Multi-responsiveness hydrogel with structural color and preparation method thereof

Abstract

The invention discloses a multi-responsive hydrogel with structural color and a preparation method thereof, and the preparation method comprises the following steps: (1) uniformly mixing a nanogel photonic crystal, a hydrophilic monomer, polyethylene glycol diacrylate, carbon black and a photoinitiator to obtain a gel precursor; (2) placing the gel precursor in a dark environment, and placing the gel precursor for at least 24 hours in a mild disturbance state; (3) standing the product in the step (2) at 1-8 DEG C for 1-2 hours; and (4) putting a product obtained in the step (3) on ice, and carrying out light curing, so as to obtain the multi-responsive hydrogel with the structural color. The multi-responsiveness hydrogel with the structural color prepared by the invention has rich and bright colors while giving consideration to the mechanical properties of materials, also has multiple responses to temperature and strain, and has application potential in the fields of flexible sensors, intelligent display and soft-bodied robots.

Description

Technical Field

[0001] This application relates to the field of functional materials technology, and in particular to a multi-responsive hydrogel with structural color and its preparation method. Background Technology

[0002] Currently, responsive hydrogels, as a class of polymer materials that combine flexibility and biocompatibility, show broad application prospects in fields such as flexible sensing, smart displays, wearable devices, medical devices, controlled drug delivery, and soft robotics. However, existing traditional hydrogels are mostly colorless or semi-transparent, lacking intuitively identifiable color changes, making it difficult to visualize and provide real-time feedback on external stimuli. This shortcoming limits their further application in intelligent sensing and visualization devices.

[0003] To overcome the above problems, researchers have introduced photochromic molecules or dyes to color hydrogels. Although color response has been achieved to some extent, these methods usually rely on the doping of organic dyes or functional molecules. During use, molecular migration and fading are likely to occur, and environmental pollution may even occur. At the same time, the introduction of dyes often weakens the mechanical properties of hydrogels, which is not conducive to the long-term stable service of materials.

[0004] Photonic crystal materials generate structural colors through the selective reflection of light by their internal periodic and ordered structures. These colors offer significant advantages, such as no need for dyes, stable color, high saturation, and resistance to fading, making them an ideal approach for achieving visual responses in hydrogels. However, existing photonic crystal hydrogel systems generally suffer from insufficient mechanical properties: their network structure is relatively fragile and prone to structural damage during stretching, bending, or repeated deformation, leading to color decay or even disappearance. Simultaneously, in some systems, the photonic crystal structure is not firmly bonded to the hydrogel matrix, making it difficult to maintain high-saturation structural colors while simultaneously ensuring material strength and toughness. This severely restricts their practical application in flexible devices and wearable devices.

[0005] Furthermore, thermosensitive hydrogels typically undergo significant volume phase transitions near the low critical solution temperature (LCST) or high critical solution temperature (UCST), a characteristic that endows the material with the ability to respond to temperature stimuli. However, existing thermosensitive photonic crystal hydrogel systems still have many shortcomings. For example, the phase transition temperature control range is limited, structural color and mechanical properties are prone to decay during temperature cycling, and response stability and repeatability are poor. Especially under conditions of multiple deformations or complex environments, these materials find it difficult to maintain both high saturation of structural color and excellent mechanical properties. Summary of the Invention

[0006] Based on this, this application provides a multi-responsive hydrogel with structural color and its preparation method. The preparation process is simple and convenient, the color of the obtained hydrogel is adjustable, it has excellent mechanical properties, and it can respond to temperature changes and different strain ratios to exhibit different colors.

[0007] A method for preparing a multi-responsive hydrogel with structural color includes the following steps: (1) The nanogel photonic crystal, hydrophilic monomer, polyethylene glycol diacrylate, carbon black and photoinitiator are mixed evenly to obtain a gel precursor; (2) Place the gel precursor in a light-protected environment and leave it under gentle disturbance for at least 24 hours; (3) Let the product from step (2) stand at 1~8℃ for 1~2 hours; (4) Place the product of step (3) on ice for photocuring to obtain the multi-responsive hydrogel with structural color.

