Photochromic composite microsphere as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photochromism, and discloses a photochromic composite microsphere as well as a preparation method and application thereof. A photochromic material and a copolymer are grafted to form a stable spherical copolymer core, and epoxy resin is further used as a shell for coating, so that the photochromic composite microsphere with a'grafted core-epoxy resin shell 'double-layer chemical embedding structure is constructed. The prepared photochromic composite microspheres are prepared into a color-changing coating, and the color-changing coating covers a unique metasurface light guide structure, so that the excellent performance of the metasurface light guide structure in the aspects of luminous efficiency and uniformity is verified.

Description

Technical Field

[0001] This invention relates to the field of photochromic technology, specifically to a photochromic composite microsphere, its preparation method, and its application. Background Technology

[0002] Photochromic materials, capable of reversibly changing to different color states under light stimulation, have been widely used in fields such as smart window films, anti-counterfeiting labels, bio-imaging, and flexible displays. Currently, common organic photochromic dyes include spiropyrans, naphthopyrans, azobenzenes, and benzoic anhydrides, which possess excellent color-changing properties. However, they suffer from problems such as easy volatility of free molecules, poor fatigue resistance, and susceptibility to environmental corrosion (e.g., oxygen, humidity, acids, and alkalis), severely limiting their practical application lifespan.

[0003] To overcome these shortcomings, existing technologies often employ polymer physical encapsulation techniques, storing photochromic materials within a polymer matrix through physical encapsulation or chemical bonding. For example, dyes are encapsulated within polymer microspheres using emulsion polymerization, or dispersed in polymer materials through simple blending. However, physically encapsulated microspheres suffer from insufficient dye-polymer compatibility and are prone to leakage; simple blending struggles to prevent dye molecule migration and degradation during long-term use, leading to a decline in color-changing performance. Furthermore, existing physically encapsulated shells are mostly single polymer layers with limited mechanical strength, making them susceptible to damage under complex environments (such as high temperatures, friction, and chemical corrosion), further shortening the material's lifespan.

[0004] Meanwhile, traditional light guide structures cannot address the issue of uneven color change in the surface-attached color-changing layer. Traditional light guide structures generally suffer from high material absorption loss and low scattering efficiency in the ultraviolet band, especially in planar transmission or long-distance ultraviolet light transmission scenarios. Conventional refractive or diffractive structures struggle to achieve a synergistic optimization of high transmittance and precise scattering. Existing scattering structure parameter designs are mostly optimized for the visible light band. Due to surface absorption of ultraviolet photochromic materials, they lack specific consideration for the energy characteristics of ultraviolet photons in planar transmission, resulting in insufficient matching between array point size and depth, and poor adaptability of periodic arrangement to phase modulation. Summary of the Invention

[0005] The first technical problem to be solved by the present invention is to provide a photochromic composite microsphere to solve the problems of poor weather resistance, insufficient mechanical strength and easy leakage of photochromic materials.

[0006] The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned photochromic composite microspheres.

[0007] The third technical problem to be solved by the present invention is to provide the application of the above-mentioned photochromic composite microspheres in detecting the light emission performance of light guide structures.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing photochromic composite microspheres includes the following steps:

[0010] (1) Dissolve the photochromic material in an organic solvent and heat to dissolve it to obtain a homogeneous solution;

[0011] (2) Add a catalyst to the homogeneous solution, add an acrylic polymer and a photoinitiator under a nitrogen atmosphere, and heat to react to obtain a graft copolymer solution;

[0012] (3) The graft copolymer solution is added to the aqueous solution of the emulsifier and sheared using a high-speed shear emulsifier to form an oil-in-water emulsion. The emulsion is heated and stirred to obtain a spherical copolymer microsphere suspension.

[0013] (4) Disperse epoxy resin in the spherical copolymer microsphere suspension, add curing agent, adjust the pH of the system to acidic using pH adjuster, and carry out reaction;

[0014] (5) After the reaction is completed, photochromic composite microspheres are prepared by filtration, washing and vacuum drying.

[0015] In step (1), the photochromic material is 3,3-diphenyl-3H-naphtho[2,1-b]pyran; and / or, the organic solvent is one or more of ethanol, DMF, THF, DMSO, ethyl acetate, and acetone; and / or, the heating and dissolving temperature is 55°C to 70°C (preferably 60°C).

[0016] In step (2), the catalyst is one or more of p-toluenesulfonic acid, concentrated sulfuric acid, methanesulfonic acid, Lewis acid, and DBTDL; and / or, the catalyst accounts for 0.01~2% of the total mass of the system, preferably 0.05~0.5%, and the system is a graft copolymer solution system.

