Photochromic nano-microsphere material and preparation method thereof

Abstract

The invention relates to a photochromic nano-microsphere material and a preparation method thereof, the material is of a core-shell structure, the core of the material is composed of nano-crystalline grains of two spiropyrane compounds as shown in a formula (a) and a formula (b), and the shell of the material is coated with a modified acrylate material; the mass ratio of the core to the shell is (1-2): (3-5), and the particle size of the microsphere is 7-15nm. The photochromic nano-microspheres can generate red and green color changes under ultraviolet and visible light illumination conditions respectively, and light rays with specific wavelengths can be effectively filtered. The color filter can be applied to a color correction optical component, plays a role in filtering and complementing color, improves the accuracy and saturation of color, improves the color discrimination capability, and has a remarkable effect on color correction. Wherein R is equal to C < 16 > H < 33 >, and R is equal to C < 16 > H < 33 >; and in the # imgabs 1 #, R is equal to C16H33.

Description

Technical Field

[0001] The invention relates to the technical field of photochromic nanomaterials, and in particular to a photochromic nanocomposite microsphere material containing a composite spiropyran compound and a preparation method thereof. Background Art

[0002] With the rapid development of modern science and technology, the demand for materials with special properties is growing. Photochromic materials, as special materials that can change color under the irradiation of light of a specific wavelength, have attracted widespread attention. In many fields, such as optical devices, sensors, anti-counterfeiting labels, etc., photochromic materials have shown great application potential.

[0003] Traditional photochromic materials have many problems in practical applications. On the one hand, they have poor stability. When used for a long time or affected by different environmental factors, they are prone to decomposition and fading, which greatly limits their service life and scope of application. For example, in outdoor environments, changes in factors such as light intensity, temperature, and humidity may cause the performance of photochromic materials to decline rapidly. On the other hand, it is usually ultraviolet light that changes the color of a single material, for example, colorless to red, blue, and gray, etc., but it is difficult to change color under visible light, especially for the integrated regulation of the color-changing properties of two different spiropyran compounds, that is, to achieve specific red and green color alternations under different lighting environments. Summary of the invention

[0004] The purpose of the present invention is to provide a photosensitive color-changing nano composite microsphere material and a preparation method thereof. The material is a core-shell structure nano microsphere, the core of which is composed of nano crystal particles of two spiropyran compounds with different structures of formula (a) and formula (b), and the shell is coated with a modified acrylic ester material, the mass ratio of the core to the shell is (1-2): (3-5), the outer diameter of the nano microsphere is 7-15nm, the diameter of the spiropyran core is 4-9nm, and the thickness of the shell is 1.5-3nm. The two spiropyran compounds can respectively undergo red and green color changes under ultraviolet and visible light conditions, and effectively filter light of a specific wavelength. It can be applied to color correction optical components, play a role in filtering and complementary colors, enhance the color purity of the red and green band spectrum and the dimension of the color vision vector space through complementary and synergistic color changes, adjust the color balance of optical components or light entering the eyes, avoid visual fatigue caused by long-term use of one color, improve color accuracy and saturation, and enhance color discrimination ability, and play a significant role in color correction.

[0005] To achieve the above objectives, this application provides the following technical solutions:

[0006] A photosensitive color-changing nano-microsphere material, which has a core-shell structure, wherein the core is composed of nano-crystals of two spiropyran compounds represented by formula (a) and formula (b), and the shell is coated with a modified acrylate material; the mass ratio of the core to the shell is (1-2): (3-5), and the microsphere particle size is 7-15 nm;

[0007] The modified acrylic ester material is polymerized from polyvinyl butyral and acrylic ester monomers or styrene monomers, and the mass ratio of the two is (0.5-1.5): (2-5);

[0008] The mass ratio of the two spiropyran compounds of formula (a) and formula (b) is 1:(0.3-3);

[0009]

[0010] Where R = C 16 H 33 ;

[0011]

[0012] Where R = C 16 H 33 .

