An electrothermally stimulated synergistic shape-changing color-changing hydrogel actuator and its preparation method and application

Abstract

The application provides a hydrogel driver based on synergic deformation and color change under electric heating stimulation, which comprises at least a composite structure of a flexible electric heating layer and fluorescent color-changing hydrogel; the flexible electric heating layer is a driving layer and has an electric heating conversion effect; the fluorescent color-changing hydrogel has a temperature response effect and is driven by the temperature of the flexible electric heating layer to synchronously deform and change color; when electrified, the flexible electric heating layer is heated and expands, the fluorescent color-changing hydrogel is heated and loses water, and the volume shrinks, so that the flexible electric heating layer bends to one side of the fluorescent color-changing hydrogel; meanwhile, the fluorescent color-changing hydrogel changes the fluorescent color. The hydrogel driver based on synergic deformation and color change under electric heating stimulation prepared by the technical scheme of the application realizes color change of the fluorescent hydrogel driver during driving, and overcomes the problem of non-synergic deformation and color change of the driver in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of intelligent hydrogel driver materials, in particular to an electrothermal stimulation synergistic deformation and color-changing hydrogel driver and a preparation method and application thereof. BACKGROUND

[0002] In nature, animals such as chameleons and squids can change the color of their skin while moving, according to the needs of the external environment, to achieve the purpose of camouflage and communication, which is a skill for these animals to survive and improves their survival rate in nature. Based on this, a driver with similar synergistic deformation and color-changing function is developed for soft robots, thereby prolonging the service life.

[0003] In 1978, Professor Tanaka of MIT discovered that transparent polyacrylamide gel would gradually become blurred as the temperature decreased during the cooling process; after the temperature increased, the gel gradually recovered to the transparent state. This gel changes with temperature, becoming an intelligent polymer hydrogel, and thus the concept of intelligent hydrogel is proposed.

[0004] Intelligent hydrogel is a three-dimensional hydrophilic polymer network containing water, has soft and wet characteristics similar to biological tissues, and has adjustable modulus and stimulation response performance, is an ideal biomimetic material, and has shown great potential in the fields of biomimetic driving, soft robots and artificial muscles. In recent years, the prior art has provided a variety of pH, metal ion stimulation responsive fluorophores by copolymerization, coordination, doping and other ways in the polymer hydrogel, and obtained a fluorescent polymer hydrogel driver with rich biomimetic ability. However, the color-changing and deformation behavior of the reported fluorescent polymer hydrogel driver is often triggered by different stimulation sources, and there is a problem of difficulty in synchronizing deformation and color change, and most of the stimulation sources are pH, metal ions, etc., which have the problem of stimulation residue, which will further affect the deformation and color-changing ability during cyclic driving.

[0005] Electric stimulation as a convenient control stimulation has the advantage of no residue, is an ideal driving stimulation source, and has universality with flexible sensing systems and robot mechatronic systems. For example, the electrostimulated fluorescent response hydrogel disclosed in Chinese invention patent CN105601955A, the electrostimulated fluorescent response hydrogel with hyperbranched polyamide as the base material, the fluorescence intensity of the gel gradually decreases with the extension of the electric field action time, thereby showing that the fluorescence intensity of the gel has responsiveness to the electric field, but the application of the gel in the driver cannot realize the synergistic deformation and color change.

[0006] Therefore, the polymer hydrogel soft driver based on the electrothermal stimulation to realize the deformation and color change in coordination can also realize the bionic driving which is easy to control and has no stimulation residue. SUMMARY

[0007] Therefore, the polymer hydrogel soft driver based on the electrothermal stimulation to realize the deformation and color change in coordination can also realize the bionic driving which is easy to control and has no stimulation residue.

[0008] To achieve the above-mentioned purpose, the application provides a hydrogel driver based on electrothermal stimulation and coordinated deformation and color change, which comprises at least a flexible electrothermal layer and a fluorescent color-changing hydrogel composite structure; the flexible electrothermal layer is a driving layer and has an electrothermal conversion effect; the fluorescent color-changing hydrogel has a temperature response effect and is driven by the temperature of the flexible electrothermal layer to realize synchronous deformation and color change; when powered on, the flexible electrothermal layer is heated and expands, the fluorescent color-changing hydrogel is dehydrated and shrinks in volume, so that the flexible electrothermal layer bends to one side of the fluorescent color-changing hydrogel to release the stress between the two layers; at the same time, the volume shrinkage causes the fluorescent color-changing hydrogel to undergo fluorescent resonance energy transfer, realizing the change of fluorescent color, and then the hydrogel driver realizes the coordinated deformation and color change.