[0017] In step (2), the acrylic polymer is any one of poly(hydroxyethyl methacrylate-co-acrylic acid), polyhydroxypropyl methacrylate, polyethylene glycol diglycidyl ether, or poly(maleic anhydride-alt-styrene) formed by copolymerization of hydroxyethyl methacrylate and acrylic acid; and / or, the acrylic polymer contains hydroxyl and carboxyl groups; and / or, the molar ratio of the photochromic material to the hydroxyl groups in the acrylic polymer is 1:0.03~0.11, and the molar ratio of the carboxyl groups to the hydroxyl groups is 1:3~5; and / or, the photoinitiator is one or more of azobisisobutyronitrile, benzoin ether, and α-hydroxyisobutyrylbenzene; and / or, the photoinitiator accounts for 0.4~5% of the total mass of the system, and the system is a graft copolymer solution system.

[0018] The preparation methods of the poly(hydroxyethyl methacrylate-co-acrylic acid) and the poly(maleic anhydride-alt-styrene) are described in reference to Marco Laurenti, Marta Grochowicz and Valentina Caudal. Porous ZnO / 2–Hydroxyethyl Methacrylate Eluting Coatings for Ureteral Stent Applications. Coatings 2018, 8(11), 376.

[0019] In step (2), the heating reaction is carried out at a temperature of 55℃~70℃ (preferably 70℃) for a time of 6-7h (preferably 6.5h).

[0020] In step (3), the volume ratio of the graft copolymer solution to the aqueous solution of the emulsifier is 1:1 to 1:10, preferably 1:3 to 1:5; and / or, the emulsifier is one or more of sodium dodecylbenzenesulfonate, polyoxyethylene octylphenyl ether, Tween 80, SDS, and OP-10; and / or, the emulsifier accounts for 2 to 10% of the total mass of the system, and the system is a spherical copolymer microsphere suspension system; and / or, the shearing is performed at a temperature of 30°C to 40°C (preferably 35°C), a rotation speed of 10,000 rpm to 150,000 rpm (preferably 80,000 rpm), and a time of 6 to 8 min (preferably 7 min); and / or, the stirring reaction is performed at a temperature of 40 to 80°C (preferably 80°C), a rotation speed of 500 rpm to 900 rpm (preferably 900 rpm), and a time of 1 to 4 h (preferably 4 h).

[0021] In step (4), the epoxy resin is a bifunctional Cardo epoxy resin or a bisphenol A type epoxy resin; and / or, the molar ratio of the epoxy group in the epoxy resin to the hydroxyl group in the acrylic polymer is 1:0.01~0.05; and / or, the curing agent is one or more of triethylamine, boron trifluoride ether complex, triphenylphosphine, 2-ethyl-4-methylimidazole, and DABCO; and / or, the curing agent accounts for 14~20% of the mass of the epoxy resin; and / or, the pH adjuster is one or more of acetic acid, citric acid, sulfuric acid, and formic acid; and / or, the acidity has a pH value of 4-5 (preferably 4.5); and / or, the reaction temperature is 90℃~95℃ (preferably 92℃), and the time is 2~3 h (preferably 2.5 h).

[0022] In step (4), the washing is performed with deionized water for 4-6 times (preferably 5 times); and / or, the vacuum drying is performed at a temperature of 60℃-65℃ (preferably 62℃), for a time of 12-14 h (preferably 13 h), and at a pressure of 0.02~0.04 MPa (preferably 0.03 MPa).

[0023] The application of the photochromic composite microspheres prepared by the above method in detecting the light emission performance of light guide structures is also within the scope of protection of this invention.

[0024] The photochromic composite microspheres were coated onto a photochromic coating to prepare a color-changing coating, which was used to verify the high efficiency and uniformity of light output from the metasurface light guide structure.

