A method for preparing and using a colloidal photonic crystal polymer coating

Abstract

This invention discloses a method for preparing a colloidal photonic crystal polymer coating. The method utilizes a "polymer surface particle embedding" process to prepare the colloidal photonic crystal polymer coating. A thin, soluble polymer layer is pre-coated onto the substrate surface, followed by a colloidal solution. The solvent in the colloidal solution dissolves the polymer, embedding the pre-assembled colloidal photonic crystals into the polymer layer. This process, combined with solvent evaporation and polymer re-curing, ultimately forms the photonic crystal polymer coating. This invention can be applied to various flat or uneven substrates such as wood, fiber, ceramics, metal, plastics, and rubber. It can controllably synthesize brightly colored, uniformly structured, and firmly adhered colloidal photonic crystal polymer coatings, significantly expanding the application scenarios of photonic crystal coatings and possessing broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of photonic crystal materials and colored coating applications, specifically relating to a method for preparing and applying a colloidal photonic crystal polymer coating. Background Technology

[0002] Colloidal photonic crystal polymer coatings are a novel type of composite material formed by the orderly arrangement of uniformly sized colloidal particles within a polymer matrix. This orderly arrangement of particles results in a periodically varying media structure within the material; when this structure undergoes coherent diffraction with visible light, it exhibits specific structural colors. As a novel colored coating material, its production and application do not involve the use of organic dyes or inorganic heavy metal salts, making it a green and environmentally friendly material. The generation of structural colors does not depend on the light absorption properties of specific chemical substances, but rather on the periodic structure of the colloidal particles in the matrix, thus possessing advantages such as radiation resistance, chemical stability, and fade resistance. Based on these characteristics, colloidal photonic crystal polymer coatings have attracted widespread and close attention in applications such as automotive manufacturing, textile printing and dyeing, packaging design, and anti-counterfeiting.

[0003] Currently, colloidal photonic crystal polymer coatings are primarily prepared using the traditional "colloidal assembly followed by polymer encapsulation" method. This method requires pre-assembly of the colloidal material on the target substrate, followed by the introduction of liquid polymer monomers or prepolymers to fill the gaps between the particles. Finally, UV curing or thermal curing is used to form a polymer-encapsulated colloidal photonic crystal—i.e., a photonic crystal coating. The key feature of this method is that colloidal assembly and polymer introduction are two independent processes, one preceding the other, and the formation of the polymer coating does not affect the colloidal assembly. Therefore, this method has the advantage of a wide range of polymer selection, enabling the combination of various functional polymers with colloidal photonic crystals to form different structural color coating materials. However, this method is extremely demanding in its substrate selection. Currently, only a few smooth and flat substrates, such as glass, single-crystal silicon wafers, and polyester fiber sheets, can meet the requirements for preparing colloidal photonic crystal films, greatly limiting the application range of photonic crystal coatings.

[0004] Besides the mainstream methods mentioned above, "in-situ assembly and curing of colloidal particles within polymer monomers" is another way to obtain colloidal photonic crystal polymer coatings. This method can introduce colloidal particles and polymer components in one step, making preparation simpler and more convenient. However, commonly used colloidal particle materials cannot assemble into photonic crystals in most polymer monomers and prepolymer liquids. Therefore, this method is only applicable to a few polymer materials such as polar acrylic resin prepolymers. Compared to the aforementioned mainstream methods, there is less choice of polymers, and it is also limited by the problem of a small number of applicable substrates, making widespread application difficult.

[0005] To address the long-standing limitation of traditional methods in terms of the limited number of applicable substrates, there is an urgent need to develop a new method for preparing colloidal photonic crystal coatings that can form on the surface of various substrates. This method would overcome the adverse effects of the substrate on colloidal assembly, and obtain a coating structure with high crystallinity, saturated color, and continuous and firm adhesion, so that structural color coating materials can be truly applied to more application scenarios. Summary of the Invention

[0006] This invention addresses the limitation of traditional methods for preparing colloidal photonic crystal polymer coatings by restricting the application to a limited range of substrates. It proposes a novel method for constructing photonic crystal coatings using a "polymer surface particle embedding" process. This process involves dissolving the polymer surface layer using a solvent in a colloidal solution, embedding a pre-assembled colloidal photonic crystal into the polymer surface, and then, through synergistic solvent evaporation and polymer re-curing, ultimately forming the colloidal photonic crystal polymer coating.