[0009] Preferably, the flexible electrothermal layer comprises a flexible layer and a carbon material layer; the flexible layer comprises a first side and a second side; the carbon material layer is attached to the first side to form the flexible electrothermal layer; the fluorescent color-changing hydrogel is attached to the second side; the second side has an adhesive ability and can contact and bond the carbon material layer and the fluorescent color-changing hydrogel into an integrated structure.

[0010] Preferably, the carbon material layer is a carbon film obtained by pressing the carbon-based material after self-assembly at the water / air interface.

[0011] Preferably, the preparation method of the carbon material layer comprises: ultrasonic dispersion of the carbon-based material in an ethanol solution to obtain a carbon material ethanol dispersion; spraying the carbon material dispersion onto the surface of the static water to self-assemble into a carbon film at the water / air interface; and extruding the carbon film to obtain the carbon material layer with a dense structure.

[0012] Preferably, the carbon material layer is transferred to the surface of the flexible layer and dried to obtain the flexible electrothermal layer.

[0013] Preferably, the carbon-based material comprises graphene or carbon nanotubes.

[0014] Preferably, the adhesion ability of the flexible layer is achieved by an adhesion layer provided on the surface of the second side.

[0015] Preferably, the adhesion layer comprises a double-sided adhesive tape.

[0016] Preferably, the adhesion layer comprises a network interpenetrating interface structure formed by interfacial polymerization between the flexible layer and the fluorescent color-changing hydrogel.

[0017] Preferably, the method of interfacial polymerization comprises forming a network interpenetrating interface structure between the flexible layer and the adhesion of the fluorescent color-changing hydrogel, thereby bonding the flexible layer and the fluorescent color-changing hydrogel into a whole structure.

[0018] Preferably, the method of interfacial polymerization comprises: soaking the flexible layer in a first initiator solution, swelling the photoinitiator into the material of the flexible layer; dissolving the polymerization monomer, the second initiator and the first crosslinking agent respectively to obtain a pre-polymerization solution, and performing photopolymerization on the second side to obtain a photopolymerization product.

[0019] Preferably, the photopolymerization product and the fluorescent color-changing hydrogel covalently react and intermolecularly interact after contact, forming an interpenetrating network interface structure, forming the adhesion layer, and adhering the fluorescent color-changing hydrogel to the surface of the flexible layer.

[0020] Preferably, the material of the flexible layer is PDMS.

[0021] Preferably, the first initiator is benzophenone.

[0022] Preferably, the polymerization monomer comprises acrylamide, acrylic acid, and acrydite.

[0023] Preferably, the second initiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

[0024] Preferably, the first crosslinking agent is N,N-methylene bisacrylamide.

[0025] Preferably, the photopolymerization product is polyacrydite.

[0026] During the photopolymerization process, two quartz glasses are used as molds, with a hollow silicone rubber in the middle,

[0027] Preferably, the photopolymerization reaction is initiated by ultraviolet light, and the power of the ultraviolet lamp is 8 W, and the polymerization time is 120-180 min.

[0028] Preferably, the photopolymerization product and the fluorescent color-changing hydrogel covalently react and intermolecularly interact after contact to form adhesion and adhere the fluorescent color-changing hydrogel to the surface of the flexible layer.

[0029] Preferably, the method for preparing the temperature-responsive fluorescent color-changing hydrogel comprises the following steps: fluorescent monomers, ethyl methacrylate, and dimethylaminoethyl methacrylate form a pre-polymer solution which is photopolymerized by a third initiator and a second crosslinking agent to form the hydrogel, and the hydrogel is used after swelling in a CO2-saturated solution.

[0030] Preferably, the fluorescent monomers comprise yellow fluorescent molecules and blue fluorescent molecules, and the yellow fluorescent molecules and the blue fluorescent molecules can undergo fluorescence resonance energy transfer when the distance is less than 10 nm in the energized state.

[0031] Preferably, the energized voltage of the hydrogel driver used in the energized state is 6-20 V.

[0032] Preferably, the method for preparing the fluorescent monomers comprises: reacting 4-bromo-1,8-naphthalene anhydride and propylamine or allylamine at 75-85°C for 7-10 h in ethanol, and obtaining an intermediate after suction filtration; directly reacting the intermediate with a substituent under inert atmosphere protection, or reacting the substituent treated by alkaline with the intermediate, and obtaining the fluorescent monomers after post-treatment.