[0008] The multi-responsive hydrogel provided in this application has a highly saturated structural color, which is a variety of colors in the visible spectrum (e.g., purple, red, green). The structural color can be adjusted by changing the size of the nanogel photonic crystal microspheres and their concentration in the gel precursor.

[0009] The multi-responsive hydrogel provided in this application also has excellent mechanical properties, such as mechanical strength, toughness, and cyclic stability, making it suitable for fields with high requirements for the comprehensive performance of materials, such as intelligent sensing and flexible devices.

[0010] In step (2), the nanogel photonic crystal is placed under mild disturbance to allow it to fully self-assemble under external force. In step (3), it is placed at low temperature to keep the self-assembled structure of the microspheres tightly packed at that temperature stable. In step (4), under the premise of stable self-assembled structure, it is photocured at 1~8℃ on a cooling platform. That is, it is kept at low temperature during the photocuring process to prevent temperature fluctuations from causing changes in the size of the nanogel photonic crystal microspheres and thus destroying the self-assembled structure.

[0011] The multi-responsiveness in this application refers to the hydrogel's ability to exhibit different colors in response to temperature changes, and also in response to changes in strain.

[0012] As the temperature gradually increases from 0℃ to 30℃, the hydrogel changes from a colorless state to a colored state.

[0013] As the strain increases from 0 to 100%, the reflected wavelength of the hydrogel shifts towards a gradually decreasing direction, resulting in different colors.

[0014] The multi-responsive hydrogel uses hydrophilic monomers as the main raw material, and adds carbon black and nano-gel photonic crystals to adjust the color, and polyethylene glycol diacrylate as a chemical crosslinking agent to improve mechanical properties.

[0015] Several alternative methods are provided below, but they are not intended as additional limitations on the overall solution above. They are merely further additions or optimizations. Provided there are no technical or logical contradictions, each alternative method can be combined individually with respect to the overall solution above, or multiple alternative methods can be combined with each other.

[0016] The nanogel photonic crystal is prepared using N-phenylmaleamic acid, N-isopropylacrylamide, and N,N'-methylenebisacrylamide, with anionic surfactant added during the preparation process. Specifically, the preparation method of the nanogel photonic crystal includes: After mixing N-isopropylacrylamide, N,N'-methylenebisacrylamide, anionic surfactant, and water evenly, a mixed solution is obtained. Under a nitrogen atmosphere, potassium persulfate was added to the mixed solution and the polymerization reaction was carried out at 60-80°C for 0.5-1 hour. Then, N-phenylmaleamic acid was added and the polymerization reaction was continued at 60-80°C for 2-4 hours. After dialysis, an anionic surfactant was added and the mixture was concentrated to obtain the nanogel photonic crystal.

[0017] Anionic surfactants are added as stabilizers after dialysis. The amount added should be appropriate, as too much or too little will affect the structural color of the multi-responsive hydrogel.

[0018] After the nucleation phase of emulsion polymerization ends and enters the constant-rate phase, N-phenylmaleamic acid monomer is copolymerized with NIPAM onto the surface of the microspheres. Since N-phenylmaleamic acid contains aromatic rings and has a relatively high refractive index, it can maximize the refractive index of the microspheres, giving them a saturated structural color during the subsequent AM photopolymerization process.

[0019] In the preparation of nanogel photonic crystals, after the polymerization reaction is completed, a concentration process is carried out. The concentration process adopts the rotary evaporation method, with a vacuum degree of less than 60 mbar and a water bath temperature of 40~60℃.

[0020] Optionally, the anionic surfactant is one of sodium dodecyl sulfate and sodium lauryl ether sulfate, and the mass fraction of the anionic surfactant added after dialysis in the gel precursor is 0.2% to 1%. The type of anionic surfactant affects the structural color of the hydrogel.

[0021] In the process of preparing nanogel photonic crystals, anionic surfactants are added before and after dialysis. The specific types of anionic surfactants before and after dialysis can be the same or different.