[0013] The photosensitive color-changing nano-microsphere material as described above, preferably, the acrylate monomer is selected from at least one of methacrylate styrene, methyl acrylate, ethyl acrylate, butyl acrylate, epoxy acrylate, isooctyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, methyl methacrylate, pentaerythritol tetraacrylate, ethoxylated nonylphenol acrylate, ethoxylated bisphenol A diacrylate, polyethylene glycol methacrylate, bisphenol A epoxy acrylate, bisphenol A-dimethacrylate glycidyl ester, triethylene glycol dimethacrylate and trimethylolpropane trimethacrylate;

[0014] In the photosensitive color-changing nanosphere material as described above, preferably, the styrene monomer is selected from styrene or methyl styrene.

[0015] In another aspect, the present invention provides a method for preparing the photosensitive color-changing nanocomposite microspheres as described above, the method comprising the following steps:

[0016] I. Preparation of color-changing solution: prepare a spiropyran color-changing solution by mixing spiropyran color-changing powder (a), spiropyran color-changing powder (b) and solvent in a mass ratio of (0.5-1.5):(0.5-1.5):(100-200);

[0017] II. Oil phase color change solution: polyvinyl butyral and acrylate monomers or styrene monomers are added to the spiropyran color change solution to obtain an oil phase color change solution; wherein the mass ratio of polyvinyl butyral, spiropyran color change powder and acrylate monomer is (0.5-1.5): (0.5-1.5): (2-5);

[0018] III. Preparation of O / W emulsion: preparing an aqueous solution by mixing an emulsifier with purified water in a mass ratio of (1-3):(200-500); homogenizing and emulsifying the aqueous solution and the oil phase solution to obtain an O / W emulsion; wherein the mass ratio of the oil phase solution to the aqueous solution is (1-2):(1-3);

[0019] IV. Preparation of core-shell nano-microspheres: Add carbodiimide crosslinking agent and initiator to O / W emulsion, keep warm at 25-40°C for 15-40 minutes, the spiropyran crystal core is coated in the polyacrylate shell to form a nano-core-shell structure, heat to 45-65°C for polymerization for 6-12 hours, filter, wash and dry to obtain nano-color-changing microsphere powder.

[0020] In the preparation method as described above, preferably, the solvent in step I is selected from at least one of isopentane, n-hexane, n-pentane, cyclohexane and petroleum ether.

[0021] In the preparation method as described above, preferably, the emulsifier in step III is selected from the group consisting of foam-free isomeric alcohol FT-625, diethyl phthalate, steareth-21, oleth-10, stearate PEG-100 and silicone oil emulsifiers.

[0022] In the preparation method as described above, preferably, the silicone oil emulsifier is selected from at least one of dimethyl silicone oil emulsifier, polydimethylsiloxane PEG-3, polydimethylsiloxane PEG-10, silicone emulsifier KF-6038 and Japan Shin-Etsu KF-6017 emulsifier.

[0023] In the preparation method as described above, preferably, the carbodiimide crosslinking agent in step IV is selected from polyethylene glycol monomethyl ether MPEG350, N,N-dimethylethanolamine, carbodiimide CDI-1171, carbodiimide XL-701 and carbodiimide INV-2000; and its usage is 1-3wt% of polyvinyl butyral.

[0024] In the preparation method as described above, preferably, the initiator in step IV is selected from at least one of dibenzoyl peroxide, diisopropyl peroxydicarbonate and azobisisobutyronitrile, and its amount is 0.3-0.6wt% of the amount of the acrylate monomer or the styrene monomer.

[0025] In one aspect, the present invention provides a spiropyran compound, the chemical structure of which is shown in formula (a):

[0026]

[0027] Where R = C 16 H 33 .

[0028] In another aspect, the present invention provides a method for preparing a compound of formula (a), the method comprising the steps of:

[0029] I. Under N2 protection, 4-hydroxyisophthalaldehyde and anhydrous ethanol are mixed, heated to reflux in an oil bath at 90-220°C, and an ethanol solution of 3,3-dimethyl-1′-hexadecyl-2-methyleneindole is added dropwise thereto, the reaction solution turns purple, and the heating and reflux are continued for 4-8 hours. After ethanol is evaporated, ether is added with stirring to completely dissolve the purple-red viscous substance, and water is added with stirring. After standing, the liquid is separated to remove the water therein, and the ether and a small amount of water are evaporated again to remove the ether and a small amount of water to obtain a light purple solid spiropyran compound c; wherein the weight ratio of 4-hydroxyisophthalaldehyde, 3,3-dimethyl-1′-hexadecyl-2-methyleneindole and anhydrous ethanol is (0.5-1):(2-5):(20-50);