[0033] Preferably, when the intermediate directly reacts with the substituent to obtain a suspension, the blue fluorescent molecules are obtained after post-treatment; the reaction conditions include a temperature of 105-115°C and a reaction time of 6-7 h; and the post-treatment includes washing the suspension with deionized water, filtering, and vacuum drying.

[0034] More preferably, when the substituent is N,N-dimethylethylenediamine or N,N-dimethylpropylenediamine, yellow fluorescent molecules are prepared.

[0035] Preferably, the structure of the yellow fluorescent molecules comprises any one of the following:

[0036] 、 、

[0037] 、 .

[0038] Preferably, when the substituent is N,N'-dimethylethanolamine, N,N'-dimethylpropanolamine, the blue fluorescent molecule is prepared. Specifically, the blue fluorescent molecule preparation step comprises: reacting the substituent with the intermediate after alkalization treatment to obtain an aqueous solution, and obtaining the blue fluorescent molecule after post-treatment; the reaction conditions include 60-70℃ for 10-15 h; the alkalization treatment comprises dissolving the substituent in an alkaline solution, and reacting at room temperature for 20-40 min; the post-treatment comprises adding dichloromethane in the aqueous solution for extraction, removing residual reactants; adding anhydrous magnesium sulfate in the organic phase after extraction to remove residual water, removing the organic phase under vacuum to obtain a solid, and the solid is washed and vacuum dried.

[0039] Preferably, the structure of the blue fluorescent molecule is any one of the following:

[0040] 、 、

[0041] 、 .

[0042] Preferably, the inert atmosphere includes a noble gas atmosphere or a nitrogen atmosphere.

[0043] Preferably, the third initiator includes any one of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, ammonium persulfate, potassium persulfate.

[0044] Preferably, the second crosslinking agent includes any one of N,N'-methylenebisacrylamide, ethylene glycol diacrylate, polyethylene glycol diacrylate.

[0045] Preferably, the addition amount of the yellow fluorescent molecule and the blue fluorescent molecule is 2-20 mg per 10 mL of the prepolymer solution, respectively.

[0046] Preferably, the addition amount of the third initiator is 60-240 mg.

[0047] Preferably, the addition amount of the second crosslinking agent is 30-120 mg.

[0048] Preferably, the addition amount of ethyl methacrylate and dimethylaminoethyl methacrylate is 1-5 g, respectively.

[0049] Preferably, the polymerization conditions are: first, low-temperature polymerization at 30-45℃ for 6-12 h, and then continue to polymerize at 60-70℃ for 6-12 h.

[0050] Preferably, the molar ratio of 4-bromo-1,8-naphthalic anhydride and propylamine or allylamine is 1:1.5~2.

[0051] Preferably, the molar ratio of the intermediate and the substituent is 1: 30~60.

[0052] To achieve another object, the application further provides a preparation method of the above hydrogel driver, and the specific steps include:

[0053] S1. Providing fluorescent monomers

[0054] 4-bromo-1,8-naphthalic anhydride and propylamine or allylamine are reacted under ethanol condition at 75~85℃ for 7~10 h, and the intermediate is obtained after suction filtration; the intermediate is directly reacted with the substituent under the protection of inert atmosphere, or the substituent treated by alkaline is reacted with the intermediate, and two different fluorescent monomers are obtained after post-treatment, respectively;

[0055] S2. Preparation of fluorescent color-changing hydrogel

[0056] The fluorescent monomers, ethyl methacrylate, dimethylaminoethyl methacrylate are polymerized under the action of an initiator and a crosslinking agent to form the fluorescent color-changing hydrogel;

[0057] S3. Preparation of carbon film

[0058] The carbon-based material is ultrasonically dispersed in an ethanol solution to obtain a carbon material ethanol dispersion; the carbon material dispersion is sprayed onto the surface of static water to self-assemble into a carbon film at the water / air interface; and the carbon film is extruded to obtain the carbon material layer with a dense structure;

[0059] S4. Preparation of flexible electrothermal layer

[0060] The carbon material layer prepared in S3 is transferred to the first side of the flexible layer for attachment and drying to form the flexible electrothermal layer;

[0061] S5. Preparation of polymer hydrogel driver

[0062] The fluorescent color-changing hydrogel prepared in S2 is placed in a CO2 saturated solution for swelling, and the adhesive layer of the flexible electrothermal layer prepared in S4 is overlaid and contacted with the swollen fluorescent color-changing hydrogel to obtain the polymer hydrogel driver; or the second side of the flexible electrothermal layer is bonded to the fluorescent color-changing hydrogel by double-sided tape. The tertiary amine in the polydimethylaminoethyl methacrylate in the network of the fluorescent hydrogel is protonated in an acidic environment (CO2 saturated solution) and becomes hydrophilic, resulting in swelling.