[0022] The anionic surfactants added before and after dialysis have different functions. The anionic surfactant added before dialysis is usually sodium dodecyl sulfate, which is a component of conventional emulsion polymerization and is used to form micelles of a specific size. This allows the synthesis of nanogel photonic crystals of different sizes, exhibiting different structural colors. This part of the anionic surfactant is removed from the system during dialysis.

[0023] After dialysis, anionic surfactants are added and then rotary evaporated to give the surface of the nanogel photonic crystals a negative charge. The nanogel photonic crystals repel each other, keeping them in a monodisperse and stable state in the gel precursor. This is beneficial for subsequent self-assembly and achieves the goal of fixing the structural color in the hydrogel.

[0024] The mass fraction of the anionic surfactant added before dialysis in the mixed solution is 0.1% to 0.5%.

[0025] Optionally, the mass fraction of the nanogel photonic crystal in the gel precursor is 3% to 7%.

[0026] Optionally, the hydrophilic monomer is one of acrylamide, N-hydroxyethylacrylamide, and N-hydroxymethylacrylamide, and the mass fraction of the hydrophilic monomer in the gel precursor is 10% to 20%.

[0027] Optionally, in the gel precursor, the molar number of polyethylene glycol diacrylate is n1, the molar number of the hydrophilic monomer is n2, and the value of n1 / n2 ranges from 0.03% to 0.14%.

[0028] Optionally, the mass fraction of carbon black in the gel precursor is 0.005~0.015wt%.

[0029] Carbon black is mainly used to make colors more vibrant. It is added in the form of an aqueous solution, for example, a 1~3 mg / mL aqueous solution of carbon black can be used.

[0030] Optionally, the gentle perturbation is achieved using a circular shaking table or a reciprocating shaking table. The rotation speed of the circular shaking table is 200~800 rpm, and the stroke of the reciprocating shaking table is 5~30 mm, with a reciprocating frequency of 50~300 rpm. Gentle perturbation is a necessary condition for the formation of structural colors. Under gentle perturbation, nanogel photonic crystals can automatically find the position with the lowest potential energy, such as a face-centered cubic (FCC) structure. After crystallization, this significantly enhances the brightness and saturation of the structural colors.

[0031] This application also provides a multi-responsive hydrogel with structural color, which is prepared by the method described above. The multi-responsive hydrogel with structural color has a fracture strength of 50~80kPa, a fracture strain of 100%~2500%, good cycle stability, and a hysteresis rate of less than 5%.

[0032] Optionally, the multi-responsive hydrogel with structural color changes from a colorless state to a colored state during the process of heating from 0°C to 30°C.

[0033] The multi-responsive hydrogel with structural color prepared in this application has rich and bright colors while taking into account the mechanical properties of the material. It also has multiple responses to temperature and strain, and has application potential in the fields of flexible sensors, smart displays and soft robots. Attached Figure Description

[0034] Figure 1 A photograph of the multi-responsive hydrogel prepared in Example 1 at room temperature; Figure 2 A photograph of the multi-responsive hydrogel prepared in Example 2 at room temperature; Figure 3 Photographs of the multi-responsive hydrogel prepared in Example 1 under different strains; Figure 4 Tensile curves of hydrogels prepared with different crosslinking agents in Examples 3a-3b; Figure 5 A photograph of the multi-responsive hydrogel prepared in Example 4 at 15°C; Figure 6 A photograph of the multi-responsive hydrogel prepared in Example 4 at 25°C; Figure 7 Cyclic tensile curves of the multi-responsive hydrogel prepared in Example 4 under different strains; Figure 8 A photograph of the multi-responsive hydrogel prepared in Example 8 at room temperature; Figure 9 Photograph of the unstructured colored hydrogel prepared for Comparative Example 1 at room temperature. Detailed Implementation

[0035] The following examples further illustrate the preparation method of the multi-responsive hydrogel with structural color of this application. The following examples are for illustrative purposes only and are not intended to limit this application.

