Fluorescent dye doped cholesteric liquid crystal microcapsule and preparation method thereof

Abstract

The invention relates to a fluorescent dye doped cholesteric liquid crystal microcapsule and a preparation method thereof, and belongs to the technical field of functional material preparation. The microcapsule is prepared by taking cholesteric liquid crystal doped with fluorescent dye as a core material and a high polymer material as a wall material through an interfacial polymerization method. The microcapsule is uniform in particle size (10-150 [mu] m), is spherical in appearance, and has excellent physical and chemical stability, optical performance and mechanical strength. The cholesteric liquid crystal in the core material forms a periodic spiral structure through the synergistic effect of the chiral agent and the micromolecular nematic liquid crystal, the cholesteric liquid crystal is doped with the fluorescent dye to generate remarkable color regulation and control capability and fluorescence characteristics, and meanwhile, the microcapsule is endowed with cpl performance. By optimizing the process conditions of emulsification, stirring, reaction and the like and regulating and controlling the concentration of the fluorescent dye, the microcapsule shows remarkable fluorescent response and excellent environmental adaptability under a multi-band excitation light source. The preparation method provided by the invention is efficient, simple and convenient, the concentration of the fluorescent dye can be regulated and controlled according to actual requirements, and precise anti-counterfeiting application of low-concentration doping and strong fluorescent anti-counterfeiting and sensor application of high-concentration doping are realized. The method has a wide application prospect in the fields of optical display, anti-counterfeiting technology and sensing.

Description

Technical Field

[0001] The present invention relates to a cholesteric liquid crystal microcapsule doped with a fluorescent dye and a preparation method thereof; this technology provides an innovative solution for the development of display technology, anti-counterfeiting labels, and optical functional materials by combining the optical properties of liquid crystals, the fluorescence properties of dyes, and the reflected colors of dyes; it belongs to the technical field of functional material preparation. Background Art

[0002] Cholesteric liquid crystals have broad application prospects in the fields of optical display and information storage due to their unique circular dichroism and selective reflection properties. However, the poor physical and chemical stability of traditional cholesteric liquid crystal materials and their sensitivity to the external environment (such as heat, light, and pH) limit their application under complex conditions.

[0003] To solve this problem, in recent years, researchers have encapsulated cholesteric liquid crystals in polymer shells through microencapsulation technology to improve their stability and processability.

[0004] Fluorescent dyes, due to their excellent optical properties, are widely used in optical labeling and anti-counterfeiting technologies. Doping fluorescent dyes into cholesteric liquid crystals can not only endow the liquid crystal material with an additional luminescent function but also regulate the fluorescence characteristics through the selective reflection and circularly polarized light effects of cholesteric liquid crystals, thereby significantly enhancing the optical properties of the overall material. In addition, this combination can also utilize the energy transfer mechanism of fluorescent dyes to enhance the stability and functional performance of liquid crystal materials in complex optical environments.

[0005] However, the molecular thermal stability and environmental adaptability of fluorescent dyes still have limitations. Especially when combined with liquid crystal materials, the uniform dispersion and stability of dyes become technical difficulties.

[0006] Therefore, how to combine cholesteric liquid crystals with fluorescent dyes through a simple and efficient microencapsulation method to form functional microcapsules with excellent optical properties and stability has become a hot and difficult point in current materials science research. Summary of the Invention

[0007] The present invention aims to overcome the deficiencies in the prior art and provides a cholesteric liquid crystal microcapsule doped with a fluorescent dye and a preparation method thereof. By optimizing the preparation process of the microcapsules and the dye doping method, the optical properties and stability of the microcapsules are significantly improved, and their application potential in the fields of display, anti-counterfeiting, and sensing is expanded.

[0008] The above object of the present invention is achieved by the following technical solutions:

[0009] A cholesteric liquid crystal microcapsule doped with a fluorescent dye, characterized in that the microcapsule comprises:

[0010] (1) Core material: Cholesteric liquid crystal obtained by thoroughly mixing fluorescent dyes with different concentrations under the assistance of a solvent for melting;

[0011] (2) Shell material: Formed from a polymer material, which is coated on the outside of the core material by interfacial polymerization and has high transparency and excellent mechanical properties;

[0012] Preferably, the microcapsules have a spherical structure with a particle size of 10 - 150 μm and exhibit significant fluorescence emission characteristics and CPL (circularly polarized light) characteristics under the excitation of a multi-band light source.

[0013] Preferably, the fluorescent dye is Rhodamine 6G (R6G), and its mass is 0.01% - 1% of the total mass of the cholesteric liquid crystal, where 0.01% - 0.15% is low-concentration doping, suitable for anti-counterfeiting display applications that emphasize structural color and fluorescent color; 0.15% - 1% is high-concentration doping, meeting anti-counterfeiting or sensing applications with higher requirements for the intensity of fluorescent signals.

[0014] Preferably, the cholesteric liquid crystal includes: the chiral agent is S5011 or R5011, and the small molecule nematic liquid crystal is NC-M-LC720600 or HNG717200-000.

[0015] Preferably, the mass percentage of the chiral agent is 2.21% - 3.71%, and the mass percentage of the small molecule nematic liquid crystal is 96.29% - 97.79%.

[0016] Preferably, the shell material is formed by thermal initiation of methyl methacrylate and azobisisoheptonitrile. The mass ratio of methyl methacrylate to cholesteric liquid crystal is 1:2 - 2:1, and the mass percentage of azobisisoheptonitrile is 0.05% - 1%.

[0017] Another object of the present invention is to provide a method for preparing the above-mentioned cholesteric liquid crystal microcapsules doped with fluorescent dyes.