[0030]

[0031] II. Take an appropriate amount of the spiropyran compound c and malonyl urea prepared in step I above and add them to a reaction vessel containing chloroform, N: protection, stir until completely dissolved, add dropwise a chloroform solution of pyridine, heat the reactants in an oil bath under reflux, cool to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash twice with water, extract the organic layer and evaporate to dryness to obtain a green solid powder; the weight ratio of malonyl urea, spiropyran compound c, pyridine and chloroform is (0.5-1): (0.7-1.5): (5-20): (50-150); the pyridine content in the pyridine solution is 3-5%.

[0032] The preparation method of the spiropyran compound (b) described in the present invention can refer to the method described in Patent ZL201711112631.2 "A Photochromic Optical Material".

[0033] The present invention starts from four aspects: raw material selection and synthesis, nano-crystal preparation, coating process optimization and color change performance regulation. First, in terms of raw material selection, a modified acrylate polymer can form chemical bonds or intermolecular forces with the surfaces of various materials, and the presence of polar groups makes the modified acrylate and the spiropyran compound more compatible in polarity, thereby improving the compatibility and binding force with the spiropyran nano-crystals. At the same time, the polymerization reaction rate can be slowed down, which is conducive to forming a uniform coating layer, thereby facilitating the control of the uniformity of the coating layer; secondly, in terms of nano-crystal preparation, the particle size and distribution are accurately controlled; the reaction conditions in the coating process are strictly controlled, such as temperature, pressure, reaction time, etc.; finally, the color change performance under different lighting environments is regulated and combined to overcome the shortcomings of traditional materials and meet the increasingly diverse application needs of materials.

[0034] The beneficial effects of the present invention are as follows:

[0035] First, the spiropyran compound (a) synthesized by the present invention is green in normal indoor light and colorless after ultraviolet light irradiation. The spiropyran compound (b) is colorless in normal indoor light and red after ultraviolet light irradiation. The two color-changing compounds have a significant complementary color effect. By precisely controlling the structure and optical properties of the material, the color complementation of red and green is achieved. The optical material prepared by the material can improve the accuracy and saturation of the color, making the image more realistic and vivid.

[0036] Secondly, the material has good light filtering properties. Using it to prepare optical materials can effectively filter light of specific wavelengths and adjust the color balance of light entering the eyes or optical devices. In the calibration of optical components, the alternating red and green color enhancement can regulate the visual nerves and avoid visual fatigue caused by long-term single color.

[0037] Third, wide applicability. The nanocrystal core size is uniform and controllable, the modified shell is transparent and stable, the optical performance is good, and the preparation process is simple and efficient, low energy consumption, low pollution, with the characteristics of small dosage, low cost and wide application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the infrared spectrum of the spiropyran color-changing powder (a) prepared in Preparation Example 1.

[0039] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the spiropyran color-changing powder (a) prepared in Preparation Example 1.

[0040] Figure 3 This is a transmission electron microscope photograph of the photosensitive color-changing nanocomposite microspheres prepared in Example 1.

[0041] Figure 4 This is the infrared spectrum of the photosensitive color-changing nanocomposite microspheres prepared in Example 1.

[0042] Figure 5 This is the absorption spectrum of the spiropyran color-changing powder (a) prepared in Preparation Example 1.

[0043] Figure 6 This is the absorption spectrum of the spiropyran color-changing powder (b) prepared in Preparation Example 1.

[0044] Figure 7 This is the absorption spectrum of the photosensitive color-changing nanocomposite microspheres prepared in Example 1. DETAILED DESCRIPTION

[0045] The present invention is further described below by means of specific examples, but this is not intended to limit the protection scope of the present invention.