[0063] The hydrogel driver prepared by adopting the technical scheme of the present application can be driven in the electrified state, realizes the cooperative deformation and color change function, and can be used in the field of bionic camouflage soft robot and the like.

[0064] The present application has the following beneficial technical effects:

[0065] 1. The electrically stimulated cooperative deformation and color change high molecular hydrogel driver prepared by adopting the technical scheme of the present application realizes the color change of the fluorescent hydrogel driver in the driving process, and overcomes the problem of non-cooperative deformation and color change of the driver in the prior art.

[0066] 2. The electrically stimulated cooperative deformation and color change high molecular hydrogel driver prepared by adopting the technical scheme of the present application realizes the color change of the fluorescent hydrogel driver in the driving process, and overcomes the problem of non-cooperative deformation and color change of the driver in the prior art.

[0067] 3. The technical scheme of the present application introduces the fluorescent resonance energy transfer system into the hydrogel, and the fluorescent resonance energy transfer of the two fluorescent groups is caused due to the volume shrinkage of the hydrogel under the heating condition, so that the fluorescent color change is realized.

[0068] 4. The technical scheme of the present application covalently reacts and intermolecularly interacts the polyacrylic acid-N-succinimidyl ester in the flexible electrothermal layer with the temperature-responsive fluorescent hydrogel to form an interpenetrating network interface layer, and then firmly combines, so as to ensure the use stability of the driver in the subsequent use process, and avoids the problem of layer separation in the driving process. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 The surface temperature change graph of the flexible electrothermal layer prepared for the embodiment 1 of the present application under different voltages.

[0070] Figure 2 The color change comparison photos of the fluorescent color change gel prepared for the embodiment 2 and the comparative examples 1-2 of the present application in the heating process at 80 DEG C.

[0071] Figure 3 The structure schematic diagram of the electrothermal stimulated cooperative deformation and color change high molecular hydrogel driver prepared for the embodiment 3 of the present application.

[0072] Figure 4 The SEM graph of the electrothermal stimulated cooperative deformation and color change high molecular hydrogel driver prepared for the embodiment 3 of the present application.

[0073] Figure 5The temperature changes of the electrothermal stimulated synergic deformation and color change polymer hydrogel driver prepared in Example 3 of the present application were measured by applying 12 V, 15 V and 20 V voltage respectively to both ends of the driver.

[0074] Figure 6 The driving speed of the electrothermal stimulated synergic deformation and color change polymer hydrogel driver prepared in Example 1 of the present application was regulated by applying different voltages.

[0075] Figure 7 The synergic deformation and color change of the electrothermal stimulated synergic deformation and color change polymer hydrogel driver prepared in Example 1 of the present application were shown in the real object picture and thermal imaging picture.

[0076] Figure 8 The patterning schematic diagram of the electrothermal stimulated synergic deformation and color change polymer hydrogel driver prepared in Example 1 of the present application was shown.

[0077] Figure 9 The patterning driving process of the electrothermal stimulated synergic deformation and color change polymer hydrogel driver prepared in Example 1 of the present application was shown. DETAILED DESCRIPTION

[0078] The purposes, technical solutions and advantages of the present application are made more clear, and the technical solutions in the present application are described clearly and completely. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0079] The present application provides an electrothermal stimulated synergic deformation and color change hydrogel driver, which comprises at least a flexible electrothermal layer and a fluorescent color change hydrogel composite structure. The flexible electrothermal layer is a driving layer with electrothermal conversion effect. The fluorescent color change hydrogel has temperature response effect and synchronously deforms and changes color under the driving of the temperature of the flexible electrothermal layer. When powered, the flexible electrothermal layer is heated and expands, and the fluorescent color change hydrogel is heated and dehydrated, shrinks in volume, so that the flexible electrothermal layer bends to the side of the fluorescent color change hydrogel to release the stress between the two layers. At the same time, the volume shrinkage causes the fluorescent color change hydrogel to occur fluorescent resonance energy transfer, realizes the change of fluorescent color, and then the hydrogel driver realizes the synergic deformation and color change.

