A Highly Durable Thermotropic Reversible Color-Changing Microcapsule Based on Multiple Pickering Emulsions and Its Preparation Method

Abstract

This invention discloses a highly durable thermochromic reversible microcapsule based on a multiple Pickering emulsion and its preparation method. This thermochromic microcapsule is prepared by in-situ polymerization using a multiple Pickering emulsion with an inner aqueous phase consisting of a thermosensitive polymer and an inner oil phase consisting of a ternary thermochromic material as a template. The use of a multiple Pickering emulsion in this invention allows for better control of the microcapsule encapsulation process, resulting in better size and color uniformity of the microcapsules. Furthermore, the presence of nanoparticles effectively increases the durability and barrier properties of the microcapsules. The introduction of the internal thermosensitive polymer gel effectively improves the color-changing performance of the microcapsules, widening the color-changing temperature range, reducing the color-changing rate, and improving color-changing uniformity. This leads to better uniformity and visual effects during wide-area application. In addition, it effectively reduces the amount of color-developing material used while maintaining color development capability, thus lowering material costs. The thermochromic microcapsules have a clear mechanism of action, a simple production process, and excellent performance, making them suitable for large-scale production. They are especially suitable for large-scale use in outdoor environments for materials such as coatings, inks, plastics, and rubber that require thermochromic properties. This is of great significance for the advancement of related technologies and the development of the industry.

Description

Technical Field

[0001] This invention belongs to the field of fine polymer materials, specifically relating to the preparation of a high-durability, multi-level responsive, thermosensitive color-changing microcapsule and its application in the color matching of materials such as coatings, inks, plastics, rubber, and fibers. Background Technology

[0002] Thermochromic materials are materials that can reversibly change color according to temperature changes. They can be used as temperature indicators to measure the surface temperature and temperature distribution of physical surfaces in certain special situations. In recent years, the application scope of thermochromic materials has expanded from simple temperature indication to smart textiles, temperature-regulating fibers, anti-counterfeiting printing, temperature sensing, food packaging, building materials, daily necessities decoration, energy utilization, and biomedicine. The demand for thermochromic materials and their promising development prospects make their research and development of significant economic and social importance, and also bring new development opportunities for future application research.

[0003] Among thermochromic materials, the ternary organic thermochromic material system, composed of pigments, color developers, and solvents, has become the most widely used thermochromic material due to its advantages such as sensitive color change reaction, narrow color change temperature range, high selectivity and adjustability of color and temperature range, low price, and long lifespan. However, because it requires a relatively stable chemical environment and its color development ability is sensitive to the composition ratio, it often needs to be protected by shaping technology in practical use. Currently, the most commonly used technology is microencapsulation.

[0004] Currently, researchers have conducted considerable research on the preparation of ternary thermochromic microcapsules. For example, patent CN113831758A discloses a thermochromic microcapsule dye. By adjusting the solvent ratio, the color-changing temperature is controlled near human body temperature at 37.5℃, allowing for a direct reflection of changes in body temperature. Furthermore, using fluorosilicone-modified polyacrylic acid as the microcapsule shell effectively improves issues such as fading after washing. Patent CN112980248B discloses a thermochromic liquid crystal microcapsule ink and color-changing coating. Using cholesteric liquid crystal as the core material and polyurethane resin as the wall material, thermochromic liquid crystal microcapsules are prepared, achieving color changes between 40-65℃, allowing for direct temperature measurement. Patent CN112980248B also discloses a thermochromic reversible multi-segment color-changing microcapsule and its preparation method. By using cationic modified melamine prepolymer as the wall material, it allows the negative charge to interact with the emulsifier, reducing bubble introduction, lowering the empty capsule rate, and improving the mechanical properties and thermal stability of the microcapsules.

[0005] Optimizing the microcapsule preparation process and structure to improve performance, based on conventional microcapsule materials, remains a research hotspot in related fields. Compared to conventional emulsions, Pickering emulsions are characterized by the use of nanoparticles as emulsifiers to stabilize the emulsion system. This results in lower emulsifier dosage, better stability, more uniform and controllable dispersed phase particle size, and lower foaming, making them ideal templates for synthesizing microcapsules. For example, patent CN114766481B used cellulose nanocrystals as an emulsifier to prepare a highly effective Pickering emulsion, and used this emulsion as a template to prepare pesticide microcapsules with high encapsulation efficiency. Patent CN115746794A used boron nitride lignin hybrids as emulsifiers to prepare Pickering emulsions, and used this as a template to prepare multifunctional phase change microcapsules.

[0006] As can be seen from the above description, although existing microcapsules possess thermotropic reversible color-changing properties and have some practical applications, the overall prepared color-changing microcapsules still face problems such as insufficient particle size uniformity, poor color uniformity, narrow color change range, strong abrupt changes, poor smoothness, insufficient durability and heat resistance, and susceptibility to external environmental influences that can cause them to lose their reversible color-changing ability. Furthermore, the relatively high price of ternary color-changing systems results in high overall costs, all of which hinder their application. Microcapsules prepared using Pickering emulsion templates can effectively improve these problems. Therefore, based on relevant research, further development of novel thermotropic reversible color-changing microcapsules to improve material performance stability, enhance color-changing capabilities, and reduce preparation costs is of great significance for promoting the further development of related technologies and advancing the industry. Summary of the Invention

[0007] The purpose of this invention is to solve the above-mentioned problems and provide a highly durable thermo-reversible color-changing microcapsule based on multiple Pickering emulsions and its preparation method.