[0046] The spiropyran photochromic compounds in the following examples and comparative examples are prepared by the following method: Preparation Example 1

[0047] 1. Preparation of spiropyran photochromic compounds (a)

[0048] A. Under N2 protection, 250 g of 4-hydroxyisophthalaldehyde was mixed with 11 kg of anhydrous ethanol, and the mixture was heated to reflux in an oil bath at 180°C. An ethanol solution containing 1400 g of 3,3-dimethyl-1′-hexadecyl-2-methyleneindole was added dropwise thereto. The reaction solution turned purple and was heated to reflux for 5.5 hours. After ethanol was evaporated, ether was added with stirring to completely dissolve the purple-red viscous substance. Water was then added with stirring. After standing, the mixture was separated to remove water. The mixture was evaporated to dryness again to remove ether and a small amount of water to obtain a pale purple solid spiropyran compound (c).

[0049] The specific reaction formula is as follows:

[0050]

[0051] B. Take 100 g of the compound of formula (c) and 45 g of malonylurea and add them to 8500 g of chloroform, protect with N2, stir until completely dissolved, add 920 g of chloroform solution of pyridine dropwise thereto, heat the reactants under reflux in an oil bath, cool to room temperature, adjust the pH to neutral with a small amount of dilute hydrochloric acid, wash with water twice, extract the organic layer, and evaporate to dryness to obtain 127 g of green solid powder, i.e., spiropyran photochromic compound (a).

[0052] The specific reaction formula is as follows:

[0053]

[0054] Infrared spectroscopy FT-IR test: The spiropyran photochromic compound (a) prepared in Preparation Example 1 was subjected to Fourier transform infrared spectroscopy FT-IR) test. The results are as follows: Figure 1 shown. Figure 1Spectral analysis shows that 3395cm -1 and 3250cm -1 The absorption peaks at 2919 and 2846 cm are caused by the stretching and bending vibrations of amino groups. -1 The absorption peak at 1640cm-1 is caused by the stretching vibration and bending vibration of amide carbonyl; the absorption peak at 1460cm-1 is caused by the stretching vibration and bending vibration of amide carbonyl; 1 The absorption peak is caused by the stretching vibration of the carbon-carbon double bond; 1103cm- 1 The absorption peak is caused by the stretching vibration of CO.

[0055] 1H NMR (δ) analysis: The spiropyran photochromic compound (a) prepared in Preparation Example 1 was subjected to H NMR spectrum analysis. Figure 2 As shown, 8.20 (s, 1H) is a hydrogen on the double bond between malonylurea and the benzene ring, 8.07 (d, 1H), 7.53 (d, 1H), 7.08 (d, 1H), δ = 7.08 ~ 8.07 ppm are three hydrogens on the connected benzene rings; 7.49 (d, 1H), 7.18 (t, 1H), 6.85 (t, 1H), δ = 6.85 ~ 7.49 ppm are three hydrogens on the indole benzene ring respectively; 1.622 (s, 6H) is six hydrogens on two substituted methyl groups on the five-membered ring; 1.55 (multiple peaks, 2H) is two hydrogens on the long chain position connected to the nitrogen atom; 1.26 (broad peak, 26H) is hydrogen on multiple methylene groups on the long chain; 0.89 (t, 3H) is three hydrogens on the terminal methyl group of the long chain, which partially overlap.

[0056] 2. Preparation of spiropyran photochromic compounds (b)

[0057] Heat 250 g of 2-hydroxy-1-naphthaldehyde ethanol solution in an oil bath, heat to 60°C under nitrogen protection until reflux, add dropwise 25 g of 3,3-dimethyl-1′-hexadecyl-2-methyleneindole ethanol solution, continue to reflux for 9 hours, cool to room temperature, evaporate the solvent and concentrate to 40%, seal and place in an ice bath at -2°C for 15 hours, filter, elute and dry to obtain a spiropyran photochromic compound (b).

[0058] Example 1: Preparation of photosensitive color-changing nanospheres

[0059] (1) Dissolve 2.5 g of spiropyran color-changing powder (a) and 1.8 g of spiropyran color-changing powder (b) in a mixed solvent of 45 g of isopentane and 130 g of petroleum ether to obtain a spiropyran solution.

[0060] (2) 4.2 g of polyvinyl butyral and 14.5 g of methyl methacrylate monomer were added to the above spiropyran solution to obtain an oil phase solution.

[0061] (3) 1.8 g of silicone emulsifier KF-6038 was added to 650 g of pure water, and the aqueous phase solution and the oil phase solution were homogenized and emulsified to obtain an O / W emulsion.

