A wide color gamut photonic gel based on monodisperse colloidal particle controllable assembly and a preparation method thereof

Abstract

This invention discloses a wide-gamut photonic gel based on the controllable assembly of monodisperse colloidal particles and its preparation method. The preparation method includes: dispersing monodisperse nanoparticles, monomers, photosensitizers, and photoinitiators in a polar solvent to obtain a precursor dispersion; inducing the spontaneous and ordered assembly of colloidal nanoparticles through solvent evaporation to obtain a pre-assembled photonic ink; leveling the obtained pre-assembled photonic ink to obtain a photonic ink layer; irradiating the photonic ink layer with a weak ultraviolet light source to obtain a photonic gel prepolymer; and irradiating the photonic gel prepolymer with a strong ultraviolet light source to obtain a wide-gamut photonic gel. This invention uses monodisperse colloidal particles of a single specification and achieves in-situ precise control of the colloidal lattice spacing through evaporation-induced self-assembly combined with a hierarchical two-stage ultraviolet irradiation process. It can prepare a photonic gel with a tunable full color gamut in visible light without changing colloidal raw materials of different particle sizes, solving the technical problems of fixed structural color and limited color gamut in traditional photonic gels.

Description

Technical Field

[0001] This invention belongs to the technical field of photonic crystal materials and smart response materials, specifically relating to a wide color gamut photonic gel based on the controllable assembly of monodisperse colloidal particles and its preparation method. Background Technology

[0002] Responsive photonic gels are a class of smart soft materials with specific periodic micro / nano structures that can undergo reversible structural changes in response to external environmental variations (such as temperature, pH, light intensity, and ion concentration), thereby enabling the manipulation of light at different wavelengths (reflection, refraction, transmission, etc.). With their superior tunable optical properties, rapid response capabilities, and intelligent adaptability, these materials show broad application prospects in smart materials, tunable optical devices, and other fields. Compared to top-down methods (such as photolithography) for fabricating periodic structures, bottom-up self-assembly strategies have attracted significant attention due to their advantages of precise control, low cost, and ease of large-area fabrication. Among these, colloidal particle self-assembly, with its designable structural diversity and multi-scale ordering capabilities, demonstrates unique development potential in structural color materials and photonic devices.

[0003] For example, invention patent CN121818225A discloses a novel temperature-sensitive color-changing medical fever-reducing patch and its preparation method. The preparation method includes the step of preparing the temperature-responsive structural color layer. This step includes: self-assembling monodisperse nanospheres on a substrate using a vertical deposition method to form an ordered photonic crystal template; preparing a prepolymer solution: dissolving a temperature-sensitive polymer monomer, comonomer, crosslinking agent, photoinitiator, and a colorant for enhancing contrast in a solvent, and mixing them uniformly to obtain the prepolymer solution; filling the gaps in the photonic crystal template with the prepolymer solution, and initiating a polymerization reaction with ultraviolet light to form a composite structure; and removing the photonic crystal template to obtain the temperature-responsive structural color layer. However, this colloidal self-assembly system highly depends on monodisperse, uniformly sized colloidal particles. The resulting colloidal photonic gel typically has only a single lattice constant and a fixed photonic band gap, corresponding to a single structural color.

[0004] To obtain multicolor output, early studies mainly focused on preparing photonic gels with different intrinsic colors by changing the system formulation. For example, the invention patent with publication number CN114989347A discloses a thermosensitive photonic crystal gel microsphere with a wide response range and high response rate. The thermosensitive photonic crystal gel microsphere is characterized by being composed of poly(N-isopropylacrylamide-copolymer-acrylamide) gel microspheres and superparamagnetic nanoparticles embedded in the three-dimensional polymer network structure of the gel microspheres. The gel microspheres are formed by cross-linking and copolymerizing N-isopropylacrylamide monomers and acrylamide monomers with a cross-linking agent, four-arm polyethylene glycol acrylamide, to create microspheres with a uniform cross-linked structure. The superparamagnetic nanoparticles are arranged in the three-dimensional polymer network structure of the gel microspheres to form several one-dimensional oriented chain structures. The thermosensitive photonic crystal gel microsphere has a uniform structural color, achieving a change in structural color from orange-yellow to blue-violet within a temperature range of 10~52℃. The wavelength range corresponding to the structural color is between 635~468 nm. Under temperature conditions of 10~55℃, the thermosensitive photonic crystal gel microsphere reaches shrinkage equilibrium within 80 seconds. However, due to the slow assembly kinetics and molecular chain entanglement effect in the polymer matrix, such methods are difficult to achieve continuous and controllable multitone harmonics.