[0018] The above object of the present invention is achieved by the following technical solutions:

[0019] A method for preparing cholesteric liquid crystal microcapsules doped with fluorescent dyes, by selecting a suitable solvent and temperature increase conditions, uniformly dispersing the fluorescent dye in the cholesteric liquid crystal while maintaining the self-assembly characteristics and optical properties of the liquid crystal; the steps are as follows:

[0020] (1) Thoroughly mix the chiral agent and the small molecule nematic liquid crystal to prepare cholesteric liquid crystals of different colors;

[0021] (2) Add a fluorescent dye to step (1), add dichloromethane and mix well. Then, pre-set the temperature of the oil bath to 40°C - 49°C, put the cholesteric liquid crystal doped with the fluorescent dye into it, and stir magnetically at a low speed for 1 h - 3 h (2 h). Allow dichloromethane to evaporate completely. Subsequently, set the temperature of the oil bath above the clearing point temperature of the liquid crystal, continue magnetic stirring for 1 h - 3 h (2 h), and finally turn off the temperature and slowly cool it to room temperature;

[0022] (3) Thoroughly mix a cholesteric liquid crystal of one color that has been doped with a fluorescent fuel with methyl methacrylate and 2,2'-azobis(2-methylbutyronitrile), add a small amount of dichloromethane, and quickly assist in melting to obtain a core-shell material mixture;

[0023] (4) Add an aqueous PVA solution to the flask and pre-heat it to 50°C - 70°C (60°C);

[0024] (5) Slowly drop the core-shell material mixture prepared in step (3) into step (4) at a rate of 0.1 ml / min - 1.0 ml / min (0.5 ml / min), while performing magnetic stirring and emulsifying for a certain period of time. After emulsification, raise the temperature to 70°C - 90°C (80°C) and react for 2 h - 8 h (5 h). After the time ends, turn off the temperature and perform annealing until room temperature, without turning off the magnetic stirring during this period;

[0025] (6) For the microcapsule product after annealing, first dilute it with deionized water, centrifuge it to obtain a microcapsule concentrate. Then, take out the microcapsule concentrate, rinse it with deionized water multiple times, and precipitate repeatedly until the microcapsule aqueous solution is clear. Centrifuge it again to obtain a clean microcapsule concentrate, or directly dry it to obtain a clean microcapsule product.

[0026] Preferably, in step (1), the chiral agent is S5011 or R5011 (Jiangsu HeCheng Display Materials Co., Ltd.), the small molecule nematic liquid crystal is NC-M-LC720600 (Nanjing NingCui Optoelectronic Technology Co., Ltd.) or HNG717200-000 (Jiangsu HeCheng Display Materials Co., Ltd.), the percentage of the chiral agent in the cholesteric liquid crystal is 2.21% - 3.71% (that is, it accounts for 2.21% - 3.71% of the total mass of the cholesteric liquid crystal, the same below), and the percentage of the small molecule nematic liquid crystal in the cholesteric liquid crystal is 96.29% - 97.79%.

[0027] Preferably, the fluorescent dye in step (2) is rhodamine 6G (R6G purchased from Shanghai McLean Biochemical Technology Co., Ltd.), and dichloromethane is purchased from Shanghai McLean Biochemical Technology Co., Ltd. The temperature above the clearing point of the liquid crystal is: 100°C-110°C for NC-M-LC720600 (Nanjing Ningcui Optical Technology Co., Ltd.); 82°C-92°C for HNG717200-000 (Jiangsu Hecheng Display Materials Co., Ltd.); the fluorescent dye is 0.01%-1% of the total mass of the cholesteric liquid crystal, 0.01%-0.15% is considered a low concentration, and 0.15%-1% is considered a high concentration; the amount of dichloromethane is more than 25% of the total mass of the cholesteric liquid crystal.

[0028] Preferably, in step (3), the mass ratio of cholesteric liquid crystal to methyl methacrylate (Shanghai Aladdin Biochemical Technology Co., Ltd.) is 2:1-1:2, the azobisisoheptanenitrile (Shanghai Aladdin Biochemical Technology Co., Ltd.) accounts for 0.625%-14% of the mass of methyl methacrylate, and the amount of dichloromethane is more than 25% of the total mass of the cholesteric liquid crystal.

[0029] Preferably, in step (4), the mass percentage of the PVA (type 1788, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) is 2%-9% (the mass percentage refers to the proportion of PVA in 100g of water).

[0030] Preferably, in step (5), the stirring speed is 800 rpm-1400 rpm (MS-H340-S4, from Dalong Xingchuang Experimental Instrument (Beijing) Co., Ltd.), and the emulsification time is more than 30 min.

[0031] Another object of the present invention is to provide a method for preparing a fluorescent dye-doped cholesteric liquid crystal microcapsule film, and to propose an optimization scheme suitable for different application scenarios according to the doping requirements of different fluorescent dye concentrations; low-concentration fluorescent dye doping is suitable for anti-counterfeiting display applications that emphasize structural color and fluorescent color, and high-concentration fluorescent dye doping meets anti-counterfeiting or sensing applications that require higher fluorescent signal intensity; high- and low-concentration fluorescent dye-doped cholesteric liquid crystal microcapsules can be excited by multiple excitation bands, and can be made into thin films as an observation method, and the scheme is as follows:

[0032] A method for preparing a fluorescent dye-doped cholesteric liquid crystal microcapsule film comprises the following steps:

[0033] (1) fully mixing a chiral agent and a small molecule nematic phase liquid crystal to prepare cholesteric phase liquid crystals of different colors;

[0034] (2) Add a fluorescent dye to step (1). The mass percentage of the fluorescent dye is not included in the mass of the cholesteric liquid crystal in step (1). Then add dichloromethane and mix well. Next, pre-set the temperature of the oil bath to 40°C - 49°C, put the cholesteric liquid crystal doped with the fluorescent dye into it, and stir magnetically at a low speed for 1 h - 3 h (2 h). Let the dichloromethane evaporate completely. Subsequently, set the temperature of the oil bath above the clearing point temperature of the liquid crystal and continue magnetic stirring for 1 h - 3 h (2 h). Finally, turn off the temperature and slowly cool it to room temperature;

[0035] (3) Thoroughly mix a cholesteric liquid crystal of one color that has been doped with a fluorescent fuel with methyl methacrylate and 2,2'-azobis(2-methylbutyronitrile), add a small amount of dichloromethane, and quickly assist in melting to obtain a core-shell material mixture;

[0036] (4) Add an aqueous PVA solution to the flask and pre-heat it to 50°C - 70°C (60°C);