[0036] Example 1 A method for preparing a multi-responsive hydrogel with structural color includes the following steps: (1) Synthesis of nanogel photonic crystals: 1.17 g N-isopropylacrylamide, 0.033 g N,N-methylenebisacrylamide, 0.01 g sodium dodecyl sulfate, and 70 g deionized water were added to a 100 mL three-necked flask and mixed thoroughly by mechanical stirring (200 rpm). After thorough mixing, high-purity nitrogen gas was bubbled through the mixture to remove oxygen for 30 min. The temperature was raised to 70 °C, and 2 mL of deionized water containing 0.02 g potassium persulfate was added dropwise to initiate the polymerization reaction. After polymerization for 30 min, 0.02 g of potassium persulfate was added to the mixture. 2 mL of N,N-dimethylformamide solution of N-phenylmaleamic acid was reacted at 70 °C for 3 h. After the reaction was completed, the resulting emulsion was placed in a dialysis bag and dialyzed for one week, with the water changed daily. After dialysis, the dialyzed emulsion was transferred to a pear-shaped flask, and 0.2 g of an aqueous solution containing 70 wt% sodium lauryl ether sulfate (manufacturer: Bid Pharmaceutical, catalog number: BD00802112) was added. After mixing evenly, the solution was concentrated to 10 mL by rotary evaporation to obtain a microsphere concentrate. The solid content in the microsphere concentrate was then determined by drying and weighing. This solid content is the polymer microsphere content in the microsphere concentrate, and the microspheres are the nanogel photonic crystals.

[0037] (2) Synthesis of photonic crystal hydrogels: Mix 0.2g acrylamide, 1μL polyethylene glycol diacrylate (weight average molecular weight of 575), 0.5μL 2-hydroxy-2-methyl-1-phenyl-1-propanone (photoinitiator), 20μL of 2mg / mL carbon black aqueous solution, and the microsphere concentrate from step (1) evenly to obtain a gel precursor. Set the mass fraction of polymer microspheres in the gel precursor to 5wt%. Determine the amount to be added based on the solid content of the microsphere concentrate. Finally, add deionized water to make up the solution to 1g to obtain the gel precursor.

[0038] The gel precursor was injected into a silicone mold (with release film protection) sandwiched between two glass plates using a syringe. It was then self-assembled for one day in the dark using a circular shaker at 500 rpm. After that, it was stabilized in a 4°C refrigerator for 1 hour and polymerized on ice for 30 minutes under 20W UV power (365nm, the same UV wavelength thereafter). When it returned to room temperature, a red structural color hydrogel with ultra-high tensile properties and stimulus response was obtained.

[0039] See Figure 1 As shown in the photograph, the hydrogel prepared in this embodiment appears red at 25°C.

[0040] See Figure 3 As shown, the hydrogel prepared in this embodiment is photographed at 25°C under different strains. Its color changes from red to blue as the strain increases.

[0041] Example 2 A method for preparing a multi-responsive hydrogel with structural color includes the following steps: (1) Synthesis of nanogel photonic crystals: 1.17 g N-isopropylacrylamide, 0.033 g N,N-methylenebisacrylamide, 0.02 g sodium dodecyl sulfate, and 70 g deionized water were added to a 100 mL three-necked flask and mixed thoroughly by mechanical stirring (200 rpm). After thorough mixing, high-purity nitrogen gas was bubbled through the mixture to remove oxygen for 30 min. The temperature was raised to 70 °C, and 2 mL of deionized water containing 0.02 g potassium persulfate was added dropwise to initiate the polymerization reaction. After polymerization for 30 min, 0.02 g of potassium persulfate was added to the mixture. 2 mL of N,N-dimethylformamide solution of N-phenylmaleamic acid was added and reacted at 70°C for 3 h. After the reaction was completed, the emulsion was placed in a dialysis bag and dialyzed for one week, with the water changed daily. After dialysis, the solution in the dialysis bag was transferred to a pear-shaped flask, and 0.2 g of an aqueous solution containing 70 wt% sodium lauryl polyoxyethylene ether sulfate (same as in Example 1) was added. After mixing evenly, the solution was concentrated to 10 mL by rotary evaporation to obtain a microsphere concentrate. The solid content in the microsphere concentrate was then determined by drying and weighing. This solid content is the polymer microsphere content in the microsphere concentrate.