[0008] The present invention discloses a high-durability thermotropic reversible color-changing microcapsule based on a multi-layer Pickering emulsion. This microcapsule is obtained by in-situ polymerization and encapsulation of a resin prepolymer using a w / o / w type multi-layer Pickering emulsion as a template. The microcapsule has a particle size of 2-10 μm and an outer wall thickness of 50-80 nm. The multi-layer Pickering emulsion comprises an inner aqueous phase of a thermosensitive polymer monomer aqueous solution, an inner emulsifier of lipophilic nanoparticles, an inner oil phase of a ternary thermosensitive color-changing system composed of pigments, color developers, and solvents, and an outer emulsifier of hydrophilic nanoparticles. The mass ratio of the inner aqueous phase to the inner oil phase is 1:(1.5~3), and the mass concentration of the multi-layer Pickering emulsion is 25~40%.

[0009] The thermosensitive polymer monomer aqueous solution in the thermotropic reversible color-changing microcapsule is composed of thermosensitive polymer monomer, crosslinking agent, initiator and water; wherein the thermosensitive polymer monomer is at least one of N-isopropylacrylamide, dimethylaminoethyl methacrylate, N-vinylcaprolactam, diethyl vinylphosphonate, and polyethylene glycol methacrylate, with a mass concentration of 8-12%; the crosslinking agent is at least one of N,N-methylenebisacrylamide, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, N-hydroxymethylacrylamide, ethylene glycol dimethacrylate, and allyl methacrylate, with an amount of 1%-10% of the thermosensitive monomer; the initiator is at least one of potassium persulfate, ammonium persulfate, azobisisopropylammoniazoline hydrochloride, and azobisisobutylammoniazoline dihydrochloride, with an amount of 0.3-3% of the thermosensitive monomer.

[0010] The pigment in the thermotropic reversible color-changing microcapsules is at least one selected from crystal violet lactone, malachite green, 2-phenylamino-3-methyl-6-dibutylaminofluorane, 3',6'-dimethoxyfluorane, 1,3-dimethyl-6-diethylaminofluorane, 3,3-di(4-ethylamino-2-ethoxyphenyl)-4-azaphenylfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, and thermogreen; the color-developing agent is bisphenol A, bisphenol F, bisphenol S, 4,4 The solvent is at least one of '-cyclohexylbisphenol, 4-allyloxy-4'-hydroxydiphenyl sulfone, bis(3-amino-4-hydroxyphenyl) sulfone, and bis(3-allyl-4-hydroxyphenyl) sulfone; the solvent is at least one of a saturated fatty alcohol or fatty acid containing a hydrocarbon chain of ten to eighteen carbon atoms, decanoic acid triglyceride, methyl stearate, and ethyl stearate; wherein the mass concentration of the pigment molecules is 0.8-6%, and the mass ratio of the pigment to the color developer is 1:(1.5-4).

[0011] The hydrophilic nanoparticles in the thermotropic reversible color-changing microcapsules are at least one of the following: surface-hydrophilic nano-SiO2, TiO2, ZnO, CaCO3, Fe3O4, graphene oxide, kaolin, montmorillonite, diatomaceous earth, attapulgite, cellulose, lignin, and alginate. Their particle size is 5-30 nm, and their amount is 0.1-1.5% of the total amount of external aqueous phase.

[0012] The hydrophobic nanoparticles in the thermotropic reversible color-changing microcapsules are at least one of the following nano-SiO2, TiO2, ZnO, CaCO3, Fe3O4, graphene oxide, kaolin, montmorillonite, diatomaceous earth, attapulgite, cellulose, lignin, and alginate that have undergone partial surface hydrophobic modification. Their particle size is 5-30 nm, and their amount is 0.5-3% of the total amount of the internal oil phase. The hydrophobic modification process involves surface grafting modification of the nanoparticles using at least one of dichlorodimethylsiloxane, trimethylchlorosilane, ethyltriethoxysilane, tridecafluorooctyltriethoxysilane, oleic acid, and stearic acid.

[0013] The resin prepolymer in the thermotropic reversible color-changing microcapsule is at least one of melamine resin prepolymer, urea-formaldehyde resin prepolymer, phenolic resin prepolymer, methyl melamine-formaldehyde resin prepolymer, polyurethane resin prepolymer, and acrylic resin, and its amount is 5-13% of the total amount of the inner oil phase and the inner water phase.

[0014] The preparation method of this thermotropic reversible color-changing microcapsule includes the following steps:

[0015] (1) Primary emulsification: Hydrophobic nanoparticles are added to the oil phase of the ternary thermosensitive color-changing system and dispersed uniformly by ultrasonication. Then, the aqueous solution of the thermosensitive polymer monomer is added to the oil phase, and a stable w / o type Pickering emulsion is obtained by high-speed stirring and ultrasonic emulsification.

[0016] (2) Secondary emulsification: Hydrophilic nanoparticles are added to water and dispersed evenly by ultrasonication. Then, w / o type Pickering emulsion is added to the aqueous phase and emulsified again by high-speed stirring to obtain a stable w / o / w type Pickering multiple emulsion.

[0017] (3) In-situ polymerization: Place the multiple emulsion in a constant temperature water bath at 50°C. Under mechanical stirring, slowly drip the resin prepolymer into the emulsion for 1-2 hours. After the dripping is completed, raise the temperature to 80-90°C to allow the temperature-sensitive polymer monomers in the resin prepolymer capsule wall and the inner aqueous phase to begin polymerization and crosslinking. After keeping warm for 2-3 hours, the microcapsule aqueous dispersion can be obtained.

[0018] (4) Separation and purification: After filtering and washing the microcapsule aqueous dispersion, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermo-reversible color-changing microcapsule powder.

[0019] The positive effects of the highly durable thermotropic reversible color-changing microcapsules based on multiple Pickering emulsions of the present invention are as follows:

[0020] The thermotropic reversible color-changing microcapsules prepared in this invention are fabricated using a w / o / w type Pickering multiple emulsion as a template. Their outer capsule wall is a composite of a three-dimensional polymer resin and nanoparticles. Compared to conventional microcapsules, they exhibit better encapsulation during synthesis, stronger particle size control, and better size uniformity and color uniformity. Furthermore, the capsule wall demonstrates greater stability during long-term use, and the contained nanoparticles provide some protection against ultraviolet radiation, preventing component leakage and reducing the aging of the color-changing components. This effectively prevents the loss of color-changing performance, giving the microcapsules potential for use in outdoor environments and long-term cyclical applications.