[0037] (5) Slowly drop the core-shell material mixture prepared in step (3) into step (4) at a rate of 0.1 ml / min - 1.0 ml / min (0.5 ml / min) while performing magnetic stirring and emulsify for a certain period of time. After emulsification, raise the temperature to 70°C - 90°C (80°C) and react for 2 h - 8 h (5 h). After the time ends, turn off the temperature and perform annealing until it reaches room temperature, without turning off the magnetic stirring during this period;

[0038] (6) For the microcapsule product after annealing, first dilute it with deionized water, centrifuge it to obtain a microcapsule concentrate. Then take out the microcapsule concentrate, rinse it with deionized water multiple times, and precipitate repeatedly until the microcapsule aqueous solution is clear. Centrifuge it again to obtain a clean microcapsule concentrate;

[0039] (7) Oscillate and mix the aqueous PVA solution, the microcapsule concentrate, and the surfactant in a certain proportion, and use the doctor blade method to dry it or air-dry it using a polytetrafluoroethylene template to obtain a film;

[0040] (8) Irradiate the film with a variety of excitation light sources and observe the emission wavelengths of the microcapsule films made with different concentrations of fluorescent dyes.

[0041] Preferably, in step (1), the chiral agent is S5011 or R5011 (Jiangsu HeCheng Display Materials Co., Ltd.), the small molecule nematic liquid crystal is NC-M-LC720600 (Nanjing NingCui Optoelectronic Technology Co., Ltd.) or HNG717200-000 (Jiangsu HeCheng Display Materials Co., Ltd.). The percentage of the chiral agent in the cholesteric liquid crystal is 2.21% - 3.71%, and the percentage of the small molecule nematic liquid crystal in the cholesteric liquid crystal is 96.29% - 97.79%.

[0042] Preferably, the fluorescent dye in step (2) is Rhodamine 6G (R6G is purchased from Shanghai Macklin Biochemical Co., Ltd.), dichloromethane is purchased from Shanghai Macklin Biochemical Co., Ltd., and the temperature above the clearing point of the liquid crystal: NC-M-LC720600 (Nanjing Ningcui Optoelectronic Technology Co., Ltd.) is 100°C - 110°C; HNG717200-000 (Jiangsu HeCheng Display Materials Co., Ltd.) is 82°C - 92°C; the fluorescent dye accounts for 0.01% - 1% of the total mass of the cholesteric liquid crystal, 0.01% - 0.15% is regarded as a low concentration, and 0.15% - 1% is regarded as a high concentration; the amount of dichloromethane is more than 25% of the total mass of the cholesteric liquid crystal.

[0043] Preferably, in step (3), the mass ratio of the cholesteric liquid crystal to methyl methacrylate (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) is 2:1 - 1:2, and azobisisobutyronitrile (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) accounts for 0.625% - 1.25% of the mass of methyl methacrylate; the amount of dichloromethane is more than 25% of the total mass of the cholesteric liquid crystal.

[0044] Preferably, in step (4), the mass percentage of the PVA (type 1788, purchased from Shanghai Macklin Biochemical Co., Ltd.) is 2% - 9% (this mass percentage refers to the proportion of PVA in 100 g of water).

[0045] Preferably, in step (5), the stirring speed is 800 rpm - 1400 rpm (MS-H340-S4, from DLAB Scientific Instruments (Beijing) Co., Ltd.), and the emulsification time is more than 30 min.

[0046] Preferably, in step (7), the concentration of the PVA aqueous solution is 5% - 15%; the surfactant is alkynediol or DuPont FS-63; the mass ratio of the PVA aqueous solution, microcapsules, and surfactant is 1 - 4:1:0.0005 - 0.001; the thickness of the film formed by the doctor blade method or polytetrafluoroethylene is 0.04 - 0.07 μm.

[0047] Preferably, in step (8), the excitation wavelengths are 340 nm, 360 nm, and 531 nm.

[0048] Another object of the present invention is to provide the application of the cholesteric liquid crystal microcapsules doped with the above fluorescent dye.

[0049] The above object of the present invention is achieved by the following technical solutions:

[0050] The application of the cholesteric liquid crystal microcapsules doped with fluorescent dyes in the fields of optical display, anti-counterfeiting labels, and optical sensors, etc.

[0051] Beneficial effects:

[0052] For the fluorescent dye-doped cholesteric liquid crystal microcapsules of the present invention, by optimizing the preparation process of the microcapsules and the dye doping method, the optical properties and stability of the microcapsules are significantly improved, and the application potential in the fields of display, anti-counterfeiting, and sensing is expanded. Specifically as follows:

[0053] 1. Different addition amounts of the chiral agents S5011 / R5011 will cause the liquid crystal system to present different colors. When the addition amount is 2.21 wt% (mass percentage in the cholesteric liquid crystal), the system presents red; when the addition amount is 2.70 wt% (mass percentage in the cholesteric liquid crystal), the system presents green; when the addition amount is 3.71 wt% (mass percentage in the cholesteric liquid crystal), the system presents blue. The color display of the microcapsules in different wavelength bands within the visible light range can be achieved by regulating the content of S5011 / R5011.

[0054] 2. The content of the initiator azodiisobutyronitrile is beneficial to the optical properties and mechanical properties of the microcapsules. For low content of the initiator (0.625%-4% of the mass of methyl methacrylate), the synthesized microcapsules have excellent optical properties but poor mechanical properties. The microcapsules synthesized with medium content (4%-9% of the mass of methyl methacrylate) of the initiator have relatively excellent optical and mechanical properties, while the microcapsules synthesized with high content (9%-14% of the mass of methyl methacrylate) of the initiator have poor optical properties and are hard and brittle.

[0055] 3. The addition of fluorescent dyes can effectively regulate the optical properties of the microcapsules, especially the luminescence characteristics within the visible light range. When a low concentration of fluorescent dye is incorporated, the microcapsules exhibit relatively distinct structural colors and fluorescent colors; when a high concentration of fluorescent dye is incorporated, the fluorescence intensity of the microcapsules is significantly enhanced, which can meet the requirements for high fluorescence intensity in anti-counterfeiting labels and sensing applications.