[0025] Beneficial effects:

[0026] (1) The present invention significantly improves the stability and response efficiency of photochromic dyes due to molecular-level covalent bonding and spatial confinement effect: the individual 3,3-diphenyl-3H-naphtho[2,1-b]pyran (DPNP) molecules are highly hydrophobic and easy to aggregate, and the open ring (colored state) is easily attacked and degraded by environmental factors such as oxygen and humidity during the photochromic process, resulting in poor fatigue resistance. In this invention, DPNP is grafted at the molecular level by forming covalent ester bonds with the phenolic hydroxyl groups of acrylic polymers (P(HEMA-co-AA) or PHPMA) to the hydroxyl / carboxyl groups. On the one hand, the long polymer chain restricts the free migration of DPNP molecules through steric hindrance, preventing a decrease in color development efficiency due to aggregation. On the other hand, the formation of ester bonds makes DPNP a rigid unit of the polymer chain, and its open-ring conjugated structure is stabilized by the polymer matrix (reducing energy dissipation caused by intramolecular rotation), significantly improving the photochromic response speed. In addition, the hydrophilic groups (such as -OH) of the polymer chain can form weak hydrogen bonds with DPNP, further suppressing the nonradiative transitions of its reverse ring-closing reaction and extending the colored lifetime.

[0027] (2) Chemical encapsulation to construct a "core-chain-shell" cross-linked structure to solve the mechanical defects of the copolymer and enhance the color stability: Although the copolymer formed by grafting DPNP with acrylic polymers improves the dye stability, the linear polymer chains have weak inter-chain forces and insufficient mechanical strength. Under repeated light stimulation, the dye molecules are easily exposed due to chain segment slippage. This invention constructs a three-dimensional cross-linked shell by chemically grafting epoxy resin with the copolymer (the ring-opening reaction of epoxy groups with the residual -OH / -COOH of the copolymer). From a molecular perspective, the rigid network formed by epoxy cross-linking "anchors" the copolymer core, preventing it from deforming under external stress. At the same time, the dense structure of the epoxy shell can isolate oxygen and moisture, reducing the oxidative degradation of the DPNP ring-opening body. In addition, the high transparency of epoxy resin does not hinder the excitation of the DPNP core by light, and the rigidity of its molecular chains can reduce the interference on the DPNP conjugated system, ensuring color intensity and monochromaticity.

[0028] (3) The functional group design of acrylic copolymers achieves dual reactivity, ensuring the synergy between grafting and embedding: P (HEMA-co-AA) contains hydroxyl (-OH) and carboxyl (-COOH) groups, and PHPMA contains hydroxyl (-OH) groups. These groups not only provide grafting sites for DPNP (through esterification), but the residual groups can also undergo ring-opening reactions with the epoxy groups of the epoxy resin to form a continuous covalent bond of "grafting-embedding". From the molecular design perspective, the -OH of the HEMA unit and the -COOH of the AA unit in P (HEMA-co-AA) are distributed in a gradient, ensuring that there are still enough -COOH (stronger acidity) to preferentially react with the epoxy groups after the grafting reaction, thus improving the embedding efficiency; although the -OH of PHPMA has slightly lower reactivity, sufficient free -OH is retained by controlling the grafting rate to form a stable ether bond with the epoxy groups. This functional group matching avoids phase separation caused by physical mixing, thus greatly improving the bonding energy of the "core-chain-shell" interface.

[0029] (4) The bifunctional Cardo epoxy resin used in this invention contains a rigid fluorene ring structure, and the bisphenol A epoxy resin contains a flexible methylene chain, both of which have high chemical stability. The ether bonds (-COC-) in their molecular chains form a conjugated stable structure with the benzene ring, which can withstand acidic and alkaline environments of pH 2~10 and temperature fluctuations below 60℃. From a microscopic perspective, the density of the epoxy cross-linking network can prevent small molecules from penetrating into the core, avoiding coordination or oxidation reactions with the phenolic hydroxyl groups of DPNP; at the same time, the rigid structure of the bifunctional Cardo epoxy resin increases the hardness of the microspheres, and the flexible segments of the bisphenol A epoxy resin improve the impact resistance of the microspheres, making the material adaptable to complex working conditions such as textile friction and coating scratching.

[0030] (5) The photochromic composite microspheres prepared in this invention are used to prepare a color-changing coating, which is then applied to the invented metasurface light guide structure with unique characteristics to verify the high efficiency and uniformity of light output of the metasurface light guide structure. By setting multiple light guide plate holes on the main body of the light guide plate, and arranging the multiple light guide plate holes in multiple rows, the multiple light guide plate holes on the main body of the light guide plate exhibit a structure with low density on both sides and high density in the center. Through this hole structure with different densities, the reflection of light at different angles and directions is enhanced, thereby improving the efficiency and uniformity of light output from the light source. At the same time, since the transmission of light energy is affected by the change in the length of the main body of the light guide plate, the depth of each row of light guide plate holes on the main body of the light guide plate increases sequentially from both sides to the center, which is beneficial for the transmission of light on the main body of the light guide plate. This further optimizes the efficiency and uniformity of light output of the main body of the light guide plate, and solves the problems of large material absorption loss and low scattering efficiency in traditional light guide structures. Attached Figure Description