[0021] Furthermore, by using a w / o / w type Pickering multiple emulsion as a template, the aqueous phase of the thermosensitive monomer aqueous solution forms inner gel particles within the microcapsules during synthesis. These particles have a nanoparticle shell and a thermosensitive polymer gel as their core. The addition of these inner gel particles significantly reduces the amount of ternary thermochromic material used in the microcapsules without altering the color development ability, thus lowering material costs. More importantly, because the contained gel is a thermosensitive gel with LCST (low-temperature chromogenicity), it effectively improves the color-changing behavior of the microcapsules, allowing for smooth and slow color changes over a wider temperature range, meeting the needs of more application scenarios. This is because the surface of the gel particles has only a single nanoparticle shell, thus possessing a certain molecular exchange capacity between the inner oil and inner aqueous phases. During heating, the hydrophilicity of the thermosensitive gel decreases, and its hydrophobicity increases, allowing some of the oil phase of the ternary color-changing system to enter the surface of the gel particles, causing the system's color to gradually lighten. Conversely, during cooling, the hydrophobicity of the thermosensitive gel decreases, and its hydrophilicity increases, repelling the ternary color-changing system into the intermediate oil phase environment, causing the system's color to gradually deepen. It can be seen that the color change trend caused by the thermosensitive polymer gel is consistent with that of the ternary color-changing material, but its color change process is relatively slow and smooth. Therefore, it can effectively improve the color change behavior of microcapsules, making its overall color change more uniform and smooth, avoiding the phenomenon of color spots caused by some areas changing color and some areas not changing color when the color of the material appearance is too fast, and effectively improving its color uniformity.

[0022] As can be seen from the above description, the thermochromic microcapsule technology has a clear mechanism of action, a simple production process, excellent product performance, strong durability, low cost, and is suitable for large-scale production applications. It is of great significance for the preparation of coatings, inks, plastics, rubbers, fibers and other materials with thermochromic properties and their application and promotion in relevant indoor and outdoor scenarios. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to specific embodiments.

[0024] Example 1: A highly durable thermotropic reversible color-changing microcapsule A based on multiple Pickering emulsions, the preparation process of which is as follows:

[0025] (1) 1.28 g of hydrophobic nano-SiO2 was added to the oil phase of a ternary thermochromic system prepared by uniformly dissolving 3.2 g of crystal violet lactone, 6.4 g of bisphenol A and 150 g of tetradecyl alcohol at 50 °C. The mixture was then uniformly dispersed by ultrasonication. Then, an aqueous solution of thermosensitive polymer monomers composed of 10 g of N-isopropylacrylamide, 0.12 g of N,N-methylenebisacrylamide, 0.05 g of potassium persulfate and 89.8 g of deionized water was added to the oil phase of the ternary thermochromic system. A stable w / o type Pickering emulsion A1 was obtained by high-speed stirring and ultrasonic emulsification.

[0026] (2) 2.64g of hydrophilic nano SiO2 was added to 528g of deionized water and dispersed evenly by ultrasonication. Then, w / o type emulsion A1 was added to water under constant temperature water bath at 50℃ and emulsified again by high-speed stirring to obtain stable w / o / w type multiple Pickering emulsion A2.

[0027] (3) Place w / o / w type multiple Pickering emulsion A2 in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 15.6g of melamine resin prepolymer into the emulsion over a period of 1.5h. After the addition is complete, raise the temperature to 85℃ to allow the resin prepolymer and the temperature-sensitive polymer monomer in the inner aqueous phase to begin polymerization and crosslinking. After keeping the temperature for 3h, the microcapsule water A dispersion can be obtained.

[0028] (4) After filtering and washing the aqueous dispersion of microcapsule A, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermo-reversible color-changing microcapsule A.

[0029] Example 2: A highly durable thermotropic reversible color-changing microcapsule B based on multiple Pickering emulsions, the preparation process of which is as follows:

[0030] (1) At 50°C, 3.6 g of hydrophobic nano-TiO2 was added to the oil phase of a ternary thermochromic system prepared by uniformly dissolving 7.2 g of 3',6'-dimethoxyfluorane, 21.6 g of bis(3-allyl-4-hydroxyphenyl) sulfone and 211 g of dodecanoic acid. The mixture was then uniformly dispersed by ultrasonication. Next, an aqueous solution of thermosensitive polymer monomers composed of 11 g of dimethylaminoethyl methacrylate, 0.33 g of trimethylolpropane trimethacrylate, 0.11 g of azobisisobutyramidine dihydrochloride and 88.6 g of deionized water was added to the oil phase of the ternary thermochromic system. A stable w / o type Pickering emulsion B1 was obtained by high-speed stirring and ultrasonic emulsification.

[0031] (2) 7g of hydrophilic nano TiO2 was added to 875g of deionized water and dispersed evenly by ultrasonication. Then, w / o type emulsion B1 was added to water under constant temperature water bath at 50℃ and emulsified again by high-speed stirring to obtain stable w / o / w type multi-Pickering emulsion B2.

[0032] (3) Place w / o / w type multiple Pickering emulsion B2 in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 34g of urea-formaldehyde resin prepolymer into the emulsion over a period of 1.5h. After the addition is complete, raise the temperature to 85℃ to allow the resin prepolymer and the temperature-sensitive polymer monomers in the inner aqueous phase to begin polymerization and crosslinking. After keeping the temperature for 2.5h, the microcapsule water B dispersion can be obtained.

[0033] (4) After filtering and washing the aqueous dispersion of microcapsule B, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermo-reversible color-changing microcapsule B.