[0056] 4. The microcapsules of the present invention can exhibit different fluorescence emission characteristics under multiple excitation bands. The main excitation bands are 340 nm excitation, 360 nm excitation, and 531 nm excitation. 340 nm and 531 nm are two strong excitation wavelengths, while 360 nm is a commonly used excitation wavelength. The emission bands of the microcapsules are around 398 nm and 558 nm. By preparing a thin film and irradiating the microcapsules with a variety of excitation light sources, it is observed that the emission wavelength changes differently with the change of the fluorescent dye concentration. This characteristic enables the microcapsules to flexibly adjust their luminescence characteristics under different light sources and excitation bands, meeting the precise requirements in multi-field applications.

[0057] 5. The microcapsule material of the present invention inherently possesses circularly polarized light (CPL) characteristics. The self-assembled structure of the cholesteric liquid crystal and the doping of the fluorescent dye act synergistically, enabling the microcapsule to produce an optical response with distinct CPL characteristics; provided that the doping of the fluorescent dye is at a medium to low concentration. The blue microcapsules with a chiral agent content of 3.963% (mass percentage in the cholesteric liquid crystal) synthesized under low-concentration dye doping have an asymmetry factor (g value) in the emission wavelength range of 398 nm, while the green microcapsules with a chiral agent content of 2.71% (mass percentage in the cholesteric liquid crystal) synthesized under medium to low-concentration dye doping have an asymmetry factor (g value) in the emission wavelength range of 558 nm. By increasing the concentration of the fluorescent dye, the CPL characteristics of the microcapsule are significantly enhanced, endowing it with broad application potential in the fields of optical regulation and imaging, polarized light display, sensing, etc. In particular, by adjusting the g value, the microcapsules of the present invention can flexibly control their reflectivity and luminescence intensity under different polarized lights, providing an innovative solution for polarized light applications.

[0058] To make the objectives, technical solutions, and advantages of the present invention clearer, the following further elaborates on the present invention in detail with reference to the accompanying drawings and specific embodiments, but this does not mean any limitation to the protection scope of the present invention. Description of the Drawings

[0059] Figure 1 is a physical picture of the cholesteric liquid crystal microcapsules synthesized in Comparative Example 1 of the present invention;

[0060] Figure 2 is a schematic diagram of the preparation process of the fluorescent dye-doped cholesteric liquid crystal microcapsules of the present invention;

[0061] Figure 3 is the polarized light, bright field, dark field, scanning electron microscope, and EDS energy spectrum of N element of the fluorescent dye-doped cholesteric liquid crystal microcapsules in Example 2 of the present invention;

[0062] Figure 4 is the infrared spectrum of the fluorescent dye-doped cholesteric liquid crystal microcapsules, R6G fluorescent dye, methyl methacrylate (MMA), and cholesteric liquid crystal in Example 1 of the present invention;

[0063] Figure 5 is the physical picture of the films of the fluorescent dye-doped cholesteric liquid crystal microcapsules in Example 2 and Example 3 of the present invention and those doped with fluorescent dyes increasing by 0.0005 g concentration under different viewing angles, different substrates, and different irradiation environments;

[0064] Figure 6 is the g value measured after the low-concentration fluorescent dye cholesteric liquid crystal microcapsules in Example 1 of the present invention are made into a film. Detailed Embodiments

[0065] To better illustrate the technical solution of the present invention, the fluorescent dye-doped cholesteric liquid crystal microcapsules of the present invention and their preparation method are described in detail below in conjunction with specific embodiments. The materials and equipment used in the implementation process are all conventional experimental materials and equipment.

[0066] Comparative Example 1

[0067] As Figure 1 shown, cholesteric liquid crystal microcapsules of different colors are synthesized, and the preparation steps are as follows:

[0068] 1. Weigh 0.027 g of chiral agent S5011 (Jiangsu HeCheng Display Materials Co., Ltd.) and 0.973 g of small molecule nematic liquid crystal NC-M-LC720600 (Nanjing NingCui Optoelectronic Technology Co., Ltd.), add 250 μl of dichloromethane, adjust the temperature to 102 °C, and stir magnetically for 2 h to obtain green cholesteric liquid crystal;

[0069] 2. Weigh 4 g of PVA 1788 powder (Shanghai Macklin Biochemical Co., Ltd.) and 96 g of deionized water, and stir magnetically at 90 °C to obtain a 4% PVA aqueous solution;

[0070] 3. Take 60 ml of 4% PVA aqueous solution with a graduated cylinder and put it into a single-neck flask. Place the single-neck flask in a water bath and heat it to 60 °C without turning on magnetic stirring;

[0071] 4. Weigh 1.1 g of methyl methacrylate (Shanghai Aladdin Biochemical Technology Co., Ltd.) and 0.03 g of azodiisooctanenitrile, put them into the cholesteric liquid crystal in step 1, add 250 μl of dichloromethane, and stir magnetically for 15 min;

[0072] 5. Slowly drip the liquid crystal mixture in step 4 into the single-neck flask that has been heated to 60 °C in step 3 at a speed of 0.5 ml / min. During the dripping process, stir magnetically at 1400 rpm. After dripping, wait for emulsification for 50 min, then add a condenser, raise the reaction temperature to 80 °C, and react for 5 h to obtain the final microcapsule product. Turn off the temperature and continue magnetic stirring, and anneal to room temperature;

[0073] 6. Take out the microcapsule product in the single-neck flask, add 30 ml of deionized water, mix well, centrifuge, pour out the supernatant in the centrifuge tube to obtain a precipitated microcapsule concentrate. Take out the microcapsule concentrate, add deionized water again, mix, wait for the microcapsules to precipitate, suck off the supernatant with a pipette, and repeat multiple times until the supernatant after the mixture precipitates is no longer turbid. Centrifuge again to obtain a clean microcapsule concentrate.