[0005] On the other hand, while most research on photonic gels has made significant progress in post-tuning strategies for multicolor output, these methods typically rely on the evolution (i.e., contraction and expansion) of polymer networks triggered by specific stimuli, which usually requires continuous application to maintain responsiveness. This severely limits the application of such materials in cutting-edge fields such as multicolor dynamic displays and broadband photonic control.

[0006] Therefore, developing a method for preparing photonic gels that can achieve a wide color gamut and continuous tunability based on a single colloidal particle can not only break through the core technical bottleneck of traditional self-assembly systems, but also promote the leap from basic research to practical application of self-assembled optical materials, which has important scientific value and engineering application prospects. Summary of the Invention

[0007] To address the shortcomings of existing colloidal photonic gels, which rely on the self-assembly of colloidal particles of fixed size, resulting in non-continuous in-situ control of lattice parameters, limited structural colors, and narrow color gamut coverage, making it difficult to achieve continuous multi-color control in the visible light range, this invention proposes a wide-gamut photonic gel based on the controllable assembly of monodisperse colloidal particles and its preparation method. Using monodisperse colloidal particles of a single specification as raw material, this invention achieves precise in-situ control of the colloidal lattice spacing through evaporation-induced self-assembly combined with a hierarchical two-stage ultraviolet irradiation process. This allows for the preparation of a photonic gel with tunable full visible light color gamut without the need to change colloidal raw materials of different particle sizes, thus solving the technical problems of fixed structural colors and limited color gamut in traditional photonic gels.

[0008] Based on the above-mentioned technical objectives, the technical solution of the present invention is as follows: A method for preparing a wide color gamut photonic gel based on the controllable assembly of monodisperse colloidal particles includes the following steps: The preparation method of this invention comprises four major steps: precursor solution preparation, evaporation-induced self-assembly, weak ultraviolet lattice regulation, and strong ultraviolet curing and shaping. The specific steps are as follows: Step 1: Disperse the monodisperse nanoparticles, monomers, photosensitizers, and photoinitiators in a polar solvent to obtain a precursor dispersion; Step 2: The precursor dispersion obtained in Step 1 is subjected to solvent evaporation treatment to induce the spontaneous and orderly assembly of colloidal nanoparticles, thus obtaining pre-assembled photonic ink; Step 3: The pre-assembled photonic ink obtained in Step 2 is leveled to obtain a photonic ink layer; the photonic ink layer is irradiated with a weak ultraviolet light source with a wavelength of 380~410 nm and a power of 5~30 W to obtain a photonic gel prepolymer; Step 4: Irradiate the photonic gel prepolymer with a strong ultraviolet light source with a wavelength of 260~380 nm and a power of 80~200 W to obtain a wide color gamut photonic gel.

[0009] This invention uses monodisperse colloidal particles of a single specification as raw materials. Based on the solvent evaporation-induced method, as the solvent evaporates, the concentration of nano-units in the solution continuously increases. When the concentration reaches a critical value, the interaction forces between units (such as van der Waals forces, hydrogen bonding / solventization forces, electrostatic forces, etc.) are significantly enhanced, overcoming the disordered thermal motion caused by Brownian motion. This drives the silica gel particles to spontaneously and orderly assemble, resulting in a viscous pre-assembled photonic ink with initially ordered particle arrangement. The viscous pre-assembled photonic ink uses capillary forces to completely level the ink and obtain a pre-assembled photonic ink layer with uniform thickness and flat structure.

[0010] Further combining strong and weak segmented ultraviolet processes, the pre-assembled photonic ink is first irradiated with a low-energy weak ultraviolet light source to activate only the photosensitive components in the system. Without triggering the overall cross-linking polymerization of monomers, by changing the weak ultraviolet irradiation time and irradiation power, microscale slippage and spacing changes between colloidal particles are induced, achieving continuous and precise control of lattice spacing and obtaining a photonic gel prepolymer intermediate with customized lattice parameters. Then, the photonic gel prepolymer is fully irradiated with a high-energy strong ultraviolet light source, causing the monomers to undergo complete photopolymerization and cross-linking to form a three-dimensional elastic gel composite network. The ordered lattice of the colloidal particles that has been regulated is permanently locked inside the gel matrix, finally obtaining a wide color gamut tunable photonic gel.