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0032] Figure 1 The infrared scanning spectrum of a photochromic composite microsphere prepared in Example 1 of this invention;

[0033] Figure 2 This is a scanning electron microscope image of a photochromic composite microsphere prepared in Example 1 of the present invention;

[0034] Figure 3 This is a comparison image of the photochromic composite microspheres prepared in Example 1 of the present invention before and after color change;

[0035] Figure 4 This is a three-dimensional structural schematic diagram of the metasurface light guide structure in Embodiment 5 of the present invention;

[0036] Figure 5 This is a top view of the structure of the multiple rows of light guide plate holes arranged on the main body of the light guide plate in Embodiment 5 of the present invention;

[0037] Figure 6 This is a schematic diagram of the structure of the single-row light guide plate with holes arranged on the main body of the light guide plate in Embodiment 5 of the present invention;

[0038] Among them, 1-light guide plate body; 2-side-inlet light source; 3-photochromic coating; 4-light guide plate hole; 5-groove. Detailed Implementation

[0039] The bifunctional Cardo epoxy resin (BFCE) used in this invention was purchased from DIC (China) Co., Ltd., and the bisphenol A type epoxy resin (E-51) was purchased from Sigma-Aldrich.

[0040] The preparation methods of poly(hydroxyethyl methacrylate-co-acrylic acid) and poly(maleic anhydride-alt-styrene) used in this invention are referenced from Marco Laurenti, Marta Grochowicz and Valentina Caudal. Porous ZnO / 2–Hydroxyethyl Methacrylate Eluting Coatings for Ureteral Stent Applications. Coatings 2018, 8(11), 376. The specific preparation steps are as follows:

[0041] Preparation of poly(hydroxyethyl methacrylate-co-acrylic acid)

[0042] 1. Setup of the reaction apparatus: Take a 50 mL single-necked round-bottom flask, add a magnetic stir bar, hydroxyethyl methacrylate (3.9 mg), acrylic acid (0.72 mg), and DMF (0.23 mL) in sequence, and stir until the monomer is completely dissolved to form a transparent solution;

[0043] 2. Oxygen removal and initiator addition: High-purity nitrogen gas is introduced into the flask at a rate of 10 mL / min for 30 min to remove oxygen from the system; then AIBN (4.71 mg) is added, and nitrogen gas is introduced for another 10 min to ensure that the initiator is completely dissolved and that there is no oxygen residue in the system.

[0044] 3. Polymerization reaction: The flask was placed in a 65℃ constant temperature water bath and stirred for 6 h under nitrogen protection (stirring rate 300 rpm). During the reaction, the system gradually changed from transparent to a pale yellow viscous liquid;

[0045] 4. Purification and Drying: After the reaction was complete, the reaction solution was slowly added dropwise to 10 times its volume of deionized water (with magnetic stirring at 500 rpm). The copolymer precipitated as a white flocculent precipitate. After standing for 30 min, the precipitate was collected by filtration and washed three times with deionized water (each time using 10 times the mass of the precipitate) to remove unreacted monomers and initiators. The washed precipitate was then dried in a vacuum drying oven at 60℃ (pressure 0.03 MPa) for 12 h to obtain a white powdery P(HEMA-co-AA). The molecular weight of the polymer was Mn≈2.0×10⁻⁶. 4 g / mol.

[0046] Preparation of poly(maleic anhydride-alt-styrene)

[0047] 1. Preparation of reaction apparatus: Take a 50mL single-necked round-bottom flask, add a magnetic stir bar, maleic anhydride (4.9 mg), styrene (5.2 mg) and ethyl acetate (0.45 mL), stir at room temperature for 15 min to form a homogeneous and transparent solution (maleic anhydride and styrene form a charge-transfer complex, and the solution is pale yellow).

[0048] 2. Deoxygenation and Initiator Addition: Purge high-purity nitrogen gas into the flask (at a rate of 10 mL / min) for 25 min to remove oxygen; add AIBN (8.28 mg), and continue purging with nitrogen gas for 10 min to ensure that the initiator dissolves and the system is oxygen-free;

[0049] 3. Polymerization reaction: The flask was placed in a 70℃ constant temperature water bath and stirred for 7 h under nitrogen protection (stirring rate 350 rpm). During the reaction, the viscosity of the system gradually increased, eventually forming a pale yellow viscous liquid;

[0050] 4. Purification and Drying: The reaction solution was added dropwise to 15 times its volume of n-hexane (magnetically stirred at 600 rpm). The copolymer precipitated as a white powder. The precipitate was collected by filtration and washed four times with n-hexane (each time using 8 times the mass of the precipitate) to remove unreacted monomers and initiators. The precipitate was then dried in a vacuum drying oven at 65℃ (0.02 MPa) for 10 hours to obtain a white, fluffy P (MA-alt-St). The molecular weight of the polymer was Mn≈2.3×10⁻⁶. 4 g / mol.