[0074] Example 1

[0075] AsFigure 2 As shown in the figure, it is a schematic diagram of the preparation process of the fluorescent dye-doped cholesteric liquid crystal microcapsules in Embodiment 1 of the present invention. The specific steps are as follows:

[0076] 1. Weigh 0.027 g of chiral agent S5011 (Jiangsu HeCheng Display Materials Co., Ltd.) and 0.973 g of small molecule nematic liquid crystal NC-M-LC720600 (Nanjing NingCui Optoelectronic Technology Co., Ltd.), add 250 μl of dichloromethane, adjust the temperature to 102 °C, and stir magnetically for 2 h to obtain green cholesteric liquid crystal;

[0077] 2. Weigh 0.0001 g of R6G fluorescent dye, put it into the green cholesteric liquid crystal in step 1, add 250 μl of dichloromethane, put it into an oil bath pot preheated to 48 °C, stir magnetically at 200 rpm for 2 h. Wait for the dichloromethane to volatilize completely, then raise the temperature to 102 °C, stir magnetically at 780 rpm for 2 h, and then turn off the temperature and cool to room temperature to obtain the fluorescent dye-doped cholesteric liquid crystal;

[0078] 3. Weigh 5 g of PVA 1788 powder (Shanghai Macklin Biochemical Co., Ltd.) and 95 g of deionized water, stir magnetically at 90 °C to obtain a 5% PVA aqueous solution;

[0079] 4. Use a graduated cylinder to take 60 ml of 5% PVA aqueous solution, put it into a single-neck flask, and heat the single-neck flask in a water bath to 60 °C;

[0080] 5. Weigh 1.1 g of methyl methacrylate (Shanghai Aladdin Biochemical Technology Co., Ltd.) and 0.03 g of azodiisobutyronitrile, put them into the fluorescent dye-doped cholesteric liquid crystal in step 2, add 250 μl of dichloromethane, and stir magnetically for 15 min to obtain a liquid crystal mixture;

[0081] 6. Slowly drop the liquid crystal mixture in step 5 into the single-neck flask that has been heated to 60 °C in step 4 at a speed of 0.5 ml / min. During the dropping process, stir magnetically at 1400 rpm. After the dropping is completed, wait for emulsification for 50 min, then add a condenser, raise the reaction temperature to 80 °C, react for 5 h to obtain the final microcapsules. Turn off the temperature, continue magnetic stirring, and anneal to room temperature;

[0082] 7. Take out the microcapsule product in the single-neck flask, add 30 ml of deionized water, mix well, centrifuge, pour out the supernatant in the centrifuge tube to obtain the precipitated microcapsule product. Take out the product, add deionized water again to mix, wait for the microcapsules to precipitate, suck off the supernatant with a pipette, repeat multiple times until the supernatant after the mixture precipitates is no longer turbid, and centrifuge again to obtain a clean fluorescent dye-doped microcapsule concentrate;

[0083] 8. Mix the clean fluorescent dye-doped cholesteric liquid crystal microcapsule concentrate, PVA (10%), and DuPont FS-63 surfactant in a mass ratio of 1:1.5:0.0001 uniformly to make a coating. Suck it up with a dropper and place it in a polytetrafluoroethylene mold with a depth of 0.07 μm to air-dry for 10 h to obtain Film 1.

[0084] Example 2

[0085] Preparation of fluorescent dye-doped cholesteric liquid crystal microcapsules, the specific steps are as follows:

[0086] 1. Weigh 0.027 g of chiral agent S5011 (Jiangsu HeCheng Display Materials Co., Ltd.) and 0.973 g of small molecule nematic liquid crystal NC-M-LC720600 (Nanjing NingCui Optoelectronic Technology Co., Ltd.), add 250 μl of dichloromethane, adjust the temperature to 102 °C, and magnetically stir for 2 h to obtain green cholesteric liquid crystal;

[0087] 2. Weigh 0.001 g of R6G fluorescent dye, put it into the green cholesteric liquid crystal in Step 1, add 250 μl of dichloromethane, put it into an oil bath pot preheated to 48 °C, magnetically stir at 200 rpm for 2 h. Wait for the dichloromethane to fully volatilize, raise the temperature to 102 °C, magnetically stir at 780 rpm for 2 h, then turn off the temperature and cool to room temperature to obtain fluorescent dye-doped cholesteric liquid crystal;

[0088] 3. Weigh 5 g of PVA 1788 powder (Shanghai Macklin Biochemical Co., Ltd.) and 95 g of deionized water, and magnetically stir at 90 °C to obtain a 5% PVA aqueous solution;

[0089] 4. Use a graduated cylinder to take 60 ml of 5% PVA aqueous solution, put it into a single-neck flask, and place the single-neck flask in a water bath pot and heat it to 60 °C;

[0090] 5. Weigh 1.1 g of methyl methacrylate (Shanghai Aladdin Biochemical Technology Co., Ltd.) and 0.03 g of azodiisobutyronitrile, put them into the fluorescent dye-doped cholesteric liquid crystal in Step 2, add 250 μl of dichloromethane, and magnetically stir for 15 min to obtain a liquid crystal mixture;

[0091] 6. Slowly drip the liquid crystal mixture in Step 5 into the single-neck flask that has been heated to 60 °C in Step 4 at a speed of 0.5 ml / min. During the dripping process, magnetically stir at 1400 rpm. After dripping, wait for emulsification for 50 min, then add a condenser, raise the reaction temperature to 80 °C, react for 5 h to obtain the final microcapsules, turn off the temperature, continue magnetic stirring, and anneal to room temperature;

[0092] 7. Take out the microcapsule product in the single-neck flask, add 30 ml of deionized water, mix well, centrifuge, pour out the supernatant in the centrifuge tube, and obtain the precipitated microcapsule concentrate. Take out the microcapsule concentrate, add deionized water again and mix. Wait for the microcapsules to precipitate, suck off the supernatant with a pipette, and repeat several times until the supernatant after the mixture precipitates is no longer turbid. Centrifuge again to obtain a clean microcapsule concentrate doped with fluorescent dye;

[0093] 8. Uniformly mix the clean microcapsule concentrate doped with fluorescent dye, cholesteric liquid crystal, PVA (10%), and DuPont FS-63 surfactant in a mass ratio of 1:1.5:0.0001 to make a coating. Use a dropper to suck it up and place it in a polytetrafluoroethylene mold with a depth of 0.07 μm to air-dry for 10 h to obtain Film 2.