[0011] This invention, by changing the weak ultraviolet irradiation parameters in step 3, enables the preparation of photonic gels with different structural colors from a single batch of raw materials, without changing the particle size of the colloidal particles or altering the raw material formulation. The structural colors cover the entire visible light spectrum. Furthermore, by using a weak ultraviolet light source with a wavelength of 380–410 nm and continuously varying the irradiation power within the range of 5–30 W, the lattice spacing of the silica particles can be precisely and continuously controlled. The corresponding photonic gel reflection spectrum can cover the visible light band of 450–650 nm, thus achieving customized structural colors across a wide color gamut. Using a strong ultraviolet light source with a wavelength of 260–380 nm and continuously varying the irradiation power within the range of 80–200 W, the monomers undergo rapid and complete photocrosslinking polymerization, forming a three-dimensional gel network with high mechanical strength. Simultaneously, the pre-controlled ordered lattice structure is fixed in situ within the gel matrix. Under normal use conditions without external stimuli, this structure effectively prevents lattice relaxation or collapse, thereby ensuring the long-term stability and reproducibility of the structural colors.

[0012] Preferably, the monodisperse nanoparticles in step 1 include at least one of silica, silica-coated zinc sulfide (ZnS@SiO2), polystyrene, and polymethyl methacrylate; The monodisperse nanoparticles have a particle size of 150~300 nm and a particle size dispersion coefficient of <5%.

[0013] The aforementioned monodisperse nanoparticles facilitate long-range ordered self-assembly during solvent evaporation, reducing the risk of assembly defects and structural color hybridization caused by uneven particle size.

[0014] More preferably, the amount of monodisperse nanoparticles added is 30.0% to 74.0% of the monomer volume fraction.

[0015] Preferably, the monomers mentioned in step 1 include, but are not limited to, ether-rich monomers such as polyethylene glycol phenyl ether acrylate (PEGPEA); The photoinitiators include, but are not limited to, oil-soluble free radical photoinitiators such as 2-hydroxy-2-methyl-1-phenyl-1-propanone and methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone.

[0016] Taking 2-hydroxy-2-methylacetophenone as an example, this free radical photoinitiator can efficiently initiate free radical polymerization and crosslinking of monomers such as PEGPEA under strong ultraviolet irradiation to construct a stable three-dimensional gel network.

[0017] Preferably, the amount of monomer added in step 1 is 0.1~2.0 mL.

[0018] The amount of monomer added can be adjusted according to the size and thickness of the target photonic gel. This is only an experimental parameter given in a specific embodiment of the present invention. It should be understood that the specific monomer selection and dosage can be determined by those skilled in the art based on the actual polymerization system and conventional technical means in the field.

[0019] More preferably, the amount of monomer added in step 1 is 0.3~1.0 mL. Within the above range, the addition ratio of photosensitizer, initiator and nanoparticles can be effectively implemented, and a photonic gel with uniform structural color can be obtained.

[0020] More preferably, the amount of photoinitiator added is 1.0% to 5.0% of the total mass of polyethylene glycol phenyl ether acrylate monomer.

[0021] Selecting the above-mentioned range of photoinitiator dosages can generate sufficient free radicals during the strong UV curing stage, ensuring complete cross-linking of polyethylene glycol phenyl ether acrylate, appropriate gel mechanical strength, and preventing the collapse of the ordered colloidal lattice. Furthermore, it will not cause yellowing due to excessive unpolymerized initiator residues in the gel matrix, thus ensuring the light transmittance and structural color purity of the photogel.

[0022] Preferably, the photosensitizer described in step 1 comprises one or more monomers with anthracene as a monosubstituted end group, such as compounds with the following structures: , That is, the photosensitizer includes at least one of 9-anthracarboxylic acid, 9-chloroanthracene, 9-anthraboronic acid, 9-anthrayl alcohol, 9-anthraacrylic acid, 9-chloromethylanthracene, and anthracene. These raw materials are readily available and can be used as preferred photosensitizer raw materials.

[0023] This invention uses anthracene-based small molecule compounds as functional agents for regulating structural colors. These compounds are doped into a mixed solution of photonic crystal precursor solutions. First, pre-assembled photonic ink is obtained by evaporation-induced self-assembly of monodisperse silica particles. Then, the lattice spacing of the pre-assembled ink is precisely controlled by weak ultraviolet irradiation to obtain a photonic gel prepolymer. Subsequently, the obtained photonic gel prepolymer is subjected to strong ultraviolet light polymerization treatment to permanently fix the ordered lattice structure of the colloidal particles. Based on the above controllable lattice control method, the controllable preparation of a wide color gamut photonic gel with customized structural colors is achieved.