[0042] (2) Synthesis of photonic crystal hydrogels: Mix 0.2g acrylamide, 1μL polyethylene glycol diacrylate (weight average molecular weight of 575), 0.5μL 2-hydroxy-2-methyl-1-phenyl-1-propanone, 20μL of 2mg / mL carbon black aqueous solution, and the microsphere concentrate from step (1) evenly to obtain a gel precursor. Set the mass fraction of polymer microspheres in the gel precursor to 5wt%. Determine the amount to be added based on the solid content of the microsphere concentrate. Finally, add deionized water to make up the solution to 1g to obtain the gel precursor.

[0043] The gel precursor was injected into a silicone mold (with release film protection) sandwiched between two glass plates using a syringe. It was then self-assembled for one day in the dark using a circular shaker at 500 rpm. After that, it was stabilized in a 4°C refrigerator for 1 hour and polymerized on ice at 20W UV (365nm) power for 30 minutes. When it returned to room temperature, a green structural color hydrogel with ultra-high tensile properties and stimulus response was obtained.

[0044] See Figure 2 The image shows a photograph of the hydrogel prepared in this embodiment at room temperature (20°C).

[0045] Example 3a A method for preparing a multi-responsive hydrogel with structural color includes the following steps: (1) For the synthesis of nanogel photonic crystals, see Example 1.

[0046] (2) Synthesis of photonic crystal hydrogels: Mix 0.2 g acrylamide (n2 = 2.82 mmol), 0.5 μL 2-hydroxy-2-methyl-1-phenyl-1-propanone, 20 μL of 2 mg / mL carbon black aqueous solution, and the microsphere concentrate from step (1) thoroughly. Finally, add 0.085 mol polyethylene glycol diacrylate (number average molecular weight 575), with a polyethylene glycol diacrylate molar fraction of 0.03 mol% (molar number of polyethylene glycol diacrylate n1 = 0.0846 mmol, n1 / n2 = 0.03%). Set the mass fraction of polymer microspheres in the gel precursor to 5 wt%. Determine the amount added based on the solid content of the microsphere concentrate. Finally, add deionized water to make up the solution to 1 g to obtain the gel precursor.

[0047] The gel precursor was injected into a silicone mold (with release film protection) sandwiched between two glass plates using a syringe. It was then self-assembled for one day in the dark using a circular shaker at 500 rpm. After that, it was stabilized in a 4°C refrigerator for 1 hour and polymerized on ice at 20W UV power for 30 minutes. When it returned to room temperature (22°C), a red structural color hydrogel with ultra-high tensile properties and stimulus response was obtained.

[0048] Example 3b Compared to Example 3a, only the molar fraction of polyethylene glycol diacrylate is different; in this example, the molar fraction of polyethylene glycol diacrylate is 0.06 mol.

[0049] Example 3c Compared to Example 3a, only the molar fraction of polyethylene glycol diacrylate is different; in this example, the molar fraction of polyethylene glycol diacrylate is 0.14 mol.

[0050] The stretching curves of the hydrogels prepared in Examples 3a to 3b are shown in the figure. Figure 4 As shown, the strain gradually decreases as the molar fraction of polyethylene glycol diacrylate increases.

[0051] Example 4 A method for preparing a multi-responsive hydrogel with structural color includes the following steps: (1) For the synthesis of nanogel photonic crystals, see Example 1.

[0052] (2) Synthesis of photonic crystal hydrogels: Mix 0.2g acrylamide, 1μL polyethylene glycol diacrylate (weight average molecular weight of 575), 0.5μL 2-hydroxy-2-methyl-1-phenyl-1-propanone, and the microsphere concentrate from step (1) evenly to obtain a gel precursor. Set the mass fraction of polymer microspheres in the gel precursor to 5wt%. Determine the amount to be added based on the solid content of the microsphere concentrate. Finally, add deionized water to make up the solution to 1g to obtain the gel precursor.