[0062] (4) Preparation of core-shell nanospheres: 0.07 g of carbodiimide XL-701 and 0.06 g of diisopropyl peroxydicarbonate were added to the O / W emulsion and reacted at 26°C for 30 min. The spiropyran crystal core was encapsulated in the polyacrylate shell to form a nano core-shell structure. The temperature was raised to 55°C for polymerization for 10 h. The mixture was filtered, washed and dried to obtain photosensitive color-changing nanosphere powder.

[0063] Structure and morphology detection: The product prepared in Example 1 was observed using a JEM-2100 transmission electron microscope. Figure 3 As shown, the appearance is spherical, wherein the dark green core is composed of many uniformly sized, monodispersed spiropyran crystal nuclei, and the transparent layer is a modified acrylic shell, which can be attributed to the composite core-shell structure formed by the aggregation of spiropyran nanocrystals and the coating of acrylic ester. Since the acrylic ester outer shell is a colorless and transparent material, it shows a white outline in the transmission electron microscope photo. The spiropyran crystal size and the size of the nanocomposite microspheres are obtained by Scherrer formula (D = K / βcoSθ) and Zeta potential analysis and calculation, wherein the diameter of the spiropyran core is about 7.5nm, the thickness of the acrylic ester shell is about 2.6nm, and the diameter of the entire composite microsphere is about 12.7nm.

[0064] Infrared spectrum FT-IR test: The product prepared in Example 1 was subjected to Fourier transform infrared spectrum FT-IR) test. Figure 4 The curve analysis shows that at 3395cm- 1 and 3250cm- 1 The absorption peaks at 2915 and 2846 cm- 1 The absorption peaks are generated by the stretching vibration of methyl and methylene; 1733cm, 1610- 1 cm and 1090cm -1 The strong peak at 810.60 is the vibration of C=O, which is the characteristic absorption peak of acrylate, indicating that the nanocomposite microspheres prepared in Example 1 are not a single spiropyran substance; -1 The absorption peak at cm is caused by the skeleton vibration of the benzene ring in the molecule.

[0065] Example 2: Preparation of photosensitive color-changing nanospheres

[0066] (1) Dissolve 1.3 g of spiropyran color-changing powder (a) and 1.2 g of spiropyran color-changing powder (b) in 180 g of petroleum ether solvent to obtain a spiropyran solution.

[0067] (2) 6 g of polyvinyl butyral and 14.5 g of pentaerythritol tetraacrylate monomer were added to the above spiropyran solution to obtain an oil phase solution.

[0068] (3) 1.8 g of polydimethylsiloxane PEG-10 emulsifier was added to 620 g of pure water, and the aqueous phase solution and the oil phase solution were homogenized and emulsified to obtain an O / W emulsion.

[0069] (4) Preparation of core-shell nanospheres: 0.08 g of carbodiimide CDI-1171 and 0.07 g of diisopropyl peroxydicarbonate were added to the O / W emulsion and reacted at 35°C for 35 min. The spiropyran crystal core was encapsulated in the polyacrylate shell to form a nano core-shell structure. The temperature was raised to 55°C for polymerization for 10 h. The mixture was filtered, washed, and dried to obtain photosensitive color-changing nanosphere powder.

[0070] Example 3: Preparation of photosensitive color-changing nanospheres

[0071] (1) 3.0 g of spiropyran color-changing powder (a) and 3.0 g of spiropyran color-changing powder (b) were dissolved in a mixed solvent of 190 g of isopentane and 230 g of n-pentane to obtain a spiropyran solution.

[0072] (2) 5.5 g of polyvinyl butyral and 16.5 g of hydroxypropyl methacrylate monomer were added to the above spiropyran solution to obtain an oil phase solution.

[0073] (3) 1.9 g of silicone emulsifier KF-6038 was added to 750 g of pure water, and the aqueous phase solution and the oil phase solution were homogenized and emulsified to obtain an O / W emulsion.

[0074] (4) Preparation of core-shell nanospheres: 0.06 g of carbodiimide CDI-1171 and 0.09 g of diisopropyl peroxydicarbonate were added to the O / W emulsion and reacted at 30°C for 30 min. The spiropyran crystal core was encapsulated in the polyacrylate shell to form a nano core-shell structure. The temperature was raised to 55°C for polymerization for 10 h. The mixture was filtered, washed, and dried to obtain photosensitive color-changing nanosphere powder.