[0007] Specifically, this invention proposes a method for preparing a colloidal photonic crystal polymer coating using polymer surface particle embedding. The method employs a sequence of polymer coating followed by colloidal embedding. Specifically, a soluble polymer thin layer is pre-coated onto the substrate surface, followed by a colloidal solution. Through multiple physicochemical processes, including synergistic particle assembly, polymer dissolution, colloidal photonic crystal embedding, polymer diffusion, solvent evaporation, and polymer re-curing, a photonic crystal structure in which the colloidal particles are orderly arranged within the polymer matrix is ​​obtained. This method can be applied to various substrates such as wood, fiber, ceramics, metal, plastics, and rubber to form brightly colored, uniformly structured, and firmly adhered colloidal photonic crystal polymer coatings. This invention uses colloidal particles of different sizes to prepare the colloidal solution, allowing for the spraying preparation of colloidal photonic crystal polymer coatings in various colors such as red, green, and blue.

[0008] The method for preparing colloidal photonic crystal polymer coatings proposed in this invention specifically includes the following steps:

[0009] (1) Spray black resin polymer onto the surface of the target substrate;

[0010] (2) The substrate sprayed with polymer in step (1) is placed in an oven for heat treatment to form a black polymer coating.

[0011] (3) Mix uniformly sized colloidal particles with a high-boiling-point, low-surface-tension, polymer-soluble solvent in a certain proportion, and then sonicate to obtain a uniform colloidal solution.

[0012] (4) Spray the colloidal solution obtained in step (3) onto the surface of the black resin polymer layer;

[0013] (5) Transfer the substrate covered by the colloidal solution in step (4) into an oven for heat treatment, and dry and cure to obtain a colloidal photonic crystal polymer coating with structural color.

[0014] In step (1), the black resin polymer includes styrene-acrylate copolymer, alkyd resin, thermoplastic polyurethane elastomer (TPU), etc. Preferably, it is styrene-acrylate copolymer.

[0015] In step (1), the substrate includes, but is not limited to, inorganic substrates, fiberboard substrates, metal substrates, plastic substrates, and rubber substrates. Preferably, inorganic substrates include glass, alumina ceramics, zirconia ceramics, silicate clay, graphite, gypsum, etc.; fiberboard substrates include wood boards, cardboard, bamboo and wood chips, paper, glass fiber, carbon fiber boards, nylon cloth, polyester fiber cloth, etc.; metal substrates include aluminum foil, copper foil, iron sheets, stainless steel sheets, brass sheets, copper, magnesium-aluminum alloys, nickel foam, etc.; plastic substrates include polyethylene terephthalate (PET) film, polypropylene (PP) film, polyvinyl chloride (PVC) boards, Teflon boards, acrylic boards, polycarbonate (PCb) boards, epoxy resin boards, phenolic resin boards, foam plastics, etc.; and rubber substrates include natural rubber boards, silicone and polyurethane (PU) rubber. In a specific implementation, preferably, the substrate includes wood, paper, nylon, carbon fiber board, gypsum, clay, ceramic, graphite, iron sheet, brass sheet, copper, magnesium-aluminum alloy, nickel foam, Teflon board, polyester fiber (PET) film, acrylic board, phenolic resin board, and natural rubber.

[0016] In step (2), the heat treatment temperature is 60-90℃; preferably 90℃, and the heat treatment time is 5min-10min, preferably 8min.

[0017] In step (2), the black polymer layer formed after thermosetting typically has a thickness of 10 μm–40 μm. Preferably, it is 30 μm.

[0018] In step (3), the uniformly sized colloidal particles include, but are not limited to, SiO2, CeO2@SiO2, ZnO@SiO2, Fe3O4@SiO2, PS, and P(St-co-AA) particles. Preferably, they are SiO2 particles. The particle size of the colloidal particles is 150nm–300nm, preferably 215nm.

[0019] In step (3), the high-boiling-point, low-surface-tension, polymer-soluble solvent will vary depending on the black resin polymer selected in step (1). That is, the choice of solvent varies depending on the black resin polymer selected in step (1).

[0020] In a specific embodiment, where the black resin polymer is a black styrene-acrylate copolymer, the appropriate solvent selected includes one or more of N,N-dimethylformamide (DMF), propylene carbonate (PCb), butenyl carbonate (BCb), acetylacetone (AA), and dipropylene glycol methyl ether (DPM). Preferably, it is PCb.