[0024] More preferably, the amount of photosensitizer added is 0.5% to 5.0% of the monomer mass.

[0025] This anthracene photosensitizer, as a key functional component for structural color regulation, can efficiently activate the photosensitizer system under weak ultraviolet light conditions, generating controllable charge transfer and local ion gradients. This alters the electrostatic shielding effect on the colloidal particle surface, driving reversible micro-slip and rearrangement of the particles, thus achieving continuous adjustment of the photonic lattice spacing. Crucially, within this dosage range, the activation effect of the photosensitizer is limited to the apparent excited state regulation level, without significantly initiating the free radical polymerization reaction of acrylate monomers in the matrix resin. This avoids overall cross-linking or gelation during the structural color regulation stage, ensuring the independent controllability of the subsequent strong ultraviolet curing step.

[0026] Preferably, the polar solvent in step 1 is ethanol as the main solvent, and includes one or more of water, dimethyl sulfoxide, and N,N-dimethylformamide as modifiers.

[0027] In the preparation of photonic gels with high particle volume fraction, ethanol can effectively disperse silica particles; the addition of the above-mentioned regulator can reduce the viscosity of the system and enhance the electrostatic repulsion between nanounits, thereby promoting the orderly self-assembly of colloidal particles and meeting the process requirements of evaporation-induced self-assembly.

[0028] Preferably, the dispersion time in step 1 is 30~120 min.

[0029] Preferably, the solvent evaporation treatment in step 2 is carried out at a temperature of 60°C to 100°C, at a pressure of atmospheric pressure, and for a time of 5 to 24 hours.

[0030] Selecting solvent evaporation treatment within the above parameter range can ensure a suitable solvent evaporation rate and production cycle, and prevent colloidal particles from being over-dispersed and thus settling and agglomerating, forming an ordered self-assembled structure, maintaining the uniformity of structural color, and preventing defects such as cracks.

[0031] Preferably, the pre-assembled photonic ink obtained in step 2 is injected into the interior of a preset cavity mold, and a photonic ink layer is obtained by leveling.

[0032] In this invention, the core function of the pre-set cavity mold is to provide a fixed external shape and boundary constraints for the pre-assembled photonic ink, ensuring that the ink forms a liquid film layer with a flat surface and controllable thickness after infusion. Without a mold, the ink will form droplet-like or lenticular-like morphologies with uneven thickness and edge shrinkage during the leveling process due to uneven surface tension, making it difficult to obtain a large-area uniform photonic gel film. However, the mold itself does not participate in the control of lattice spacing, but only determines the macroscopic geometry of the product (such as film thickness, shape, and size), without affecting the microscopic lattice structure and optical properties of the photonic gel. Therefore, as long as a flat and uniform ink layer can be formed, a mold of any material or structure can be used.

[0033] More preferably, the thickness of the cavity spacer layer inside the cavity mold is 40 μm to 1 mm.

[0034] The thickness of the cavity spacer layer is no greater than 1 mm to avoid insufficient capillary force due to excessive thickness, which would hinder the orderly self-assembly of nanoparticles. At the same time, the thickness of the cavity spacer layer is no less than 40 μm to ensure that the precursor solution can smoothly fill the cavity. Within this thickness range, both smooth filling and self-assembly driving force can be balanced.

[0035] Preferably, the time for irradiating the photonic ink layer with a weak ultraviolet light source in step 3 is 5~60 s; In step 4, the photonic gel prepolymer is irradiated with a strong ultraviolet light source for 2 to 10 minutes.

[0036] On the other hand, the present invention also provides a wide color gamut photonic gel based on the controllable assembly of monodisperse colloidal particles prepared by the preparation method described above.

[0037] This invention relates to a wide-gamut photonic gel based on the controllable assembly of monodisperse colloidal particles. Using a polymer matrix, it exhibits excellent processability, allowing for the fabrication of products of arbitrary shapes through methods such as mold casting, cutting, and hot pressing, meeting the device shape requirements of various application scenarios. The polymer matrix in the photonic gel is stimuli-responsive. Under the influence of external stimuli (including but not limited to temperature, humidity, pH, solvent, and mechanical force), the polymer matrix can undergo reversible volume expansion or contraction, or produce changes in refractive index, thereby dynamically adjusting the lattice spacing of the internal colloidal particles. This enables real-time, reversible changes in the structural color of the photonic gel, thus endowing the material with a visual response to changes in the external environment.