[0053] The gel precursor was injected into a silicone mold (with release film protection) sandwiched between two glass plates using a syringe. It was then self-assembled for one day in the dark using a circular shaker at 500 rpm. After that, it was stabilized in a 4°C refrigerator for 1 hour and polymerized on ice at 20W UV power for 30 minutes. When it returned to room temperature, a structured color hydrogel with ultra-high tensile properties and stimulus response was obtained.

[0054] See Figure 5 The image shows a photograph of the hydrogel prepared in this embodiment at 15°C. At 15°C, the hydrogel is transparent, and the screw underneath can be clearly seen.

[0055] See Figure 6 The image shows a photograph of the hydrogel prepared in this embodiment at 25°C. At 25°C, the hydrogel is no longer transparent but exhibits color.

[0056] See Figure 7 As shown, the cyclic tensile curves of the hydrogel prepared in this embodiment under different strains are presented. Figure 7 It involves cyclic stretching 50 times under different strains (stretching rate 0.1 s). -1 The curves obtained were smooth and without obvious fluctuations, indicating that the mechanical properties of the hydrogel remained stable after cyclic stretching, without any obvious fatigue damage or performance degradation.

[0057] Example 5 A method for preparing a multi-responsive hydrogel with structural color includes the following steps: (1) For the synthesis of nanogel photonic crystals, see Example 1.

[0058] (2) Synthesis of photonic crystal hydrogels: Mix 0.2g acrylamide, 1μL polyethylene glycol diacrylate (number average molecular weight of 575), 0.5μL 2-hydroxy-2-methyl-1-phenyl-1-propanone, and the microsphere concentrate from step (1) evenly to obtain a gel precursor. Set the mass fraction of polymer microspheres in the gel precursor to 7wt%. Determine the amount to be added based on the solid content of the microsphere concentrate. Finally, add deionized water to make up the solution to 1g to obtain the gel precursor.

[0059] The gel precursor was injected into a silicone mold (with release film protection) sandwiched between two glass plates using a syringe. It was then self-assembled for one day in the dark using a circular shaker at 500 rpm. After that, it was stabilized in a 4°C refrigerator for 1 hour and polymerized on ice at 20W UV power for 30 minutes. When it returned to room temperature (24°C), a green structural color hydrogel with ultra-high tensile properties and stimulus response was obtained.

[0060] Example 6 A method for preparing a multi-responsive hydrogel with structural color includes the following steps: (1) For the synthesis of nanogel photonic crystals, see Example 1.

[0061] (2) Synthesis of photonic crystal hydrogels: Mix 0.2g N-hydroxymethylacrylamide, 1μL polyethylene glycol diacrylate (molecular weight 575), 0.5μL 2-hydroxy-2-methyl-1-phenyl-1-propanone, and the microsphere concentrate from step (1) evenly to obtain a gel precursor. Set the mass fraction of polymer microspheres in the gel precursor to 5wt%. Determine the amount to be added based on the solid content of the microsphere concentrate. Finally, add deionized water to make up the solution to 1g to obtain the gel precursor.

[0062] The gel precursor was injected into a silicone mold (with release film protection) sandwiched between two glass plates using a syringe. It was then self-assembled for one day in the dark using a circular shaker at 500 rpm. After that, it was stabilized in a 4°C refrigerator for 1 hour and polymerized on ice at 20W UV power for 30 minutes. When it returned to room temperature (23°C), a red structural color hydrogel with ultra-high tensile properties and stimulus response was obtained.