[0051] Example 1

[0052] (1) Add 0.1 g of photochromic dye 3,3-diphenyl-3H-naphtho[2,1-b]pyran and solvent (1.58 g of ethanol and 8.62 g of DMF) to the flask and stir in an oil bath at 60 °C for 2 h until completely dissolved to form a homogeneous and stable yellow transparent solution;

[0053] (2) Under a nitrogen atmosphere, add 0.05 g of p-toluenesulfonic acid catalyst to the solution obtained in step (1), stir for 40 min, and then add 0.2 g of poly(hydroxyethyl methacrylate-co-acrylic acid) (the carboxyl content of poly(hydroxyethyl methacrylate-co-acrylic acid) is 1×10⁻⁶). -5 mol, hydroxyl content: 3×10 -5 0.05 g of azobisisobutyronitrile (azobisisobutyronitrile) and 0.05 g of azobisisobutyronitrile were heated to 70 °C and stirred for 6.5 h to obtain a graft copolymer solution.

[0054] (3) Mix 10 mL of the graft copolymer solution with an emulsifier aqueous solution at a volume ratio of 1:4 (i.e., 40 mL of emulsifier aqueous solution with a density of 1 g / mL, wherein the mass of the emulsifier sodium dodecylbenzenesulfonate is 2.5 g), and shear at 80,000 rpm for 7 min at 35°C to form an oil-in-water emulsion. Transfer the emulsion to a four-necked flask, heat it to 80°C, mechanically stir it at 900 rpm for 4 h, and cool it to room temperature to obtain a spherical copolymer microsphere suspension.

[0055] (4) Add 0.14 g of bisphenol A type epoxy resin (E-51, epoxy group content: 7.14 × 10⁻⁶) to the spherical copolymer microsphere suspension. -4 0.02 g of triethylamine was added, and the pH of the system was adjusted to 4.5 with acetic acid. The temperature was raised to 92°C, and the reaction was stirred for 2.5 h.

[0056] (5) After the reaction was completed, the mixture was vacuum filtered, washed 5 times with deionized water, and vacuum dried for 13 h at 62°C and 0.03 MPa to obtain a photochromic composite microsphere.

[0057] Figure 1 The infrared spectrum of a photochromic composite microsphere prepared in Example 1, wherein the 1089 cm⁻¹... -1 1267cm -1 The peak at 1488 cm⁻¹ represents the superposition of ether and ester bonds in the COC structure, demonstrating the crosslinking of the epoxy resin and the formation of the overall network; -1 1589cm -1 The presence of the aromatic ring framework vibration peak at this point proves that the photochromic material was successfully introduced into the system and grafted.

[0058] Figure 2 The image shows a scanning electron microscope (SEM) image of a photochromic composite microsphere prepared in Example 1, with an average particle size of 4.01 µm.

[0059] Figure 3 This is a comparison image of the photochromic composite microspheres prepared in Example 1 before and after color change.

[0060] The operation steps for the photochromic composite microspheres to change color are as follows: use an ultraviolet flashlight to irradiate the surface of the photochromic composite microspheres for 5 seconds, and the photochromic composite microspheres will change from the initial colorless state to the orange state.

[0061] Example 2

[0062] The difference between this embodiment and Example 1 is that the added epoxy resin is 0.28 g of bifunctional Cardo epoxy resin (BFCE, with an epoxy group content of 1.26 × 10⁻⁶).-3 (mol), while other parameters and conditions are the same as in Example 1.

[0063] Example 3

[0064] The difference between this embodiment and Example 1 is that the added acrylic polymer is 0.4 g of polyhydroxypropyl methacrylate (PHPMA) (hydroxyl content: 2 × 10⁻⁶). -5 (mol), while other parameters and conditions are the same as in Example 1.

[0065] Example 4

[0066] The difference between this embodiment and Example 1 is that the added acrylic polymer is 0.4 g of polyhydroxypropyl methacrylate (hydroxyl: 2×10). -5 0.14 g of bisphenol A type epoxy resin (E-51, epoxy group: 7.14 × 10⁻⁶ mol) was used as the epoxy resin. - 4 (mol), while other parameters and conditions are the same as in Example 1.