[0034] Example 3: A highly durable thermotropic reversible color-changing microcapsule C based on multiple Pickering emulsions, the preparation process of which is as follows:

[0035] (1) 2.5g of hydrophobic nano Fe3O4 was added to the oil phase of a ternary thermochromic system prepared by uniformly dissolving 3.75g of 2-phenylamino-3-methyl-6-dibutylaminofluorane, 13.2g of bisphenol S and 235g of glyceryl tridecanoate at 50℃. The mixture was then uniformly dispersed by ultrasonication. Then, an aqueous solution of thermosensitive polymer monomers composed of 8.5g of N-isopropylacrylamide, 0.34g of pentaerythritol tetramethacrylate, 0.13g of azodiisopropylammoniazoline hydrochloride and 91g of deionized water was added to the oil phase of the ternary thermochromic system. A stable w / o type Pickering emulsion C1 was obtained by high-speed stirring and ultrasonic emulsification.

[0036] (2) 5.85g of hydrophilic nano Fe3O4 was added to 650g of deionized water and dispersed evenly by ultrasonication. Then, w / o type emulsion C1 was added to water under constant temperature water bath at 50℃ and emulsified again by high-speed stirring to obtain stable w / o / w type multiple Pickering emulsion C2.

[0037] (3) Place w / o / w type multiple Pickering emulsion C2 in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 42g of methyl melamine formaldehyde resin prepolymer into the emulsion over a period of 1.5h. After the addition is complete, raise the temperature to 85℃ to allow the resin prepolymer and the temperature-sensitive polymer monomers in the inner aqueous phase to begin polymerization and crosslinking. After keeping the temperature for 2.5h, the microcapsule water C dispersion can be obtained.

[0038] (4) After filtering and washing the aqueous dispersion of microcapsule C, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermo-reversible color-changing microcapsule C.

[0039] Example 4: A highly durable thermotropic reversible color-changing microcapsule D based on multiple Pickering emulsions, the preparation process of which is as follows:

[0040] (1) At 50°C, 3.6 g of hydrophobic nano-SiO2 was added to the oil phase of a ternary thermochromic system prepared by uniformly dissolving 7.2 g of 3',6'-dimethoxyfluorane, 18 g of 4-allyloxy-4'-hydroxydiphenyl sulfone and 155 g of dodecanol. The mixture was then uniformly dispersed by ultrasonication. Next, an aqueous solution of a thermosensitive polymer monomer composed of 9 g of N-vinylcaprolactam, 0.315 g of ethylene glycol dimethacrylate, 0.072 g of ammonium persulfate and 91 g of deionized water was added to the oil phase of the ternary thermochromic system. A stable w / o type Pickering emulsion D1 was obtained by high-speed stirring and ultrasonic emulsification.

[0041] (2) 3.92g of hydrophilic nano SiO2 was added to 653g of deionized water and dispersed evenly by ultrasonication. Then, w / o type emulsion D1 was added to water under constant temperature water bath at 50℃ and emulsified again by high-speed stirring to obtain stable w / o / w type multi-Pickering emulsion D2.

[0042] (3) Place w / o / w type multiple Pickering emulsion D2 in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 21g of melamine resin prepolymer into the emulsion over a period of 1.5h. After the addition is complete, raise the temperature to 85℃ to allow the resin prepolymer and the temperature-sensitive polymer monomers in the inner aqueous phase to begin polymerization and crosslinking. After keeping the temperature for 2.5h, the microcapsule water D dispersion can be obtained.

[0043] (4) After filtering and washing the aqueous dispersion of microcapsule D, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermo-reversible color-changing microcapsule D.

[0044] Example 5: A highly durable thermotropic reversible color-changing microcapsule E based on multiple Pickering emulsions, the preparation process of which is as follows:

[0045] (1) At 50°C, 3.3g of hydrophobic nano-attapulgite clay was added to the oil phase of a ternary thermochromic system prepared by uniformly dissolving 11g of crystal violet lactone, 24.2g of 4,4'-cyclohexylene bisphenol A and 185g of methyl stearate. The mixture was then uniformly dispersed by ultrasonication. Then, an aqueous solution of thermosensitive polymer monomers composed of 10.4g of oligoethylene glycol methacrylate, 0.7g of N-hydroxymethylacrylamide, 0.08g of potassium persulfate and 88.8g of deionized water was added to the oil phase of the ternary thermochromic system. A stable w / o type Pickering emulsion E1 was obtained by high-speed stirring and ultrasonic emulsification.

[0046] (2) 11g of hydrophilic nano-attapulgite clay was added to 910g of deionized water and dispersed evenly by ultrasonication. Then, w / o type emulsion E1 was added to water under constant temperature water bath at 50℃ and emulsified again by high-speed stirring to obtain stable w / o / w type multi-Pickering emulsion E2.

[0047] (3) Place w / o / w type multiple Pickering emulsion E2 in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 25.6g of acrylic resin prepolymer into the emulsion over a period of 1.5h. After the addition is complete, raise the temperature to 85℃ to allow the resin prepolymer and the temperature-sensitive polymer monomer in the inner aqueous phase to begin polymerization and crosslinking. After keeping the temperature for 3h, the microcapsule water E dispersion can be obtained.

[0048] (4) After filtering and washing the aqueous dispersion of microcapsule E, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermo-reversible color-changing microcapsule E.

[0049] Example 6: A highly durable thermotropic reversible color-changing microcapsule F based on multiple Pickering emulsions, the preparation process of which is as follows:

[0050] (1) At 50°C, 1.6 g of hydrophobic nano-SiO2 was added to the oil phase of a ternary thermochromic system prepared by uniformly dissolving 6 g of 3-diethylamino-6-methyl-7-chlorofluorane, 10.8 g of bisphenol F, 90 g of tetradecyl alcohol and 95 g of dodecanol. The mixture was then uniformly dispersed by ultrasonication. Then, an aqueous solution of thermosensitive polymer monomers composed of 11.2 g of diethyl vinylphosphonate, 0.84 g of N,N-methylenebisacrylamide, 0.13 g of azobisisobutyramidine dihydrochloride and 88 g of deionized water was added to the oil phase of the ternary thermochromic system. A stable w / o type Pickering emulsion F1 was obtained by high-speed stirring and ultrasonic emulsification.