[0038] On the other hand, the present invention also provides the application of the wide color gamut photonic gel based on the controllable assembly of monodisperse colloidal particles in intelligent display, sensing, information encryption or anti-counterfeiting.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Achieving full color gamut control with single-size colloids, overcoming raw material limitations: This invention uses only one type of monodisperse nanoparticles. By using anthracene photosensitizers in conjunction with a graded ultraviolet process to finely adjust the lattice spacing in situ, the reflection wavelength can be continuously controlled by changing the weak ultraviolet irradiation parameters, achieving full color gamut color rendering in visible light, greatly simplifying the raw material preparation and production feeding process. The anthracene photosensitizers are uniformly doped in the precursor solution, which efficiently activates the photosensitive system in the weak ultraviolet stage, assisting the colloidal particles to undergo micro-displacement to complete the lattice fine-tuning. In the subsequent strong ultraviolet curing stage, it does not interfere with monomer crosslinking polymerization, has strong compatibility with the matrix, a wide process window, and high product reproducibility.

[0040] (2) The strong and weak segmented ultraviolet process separates and controls the curing process, and the crystal lattice has excellent controllability: The present invention first uses low power weak ultraviolet to activate only the anthracene photosensitive component without initiating the overall cross-linking of the matrix. It relies on the photosensitive effect to induce the micro-slip of colloidal particles to precisely control the crystal lattice. By adjusting the irradiation power or time of the weak ultraviolet, the maximum reflection wavelength of the photonic gel can be continuously adjusted in the visible light band of 450~650 nm. Then, the full cross-linking and crystal lattice is locked by high power strong ultraviolet. The control and curing are carried out in steps, and the crystal size is adjustable in a wide range and the color customization is highly accurate.

[0041] (3) Combined with spatiotemporal mask weak ultraviolet exposure, personalized color patterns can be prepared in one piece: In the weak ultraviolet lattice control step, the present invention can be combined with the spatiotemporal programming method of spatial mask and partitioned time sequence exposure to apply differentiated weak ultraviolet irradiation conditions to different regions of photonic ink, so that different positions of the film form differentiated lattice spacing. After strong ultraviolet uniform curing, a single piece of photonic gel can simultaneously present multiple different structural colors. Without multiple coatings and multi-layer composites, personalized color patterns such as text, portraits, and decorative patterns can be customized in one step, expanding the application of photonic gel in decoration, anti-counterfeiting, art substrates and other scenarios.

[0042] (4) Evaporation-induced self-assembly is low-cost and easy to prepare on a large scale: This invention uses solvent evaporation to induce colloidal self-assembly to construct ordered photonic structures. Compared with top-down microfabrication technologies such as photolithography and nanoimprinting, it does not require expensive precision equipment, the reaction conditions are mild, and photonic gel films can be prepared on a large scale, which is convenient for industrial mass production. Attached Figure Description

[0043] Figure 1 The images show the wide color gamut photonic gel prepared in Example 1, after being treated with different weak ultraviolet irradiation times under natural light.

[0044] Figure 2 The reflectance spectra of the wide color gamut photonic gel based on the controllable assembly of monodisperse colloidal particles prepared in Example 1 after treatment with different weak ultraviolet irradiation times.

[0045] Figure 3 The image shows a physical image of the simple pattern-carrying photonic gel prepared using a weak ultraviolet light mask partitioning exposure technique, based on the controllable assembly of monodisperse colloidal particles obtained in Example 2.

[0046] Figure 4 The image shows a physical image of a simple circular pattern carrying the photonic gel, which is based on the controllable assembly of monodisperse colloidal particles and is a wide color gamut photonic gel prepared using a weak ultraviolet light mask partitioning exposure technique, as shown in Example 3.

[0047] Figure 5The image shows a physical image of the calligraphy-bearing photonic gel prepared using a weak ultraviolet light mask partitioning exposure technique, based on the wide color gamut photonic gel obtained in Example 4, which is based on the controllable assembly of monodisperse colloidal particles.

[0048] Figure 6 The photon gel prepared in Comparative Example 1 after treatment with different weak ultraviolet irradiation times is photographed under natural light.

[0049] Figure 7 The image shows the thermal map of the reflectance spectrum contour lines for Comparative Example 1.

[0050] Figure 8 This is the CIE 1931 chromaticity coordinate diagram for Comparative Example 1.