[0075] Example 4: Preparation of photosensitive color-changing nanospheres

[0076] (1) 4.0 g of spiropyran color-changing powder (a) and 3.5 g of spiropyran color-changing powder (b) were dissolved in a mixed solvent of 180 g of n-pentane and 350 g of petroleum ether to obtain a spiropyran solution.

[0077] (2) 4.5 g of polyvinyl butyral and 16.5 g of epoxy acrylate monomer were added to the above spiropyran solution to obtain an oil phase solution.

[0078] (3) 2.0 g of polydimethylsiloxane PEG-10 was added to 750 g of pure water, and the aqueous phase solution and the oil phase solution were homogenized and emulsified to obtain an O / W emulsion.

[0079] (4) Preparation of core-shell nanospheres: 0.07 g of carbodiimide XL-701 and 0.08 g of diisopropyl peroxydicarbonate were added to the O / W emulsion and reacted at 33°C for 35 min. The spiropyran crystal core was encapsulated in the polyacrylate shell to form a nano core-shell structure. The temperature was raised to 55°C for polymerization for 10 h. The mixture was filtered, washed and dried to obtain photosensitive color-changing nanosphere powder.

[0080] Example 5: Preparation of photosensitive color-changing nanospheres

[0081] (1) Dissolve 1.5 g of spiropyran color-changing powder (a) and 1.5 g of spiropyran color-changing powder (b) in 180 g of petroleum ether solvent to obtain a spiropyran solution.

[0082] (2) 5.5 g of polyvinyl butyral and 13.0 g of hydroxypropyl methacrylate monomer were added to the above spiropyran solution to obtain an oil phase solution.

[0083] (3) 2.2 g of polydimethylsiloxane PEG-10 was added to 620 g of pure water, and the aqueous phase solution and the oil phase solution were homogenized and emulsified to obtain an O / W emulsion.

[0084] (4) Preparation of core-shell nanospheres: 0.07 g of carbodiimide CDI-1171 and 0.06 g of diisopropyl peroxydicarbonate were added to the O / W emulsion and reacted at 35°C for 30 min. The spiropyran crystal core was encapsulated in the polyacrylate shell to form a nano core-shell structure. The temperature was raised to 55°C for polymerization for 10 h. The mixture was filtered, washed and dried to obtain photosensitive color-changing nanosphere powder.

[0085] Example 6: Preparation of photosensitive color-changing nanospheres

[0086] (1) 2.2 g of spiropyran color-changing powder (a) and 3.1 g of spiropyran color-changing powder (b) were dissolved in a mixed solvent of 110 g of isopentane and 220 g of petroleum ether to obtain a spiropyran solution.

[0087] (2) 6.0 g of polyvinyl butyral and 13.5 g of epoxy acrylate monomer were added to the above spiropyran solution to obtain an oil phase solution.

[0088] (3) 2.5 g of silicone emulsifier KF-6038 was added to 650 g of pure water, and the aqueous phase solution and the oil phase solution were homogenized and emulsified to obtain an O / W emulsion.

[0089] (4) Preparation of core-shell nanospheres: 0.08 g of carbodiimide XL-701 and 0.07 g of diisopropyl peroxydicarbonate were added to the O / W emulsion and reacted at 26°C for 30 min. The spiropyran crystal core was encapsulated in the polyacrylate shell to form a nano core-shell structure. The temperature was raised to 55°C for polymerization for 10 h. The mixture was filtered, washed and dried to obtain photosensitive color-changing nanosphere powder.

[0090] Example 7: Photochromic performance test

[0091] Take the color-changing powder samples prepared in the Preparation Example and the Example, dissolve them in a dichloromethane solution containing 10% styrene, the concentration of the color-changing powder is 0.2wt%, and pour them into multiple glass test tubes. After marking, put them into the test box respectively, turn on the solar simulator light source, record the color change of the sample and the time required, turn off the simulated light source, record the color change of the sample and the time required, and the test results are shown in Table 1.