[0094] Example 3

[0095] Preparation of cholesteric liquid crystal microcapsules doped with fluorescent dye, the specific steps are as follows:

[0096] 1. Weigh 0.027 g of chiral agent S5011 (Jiangsu HeCheng Display Materials Co., Ltd.) and 0.973 g of small molecule nematic liquid crystal NC-M-LC720600 (Nanjing NingCui Optoelectronic Technology Co., Ltd.), add 250 μl of dichloromethane, adjust the temperature to 102 °C, and stir magnetically for 2 h to obtain green cholesteric liquid crystal;

[0097] 2. Weigh 0.003 g of R6G fluorescent dye, put it into the green cholesteric liquid crystal in step 1, add 250 μl of dichloromethane, put it into an oil bath pot preheated to 48 °C, stir magnetically at 200 rpm for 2 h. Wait for the dichloromethane to volatilize completely, raise the temperature to 102 °C, stir magnetically at 780 rpm for 2 h, then turn off the temperature and cool to room temperature to obtain cholesteric liquid crystal doped with fluorescent fuel;

[0098] 3. Weigh 6 g of PVA 1788 powder (Shanghai Macklin Biochemical Co., Ltd.) and 94 g of deionized water, stir magnetically at 90 °C to obtain a 6% PVA aqueous solution;

[0099] 4. Use a graduated cylinder to take 60 ml of 5% PVA aqueous solution, put it into a single-neck flask, and place the single-neck flask in a water bath and heat it to 60 °C;

[0100] 5. Weigh 1.1 g of methyl methacrylate (Shanghai Aladdin Biochemical Technology Co., Ltd.) and 0.03 g of azodiisooctanenitrile, put them into the cholesteric liquid crystal doped with fluorescent fuel in step 2, add 250 μl of dichloromethane, and stir magnetically for 15 min to obtain a liquid crystal mixture;

[0101] 6. Slowly drop the liquid crystal mixture in step 5 into the single-necked flask heated to 60 °C in step 4 at a rate of 0.5 ml / min. During the dropping process, stir magnetically at 1400 rpm. After dropping, wait for emulsification for 50 min, then add a condenser, raise the reaction temperature to 80 °C, react for 5 h to obtain the final microcapsules, turn off the temperature, continue magnetic stirring, and anneal to room temperature;

[0102] 7. Take out the microcapsules in the single-necked flask, add 30 ml of deionized water, mix well, centrifuge, pour out the supernatant in the centrifuge tube to obtain the precipitated microcapsule concentrate. Take out the microcapsule concentrate, add deionized water again to mix, wait for the microcapsules to precipitate, suck off the supernatant with a pipette, repeat many times until the supernatant after the mixture precipitates is no longer turbid, and centrifuge again to obtain a clean microcapsule concentrate doped with fluorescent dye;

[0103] 8. Uniformly mix the clean microcapsule concentrate doped with fluorescent dye, cholesteric liquid crystal, PVA (10%), and DuPont FS-63 surfactant in a mass ratio of 1:1.5:0.0001 to make a coating. Use a dropper to suck it and place it in a polytetrafluoroethylene mold with a depth of 0.07 μm to air-dry for 10 h to obtain Film 3.

[0104] Use a LEICA DM2700 M polarized optical microscope and a scanning electron microscope SU8020 to characterize the fluorescent dye-doped cholesteric liquid crystal microcapsules prepared in Example 2 at room temperature. As Figure 3 shown, the first three pictures above are the polarized light, bright field, and dark field pictures of the fluorescent dye-doped cholesteric liquid crystal microcapsules prepared in Example 2 taken by a polarized optical microscope. The "Maltese cross" appears under polarized light, indicating that the inside of the microcapsules has a regular radial orientation. The first picture below is a picture of the fluorescent dye-doped cholesteric liquid crystal microcapsules prepared in Example 2 with a particle size of about 20 μm taken by a scanning electron microscope. It can be seen that the surface of the microcapsules is smooth and round, and is completely coated. The two pictures on the right below are the EDS energy spectrum tests for nitrogen element. Because there is an amino group in the fluorescent dye R6G, the detection of nitrogen element can determine whether R6G exists in the microcapsules. According to Figure 3 the third picture below, it can be seen that there is nitrogen element in the shell of the microcapsules prepared in Example 2, which can prove that R6G is in the shell material.

[0105] Use a Nicolet IS10 Fourier transform infrared spectrometer. Mix the fluorescent dye-doped cholesteric liquid crystal microcapsules prepared in Example 1 with potassium bromide (KBr) powder by grinding evenly, press them into a tablet, and then measure the microcapsule sample (Example 1), methyl methacrylate (MMA), rhodamine 6G (R6G), and cholesteric liquid crystal (step 1 in Example 1); As Figure 4As shown, it is the infrared spectra of the fluorescent dye-doped cholesteric liquid crystal microcapsules, green cholesteric liquid crystal, rhodamine 6G, and methyl methacrylate in Example 1 of the present invention. The characteristic peaks at 3000 - 2750 cm -1 are from the C-H stretching vibrations of saturated alkanes -CH3 and -CH2- on CLC and PMMA; the characteristic absorption peak at 2231 cm -1 is from the vibration of the cyano group -CN in the liquid crystal molecules; the vibration absorption peak of the C=O bond is at 1724 cm -1 ; the characteristic peaks caused by the in-plane bending vibration of C-H and the skeletal vibration of the C-C single bond in the green cholesteric liquid crystal and R6G dye are at 1447 cm -1 , 1298 cm -1 ; the absorption peak at 1147 cm -1 is from the stretching vibration absorption peak of C-O in the liquid crystal molecules; the absorption peak of the N-H bond from the rhodamine 6G dye is at 1240 cm -1 ; and the infrared spectrum curve of the fluorescent dye-doped cholesteric liquid crystal microcapsules in Example 1 does not contain the absorption peak of the vinyl double bond (1636 cm-1), indicating that the fluorescent dye-doped cholesteric liquid crystal microcapsules have been successfully prepared.