[0051] Figure 9 This is a photograph of the photonic gel prepared after strong ultraviolet irradiation treatment in Comparative Example 3 under natural light. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described and illustrated below with reference to examples. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials were purchased commercially.

[0053] Example 1 A method for preparing a wide color gamut photonic gel based on the controllable assembly of monodisperse colloidal particles includes the following steps: S1. Preparation of photon gel precursor dispersion Monodisperse silica (SiO2) colloidal nanoparticles with a particle size of 220 nm and a particle size distribution coefficient of less than 5% were used as structural units (50% of the volume of PEGPEA). 0.3 mL of polyethylene glycol phenyl ether acrylate (PEGPEA) monomer, 5.0% of the mass of PEGPEA photosensitizer 9-anthracarboxylic acid, and 5.0% of the mass of PEGPEA initiator 2-hydroxy-2-methyl-1-phenyl-1-propanone were added to the dispersion solvent. The dispersion solvent was a mixture of ethanol (90% by volume) and water (10% by volume). After magnetic stirring for 30 min, the mixture was ultrasonically dispersed for 60 min to obtain a homogeneous photonic gel precursor dispersion.

[0054] S2. Evaporation-induced self-assembly preparation of pre-assembled photonic ink The precursor dispersion obtained in step S1 was placed in an 80℃ atmospheric pressure oven and evaporated for 12 h under controlled temperature. As ethanol and water slowly evaporated, the concentration of monodisperse SiO2 particles in the system gradually increased. When the concentration reached a critical value, the interactions between particles, such as van der Waals forces and electrostatic repulsion, overcame Brownian motion, driving the particles to spontaneously assemble in an ordered manner. After removing most of the solvent, a viscous pre-assembled photonic ink was obtained, in which the SiO2 particles were initially arranged in an ordered manner.

[0055] S3, Precise control of lattice spacing under weak ultraviolet irradiation The viscous pre-assembled photonic ink obtained in step S2 was poured into a mold with a cavity thickness of 200 μm. Capillary action was used to completely fill the cavity and form a smooth and uniform ink layer. Subsequently, a weak ultraviolet LED light source with a wavelength of 395 nm and a power of 15 W was used for 30 s of irradiation. This process only activates the photosensitizer, causing a weak local photochemical reaction and adjusting the lattice spacing between particles, but does not trigger the overall cross-linking polymerization of PEGPEA monomers, thus obtaining a photonic gel prepolymer with the target lattice spacing. By adjusting the irradiation time (5~60 s) or power (5~30 W), the maximum reflection wavelength of the photonic gel can be continuously varied within the visible light range of 450~600 nm. To visually characterize the lattice and structural color regulation, in this embodiment, 13 sets of gradient irradiation times (5 s intervals) were uniformly selected within the 0~60 s irradiation range using a 395 nm, 15 W weak ultraviolet LED to prepare parallel samples. The corresponding physical appearance is as follows: Figure 1 As shown, from left to right, the substrate structural color of the sample gradually changes from red-orange, yellow, and yellow-green to green and cyan-green as the weak ultraviolet irradiation time increases.

[0056] S4, Strong Ultraviolet Light Polymerization and Shaping A high-pressure mercury lamp with a wavelength of 365 nm and a power of 150 W was used as a strong ultraviolet light source to irradiate the photonic gel prepolymer obtained in step S3 with full amplitude irradiation for 5 min. Under these conditions, the PEGPEA monomers underwent complete photocrosslinking polymerization to form a three-dimensional gel network, and the ordered lattice of SiO2 was permanently fixed in the gel matrix, ultimately yielding a photonic gel with multiple structural colors.

[0057] Subsequently, ultraviolet-visible reflectance spectra were measured on 13 groups of photonic gel samples prepared with different weak ultraviolet irradiation durations. The reflectance spectra results are as follows: Figure 2 As shown, each group of samples exhibits a sharp, high-reflectance characteristic Bragg diffraction peak. With prolonged weak ultraviolet irradiation time, the diffraction peak wavelength continuously red-shifts from the 498 nm range to the 632 nm range, perfectly matching the color gradient pattern of the actual structure.