[0051] (2) 4.27g of hydrophilic nano SiO2 was added to 533g of deionized water and dispersed evenly by ultrasonication. Then, w / o type emulsion F1 was added to water under constant temperature water bath at 50℃ and emulsified again by high-speed stirring to obtain stable w / o / w type multiple Pickering emulsion F2.

[0052] (3) Place w / o / w type multiple Pickering emulsion F2 in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 27g of phenolic resin prepolymer into the emulsion over a period of 1.5h. After the addition is complete, raise the temperature to 88℃ to allow the resin prepolymer and the temperature-sensitive polymer monomer in the inner aqueous phase to begin polymerization and crosslinking. After keeping warm for 2.5h, the microcapsule water F dispersion can be obtained.

[0053] (4) After filtering and washing the aqueous dispersion of microcapsule F, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermo-reversible color-changing microcapsule F.

[0054] Example 7: A highly durable thermotropic reversible color-changing microcapsule G based on multiple Pickering emulsions, the preparation process of which is as follows:

[0055] (1) 2.16 g of hydrophobic nano-lignin was added to the oil phase of a ternary thermo-sensitive color-changing system prepared by uniformly dissolving 7.2 g of 2-phenylamino-3-methyl-6-dibutylaminofluorane, 21.6 g of bisphenol A and 151 g of tetradecyl alcohol at 50 °C. The mixture was then uniformly dispersed by ultrasonication. Then, an aqueous solution of thermo-sensitive polymer monomers composed of 10.5 g of N-isopropylacrylamide, 0.315 g of allyl methacrylate, 0.06 g of ammonium persulfate and 89 g of deionized water was added to the oil phase of the ternary thermo-sensitive color-changing system. A stable w / o type Pickering emulsion G1 was obtained by high-speed stirring and ultrasonic emulsification.

[0056] (2) Add 2g of hydrophilic nano lignin to 568g of deionized water and disperse it evenly by ultrasonication. Then, add w / o type emulsion G1 to water under constant temperature water bath at 50℃ and emulsify it again by high speed stirring to obtain stable w / o / w type multi-Pickering emulsion G2.

[0057] (3) Place w / o / w type multiple Pickering emulsion G2 in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 28g of melamine resin prepolymer into the emulsion over a period of 1.5h. After the addition is complete, raise the temperature to 80℃ to allow the resin prepolymer and the temperature-sensitive polymer monomer in the inner aqueous phase to begin polymerization and crosslinking. After keeping the temperature for 2.5h, the microcapsule water A dispersion can be obtained.

[0058] (4) After filtering and washing the aqueous dispersion of microcapsule A, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermo-reversible color-changing microcapsule A.

[0059] Example 8: A highly durable thermotropic reversible color-changing microcapsule H based on multiple Pickering emulsions, the preparation process of which is as follows:

[0060] (1) At 50°C, 4.2 g of hydrophobic nano Fe3O4 was added to the oil phase of a ternary thermochromic system prepared by uniformly dissolving 7.35 g of crystal violet lactone, 22 g of bis(3-amino-4-hydroxyphenyl) sulfone and 180 g of methyl octadecanoate. The mixture was then uniformly dispersed by ultrasonication. Next, an aqueous solution of thermosensitive polymer monomers composed of 12 g of polyethylene glycol methacrylate, 0.6 g of N,N-methylenebisacrylamide, 0.24 g of potassium persulfate and 87 g of deionized water was added to the oil phase of the ternary thermochromic system. A stable w / o type Pickering emulsion H1 was obtained by high-speed stirring and ultrasonic emulsification.

[0061] (2) 5.43g of hydrophilic nano Fe3O4 was added to 720g of deionized water and dispersed evenly by ultrasonication. Then, w / o type emulsion H1 was added to water under constant temperature water bath at 50℃ and emulsified again by high-speed stirring to obtain stable w / o / w type multiple Pickering emulsion H2.

[0062] (3) Place w / o / w type multiple Pickering emulsion H2 in a constant temperature water bath at 50℃ and mechanically stir. Mix 34g of polyurethane resin prepolymer and 7g of latent curing agent evenly and slowly drip into the emulsion. The dripping time is 1.5h. After the dripping is completed, raise the temperature to 85℃ so that the resin prepolymer and the temperature-sensitive polymer monomer in the inner aqueous phase can start to polymerize and crosslink. After keeping warm for 2~3h, the microcapsule water H dispersion can be obtained.

[0063] (4) After filtering and washing the aqueous dispersion of microcapsules H, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermo-reversible color-changing microcapsules H.

[0064] Comparative Example 1: Commercially available thermochromic pigments

[0065] A commercially available brand of thermochromic pigment was compared with the performance of the examples.

[0066] Comparative Example 2: Conventional thermochromic microcapsules, the preparation process of which is as follows:

[0067] (1) 5.25g of 2-phenylamino-3-methyl-6-dibutylaminofluorane, 18.375g of bisphenol S and 325g of glyceryl tridecanoate were dissolved and homogenized at 50℃ to prepare the oil phase of a ternary thermosensitive color-changing system.

[0068] (2) Add 5.85g of sodium dodecyl sulfonate to 650g of deionized water, and then add the oil phase of the ternary thermosensitive color-changing system to the water under a constant temperature water bath at 50℃. Emulsify by high-speed stirring to obtain an o / w type color-changing material emulsion.