[0021] Since the black resin polymer is an alkyd resin, the appropriate solvent selected includes one or more of ethanol (EtOH) and N,N-dimethylformamide (DMF). Preferably, it is DMF.

[0022] Since the black resin polymer is a thermoplastic polyurethane elastomer (TPU), the appropriate solvent selected includes one or more of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Preferably, it is DMF.

[0023] In step (3), the volume fraction of colloidal particles in the colloidal solution is 15%–20%; preferably, it is 18%.

[0024] In step (3), the volume fraction of the solvent in the colloidal solution is 80%–85%; preferably, it is 82%.

[0025] In step (4), during the spraying process, the distance between the spray gun and the substrate is 5–10 cm; preferably, the distance is 5 cm. The working pressure of the spray gun is 0.2–0.4 MPa; preferably, the pressure is 0.3 MPa. The spray gun moves at a right angle and parallel to the substrate, with a moving speed of 15–30 cm / s, which remains constant; preferably, the moving speed is 20 cm / s.

[0026] In step (5), the heat treatment temperature is 60℃–150℃ and the heat treatment time is 3min–30min; preferably, the temperature is 90℃ and the heat treatment time is 5min.

[0027] In the preparation method of the present invention, the photonic bandgap of the colloidal photonic crystal polymer coating prepared by the method is distributed in the visible region of 400–700 nm. As the particle size of the monodisperse colloidal particles decreases, the peak position of the reflection spectrum of the obtained colloidal photonic crystal film undergoes a blue shift.

[0028] The colloidal photonic crystal polymer coating obtained by the preparation method of the present invention has saturated color, uniform structure, and strong adhesion.

[0029] This invention also proposes a colloidal photonic crystal polymer coating prepared by the method described above. The colloidal photonic crystal polymer coating is a composite material formed by the orderly arrangement of uniformly sized colloidal particles in a polymer matrix; the photonic crystal is an artificial crystal structure formed by the periodic arrangement of materials with different refractive indices, possessing a photonic bandgap. Light of a specific wavelength cannot pass through the photonic bandgap and is thus reflected, forming correlation diffraction on its surface, thereby exhibiting a dazzling array of structural colors. Preferably, the photonic bandgap of the colloidal photonic crystal polymer coating is distributed in the visible region of 400–700 nm.

[0030] This invention also proposes the application of the above-described colloidal photonic crystal polymer coating and the preparation method in optical coatings and color printing.

[0031] Compared with existing technologies, the method for preparing colloidal photonic crystal polymer coatings using polymer surface particle embedding proposed in this invention has the following innovations and advantages: Compared with traditional preparation methods of "colloidal assembly first - polymer encapsulation" or "colloidal particles are assembled and cured in situ in polymer monomers," the "polymer surface particle embedding" process proposed in this invention is a completely new preparation method, fundamentally different from traditional methods in terms of preparation process, photonic crystal coating formation mechanism, and other aspects. Figure 1 As shown, unlike traditional methods, the method described in this invention employs a "polymer coating followed by colloidal embedding" strategy. First, a polymer coating is formed on the substrate surface, followed by a colloidal solution. The solvent in the colloidal solution dissolves the polymer, embedding the pre-assembled colloidal photonic crystal into the polymer layer. Through synergistic solvent evaporation and polymer re-curing, a photonic crystal polymer coating is ultimately formed. This is a novel mechanism for forming photonic crystal polymer coatings.

[0032] Compared to traditional preparation methods, the novel method for preparing colloidal photonic crystal polymer coatings using polymer surface particles proposed in this invention benefits from the stable adhesion of the polymer thin layer to the substrate surface. This allows for the formation of brightly colored and firmly adhered photonic crystal polymer coatings on a wide range of substrates, including wood, fiber, ceramics, metals, plastics, and rubber. Traditional methods, on the other hand, are very demanding in their substrate selection, only achieving coatings on a few smooth and flat substrates such as glass, silicon wafers, and polyester fiberboard. The novel preparation method proposed in this invention can be applied to various flat or non-flat substrates, including wood, fiber, ceramics, metals, plastics, and rubber, and can also retain the texture and feel of the substrate to a certain extent. This significantly expands the application scenarios of photonic crystal coatings and has broad application prospects. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the process for preparing a polymer coating for colloidal photonic crystals using "polymer surface particle embedding". (1) A styrene-acrylic resin layer, i.e., a polystyrene-acrylic polymer coating, is formed by coating the substrate surface; (2) A SiO2 colloidal solution is sprayed onto the surface of the polymer layer to form a liquid film containing SiO2 liquid colloidal photonic crystals; (3) The solvent in the colloidal solution dissolves the polymer layer downwards, causing the SiO2 photonic crystals to sink, while the dissolved polymer diffuses into the interparticle gaps of the colloidal crystals, forming a liquid colloidal photonic crystal with SiO2 particles in the polymer solution; (4) After the solvent evaporates, the polymer surface is cured again to form a photonic crystal polymer coating with SiO2 particles embedded in the styrene-acrylic resin surface.