[0092] Test conclusion:

[0093] 1. The solution of spiropyran color-changing powder a is green under normal light in the room, but becomes colorless after ultraviolet light irradiation, and gradually returns to green after a few minutes of returning to the room. The color-changing solution changes color under visible light.

[0094] 2. The solution of spiropyran color-changing powder b is colorless under normal indoor light, turns red after ultraviolet light irradiation, and gradually returns to colorless after the irradiation stops. This color-changing solution changes color under ultraviolet light irradiation.

[0095] 3. The photosensitive color-changing nano-microsphere solution is green in normal indoor light, and gradually turns yellow and finally red after ultraviolet light irradiation. The microsphere solution can change color not only under ultraviolet light irradiation, but also under visible light, that is, it can automatically achieve red and green alternating complementary color changes under different light conditions.

[0096] Table 1 Photosensitive color change of test samples

[0097]

[0098] Example 8: UV-Visible Absorption Spectrum Detection

[0099] Take the spiropyran color-changing powder a, spiropyran color-changing powder b and photosensitive color-changing nano-microsphere samples prepared in Preparation Example 1 and Example 1, dissolve them in a dichloromethane solution containing 10% styrene, the color-changing powder concentration is 0.1wt%, and pour them into multiple glass test tubes. After marking, irradiation detection is performed separately. Irradiation is performed at room temperature for 15 minutes. The distance between the solution and the light source is 20CM. The absorption spectrum of the solution before and after irradiation is recorded. The detection is as follows: Figure 5 , Figure 6 and Figure 7 The test results show that:

[0100] 1. The absorption peak of spiropyran color-changing powder a solution in the ultraviolet region is strong in the range of 200-280nm, the absorption peak in the ultraviolet region of 300-380nm gradually weakens, the absorption peak in the blue light region of 400-480nm gradually increases, there is a certain absorption in the red light region of 600-750nm, and there is basically no absorption in the green light region of 540-590nm.

[0101] 2. The absorption peak of spiropyran color-changing powder b solution in the ultraviolet region below 330nm is relatively strong, the absorption gradually weakens in the spectral region of 350-490nm, there is a small amount of absorption in the green region of 510-560nm, and there is basically no absorption in the red region above 640nm.

[0102] 3. The solution of photosensitive color-changing nano-microspheres has a strong absorption peak in the ultraviolet region below 350nm, a certain absorption in the spectral range of 360-490nm, and basically no absorption in the spectral range of 500-780nm, indicating that the transmittance of the green and red light bands is high, and the sensitivity to red and green colors is relatively high.

[0103] The photosensitive color-changing nano-microspheres are prepared into a coating liquid, which can improve the resolution of red and green colors under different light environments.

Claims

1. A photosensitive color-changing nano-microsphere material, characterized in that: The material has a core-shell structure, wherein the core is composed of nano-crystals of two spiropyran compounds represented by formula (a) and formula (b), and the shell is coated with a modified acrylic ester material; the mass ratio of the core to the shell is (1-2): (3-5), and the particle size of the microspheres is 7-15 nm; The modified acrylic ester material is polymerized from polyvinyl butyral and acrylic ester monomers or styrene monomers, and the mass ratio of the two is (0.5-1.5): (2-5); The mass ratio of the two spiropyran compounds of formula (a) and formula (b) is 1:(0.3-3); Where R = C 16 H 33 ; Where R = C 16 H 33 .

2. The photosensitive color-changing nano-microsphere material according to claim 1, characterized in that: The acrylic acid ester monomer is selected from at least one of methacrylate styrene, methyl acrylate, ethyl acrylate, butyl acrylate, epoxy acrylate, isooctyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, methyl methacrylate, pentaerythritol tetraacrylate, ethoxylated nonylphenol acrylate, ethoxylated bisphenol A diacrylate, polyethylene glycol methacrylate, bisphenol A epoxy acrylate, bisphenol A-dimethacrylate glycidyl ester, triethylene glycol dimethacrylate and trimethylolpropane trimethacrylate; The styrene monomer is selected from styrene or methylstyrene.