[0063] Example 7 A method for preparing a multi-responsive hydrogel with structural color includes the following steps: (1) Synthesis of nanogel photonic crystals: 1.17 g N-isopropylacrylamide, 0.033 g N,N-methylenebisacrylamide, 0.01 g sodium dodecyl sulfate, and 70 g deionized water were added to a 100 mL three-necked flask and mixed thoroughly by mechanical stirring (200 rpm). After thorough mixing, high-purity nitrogen gas was bubbled through the mixture to remove oxygen for 30 min. The temperature was raised to 70 °C, and 2 mL of deionized water containing 0.02 g potassium persulfate was added dropwise to initiate the polymerization reaction. After 30 min, 2 mL of water containing 0.02 g N-phenylmaleic acid was added. N,N-dimethylformamide solution; react at 70℃ for 3 hours; after the reaction is complete, place the resulting emulsion in a dialysis bag and dialyze for one week, changing the water daily during this period; after dialysis, transfer the dialyzed emulsion to a pear-shaped flask, add 0.14g sodium dodecyl sulfate, mix well, and then concentrate the solution to 10mL by rotary evaporation to obtain a microsphere concentrate. At this point, the solid content in the microsphere concentrate is determined by the drying and weighing method, and this solid content is the polymer microsphere content in the microsphere concentrate.

[0064] (2) Synthesis of photonic crystal hydrogels: Mix 0.2g acrylamide, 1μL polyethylene glycol diacrylate (weight average molecular weight of 575), 0.5μL 2-hydroxy-2-methyl-1-phenyl-1-propanone, 20μL of 2mg / mL carbon black aqueous solution, and the microsphere concentrate from step (1) evenly to obtain a gel precursor. Set the mass fraction of polymer microspheres in the gel precursor to 5wt%. Determine the amount to be added based on the solid content of the microsphere concentrate. Finally, add deionized water to make up the solution to 1g to obtain the gel precursor.

[0065] The gel precursor was injected into a silicone mold (with release film protection) sandwiched between two glass plates using a syringe. It was then self-assembled for one day in the dark using a circular shaker at 500 rpm. After that, it was stabilized in a 4°C refrigerator for 1 hour and polymerized on ice at 20W UV power for 30 minutes. When it returned to room temperature (22°C), a red structural color hydrogel with ultra-high tensile properties and stimulus response was obtained.

[0066] Example 8 A method for preparing a multi-responsive hydrogel with structural color includes the following steps: (1) For the synthesis of nanogel photonic crystals, see Example 1.

[0067] (2) Synthesis of photonic crystal hydrogels: Mix 0.2g acrylamide, 1μL polyethylene glycol diacrylate (weight average molecular weight of 575), 0.5μL 2-hydroxy-2-methyl-1-phenyl-1-propanone, 20μL of 2mg / mL carbon black aqueous solution, and the microsphere concentrate from step (1) evenly to obtain a gel precursor. Set the mass fraction of polymer microspheres in the gel precursor to 5wt%. Determine the amount to be added based on the solid content of the microsphere concentrate. Finally, add deionized water to make up the solution to 1g to obtain the gel precursor.

[0068] The gel precursor was injected into a silicone mold (with release film protection) sandwiched between two glass plates using a syringe. It was then stabilized in a 4°C refrigerator for 1 hour and polymerized on ice at 20W UV power for 30 minutes. When it returned to room temperature (20°C), since no self-assembly was performed, a low-saturation red structural color hydrogel with ultra-high tensile properties and stimulus response was obtained.

[0069] See Figure 8 The image shown is a photograph of the photonic crystal hydrogel prepared in this embodiment at room temperature.

[0070] Comparative Example 1 A method for preparing a multi-responsive hydrogel with structural color includes the following steps: (1) For the synthesis of nanogel photonic crystals, see Example 1.

[0071] (2) Synthesis of photonic crystal hydrogels: Mix 0.3g acrylamide, 1μL polyethylene glycol diacrylate (weight average molecular weight of 575), 0.5μL 2-hydroxy-2-methyl-1-phenyl-1-propanone, and the microsphere concentrate from step (1) evenly to obtain a gel precursor. Set the mass fraction of polymer microspheres in the gel precursor to 5wt%. Determine the amount to be added based on the solid content of the microsphere concentrate. Finally, add deionized water to make up the solution to 1g to obtain the gel precursor.