[0067] Example 5

[0068] like Figures 4-6 As shown, the metasurface light guide structure includes a light guide plate body 1, with a side-incident light source 2 on each side of the light guide plate body 1. The surface of the light guide plate body 1 is provided with a photochromic coating 3. The light guide plate body 1 is provided with a plurality of light guide plate holes 4, which are arranged mirror-symmetrically along the center of the light guide plate body 1. The distribution density and hole depth of the plurality of light guide plate holes 4 increase sequentially from the side-incident light source 2 to the center of the light guide plate body 1.

[0069] Specifically, the light guide plate body 1 has a square structure with a side length of 95mm~100mm and a thickness of 2.5mm~3.5mm. Grooves 5 are provided on both sides of the light guide plate body 1, and each side-incident light source 2 is fixedly connected to the side of the light guide plate body 1 through the groove 5, so that the side-incident light source 2 is stably installed and fixed on the side of the light guide plate body 1, thereby enhancing the structural stability of the metasurface light guide structure.

[0070] Furthermore, the multiple light guide plate holes 4 are arranged in multiple rows and columns, and the multiple rows of light guide plate holes 4 are mirror-symmetrically arranged along the center of the light guide plate body 1. Each row of light guide plate holes 4 is parallel to the side-incident light source 2.

[0071] like Figure 6As shown, in the multi-row light guide plate holes 4, the depth of the light guide plate holes 4 increases sequentially from the side of the light guide plate body 1 towards the center of the light guide plate body 1; specifically, the diameter of the light guide plate holes 4 is 0.5mm~1mm, and the depth is 0.1mm~2mm. In the single-row light guide plate holes 4, the spacing between two adjacent light guide plate holes 4 decreases sequentially from the side of the light guide plate body 1 towards the center of the light guide plate body 1; specifically, the vertical spacing between two adjacent light guide plate holes 4 is 1.5mm~15mm.

[0072] like Figure 5 As shown, in the multi-row light guide plate holes 4, from the side of the light guide plate body 1 towards the middle position of the light guide plate body 1, the row spacing of two adjacent rows of light guide plate holes 4 decreases sequentially; the row spacing between two adjacent rows of light guide plate holes 4 is 1mm~8mm. The horizontal spacing between the multi-row light guide plate holes 4 located on both sides of the light guide plate body 1 is greater than the horizontal spacing between the multi-row light guide plate holes 4 located in the middle position of the light guide plate body 1.

[0073] The principle of the metasurface light guide structure in this invention is as follows: Multiple light guide plate holes 4 are provided on the light guide plate body 1, arranged in multiple rows. These holes exhibit a structure where the density is low on the sides and high in the center of the light guide plate body 1. This varying density enhances the reflection of light at different angles and directions, improving the efficiency and uniformity of light emission. Furthermore, because the transmission of light energy is affected by the length variation of the light guide plate body 1, the depth of each row of light guide plate holes 4 on the light guide plate body 1 increases sequentially from the sides towards the center, which is beneficial for light to pass through the light guide plate body 1. The transmission through the body 1 further optimizes the efficiency and uniformity of light output of the light guide plate body 1. Specifically, the depth of the holes 4 in each row of the light guide plate increases sequentially from both sides towards the center. This arrangement allows for secondary scattering and distribution of the incident light, resulting in more uniform light reaching the surface and improving overall light extraction efficiency. The depth gradient of the holes 4 in each row of the light guide plate allows for adjustment of light scattering intensity. Shallower holes 4 closer to the side-incident light source 2 reduce excessive scattering, while deeper holes 4 farther from the side-incident light source 2 compensate for light attenuation and widen the scattering angle, thereby balancing the light intensity distribution and achieving uniform brightness across the entire area. This solves the problems of high material absorption loss and low scattering efficiency inherent in traditional light guide structures.