[0058] Example 2 The preparation steps of Example 2 are the same as those of Example 1, except that: in step S1, the monodisperse nanoparticles used are silica particles with a particle size of 260 nm and a particle size dispersion coefficient of <5%; the photosensitizer is 9-vinylanthracene, added at 3.0% of the monomer mass; the initiator is added at 3.0% of the monomer mass; the dispersion solvent is a mixed solvent of ethanol, water, and dimethyl sulfoxide (DMSO) (volume ratio 85:10:5); and the ultrasonic dispersion time is 90 min. In step S2, the evaporation temperature is 90℃ and the evaporation time is 8 h. In step S3, the weak ultraviolet wavelength is 400 nm, the power is 20 W, the irradiation time is 40 s, and a customized ring pattern is written using photomask-assisted technology. In step S4, the strong ultraviolet power is 120 W and the curing time is 8 min. The remaining steps are the same.

[0059] The actual appearance is as follows Figure 3 As shown, the physical substrate exhibits a red structural color, while the patterned area displays yellow rings, creating a striking color contrast. The gel as a whole is free of cracks and assembly defects.

[0060] Example 3 The preparation steps of Example 3 are the same as those of Example 1, except that: in step S1, the monodisperse nanoparticles are silica-coated zinc sulfide core-shell particles with a particle size of 215 nm and a particle size dispersion coefficient of <5%; the photosensitizer is 9-anthraboric acid, added at 5.0% of the monomer mass; the initiator is added at 5.0% of the monomer mass; the dispersion solvent is a mixture of ethanol and DMSO (volume ratio 95:5); and the ultrasonic dispersion time is 120 min. In step S2, the evaporation temperature is 100℃ and the evaporation time is 5 h. In step S3, the weak ultraviolet wavelength is 380 nm, the power is 30 W, and the irradiation time is 5 s. A specific area is selectively exposed during the weak ultraviolet irradiation process using photomask-assisted technology, thereby custom-writing a ring pattern inside the photonic gel. In step S4, the strong ultraviolet power is 200 W and the curing time is 2 min.

[0061] The actual appearance is as follows Figure 4 As shown, the physical base exhibits a bright yellow-orange structural color, while the pattern area displays a green ring. The outline and color contrast of the pattern are clear and distinct after it is drawn.

[0062] Example 4 The preparation steps of Example 4 are the same as those of Example 1, with the following differences: In step S1, the monodisperse nanoparticles are polystyrene microspheres with a particle size of 190 nm, and the particle size dispersion coefficient is <5%; the photosensitizer is 9-chloroanthracene, added in an amount of 1.0% of the mass of the monomer; the initiator is added in an amount of 1.0% of the mass of the monomer; the dispersion solvent is absolute ethanol; and the ultrasonic dispersion time is 30 min. In step S2, the evaporation temperature is 60°C, and the volatilization time is 24 h. In step S3, the weak ultraviolet wavelength is 405 nm, the power is 5 W, and the irradiation time is 60 s. By means of photomask-assisted technology, specific regions are selectively exposed during weak ultraviolet irradiation, so that the calligraphy characters "韶华不为少年留,恨悠悠,几时休" are custom-written inside the photonic gel. In step S4, the power of high-intensity ultraviolet is 80 W, and the curing time is 10 min. The remaining steps are the same.

[0063] The physical appearance is shown in Figure 5 , the base color of the photonic gel is uniform and soft, has stable cyan and red structural colors, can clearly carry brush calligraphy characters, and is free of cracks and color mottling defects.

[0064] Comparative Example 1 (no photosensitizer added) The preparation steps of Comparative Example 1 are the same as those of Example 1, with the only difference that: no photosensitizer is added in step S1, and the remaining components, dosages and operation steps are exactly the same as those in Example 1. In step S2, the evaporation-induced self-assembly conditions remain unchanged to obtain pre-assembled photonic ink. To form a parallel control with Example 1, in step S3, a 395 nm, 15 W weak ultraviolet LED was also used, and 13 groups of gradient durations were uniformly selected within the 0-60 s irradiation interval to prepare parallel samples. After high-intensity ultraviolet curing in step S4, the obtained photonic gel only presents a single orange-red structural color, the appearance of 13 samples is highly uniform, and there is no color gradient or color gamut distinction between sections. The corresponding physical diagram of the segmented long strip is shown in the physical appendix of this case Figure 6 . Due to the absence of photosensitizer, weak ultraviolet irradiation cannot change the lattice spacing, and the maximum reflection wavelength of the photonic gel prepolymer is fixed at about 605 nm ( Figure 7 ).

[0065] CIE 1931 chromaticity coordinates were uniformly collected for the comparative samples prepared with 13 groups of gradient irradiation durations, and the results are shown in the CIE chromaticity diagram ( Figure 8 ): the chromaticity coordinates of all samples highly overlap and are concentrated in a narrow area, with no coordinate dispersion and color trajectory extension. The above results prove that in the anthracene-based photosensitizer-free system, no matter how the weak ultraviolet exposure parameters change, the photonic gel can only output a single fixed color, and cannot achieve continuous multi-color tuning in the visible light band.

