases, the strength of the photonic crystal structure color coating also increases. The photonic crystal structural color coating without the addition of silk fibroin aqueous solution has very poor adhesion and cannot be used in practice. The silk-based photonic crystal structural color coating with the addition of silk fibroin aqueous solution has significantly increased mechanical strength, which broadens the practical application of photonic crystals.

[0100] Figure 5 The optical images and UV reflection images of the silk-based photonic crystal structure color coatings prepared in Examples 1 to 6 and the photonic crystal structure color coating prepared in Comparative Example 1 after strength testing (peeling test) are shown. Figure 5 It can be seen that the color of the silk-based photonic crystal coating remaining on the substrate is still obvious after the peeling test, indicating that the adhesion of the coating is enhanced after the addition of silk fibroin aqueous solution.

[0101] Figure 6 The displacement-stress diagram of the silk-based photonic crystal structure color coating prepared in Examples 1 to 6 after strength testing (nanoindentation test). Figure 6 As can be seen from the figure, the stresses are, from largest to smallest, respectively, Example 6, Example 5, Example 4, Example 3, Example 2, and Example 1. Each image in the figure is divided into an indentation segment and an unloading segment. The slope of the unloading segment curve can be calculated using the formula to obtain the elastic modulus of the silk-based photonic crystal structured color coating, and the lowest value of the unloading segment can be calculated to obtain the adhesion force of the silk-based photonic crystal structured color coating.

[0102] Figure 7 The elastic modulus of the silk-based photonic crystal structure color coating prepared in Examples 1 to 6 after strength testing (nanoindentation test) is shown. The elastic modulus of the coating characterizes the ease with which the photonic crystal coating undergoes elastic deformation under a certain stress. Figure 7As can be seen from the figure, when the content of silk fibroin aqueous solution accounts for 13.5% of the monodisperse SiO2 microsphere solution, the elastic modulus of the photonic crystal coating is 5.02 Pa. When the content of silk fibroin in the monodisperse SiO2 microsphere solution increases to 55.6%, the elastic modulus of the photonic crystal coating increases to 29.2 Pa. The elastic modulus increases with the increase of the content of silk fibroin aqueous solution, indicating that the stiffness of the silk-based photonic crystal structure color coating increases with the increase of the content of silk fibroin aqueous solution. The stress required for a certain elastic deformation is also greater, which means that the force between particles is greater, indicating that the addition of silk fibroin aqueous solution increases the mechanical properties between SiO2 microspheres.

[0103] Figure 8 The adhesion diagram of the silk-based photonic crystal structure color coating prepared in Examples 1 to 6 after strength testing (nanoindentation test). Figure 8 It can be seen that when the content of silk fibroin aqueous solution accounts for 13.5% of the monodisperse SiO2 microsphere solution, the adhesion value of the silk-based photonic crystal structural color coating is 4.88μN. When the silk fibroin content accounts for 55.6% of the monodisperse SiO2 microsphere solution, the adhesion value of the silk-based photonic crystal structural color coating reaches 9.95μN, which is twice the adhesion value of the photonic crystal coating with a silk fibroin content of 13.5%. As the amount of silk fibroin aqueous solution added increases, the adhesion force gradually increases.

[0104] Figure 9 The surface morphology of the silk-based photonic crystal structure color coating prepared in Examples 2 and 6 is shown in Figure (a) for Example 2 and Figure (b) for Example 6. Figure 9 It can be seen from the figure that the surface of the silk-based photonic crystal structure color coating prepared by the present invention is relatively smooth and uniform, and the average thickness of the coating is 200 to 300 μm.

[0105] Figure 10 This is an optical picture of the silk-based photonic crystal structure color coating of the present invention. Figure 10 It can be seen that the surface of the prepared silk-based photonic crystal structural color coating is uniform and beautiful, and the coating can be prepared in details.

[0106] The above embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A method for preparing a silk-based photonic crystal structure color coating applied to skin surface materials, characterized in that: The following steps are involved: coating a silk-based photonic crystal structure color coating solution on a surface of a substrate to obtain the silk-based photonic crystal structure color coating; treating the silk-based photonic crystal structure color coating with an alcohol compound; The silk-based photonic crystal structural color coating solution is prepared by mixing a monodisperse SiO2 microsphere aqueous solution and a silk fibroin aqueous solution, wherein the silk fibroin aqueous solution accounts for 13.5 wt% to 55.6 wt% of the monodisperse SiO2 microsphere aqueous solution; The mass fraction of SiO2 microspheres in the monodisperse SiO2 microsphere aqueous solution is 3-15%; the solid content of the silk fibroin aqueous solution is 4-6%.

2. The preparation method according to claim 1, characterized in that The average particle size of the SiO2 microspheres in the monodisperse SiO2 microsphere aqueous solution is 140 to 575 nm.

3. The preparation method according to claim 1, characterized in that The preparation method of the silk fibroin aqueous solution comprises the following steps: dissolving the silk fibroin obtained after degumming silk cocoons in a mixture of calcium salt, organic solvent and water to obtain the silk fibroin aqueous solution.

4. The preparation method according to claim 3, characterized in that The mass ratio of the silkworm cocoon, calcium salt, organic solvent and water is 5: (50-60): (60-70): (70-80).

5. The preparation method according to claim 1, characterized in that The alcohol compound is methanol or ethanol.

6. The preparation method according to claim 1, characterized in that The substrate is simulated skin, glass or aluminum plate.

7. The preparation method according to claim 1, characterized in that The coating is carried out by spraying.

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