[0074] The photochromic coating 3 is used to verify the light output efficiency and uniformity of the metasurface light guide structure. When verifying the uniformity and efficiency of the light output of the metasurface light guide structure, firstly, the power supply of the side-inlet light source 2 on both sides of the light guide plate body 1 is turned on. According to the principle of optical waveguide, since the light propagates from both sides of the light guide plate body 1, the side-inlet light source 2 is reflected and transmitted through the light guide plate holes 4 designed on the light guide plate body 1 at different angles and directions, causing the photochromic layer to change color. The light output efficiency and uniformity of the present invention are verified by the uniformity of the color change of the photochromic layer.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 1 is that the outermost shell structure added is 3-mercaptopropionic acid. The specific steps are adjusted as follows, while other parameters and conditions are the same as in Example 1:

[0077] (1)-(3) are exactly the same as in Example 1;

[0078] (4) Add 0.3 g of 3-mercaptopropionic acid and 0.01 g of photoinitiator α-hydroxyisobutyrylbenzene to the spherical copolymer microsphere suspension. Under nitrogen protection, irradiate with a 365 nm ultraviolet lamp (power 100W) for 30 min to initiate polymerization. Then add 0.05 g of crosslinking agent ethylene glycol dimethacrylate and continue to irradiate with ultraviolet light for 1 h to form a poly-3-mercaptopropionic acid shell.

[0079] (5) After the reaction was completed, the mixture was vacuum filtered, washed 5 times with deionized water, and vacuum dried at 62°C for 13 h to obtain photochromic composite microspheres.

[0080] Comparative Example 2

[0081] The difference between this comparative example and Example 1 is that the outermost shell structure added is poly(maleic anhydride-alt-styrene). The specific steps are adjusted as follows, while other parameters and conditions are the same as in Example 1:

[0082] (1)-(3) are exactly the same as in Example 1;

[0083] (4) Take 0.2g of poly(maleic anhydride-alt-styrene), add 10 mL of DMF to dissolve it, hydrolyze it at 65℃ for 30 min, add the hydrolyzed poly(maleic anhydride-alt-styrene) solution to the spherical copolymer microsphere suspension, stir at 50℃ and 300 rpm for 1 h, add 0.01 g of the catalyst p-toluenesulfonic acid, heat to 75℃, and react for 3 h;

[0084] (5) After the reaction was completed, the mixture was vacuum filtered, washed 5 times with deionized water, and vacuum dried at 62°C for 13 h to obtain photochromic composite microspheres.

[0085] Comparative Example 3

[0086] The difference between this comparative example and Example 1 is that the material grafted with the color-changing material is polyurethane. The specific steps are adjusted as follows, while other parameters and conditions are the same as in Example 1.

[0087] (1) Add photochromic dye (3,3-diphenyl-3H-naphtho[2,1-b]pyran 0.1 g) and solvent (ethanol 2 mL, DMF 8 mL) to the flask, and stir in an oil bath at 60°C for 2 h until completely dissolved to form a homogeneous and stable yellow transparent solution;

[0088] (2) Under a nitrogen atmosphere, add 0.03 g of catalyst DBTDL to the solution obtained in step (1), stir for 40 min, then add 0.2 g of polyurethane (polybutylene adipate type polyurethane) and 0.05 g of photoinitiator azobisisobutyronitrile, heat to 70 °C, stir for 6.5 h to obtain the graft copolymer solution.

[0089] (3) The procedure is exactly the same as step (3) in Example 1 (10 mL of graft copolymer solution, 2.5 g of sodium dodecylbenzenesulfonate emulsifier, shearing at 35°C and 80,000 rpm for 7 min, and reaction at 80°C and 900 rpm for 4 h).

[0090] (4) Add 0.23 g of epoxy resin (bisphenol A type epoxy resin E-51) to the spherical copolymer microsphere suspension and disperse it at 40℃ and 250 rpm for 1 h; add 0.02 g of curing agent triethylamine, adjust the pH value to 4.5 with acetic acid, raise the temperature to 92℃, and stir for 7 h.

[0091] (5) The process is exactly the same as step (5) in Example 1 (washing 5 times and vacuum drying at 62°C for 13 h) to obtain photochromic composite microspheres.

[0092] Example 6

[0093] Color change response test: The various performance indicators of the photochromic composite microspheres prepared in Examples 1-4 and Comparative Examples 1-3 were measured. The photochromic composite microspheres prepared in Example 1 showed the best color change response and recovery time. The specific results are shown in Table 1.

[0094] Table 1

[0095] Sample number Yield (%) Response time (s) Recovery time (s) Example 1 95 5 10 Example 2 93 6 12 Example 3 92 6 14 Example 4 90 7 17 Comparative Example 1 86 9 18 Comparative Example 2 82 10 23 Comparative Example 3 80 11 36

[0096] In performance testing, the photochromic composite microspheres prepared in Example 1 exhibited the best overall performance: their color-changing response and recovery time were the shortest.