[0035] Figure 2 The images show a) digital photographs, b) optical microscope photographs, and c) reflection spectra of red, green, and blue SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coatings.

[0036] Figure 3 The results are the test results of the uniformity of the colloidal photonic crystal polymer coating. Figure a) is a digital photograph of the green SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coating. The others are the color deviation in Lab space, c) CIE colorimetric diagram, d), e) reflection spectrum, and f) maximum reflection wavelength and intensity obtained at 9 orthogonally arranged positions on the above coating.

[0037] Figure 4 These are scanning electron microscope (SEM) images of the SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coating. Figure a) is an overall cross-sectional view of the composite coating on the substrate surface, Figure b) is a cross-sectional view of the interface between the SiO2 / styrene-acrylic resin surface layer and air, Figure c) is a top view of the SiO2 / styrene-acrylic resin surface layer, and Figure d) is a cross-sectional view of the interface between the SiO2 / styrene-acrylic resin surface layer and the styrene-acrylic resin inner layer.

[0038] Figure 5 This is an optical characterization of the structural color coatings obtained by heat treatment at different temperatures after spraying the colloidal solution. Figure a) shows digital photographs of four structural color coatings obtained by heat treatment at 30℃, 60℃, 90℃, and 120℃; Figure b) shows digital photographs of the above coatings after rinsing and brushing with ethanol; Figure c) shows a comparison of the reflectance spectra of the four coatings before and after brushing.

[0039] Figure 6 The images are a) digital photographs and b) reflection spectra of colloidal photonic crystal polymer coatings after undergoing corresponding treatments such as friction, brushing, and tape peeling.

[0040] Figure 7 Digital photographs of 18 substrates are displayed, along with digital photographs of their surfaces coated with a SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coating. The substrates include: wood panels, paper, nylon, carbon fiber panels, plaster, clay, ceramics, graphite, iron sheets, brass sheets, copper, magnesium-aluminum alloys, nickel foam, Teflon sheets, polyester fiber (PET) film, acrylic sheets, phenolic resin sheets, and natural rubber. Detailed Implementation

[0041] The invention will be further described in detail below with reference to the specific embodiments and accompanying drawings. The processes, conditions, and experimental methods for implementing the invention, except as specifically mentioned below, are all common knowledge and general knowledge in the art, and the invention does not have any particular limitations. The invention will be further illustrated below through specific embodiments.

[0042] This invention proposes a method for preparing a colloidal photonic crystal polymer coating. The method utilizes a "polymer surface particle embedding" process to prepare the colloidal photonic crystal polymer coating. A thin, soluble polymer layer is pre-coated onto the substrate surface, followed by a colloidal solution. The solvent in the colloidal solution dissolves the polymer, embedding the pre-assembled colloidal photonic crystals into the polymer layer. Combined with solvent evaporation and polymer re-curing, a firmly adhered and brightly colored photonic crystal polymer coating is ultimately formed. This invention can be applied to various flat or uneven substrates such as wood, fiber, ceramics, metal, plastics, and rubber. It can controllably synthesize brightly colored, uniformly structured, and firmly adhered colloidal photonic crystal polymer coatings, significantly expanding the application scenarios of photonic crystal coatings and possessing broad application prospects.

[0043] Example 1. Preparation of a red SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coating on a glass substrate surface

[0044] Taking the preparation of a red coating on a glass substrate as an example, this paper illustrates a novel method for preparing a photonic crystal polymer coating based on "polymer surface particle embedding". First, a 4×4cm... 2 Square glass slides were ultrasonically cleaned and dried, and then coated with styrene-acrylic resin paint. They were then transferred to a 90°C oven for heat curing, forming a 20–30 μm thick black polymer layer. A SiO2 / PCb colloidal solution with a particle diameter of 240 nm and a volume fraction of 18% was sprayed onto the polymer layer surface to form a uniform liquid film. This was then transferred back to a 90°C oven for further heat drying until the solvent completely evaporated, thus forming the desired finish. Figure 2The red photonic crystal coating shown in sample 3 of section a. Under a microscope, red colloidal photonic crystal blocks can be observed in this coating, and the corresponding reflection spectrum shows a characteristic reflection peak of photonic crystals at 610 nm, consistent with the observed coating color.