[0066] Comparative Example 2 The preparation steps of Comparative Example 2 are the same as those of Example 1, except that no initiator is added in step S1, while the remaining components, amounts, and operating steps are exactly the same as in Example 1. Steps S2 and S3 are operated in the same way as in Example 1. The presence of the photosensitizer allows for normal control of the lattice spacing in step S3 (the maximum reflection wavelength can be adjusted to 450~600 nm). Step S4 uses strong ultraviolet light at 365 nm and 150 W for 5 min for curing. However, due to the absence of an initiator, the monomers cannot undergo cross-linking polymerization, the system remains a viscous liquid, and a solid three-dimensional gel cannot be formed. The ordered lattice cannot be fixed, and the structural color disappears under slight disturbance.

[0067] Comparative Example 3 (without weak UV regulation) The preparation steps of Comparative Example 3 are the same as those of Example 1, except that after obtaining the pre-assembled photonic ink in step S2, it is directly poured into a mold and subjected to strong ultraviolet curing in step S4 (365 nm, 150 W, 5 min), omitting the step of adjusting the lattice spacing by weak ultraviolet irradiation in step S3. The remaining steps are the same as those of Example 1. The resulting photonic gel only exhibits a single red structural color (maximum reflection wavelength of approximately 625 nm), and it is impossible to achieve continuous variation of the structural color in the visible light band by adjusting any process parameters. Figure 9 This indicates that weak ultraviolet irradiation is a necessary step for wide color gamut tuning.

Claims

1. A method for preparing a wide color gamut photonic gel based on the controllable assembly of monodisperse colloidal particles, characterized in that, Includes the following steps: Step 1: Disperse the monodisperse nanoparticles, monomers, photosensitizers, and photoinitiators in a polar solvent to obtain a precursor dispersion; Step 2: The precursor dispersion obtained in Step 1 is subjected to solvent evaporation treatment to induce the spontaneous and orderly assembly of colloidal nanoparticles, thus obtaining pre-assembled photonic ink; Step 3: The pre-assembled photonic ink obtained in Step 2 is leveled to obtain a photonic ink layer; the photonic ink layer is irradiated with a weak ultraviolet light source with a wavelength of 380~410 nm and a power of 5~30 W to obtain a photonic gel prepolymer; Step 4: Irradiate the photonic gel prepolymer with a strong ultraviolet light source with a wavelength of 260~380 nm and a power of 80~200 W to obtain a wide color gamut photonic gel.

2. The preparation method according to claim 1, characterized in that, The monodisperse nanoparticles mentioned in step 1 include at least one of silica, silica-coated zinc sulfide, polystyrene, and polymethyl methacrylate; The monodisperse nanoparticles have a particle size of 150~300 nm and a particle size dispersion coefficient of <5%.

3. The preparation method according to claim 1, characterized in that, The photosensitizer includes at least one of 9-anthracarboxylic acid, 9-chloroanthracene, 9-anthraboronic acid, 9-anthrayl alcohol, 9-anthraacrylic acid, 9-chloromethylanthracene, and anthracene.

4. The preparation method according to claim 1, characterized in that, In step 1, the polar solvent is mainly ethanol, and one or more of water, dimethyl sulfoxide, and N,N-dimethylformamide are used as modifiers.

5. The preparation method according to claim 2, characterized in that, The amount of monodisperse nanoparticles added is 30.0% to 74.0% of the monomer volume fraction.

6. The preparation method according to claim 3, characterized in that, The amount of photosensitizer added is 0.5% to 5.0% of the monomer mass.

7. The preparation method according to claim 1, characterized in that, In step 2, the solvent evaporation process is carried out at a temperature of 60℃~100℃, a pressure of atmospheric pressure, and a time of 5~24 h.

8. The preparation method according to claim 1, characterized in that, In step 3, the photonic ink layer is irradiated with a weak ultraviolet light source for 5~60 s; In step 4, the photonic gel prepolymer is irradiated with a strong ultraviolet light source for 2 to 10 minutes.

9. A wide color gamut photonic gel based on the controllable assembly of monodisperse colloidal particles prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the wide color gamut photonic gel based on the controllable assembly of monodisperse colloidal particles as described in claim 9 in intelligent display, sensing, information encryption or anti-counterfeiting.

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