[0072] The gel precursor was injected into a silicone mold (with release film protection) sandwiched between two glass plates using a syringe. It was then self-assembled for one day in the dark using a circular shaker at 500 rpm. After that, it was stabilized in a 4°C refrigerator for 1 hour and polymerized on ice at 20W UV power for 30 minutes. When it was restored to room temperature (24°C), due to the unsuitable acrylamide content, a red structural color hydrogel with ultra-high tensile properties and stimulus response was not obtained.

[0073] See Figure 9 The image shown is a photograph of the structureless colored hydrogel prepared in this comparative example at room temperature.

[0074] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a multi-responsive hydrogel with structural color, characterized in that, Includes the following steps: (1) The nanogel photonic crystal, hydrophilic monomer, polyethylene glycol diacrylate, carbon black and photoinitiator are mixed evenly to obtain a gel precursor; (2) Place the gel precursor in a light-protected environment and leave it under gentle disturbance for at least 24 hours; (3) Let the product from step (2) stand at 1~8℃ for 1~2 hours; (4) Place the product of step (3) on ice for photocuring to obtain the multi-responsive hydrogel with structural color.

2. The method for preparing a multi-responsive hydrogel with structural color as described in claim 1, characterized in that, The preparation method of the nanogel photonic crystal includes: After mixing N-isopropylacrylamide, N,N'-methylenebisacrylamide, anionic surfactant, and water evenly, a mixed solution is obtained. Under a nitrogen atmosphere, potassium persulfate was added to the mixed solution and the polymerization reaction was carried out at 60-80°C for 0.5-1 hour. Then, N-phenylmaleamic acid was added and the polymerization reaction was continued at 60-80°C for 2-4 hours. After dialysis, an anionic surfactant was added and the mixture was concentrated to obtain the nanogel photonic crystal.

3. The method for preparing a multi-responsive hydrogel with structural color as described in claim 2, characterized in that, The anionic surfactant is either sodium dodecyl sulfate or sodium lauryl ether sulfate, and the mass fraction of the anionic surfactant added after dialysis in the gel precursor is 0.2% to 1%.

4. The method for preparing a multi-responsive hydrogel with structural color as described in claim 1, characterized in that, In the gel precursor, the mass fraction of the nanogel photonic crystal is 3% to 7%.

5. The method for preparing a multi-responsive hydrogel with structural color as described in claim 1, characterized in that, The hydrophilic monomer is one of acrylamide, N-hydroxyethylacrylamide, and N-hydroxymethylacrylamide, and the mass fraction of the hydrophilic monomer in the gel precursor is 10% to 20%.

6. The method for preparing a multi-responsive hydrogel with structural color as described in claim 1, characterized in that, The number of moles of the polyethylene glycol diacrylate is n1, the number of moles of the hydrophilic monomer is n2, and the value of n1 / n2 ranges from 0.03% to 0.14%.

7. The method for preparing a multi-responsive hydrogel with structural color as described in claim 1, characterized in that, The mass fraction of carbon black in the gel precursor is 0.005~0.015wt%.

8. The method for preparing a multi-responsive hydrogel with structural color as described in claim 1, characterized in that, The gentle disturbance is achieved using a circular shaking table or a reciprocating shaking table. The rotation speed of the circular shaking table is 200~800 rpm, and the stroke of the reciprocating shaking table is 5~30 mm, with a reciprocating frequency of 50~300 rpm.

9. A multi-responsive hydrogel with structural color, characterized in that, The multi-responsive hydrogel with structural color is prepared by the preparation method of any one of claims 1 to 8, wherein the tensile strength of the multi-responsive hydrogel with structural color is 50 to 80 kPa and the tensile strain of the multi-responsive hydrogel with structural color is 100% to 2500%.

10. The multi-responsive hydrogel with structural color as described in claim 9, characterized in that, The multi-responsive hydrogel with structural color changes from a colorless state to a colored state when heated from 0°C to 30°C.

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