[0045] Example 2. Preparation of a green SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coating on a glass substrate surface

[0046] Taking the preparation of a green coating on a glass substrate as an example, this paper illustrates a novel method for preparing a photonic crystal polymer coating based on "polymer surface particle embedding". First, a 4×4cm... 2 Square glass slides were ultrasonically cleaned and dried, and then coated with styrene-acrylic resin paint. They were then transferred to a 90°C oven for heat curing, forming a 20–30 μm thick black polymer layer. A SiO2 / PCb colloidal solution with a particle diameter of 215 nm and a volume fraction of 18% was sprayed onto the polymer layer surface to form a uniform liquid film. This was then transferred back to a 90°C oven for further heat drying until the solvent completely evaporated, thus forming the desired finish. Figure 2 The green photonic crystal coating shown in sample 2 of section a. Under a microscope, green colloidal photonic crystal blocks can be observed in this coating, and the corresponding reflection spectrum shows a characteristic reflection peak of photonic crystals at 550 nm, consistent with the observed coating color.

[0047] Example 3. Preparation of a blue SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coating on a glass substrate surface

[0048] Taking the preparation of a blue coating on a glass substrate as an example, this paper illustrates a novel method for preparing a photonic crystal polymer coating based on "polymer surface particle embedding". First, a 4×4cm... 2 Square glass slides were ultrasonically cleaned and dried, and then coated with styrene-acrylic resin paint. They were then transferred to a 90°C oven for heat curing, forming a 20–30 μm thick black polymer layer. A SiO2 / PCb colloidal solution with a particle diameter of 187 nm and a volume fraction of 18% was sprayed onto the polymer layer surface to form a uniform liquid film. This was then transferred back to a 90°C oven for further drying until the solvent completely evaporated, thus forming the desired finish. Figure 2 The blue photonic crystal coating shown in sample 1 of section a. Under a microscope, blue colloidal photonic crystal blocks can be observed in this coating, and the corresponding reflection spectrum shows a characteristic reflection peak of photonic crystals at 480 nm, consistent with the observed coating color.

[0049] Example 4. Test of uniformity of polymer coating for colloidal photonic crystals

[0050] To evaluate the uniformity of the sprayed colloidal photonic crystal polymer coating, the reflectance spectrum and chromaticity at nine orthogonally arranged positions on the coating were measured. Figure 3 Figures b and 3c show the chromaticity deviation and CIE chromaticity measured at nine locations in Lab color space. The chromaticity measurements indicate that the color difference (ΔE*ab) is less than 1.0, representing uniform color. In the CIE chromaticity diagram, the points representing the coating color are far from the central origin and closer to the edges, indicating high color saturation in the coating. Figure 3 Images d, 3e, and 3f show the reflection spectra at nine orthogonal positions on the coating and the resulting reflection wavelengths and intensities. Experimental results show that the reflection spectra at the nine positions are consistent with each other, with a reflection wavelength of around 538 nm and a reflection intensity of 35%, exhibiting very little fluctuation, demonstrating that it possesses a uniform structural color.

[0051] Example 5. Microstructure characterization of SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coating

[0052] Microstructure characterization of the SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coating demonstrates that the preparation method based on "polymer surface particle embedding" described in this invention has a different preparation process and photonic crystal coating formation mechanism than traditional methods. The core of this novel method is to further coat a colloidal solution onto a substrate pre-coated with a polymer coating. Utilizing the solvent in the colloidal solution to dissolve the polymer, the pre-assembled colloidal photonic crystal in the solution is embedded into the polymer layer. Combined with solvent evaporation and polymer re-curing, the photonic crystal polymer coating is ultimately formed. Figure 4 Image a is a scanning electron microscope cross-sectional image of the SiO2 / styrene-acrylic resin photonic crystal coating, proving that the SiO2 colloidal photonic crystal does indeed form a composite coating with structural color by embedding itself in the styrene-acrylic resin surface layer. Figure 4 b and 4d show that styrene-acrylic resin filled the spaces between the SiO2 particles, forming a SiO2 / styrene-acrylic resin composite structure. This indicates that the styrene-acrylic resin in the composite structure is entirely derived from the pre-coated styrene-acrylic resin layer, thus proving that the dissolution of the polymer (styrene-acrylic resin) surface layer, the sinking of the pre-assembled photonic crystal, and the diffusion of polymer molecules into the gaps between the particles did indeed occur during the preparation process. Figure 4 c shows that the SiO2 particles are arranged in an ordered manner in the styrene-acrylic resin matrix, which proves that the preparation method based on "polymer surface particle embedding" can prepare a highly crystalline photonic crystal polymer coating, ensuring that the coating has a bright structural color.