[0080] The hydrogel driver comprises a graphene film (carbon film)-PDMS layer (flexible layer)-adhesive layer-fluorescent color change hydrogel, wherein the graphene film (carbon film), the PDMS layer (flexible layer) and the adhesive layer constitute the flexible electrothermal layer.

[0081] The flexible electrothermal layer comprises a flexible layer and a carbon material layer; the flexible layer comprises a first side and a second side; the carbon material layer is attached to the first side to form the flexible electrothermal layer; the fluorescent color-changing hydrogel is attached to the second side; the second side has an adhesive ability, and the carbon material layer and the fluorescent color-changing hydrogel can be bonded into an integrated structure after being contacted; and the carbon material layer is a carbon film obtained by pressing a carbon-based material after self-assembly at a water / air interface.

[0082] As one of the preferred embodiments, the preparation method of the flexible electrothermal layer comprises the following steps: dispersing a carbon-based material in an ethanol solution by ultrasonic to obtain a carbon material ethanol dispersion; spraying the carbon material dispersion onto a static water surface to self-assemble into a carbon film at a water / air interface; extruding the carbon film to obtain a carbon material layer with a dense structure; and transferring the carbon material layer to the surface of a flexible layer and drying to obtain the flexible electrothermal layer.

[0083] The flexible layer is a base layer, and the material is PDMS, which can bond the carbon material layer and the fluorescent color-changing hydrogel into an integrated structure after being contacted. The adhesive ability of the flexible layer is obtained by providing an adhesive layer on the surface of the second side; and the adhesive layer and the fluorescent color-changing hydrogel can produce an adhesive effect after surface contact.

[0084] As one of the preferred embodiments, the adhesive layer comprises a double-sided tape.

[0085] As one of the preferred embodiments, a network interpenetrating interface structure is formed by the reaction of a photopolymerization product formed by interfacial polymerization between the flexible layer and the fluorescent color-changing hydrogel; and the flexible layer and the fluorescent color-changing hydrogel are bonded into an integrated structure.

[0086] As one of the preferred embodiments, a fluorescent resonance energy transfer system is introduced into the fluorescent hydrogel, and the fluorescent resonance energy transfer between two different fluorescent color-changing monomers is triggered due to the volume shrinkage of the hydrogel under heating, so that the fluorescent color changes.

[0087] The technical solutions of the present application are further illustrated by specific examples.

[0088] Example 1

[0089] The present application provides a flexible electrothermal layer, and the specific preparation steps include:

[0090] (1) Preparation of carbon film

[0091] A concentration of 2 mg / mL graphene ethanol suspension was prepared, which was ultrasonically treated for 6 h to obtain a uniformly dispersed graphene suspension. Then, 35 mL of the uniformly dispersed graphene suspension was sprayed onto the surface of the static water using a watering can to obtain an assembled graphene film. Subsequently, the assembled carbon film on the water surface was extruded using a nano-sponge to obtain a dense carbon film.

[0092] (2) Preparation of the flexible layer

[0093] The PDMS with a thickness of 0.2 mm was soaked in a benzophenone ethanol solution with a mass fraction of 10% for 12 h. Then, the PDMS was used as a base layer, and a 0.2 mm-thick silicone rubber mold was placed on the upper layer. 0.9 g of acrylamide, 0.9 mL of acrylic acid, 0.04 g of acrydite, 0.08 g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, and 0.005 g of N,N-methylenebisacrylamide were added to 8 mL of deionized water to obtain a prepolymer solution. The prepolymer solution was transferred into the mold, which was sealed with a quartz glass. After polymerization under an 8 w 365 nm ultraviolet lamp for 2 h, a PDMS containing an adhesive gel was obtained. Subsequently, the PDMS containing the adhesive gel was placed at room temperature, and the gel was naturally volatilized to dryness to obtain a PDMS containing an adhesive gel.

[0094] The PDMS containing the adhesive gel was placed on a glass sheet with the PDMS facing away from the glass sheet, and the edges of the PDMS were sealed to the glass sheet using a waterproof tape. The carbon film prepared in step (1) was transferred using the sealed PDMS containing the adhesive gel, and then the carbon film was dried in a 60°C oven for 10 min. The transfer and drying operations were repeated 4 times to obtain a flexible electrothermal layer with adhesive capacity. The thickness of the carbon film was adjusted to 430 nm by repeating the transfer and drying operations different numbers of times.

[0095] Reference Figure 1 The surface temperature of the flexible electrothermal layer prepared in this embodiment under different voltages was measured. As shown in the figure, the surface temperature of the flexible electrothermal layer increased from about 37°C to about 120°C as the applied voltage increased from 6 V to 20 V. This indicates that the applied voltage should be at least greater than 6 V, otherwise there will be almost no heating effect.