3. The method for preparing photosensitive color-changing nanocomposite microspheres according to claim 1 or 2, characterized in that: The method comprises the following steps: I. Preparation of color-changing solution: prepare a spiropyran color-changing solution by mixing spiropyran color-changing powder (a), spiropyran color-changing powder (b) and solvent in a mass ratio of (0.5-1.5):(0.5-1.5):(100-200); II. Oil phase color change solution: polyvinyl butyral and acrylate monomers or styrene monomers are added to the spiropyran color change solution to obtain an oil phase color change solution; wherein the mass ratio of polyvinyl butyral, spiropyran color change powder and acrylate monomer is (0.5-1.5): (0.5-1.5): (2-5); III. Preparation of O / W emulsion: preparing an aqueous solution by mixing an emulsifier with purified water in a mass ratio of (1-3):(200-500); homogenizing and emulsifying the aqueous solution and the oil phase solution to obtain an O / W emulsion; wherein the mass ratio of the oil phase solution to the aqueous solution is (1-2):(1-3); IV. Preparation of core-shell nano-microspheres: Add carbodiimide crosslinking agent and initiator to O / W emulsion, keep warm at 25-40°C for 15-40 minutes, the spiropyran crystal core is coated in the polyacrylate shell to form a nano-core-shell structure, heat to 45-65°C for polymerization for 6-12 hours, filter, wash and dry to obtain nano-color-changing microsphere powder.

4. The preparation method according to claim 3, characterized in that: The solvent in step I is selected from at least one of isopentane, n-hexane, n-pentane, cyclohexane and petroleum ether.

5. The preparation method according to claim 3, characterized in that: The emulsifier in step III is selected from the group consisting of foam-free isomeric alcohol FT-625, diethyl phthalate, steareth-21, oleth-10, stearate PEG-100 and silicone oil emulsifiers.

6. The preparation method according to claim 5, characterized in that: The silicone oil emulsifier is selected from at least one of dimethyl silicone oil emulsifier, polydimethylsiloxane PEG-3, polydimethylsiloxane PEG-10, silicone emulsifier KF-6038 and Japan Shin-Etsu KF-6017 emulsifier.

7. The preparation method according to claim 3, characterized in that: The carbodiimide crosslinking agent in step IV is selected from polyethylene glycol monomethyl ether MPEG350, N,N-dimethylethanolamine, carbodiimide CDI-1171, carbodiimide XL-701 and carbodiimide INV-2000; and its usage is 1-3wt% of polyvinyl butyral.

8. The preparation method according to claim 3, characterized in that: The initiator in step IV is selected from at least one of dibenzoyl peroxide, diisopropyl peroxydicarbonate and azobisisobutyronitrile, and its usage is 0.3-0.6wt% of the usage of the acrylic acid ester monomer or the styrene monomer.

9. A spiropyran compound, characterized in that: Its chemical structure is shown in formula (a): Where R = C 16 H 33 .

10. The method for preparing the compound of formula (a) as claimed in claim 9, characterized in that: The method comprises the following steps: I. Under N2 protection, 4-hydroxyisophthalaldehyde and anhydrous ethanol are mixed, heated to reflux in an oil bath at 90-220°C, and an ethanol solution of 3,3-dimethyl-1′-hexadecyl-2-methyleneindole is added dropwise thereto, the reaction solution turns purple, and the heating and reflux are continued for 4-8 hours. After ethanol is evaporated, ether is added with stirring to completely dissolve the purple-red viscous substance, and water is added with stirring. After standing, the liquid is separated to remove the water therein, and the ether and a small amount of water are evaporated again to remove the ether and a small amount of water to obtain a light purple solid spiropyran compound c; wherein the weight ratio of 4-hydroxyisophthalaldehyde, 3,3-dimethyl-1′-hexadecyl-2-methyleneindole and anhydrous ethanol is (0.5-1):(2-5):(20-50); II. Take an appropriate amount of the spiropyran compound c and malonyl urea prepared in step I above and add them to a reaction vessel containing chloroform, protect with N2, stir until completely dissolved, add dropwise a chloroform solution of pyridine, heat the reactants in an oil bath under reflux, cool to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash twice with water, extract the organic layer and evaporate to dryness to obtain a green solid powder; the weight ratio of malonyl urea, spiropyran compound c, pyridine and chloroform is (0.5-1): (0.7-1.5): (5-20): (50-150); the pyridine content in the pyridine solution is 3-5%.

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