[0069] (3) Place the o / w type color-changing material emulsion in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 42g of methyl melamine formaldehyde resin prepolymer into the emulsion. The dropping time is 1.5h. After the dropping is completed, raise the temperature to 85℃ so that the resin prepolymer and the temperature-sensitive polymer monomer in the inner aqueous phase can begin to polymerize and crosslink. After keeping warm for 2.5h, a conventional thermochromic microcapsule dispersion can be obtained.

[0070] (4) After filtering and washing the microcapsule aqueous dispersion, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain conventional thermochromic microcapsules.

[0071] Comparative Example 3: Conventional Pickering emulsion thermochromic microcapsules, the preparation process of which is as follows:

[0072] (1) 5.25g of 2-phenylamino-3-methyl-6-dibutylaminofluorane, 18.375g of bisphenol S and 325g of glyceryl tridecanoate were dissolved and homogenized at 50℃ to prepare the oil phase of a ternary thermosensitive color-changing system.

[0073] (2) 5.85g of hydrophilic nano Fe3O4 was added to 650g of deionized water. Then, the oil phase of the ternary thermosensitive color-changing system was added to the water under a constant temperature water bath at 50℃. The mixture was emulsified by high-speed stirring to obtain the O / W type color-changing material Pickering emulsion.

[0074] (3) Place the o / w type color-changing material emulsion in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 42g of methyl melamine formaldehyde resin prepolymer into the emulsion. The dropping time is 1.5h. After the dropping is completed, raise the temperature to 85℃ so that the resin prepolymer and the temperature-sensitive polymer monomer in the inner aqueous phase can begin to polymerize and crosslink. After keeping warm for 2.5h, the conventional Pickering emulsion thermochromic microcapsule dispersion can be obtained.

[0075] (4) After filtering and washing the microcapsule aqueous dispersion, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain conventional Pickering emulsion thermochromic microcapsules.

[0076] Comparative Example 4: Conventional internal aqueous dual Pickering emulsion thermochromic microcapsules, the preparation process of which is as follows:

[0077] (1) 1.28 g of hydrophobic nano-SiO2 was added to the oil phase of a ternary thermochromic system prepared by uniformly dissolving 3.2 g of crystal violet lactone, 6.4 g of bisphenol A and 150 g of tetradecyl alcohol at 50 °C. The mixture was then uniformly dispersed by ultrasonication. Then, an aqueous solution of polymer monomers consisting of 10 g of acrylamide, 0.12 g of N,N-methylenebisacrylamide, 0.05 g of potassium persulfate and 89.8 g of deionized water was added to the oil phase of the ternary thermochromic system. A stable w / o type Pickering emulsion was obtained by high-speed stirring and ultrasonic emulsification.

[0078] (2) 2.64g of hydrophilic nano SiO2 was added to 528g of deionized water and dispersed evenly by ultrasonication. Then, the w / o type emulsion was added to the water under a constant temperature water bath at 50℃ and emulsified again by high-speed stirring to obtain a w / o / w type multiple Pickering emulsion.

[0079] (3) Place the w / o / w type multiple Pickering emulsion in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 15.6g of melamine resin prepolymer into the emulsion over a period of 1.5h. After the addition is complete, raise the temperature to 85℃ to allow the resin prepolymer and the temperature-sensitive polymer monomer in the inner aqueous phase to begin polymerization and crosslinking. After keeping the temperature for 3h, the microcapsule aqueous dispersion can be obtained.

[0080] (4) After filtering and washing the microcapsule aqueous dispersion, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermochromic microcapsules of thermally normal aqueous double Pickering emulsion.

[0081] Comparative Example 5: Low internal aqueous phase content dual Pickering emulsion thermochromic microcapsules, the preparation process of which is as follows:

[0082] (1) 2.16 g of hydrophobic nano-lignin was added to the oil phase of a ternary thermo-sensitive color-changing system prepared by uniformly dissolving 7.2 g of 2-phenylamino-3-methyl-6-dibutylaminofluorane, 21.6 g of bisphenol A and 151 g of tetradecyl alcohol at 50 °C. The mixture was then uniformly dispersed by ultrasonication. Then, an aqueous solution of thermo-sensitive polymer monomers composed of 3.15 g of N-isopropylacrylamide, 0.01 g of allyl methacrylate, 0.018 g of ammonium persulfate and 26.7 g of deionized water was added to the oil phase of the ternary thermo-sensitive color-changing system. A stable w / o type Pickering emulsion was obtained by high-speed stirring and ultrasonic emulsification.

[0083] (2) Add 2g of hydrophilic nano-lignin to 568g of deionized water and disperse it evenly by ultrasonication. Then, add the w / o type emulsion to the water under a constant temperature water bath at 50℃ and emulsify it again by high-speed stirring to obtain w / o / w type multiple Pickering emulsion.

[0084] (3) Place the w / o / w type multiple Pickering emulsion in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 28g of melamine resin prepolymer into the emulsion over a period of 1.5h. After the addition is complete, raise the temperature to 80℃ to allow the resin prepolymer and the temperature-sensitive polymer monomers in the inner aqueous phase to begin polymerization and crosslinking. After keeping the temperature for 2.5h, the microcapsule aqueous dispersion can be obtained.

[0085] (4) After filtering and washing the microcapsule aqueous dispersion, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain low internal aqueous content double Pickering emulsion thermochromic microcapsules.

[0086] Comparative Example 6: High internal aqueous phase content dual Pickering emulsion thermochromic microcapsules, the preparation process of which is as follows:

[0087] (1) 2.16 g of hydrophobic nano-lignin was added to the oil phase of a ternary thermo-sensitive color-changing system prepared by uniformly dissolving 7.2 g of 2-phenylamino-3-methyl-6-dibutylaminofluorane, 21.6 g of bisphenol A and 151 g of tetradecyl alcohol at 50 °C. The mixture was then uniformly dispersed by ultrasonication. Then, an aqueous solution of a thermo-sensitive polymer monomer composed of 21 g of N-isopropylacrylamide, 0.63 g of allyl methacrylate, 0.12 g of ammonium persulfate and 178 g of deionized water was added to the oil phase of the ternary thermo-sensitive color-changing system. The mixture was then emulsified by high-speed stirring and ultrasonication to obtain a w / o type Pickering emulsion.