[0106] The dye films with different concentrations were irradiated with 360 nm UV light and natural light. As Figure 5 shown, from left to right, the dye concentration gradually increases from 0.0005 to 0.0035 with a gradient of 0.0005; Example 2 and Example 3 correspond to the second and the second-to-last films respectively, showing different structural colors, fluorescent colors, and reflection colors under different viewing angles and different substrates (black and white). At low concentrations (0.0001 g - 0.0015 g R6G), when viewed directly, the structural color covers other colors, but as the viewing angle changes, the dye reflection color gradually affects the structural color; meanwhile, the main emission band excited by 360 nm is around 398 nm. Therefore, blue light will be shown at extremely low fluorescent dye concentrations, and orange light near 558 nm will be shown as the concentration slightly increases; thus, in order to pursue a high asymmetry factor (g value), fluorescent dye-doped microcapsules with two structural colors, blue (398 nm) and orange (558 nm), can be fabricated. Multiple applications of the same fluorescent dye are achieved. For high concentrations of fluorescent dyes, the fluorescent color is enhanced, and there is mainly a strong emission fluorescence peak near 558 nm. At the same time, the dye reflection color also has a covering effect on the structural color of the liquid crystal.

[0107] The asymmetry factor of the film made of the fluorescent dye-doped cholesteric liquid crystal microcapsules with a concentration of 0.0001 g in Example 1 was tested using CPL-300. As Figure 6As shown, it can be seen that the g value is around 0.12. During the test, the excitation light in the 520 nm band was used for the test.

[0108] Application Example 1

[0109] Application of Cholesteric Liquid Crystal Microcapsules Doped with Low-Concentration Fluorescent Fuel in Anti-Counterfeiting

[0110] The cholesteric liquid crystal microcapsules doped with fluorescent fuel prepared in Example 2 of the present invention belong to the low-concentration range and have good anti-counterfeiting performance; the reflection color of the fluorescent dye itself is relatively weak, while the structural color and fluorescent color are relatively strong. The cholesteric liquid crystal microcapsules doped with fluorescent dye are mixed with PVA (10%) and surfactant in a certain mass ratio to form an anti-counterfeiting coating. By scraping or screen printing on a dark-colored substrate (PET, fabric, etc.) and drying, the coating presents distinct structural colors under natural light, showing red, green or blue. However, when irradiated with ultraviolet light or other excitation light (such as 360 nm or 531 nm), it emits fluorescence of different colors. At the same time, when combined with the cholesteric liquid crystal microcapsules of Comparative Example 1, information encryption can be achieved, and different patterns are designed to show different patterns under natural light and excitation light, with high replication difficulty and high anti-counterfeiting ability.

[0111] Application Example 2

[0112] Application of Cholesteric Liquid Crystal Microcapsules Doped with High-Concentration Fluorescent Fuel in Warning

[0113] The cholesteric liquid crystal microcapsules doped with fluorescent fuel prepared in Example 3 of the present invention belong to the high-concentration range, have strong fluorescence, a wide excitation band, and after microencapsulation, the disadvantages of dyes and liquid crystals being stimulated by the external environment are solved. At the same time, the optimized microcapsules have good mechanical and optical properties, and replacing ordinary fluorescent warning materials with this functional material has more advantages. In dangerous working areas, using this functional material, within its excitation light range, the cholesteric liquid crystal microcapsules doped with high-concentration fluorescent fuel will emit strong orange-yellow light, having excellent warning effects.

[0114] The fluorescent dye-doped cholesteric liquid crystal microcapsules of the present invention are prepared by introducing a composite system of fluorescent dye and polymer material into cholesteric liquid crystal and using the interfacial polymerization method. Since cholesteric liquid crystal has unique selective reflection characteristics, while fluorescent dye has excellent luminescence performance, the present invention realizes the synergistic effect of the two functions by doping fluorescent dye into cholesteric liquid crystal, and at the same time forms a microcapsule structure with excellent optical properties.

[0115] By optimizing the components of the cholesteric liquid crystal (small molecule nematic liquid crystal, chiral agent) and the doping ratio of the fluorescent dye, the doped liquid crystal further enhances the fluorescence emission and reflection intensity while maintaining its helical periodic structure. During the preparation process of the microcapsules, the fluorescent dye is uniformly dispersed in the liquid crystal, and through the protection of the polymer shell layer, the stability and environmental adaptability of the fluorescent dye and the liquid crystal are significantly improved.

[0116] The main innovation points of the present invention are as follows: introducing the fluorescent dye into the core material of the cholesteric liquid crystal microcapsules enriches the color display mechanism; at the same time, by utilizing the self-assembled helical structure and the characteristic of the asymmetry factor (g value) of the cholesteric liquid crystal, the optimization and regulation of the circularly polarized light (CPL) characteristics of the microcapsules are realized; through the synergistic effect of the fluorescent dye and the cholesteric liquid crystal, the present invention not only realizes the multi-band excitation response of the microcapsules, but also improves the fluorescence intensity, optical stability and reflectivity of the microcapsules.

[0117] While improving the optical and mechanical properties of the cholesteric liquid crystal microcapsules, the present invention realizes the functional design, providing a new idea for the development of multifunctional liquid crystal materials; at the same time, the fluorescent dye-doped cholesteric liquid crystal microcapsules of the present invention can be widely applied in the fields of optical display, anti-counterfeiting labels, optical sensors, etc.

[0118] The fluorescent dye-doped cholesteric liquid crystal microcapsules of the present invention are prepared by an interfacial polymerization method with the cholesteric liquid crystal doped with the fluorescent dye as the core material and the polymer material as the wall material. The microcapsules have uniform particle sizes (10 - 150 μm), are spherical in appearance, and have excellent physical and chemical stability, optical properties and mechanical strength. The cholesteric liquid crystal in the core material forms a periodic helical structure through the synergistic effect of the chiral agent and the small molecule nematic liquid crystal, and the doping with the fluorescent dye produces significant color regulation ability and fluorescence characteristics, and also endows the microcapsules with CPL performance. By optimizing process conditions such as emulsification, stirring, reaction, etc., and regulating the concentration of the fluorescent dye, the microcapsules show significant fluorescence response and excellent environmental adaptability under multi-band excitation light sources. The preparation method proposed by the invention is efficient and simple, can regulate the concentration of the fluorescent dye according to actual needs, and realizes precise anti-counterfeiting applications with low-concentration doping, as well as strong fluorescence anti-counterfeiting and sensor applications with high-concentration doping. The present invention has broad application prospects in the fields of optical display, anti-counterfeiting technology and sensing.