[0053] Example 6. Preparation of photonic crystal polymer coatings by heat treatment at different temperatures after coating with colloidal solution.

[0054] In the preparation of the green coating in Example 2, after spraying the SiO2 / PCb colloidal solution, different photonic crystal coatings can be obtained by performing heat treatments at 30°C, 60°C, 90°C, and 120°C respectively. For example... Figure 5 As shown, the photonic crystal coating obtained under heat treatment at 30℃ failed to adhere completely. After rinsing with ethanol, the SiO2 photonic crystals completely detached, ultimately revealing the black color of the pre-coated styrene-acrylic resin. This is because at low temperatures, the solvent in the colloidal solution cannot quickly dissolve the styrene-acrylic resin. After the solvent evaporates, it fails to form SiO2 / styrene-acrylic resin photonic crystals, instead forming easily detachable SiO2 photonic crystals. The photonic crystal coating obtained under heat treatment at 60℃ showed a dark green color after rinsing with ethanol, indicating that the dissolution of styrene-acrylic resin accelerated at higher temperatures. This resulted in some SiO2 particles ultimately forming a green SiO2 / styrene-acrylic resin photonic crystal coating, while others formed easily detachable SiO2 photonic crystals. The photonic crystal coatings obtained under heat treatment at 90℃ and 120℃ showed strong adhesion and retained a bright green color after rinsing with ethanol. This indicates that the styrene-acrylic resin dissolves rapidly at high temperatures, and the SiO2 colloidal photonic crystal sinking and polymer diffusion into the interparticle gaps occur before the solvent has completely evaporated. Therefore, a firmly adhered SiO2 / styrene-acrylic resin photonic crystal coating can be formed after the solvent has completely evaporated. In contrast, the structural color coating obtained under heat treatment at 120℃ is not uniform enough; therefore, the optimal heat treatment temperature is 90℃. Furthermore, the above examples regarding heat treatment temperatures further demonstrate the novel preparation method based on "polymer surface particle embedding" proposed in this invention.

[0055] Example 7: Test of adhesion of colloidal photonic crystal polymer coating

[0056] Figure 6 Figures a and 6b show digital photographs and reflectance spectra of the colloidal photonic crystal polymer coating after undergoing rubbing, brushing, and tape peeling, respectively. Experimental results show that after rubbing the colloidal photonic crystal polymer coating 50 times with an eraser, brushing it back and forth 50 times with a toothbrush, and repeatedly peeling it off with tape 50 times, no coating peeling was observed, the structural color remained a bright green, and the tested reflectance spectrum was indistinguishable from the original coating. This demonstrates its good adhesion and mechanical stability.

[0057] Example 8. Preparation of green SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coatings on the surfaces of various substrates such as wood, fiber, ceramics, metal, plastic, and rubber.

[0058] Eighteen different substrates were selected, including wood panels, paper, nylon, carbon fiber panels, gypsum, clay, ceramics, graphite, iron sheets, brass sheets, copper, magnesium-aluminum alloys, nickel foam, Teflon sheets, polyester fiber (PET) film, acrylic sheets, phenolic resin sheets, and natural rubber. For metal and plastic substrates, ultrasonic cleaning was used; for other substrates, compressed air was used for surface cleaning. After vertically fixing the substrates, a styrene-acrylic resin paint was sprayed on. The substrates were then transferred to a 90°C oven for heat curing, forming a uniform black polymer layer. A SiO2 / PCb colloidal solution with a particle diameter of 215 nm and a volume fraction of 18% was sprayed onto the polymer layer surface, forming a uniform liquid film. The substrates were again transferred to a 90°C oven for drying. After the solvent completely evaporated, a green photonic crystal polymer coating was formed. Figure 7 The images showcase green SiO2 / styrene-acrylic resin colloidal photonic crystal polymer coatings on the surfaces of the aforementioned 18 substrates. The coatings on the substrate surfaces in the photographs exhibit bright, uniform structural colors, and the texture and feel of the substrates are also preserved, fully demonstrating the broader applicability of the preparation method described in this invention to various substrates.