[0088] (2) Add 2g of hydrophilic nano-lignin to 568g of deionized water and disperse it evenly by ultrasonication. Then, add the w / o type emulsion to the water under a constant temperature water bath at 50℃ and emulsify it again by high-speed stirring to obtain a stable w / o / w type multiple Pickering emulsion.

[0089] (3) Place the w / o / w type multiple Pickering emulsion in a constant temperature water bath at 50℃ and mechanically stir. Slowly drop 28g of melamine resin prepolymer into the emulsion over a period of 1.5h. After the addition is complete, raise the temperature to 80℃ to allow the resin prepolymer and the temperature-sensitive polymer monomers in the inner aqueous phase to begin polymerization and crosslinking. After keeping the temperature for 2.5h, the microcapsule aqueous dispersion can be obtained.

[0090] (4) After filtering and washing the microcapsule aqueous dispersion, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain high internal aqueous content double Pickering emulsion thermochromic microcapsules.

[0091] Effect description:

[0092] The high-durability thermochromic microcapsules based on multiple Pickering emulsions prepared in Examples 1-8 of this invention were compared with the comparative thermochromic microcapsules in Comparative Examples 1-6 in terms of performance.

[0093] First, the encapsulation efficiency, uniformity, color-changing temperature range, and color-changing rate of the thermochromic microcapsules were tested, and the relevant test results are summarized in Table 1:

[0094] Table 1 Performance test results of thermochromic microcapsules

[0095]

[0096] As can be seen from the data in Table 1, the high-durability thermotropic reversible color-changing microcapsules based on multiple Pickering emulsions prepared in the examples have a high encapsulation rate, a relatively uniform distribution of microcapsule particle size, a large temperature range for color change of microcapsules, and a significantly slower color change rate. They have better performance under a wide range of use conditions, more uniform overall color change, and better visual appearance.

[0097] A comparison of the performance of Comparative Examples 1-6 with that of the Examples shows that, compared to the Examples, the Comparative Examples have a lower overall encapsulation efficiency, poorer particle size uniformity, a narrower color change temperature range, a faster color change rate, and poorer controllability. Under large-area application conditions, uneven color distribution and color patches may occur. This is mainly due to the different microstructures of the microcapsules. A detailed analysis follows.

[0098] Comparative Example 1 is a commercially available thermochromic microcapsule, and Comparative Example 2 is a self-made conventional thermochromic microcapsule with melamine resin as the capsule wall and ternary reversible thermochromic material as the core. The structures of the two are quite similar. However, because it uses a conventional surfactant emulsion as a template, the adhesion and encapsulation effect during the encapsulation process is poor, and the stability of the emulsion droplets is weak, resulting in a low encapsulation rate and poor uniformity of microcapsule size after encapsulation. On the other hand, because the microcapsule structure is relatively simple and the capsule wall is pure melamine resin, its color-changing temperature range is narrow and the color-changing rate is fast, resulting in some color-changing inhomogeneity and poor performance in large-area applications.

[0099] Comparative Example 3 is a microcapsule synthesized using ordinary Pickering emulsion as a template. Since Pickering emulsion has better stability and particle size uniformity than conventional surfactant emulsion, and is easier to adsorb during the encapsulation process, the encapsulation rate is relatively high and the particle uniformity is improved compared with Comparative Examples 1-2. However, it still faces the problem of a narrow color change temperature range and a fast color change rate, and there is a certain degree of color change inhomogeneity.

[0100] Comparative Example 4 shows thermochromic microcapsules prepared using a conventional internal aqueous phase double Pickering emulsion as a template. Due to the use of the double Pickering emulsion, the particle size distribution and encapsulation efficiency were improved. However, the conventional hydrogel inside could not act as a color-changing buffer as the thermosensitive hydrogel. Therefore, its color-changing ability was not significantly improved compared to conventional microcapsules. The improvement was only slight due to the higher specific heat capacity of the internal aqueous phase.

[0101] Comparative Examples 5-6 are thermochromic microcapsules prepared using dual Pickering emulsions with less or more temperature-sensitive internal aqueous phase as templates. Due to the uneven water-oil ratio inside the dual emulsions, their performance is significantly lower than that of the comparative examples. In particular, when there is more internal aqueous phase, the oil phase ratio is reduced, so the stability of the emulsion and the color development performance of the oil phase are significantly affected, resulting in poor performance.

[0102] Next, the thermochromic microcapsules were further prepared into protective coating samples to test their microcapsule content and colorfastness at similar depths of appearance. The relevant test results are summarized in Table 2:

[0103] Table 2. Performance test results of coatings prepared from thermochromic microcapsules

[0104]

[0105] As can be seen from the data in Table 2, the protective coatings prepared in Examples 1-8 require relatively low microcapsule dosages to achieve suitable color development effects, and their color-changing ability remains at a good level even after multiple cycles or UV aging. In contrast, the protective coatings prepared in Comparative Examples 1-6 require larger microcapsule dosages, and their color-changing performance declines significantly after multiple cycles or prolonged UV aging. This indicates poor durability and insufficient color-changing lifespan in outdoor or relatively harsh environments.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments without departing from the technical essence of the present invention shall still fall within the scope of the present invention.