[0119] The specific embodiments described above further elaborate on the purpose, technical solutions and beneficial effects of the present invention, but do not limit the present invention. Any modification, equivalent replacement or improvement made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A fluorescent dye-doped cholesteric liquid crystal microcapsule, characterized in that: The microcapsules include: (1) Core material: cholesteric liquid crystals that are fully mixed with different concentrations of fluorescent dyes in the presence of solvents; (2) Wall material: formed of a polymer material, and the polymer material is coated on the outside of the core material by interfacial polymerization.

2. The fluorescent dye-doped cholesteric liquid crystal microcapsule according to claim 1, characterized in that: The microcapsule has a spherical structure with a particle size of 10-150 μm.

3. The fluorescent dye-doped cholesteric liquid crystal microcapsule according to claim 1, characterized in that: The fluorescent dye is rhodamine 6G, and its mass percentage is 0.01%-1% of the total mass of the cholesteric liquid crystal, wherein 0.01%-0.15% is low-concentration doping; and 0.15%-1% is high-concentration doping.

4. The fluorescent dye-doped cholesteric liquid crystal microcapsule according to claim 1, characterized in that: The wall material is formed by thermal initiation from methyl methacrylate and azobisisoheptanonitrile, the mass ratio of methyl methacrylate to cholesteric liquid crystal is 1:2-2:1, and the mass of azobisisoheptanonitrile accounts for 0.625%-1.25% of the mass of methyl methacrylate.

5. A method for preparing the fluorescent dye-doped cholesteric liquid crystal microcapsules according to any one of claims 1 to 4, comprising the following steps: (1) fully mixing a chiral agent and a small molecule nematic phase liquid crystal to prepare cholesteric phase liquid crystals of different colors; (2) Add fluorescent dye to step (1), add dichloromethane and mix well, then set the temperature of the oil bath to 40°C-49°C in advance, put the fluorescent dye-doped cholesteric liquid crystal in, stir at a low speed for 1h-3h to fully volatilize the dichloromethane, then set the temperature of the oil bath to above the clearing point temperature of the liquid crystal, continue magnetic stirring for 1h-3h, and finally turn off the temperature and slowly reduce to room temperature; (3) fully mixing a color of cholesteric liquid crystal doped with fluorescent dye with methyl methacrylate and azobisisoheptanenitrile, adding a small amount of dichloromethane to quickly assist melting, and obtaining a core material and wall material mixture; (4) Add PVA aqueous solution into the flask and heat it to 50°C-70°C in advance; (5) slowly adding the core material and wall material mixture prepared in step (3) to step (4) at a rate of 0.1 ml / min-1.0 ml / min, while performing magnetic stirring, and emulsifying for a certain time; after the emulsification is completed, the temperature is raised to 70° C.-90° C., and the reaction is performed for 2 h-8 h; after the time is up, the temperature is turned off, and annealing is performed until it reaches room temperature, and the magnetic stirring is not turned off during the period; (6) After annealing, the microcapsule product is first diluted with deionized water and centrifuged to obtain a microcapsule concentrate. The microcapsule concentrate is then taken out and rinsed with deionized water for multiple times. The microcapsule solution is repeatedly precipitated until the microcapsule aqueous solution is clear and centrifuged again to obtain a clean microcapsule concentrate. Alternatively, the microcapsule concentrate is directly dried to obtain a clean microcapsule product.

6. The method for preparing fluorescent dye-doped cholesteric liquid crystal microcapsules according to claim 5, characterized in that: In step (1), the chiral agent is S5011 or R5011, the small molecule nematic liquid crystal is NC-M-LC720600 or HNG717200-000, the mass percentage of the chiral agent in the cholesteric liquid crystal is 2.21%-3.71%, and the mass percentage of the small molecule nematic liquid crystal in the cholesteric liquid crystal is 96.29%-97.79%.

7. The method for preparing fluorescent dye-doped cholesteric liquid crystal microcapsules according to claim 5, characterized in that: The fluorescent dye in step (2) is rhodamine 6G, the temperature above the clearing point of the liquid crystal is: 100°C-110°C for NC-M-LC720600; 82°C-92°C for HNG717200-000; the fluorescent dye is 0.01%-1% of the total mass of the cholesteric liquid crystal, 0.01%-0.15% is considered a low concentration, and 0.15%-1% is considered a high concentration. The amount of dichloromethane is more than 25% of the total mass of the cholesteric liquid crystal.

8. The method for preparing fluorescent dye-doped cholesteric liquid crystal microcapsules according to claim 5, characterized in that: In step (3), the mass ratio of cholesteric liquid crystal to methyl methacrylate is 2:1-1:2, the azobisisoheptanenitrile accounts for 0.625%-1.25% of the mass of methyl methacrylate; the amount of dichloromethane is more than 25% of the total mass of cholesteric liquid crystal; in step (4), the mass percentage of PVA is 2%-9%; in step (5), the stirring speed is 800rpm-1400rpm, and the emulsification time is more than 30min.

9. The method for preparing fluorescent dye-doped cholesteric liquid crystal microcapsules according to claim 5, characterized in that: The microcapsules are prepared into coatings by uniformly mixing clean fluorescent dye-doped cholesteric liquid crystal microcapsule concentrate, 10% PVA, and DuPont FS-63 surfactant at a mass ratio of 1:1.5:0.0001 to prepare coatings, and then preparing films by a scraping method or a template method, with a film thickness of 0.04-0.07 μm.

10. Use of the fluorescent dye-doped cholesteric liquid crystal microcapsule according to any one of claims 1 to 4 in the fields of optical display, anti-counterfeiting label and optical sensor.

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