[0059] The scope of protection of this invention is not limited to the above embodiments. Any variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of this invention are included in this invention and are protected by the appended claims.

Claims

1. A method for preparing a colloidal photonic crystal polymer coating, characterized in that, The method utilizes a polymer surface layer colloidal particle embedding process to construct a photonic crystal coating; the method is: a soluble polymer thin layer is coated on the surface of a substrate in advance, then a colloidal solution is coated on the surface, and a colloidal photonic crystal polymer coating is constructed by utilizing the polymer surface layer colloidal particle embedding process; wherein the polymer surface layer colloidal particle embedding process refers to the dissolution of the polymer by the solvent in the colloidal solution, the colloidal photonic crystal is embedded in the polymer layer, and finally the colloidal photonic crystal polymer coating is formed by the synergistic solvent evaporation and polymer resolidification; The method comprises the following steps: (1) spraying a black resin polymer on the surface of a target substrate; the substrate includes glass, alumina ceramic, zirconia ceramic, silicate clay, graphite, gypsum, wood board, hardboard, bamboo wood sheet, paper, glass fiber, carbon fiber plate, nylon cloth, polyester fiber cloth, metal substrate, plastic substrate, and rubber substrate; the black resin polymer is a styrene-acrylate copolymer, an alkyd resin, or a thermoplastic polyurethane elastomer (TPU); (2) placing the substrate with the sprayed polymer in the step (1) into an oven for heat treatment to form a black polymer coating; (3) mixing uniformly sized colloidal particles with a high-boiling, low-surface-tension, polymer-soluble solvent in a certain proportion, and obtaining a uniform colloidal solution by ultrasonic treatment; the selection of the high-boiling, low-surface-tension, polymer-soluble solvent corresponds to the black resin polymer selected in the step (1); if the black resin polymer is a black styrene-acrylate copolymer, the solvent includes one or more of N,N-dimethylformamide, propylene carbonate, butylene carbonate, acetylacetone, and dipropylene glycol methyl ether; if the black resin polymer is an alkyd resin, the solvent is selected from N,N-dimethylformamide; if the black resin polymer is a thermoplastic polyurethane elastomer, the solvent includes one or more of N,N-dimethylformamide and dimethyl sulfoxide; (4) spraying the colloidal solution obtained in the step (3) on the surface of the black resin polymer layer; (5) transferring the substrate covered with the colloidal solution obtained in the step (4) into an oven for heat treatment, drying and curing to obtain the colloidal photonic crystal polymer coating; the heat treatment temperature is 90-150°C.

2. The method of claim 1, wherein, In the step (2), the heat treatment temperature is 60-90°C, and the heat treatment time is 5-10 min; the thickness of the black polymer coating formed after heat curing is 10-40 μm.

3. The method of claim 1, wherein, In the step (3), the uniformly sized colloidal particles include SiO2, CeO2@SiO2, ZnO@SiO2, Fe3O4@SiO2, PS, and P(St-co-AA) colloidal particles; the particle size of the colloidal particles is 150-300 nm; in the uniform colloidal solution obtained in the step (3), the volume fraction of the colloidal particles is 15-20%, and the volume fraction of the solvent is 80-85%.

4. The method of claim 1, wherein In the step (4), the distance between the spray gun and the substrate is 5-10 cm; the working pressure of the spray gun is 0.2-0.4 Mpa; the spray gun and the substrate are operated in a right angle and parallel, the moving speed is 15-30 cm / s and is kept constant; and / or, In the step (5), the heat treatment time is 3 min-30 min.

5. The method of claim 1, wherein, The photonic band gap of the colloidal photonic crystal polymer coating prepared by the method is distributed in the visible region of 400-700 nm, and with the decrease of the monodisperse colloidal particle size, the peak position of the reflection spectrum of the obtained colloidal photonic crystal film is blue shifted; the colloidal photonic crystal polymer coating is color-saturated, uniform in structure and firmly attached.

6. Use of the method according to any one of claims 1-5 in optical coatings, color printing.

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