Claims

1. A highly durable thermoreversible color-changing microcapsule based on a multiple Pickering emulsion, characterized in that it is Thermotropic reversible color-changing microcapsules were obtained by in-situ polymerization and encapsulation of a w / o / w type multiple Pickering emulsion as a template using a resin prepolymer. The microcapsules had a particle size of 2-10 μm and an outer wall thickness of 50-80 nm. The multiple Pickering emulsion consisted of an inner aqueous phase of a thermosensitive polymer monomer aqueous solution, an inner emulsifier of lipophilic nanoparticles, an inner oil phase of a ternary thermosensitive color-changing system composed of pigments, color developers, and solvents, and an outer emulsifier of hydrophilic nanoparticles. The mass ratio of the inner aqueous phase to the inner oil phase was 1:(1.5~3), and the mass concentration of the multiple Pickering emulsion was 25-40%. The thermosensitive polymer monomer aqueous solution was composed of thermosensitive polymer monomers, crosslinking agents, initiators, and water. The thermosensitive polymer monomers were at least one of N-isopropylacrylamide, dimethylaminoethyl methacrylate, N-vinylcaprolactam, diethyl vinylphosphonate, and polyethylene glycol oligoacrylate, with a mass concentration of 8-12%.

2. A thermoreversible colour-changing microcapsule as claimed in claim 1, characterised in that The crosslinking agent in the aqueous solution of the thermosensitive polymer monomer is at least one selected from N,N-methylenebisacrylamide, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, N-hydroxymethylacrylamide, ethylene glycol dimethacrylate, and allyl methacrylate, and the amount used is 1% to 10% of the thermosensitive monomer; the initiator in the aqueous solution of the thermosensitive polymer monomer is at least one selected from potassium persulfate, ammonium persulfate, azobisisopropylammoniazoline hydrochloride, and azobisisobutylammoniazoline dihydrochloride, and the amount used is 0.3% to 3% of the thermosensitive monomer.

3. The thermotropic reversible color-changing microcapsule according to claim 1, characterized in that... The pigment is at least one of crystal violet lactone, malachite green, 2-phenylamino-3-methyl-6-dibutylaminofluorane, 3',6'-dimethoxyfluorane, 1,3-dimethyl-6-diethylaminofluorane, 3,3-di(4-ethylamino-2-ethoxyphenyl)-4-azaphenylfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, and thermoluminescent green; the color developer is at least one of bisphenol A, bisphenol F, bisphenol S, 4,4'-cyclohexylenebisphenol, 4-allyloxy-4'-hydroxydiphenyl sulfone, bis(3-amino-4-hydroxyphenyl) sulfone, and bis(3-allyl-4-hydroxyphenyl) sulfone; the solvent is at least one of a saturated fatty alcohol or fatty acid containing a hydrocarbon chain of ten to eighteen carbon atoms, triglyceride decanoate, methyl octadecanoate, and ethyl octadecanoate; wherein the mass concentration of the pigment molecules is 0.8-6%, and the mass ratio of pigment to color developer is 1:(1.5-4).

4. The thermotropic reversible color-changing microcapsule according to claim 1, characterized in that... The hydrophilic nanoparticles are at least one of the following: surface-hydrophilic nano-SiO2, TiO2, ZnO, CaCO3, Fe3O4, graphene oxide, kaolin, montmorillonite, diatomaceous earth, attapulgite, cellulose, lignin, and alginate. Their particle size is 5-30 nm, and their amount is 0.1-1.5% of the total amount of external aqueous phase.

5. The thermotropic reversible color-changing microcapsule according to claim 1, characterized in that... The oleophilic nanoparticles are at least one of the following: nano-SiO2, TiO2, ZnO, CaCO3, Fe3O4, graphene oxide, kaolin, montmorillonite, diatomaceous earth, attapulgite, cellulose, lignin, and alginate, after surface partial hydrophobic modification. The particle size is 5-30 nm, and the amount used is 0.5-3% of the total amount of the internal oil phase. The hydrophobic modification process involves surface grafting modification of the nanoparticles using at least one of dichlorodimethylsiloxane, trimethylchlorosilane, ethyltriethoxysilane, tridecafluorooctyltriethoxysilane, oleic acid, and stearic acid.

6. The thermotropic reversible color-changing microcapsule according to claim 1, characterized in that... The resin prepolymer is at least one of melamine resin prepolymer, urea-formaldehyde resin prepolymer, phenolic resin prepolymer, methyl melamine-formaldehyde resin prepolymer, polyurethane resin prepolymer, and acrylic resin, and its dosage is 5-13% of the total amount of the inner oil phase and the inner water phase.

7. The method for preparing a thermotropic reversible color-changing microcapsule according to claim 1, characterized in that... Includes the following steps: (1) One-time emulsification: At 50°C, lipophilic nanoparticles were added to the oil phase of the ternary thermosensitive color-changing system and dispersed evenly by ultrasonication. Then, the aqueous solution of the thermosensitive polymer monomer was added to the oil phase and a stable w / o type Pickering emulsion was obtained by high-speed stirring and ultrasonic emulsification. (2) Secondary emulsification: Hydrophilic nanoparticles are added to water and dispersed evenly by ultrasonication. Then, w / o type emulsion is added to the aqueous phase under constant temperature water bath at 50℃ and emulsified again by high-speed stirring to obtain a stable w / o / w type multiple Pickering emulsion. (3) In-situ polymerization: Place the multiple emulsion in a 50°C constant temperature water bath. Under mechanical stirring, slowly drip the resin prepolymer into the emulsion for 1-2 hours. After the dripping is completed, raise the temperature to 80-90°C to allow the temperature-sensitive polymer monomers in the resin prepolymer capsule wall and the inner aqueous phase to begin polymerization and crosslinking. After keeping warm for 2-3 hours, the microcapsule aqueous dispersion can be obtained. (4) Separation and purification: After filtering and washing the aqueous dispersion of microcapsules, place it in a vacuum oven and dry it at 60°C for 24 hours to obtain thermo-reversible color-changing microcapsules.

8. The application of the high-durability thermotropic reversible color-changing microcapsules based on multiple Pickering emulsions as described in claim 1 as a pigment component in coatings, inks, plastics, rubber, and fibers.

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