[0097] This invention provides a concept and method for the preparation and application of photochromic composite microspheres. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing photochromic composite microspheres, characterized in that, Includes the following steps: (1) Dissolve the photochromic material in an organic solvent and heat to dissolve it to obtain a homogeneous solution; (2) Add a catalyst to the homogeneous solution, add an acrylic polymer and a photoinitiator under a nitrogen atmosphere, and heat to react to obtain a graft copolymer solution; (3) The graft copolymer solution is added to the aqueous solution of the emulsifier and sheared using a high-speed shear emulsifier to form an oil-in-water emulsion. The emulsion is heated and stirred to obtain a spherical copolymer microsphere suspension. (4) Disperse epoxy resin in the spherical copolymer microsphere suspension, add curing agent, adjust the pH of the system to acidic using pH adjuster, and carry out reaction; (5) After the reaction is completed, photochromic composite microspheres are prepared by filtration, washing and vacuum drying.

2. The preparation method according to claim 1, characterized in that, In step (1), the photochromic material is 3,3-diphenyl-3H-naphtho[2,1-b]pyran; and / or, the organic solvent is one or more of ethanol, DMF, THF, DMSO, ethyl acetate, and acetone; and / or, the heating and dissolving temperature is 55℃~70℃.

3. The preparation method according to claim 1, characterized in that, In step (2), the catalyst is one or more of p-toluenesulfonic acid, concentrated sulfuric acid, methanesulfonic acid, Lewis acid, and DBTDL; and / or, the catalyst accounts for 0.01~2% of the total mass of the system, preferably 0.05~2%.

4. The preparation method according to claim 1, characterized in that, In step (2), the acrylic polymer is any one of poly(hydroxyethyl methacrylate-co-acrylic acid), polyhydroxypropyl methacrylate, polyethylene glycol diglycidyl ether, or poly(maleic anhydride-alt-styrene) formed by copolymerization of hydroxyethyl methacrylate and acrylic acid; and / or, the acrylic polymer contains hydroxyl and carboxyl groups; and / or, the molar ratio of the photochromic material to the hydroxyl groups in the acrylic polymer is 1:0.03~0.11, and the molar ratio of the carboxyl groups to the hydroxyl groups is 1:3~5; and / or, the photoinitiator is one or more of azobisisobutyronitrile, benzoin ether, and α-hydroxyisobutyrylbenzene; and / or, the photoinitiator accounts for 0.4~5% of the total mass of the system.

5. The preparation method according to claim 1, characterized in that, In step (2), the heating reaction is carried out at a temperature of 55℃~70℃ for 6-7 hours.

6. The preparation method according to claim 1, characterized in that, In step (3), the volume ratio of the graft copolymer solution to the aqueous solution of the emulsifier is 1:1 to 1:10; and / or, the emulsifier is one or more of sodium dodecylbenzenesulfonate, polyoxyethylene octylphenyl ether, Tween 80, SDS, and OP-10; and / or, the emulsifier accounts for 2 to 10% of the total mass of the system; and / or, the shearing is carried out at a temperature of 30°C to 40°C, a rotation speed of 10,000 rpm to 150,000 rpm, and a time of 6 to 8 minutes; and / or, the stirring reaction is carried out at a temperature of 40 to 80°C, a rotation speed of 500 rpm to 900 rpm, and a time of 1 to 4 hours.

7. The preparation method according to claim 1, characterized in that, In step (4), the epoxy resin is a bifunctional Cardo epoxy resin or a bisphenol A type epoxy resin; and / or, the molar ratio of the epoxy groups in the epoxy resin to the hydroxyl groups in the acrylic polymer is 1:0.01~0.05; and / or, the curing agent is one or more of triethylamine, boron trifluoride ether complex, triphenylphosphine, 2-ethyl-4-methylimidazolium, and DABCO; and / or, the curing agent accounts for 14~20% of the mass of the epoxy resin; and / or, the pH adjuster is one or more of acetic acid, citric acid, sulfuric acid, and formic acid; the acidity is a pH value of 4-5; and / or, the reaction temperature is 90℃~95℃, and the time is 2~3 h.

8. The preparation method according to claim 1, characterized in that, In step (4), the washing is performed with deionized water 4-6 times; and / or the vacuum drying is performed at a temperature of 60℃-65℃ for 12-14 h and a pressure of 0.02~0.04 MPa.

9. Photochromic composite microspheres prepared by the preparation method according to any one of claims 1-8.

10. The application of the photochromic composite microspheres according to claim 9 in detecting the light emission performance of a light guide structure.

Images