[0096] Example 2

[0097] The present application provides a fluorescent color-changing hydrogel, and the specific preparation steps include:

[0098] (1) Preparation of yellow fluorescent monomer

[0099] To a 100 mL round bottom flask containing 40 mL of ethanol, 2.77 g of 4-bromo-1,8-naphthalic anhydride and 0.838 g of allylamine were added. After stirring at 85 °C for 7 h, the reaction mixture was cooled to room temperature and then poured into 500 mL of ice water and then filtered. Finally, 4-bromo-N-allyl-1,8-naphthalimide (BD-Br) was obtained as a light gray powder after drying in a vacuum oven overnight at room temperature. Then, 1.97 g of BD-Br was added to a 50 mL round bottom flask containing 20 mL of N,N-dimethylethylenediamine under N2 protection. The mixture was stirred at 110 °C for 6 h. After cooling to room temperature, the suspension was washed with deionized water and then filtered. Finally, the blue-fluorescent monomer DEAN (4-(N,N-dimethylamino ethylene)amino-N-allyl-1,8-naphthalimide) was obtained as a blue fluorescent powder after vacuum drying. .

[0100] (2) Preparation of blue-fluorescent monomer

[0101] Under nitrogen protection, 0.9 g of sodium hydroxide and 36 mL of N,N'-dimethylethanolamine were dissolved in 18 mL of deionized water in a 250 mL three-necked flask. After stirring at room temperature for 20 min, 0.948 g of 4-bromo-N-allyl-1,8-naphthalimide (BD-Br) was added, and then stirred at 60 °C for 12 h. Then the mixture was extracted with CH2Cl2 three times and washed with an aqueous solution to remove residual reactants. Next, anhydrous magnesium sulfate was added to the organic phase to remove residual water. After removing the organic phase under vacuum, the obtained solid was washed with deionized water to remove residual N,N'-dimethylethanolamine, and vacuum dried to obtain the yellow-fluorescent monomer DAEAN 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthalimide, with the structure as .

[0102] (3) Preparation of fluorescent color-changing hydrogel

[0103] After completely dissolving 5 mg of yellow-fluorescent DAEAN prepared in step (2) and 5 mg of blue-fluorescent DEAN prepared in step (1) in 5 mL of dimethyl sulfoxide, respectively, 5 mL of deionized water was added and mixed uniformly, followed by adding 1.5 mL of ethyl methacrylate, 1.5 mL of dimethylaminoethyl methacrylate, and 30 mg of N,N-methylene bisacrylamide and stirring uniformly to obtain a mixed solution. After placing the mixed solution in a 4 °C refrigerator for 12 h, 120 mg of ammonium persulfate was added, and then immediately injected into a 0.5 mm thick mold, followed by sealing with a glass sheet, and reacting at 35 °C for 12 h, and then at 65 °C for 12 h to obtain a fluorescent color-changing hydrogel with temperature response.

[0104] Comparative Example 1

[0105] The difference between this example and Example 2 is that the amount of crosslinking agent N,N-methylene bisacrylamide is different in the preparation step of the fluorescent color-changing gel, and the others are the same.

[0106] The preparation method of the fluorescent color-changing gel of this example comprises: after 5 mg of yellow fluorophore DAEAN prepared in step (2) of Example 2 and 5 mg of blue fluorophore DEAN prepared in step (1) of Example 2 are completely dissolved in 5 mL of dimethyl sulfoxide, 5 mL of deionized water is added and uniformly mixed, then 1.5 mL of ethyl methacrylate, 1.5 mL of dimethylaminoethyl methacrylate, and 60 N, N-methylene bisacrylamide are added and uniformly stirred to obtain a mixed solution. After the mixed solution is placed in a 4℃ refrigerator for 12h, 120 mg of ammonium persulfate is added, and then the mixed solution is immediately injected into a 0.5 mm thick mold, followed by sealing with a glass sheet, and then reacted at 35℃ for 12h, and then reacted at 65℃ for 12h to obtain a fluorescent color-changing hydrogel with temperature response.

[0107] Comparative Example 2

[0108] The difference between this comparative example and Comparative Example 1 is that the amount of N,N-methylene bisacrylamide added is different. The amount of N,N-methylene bisacrylamide added in this comparative example is 120 mg.

[0109] Reference Figure 2 , the color change photos of the fluorescent color-changing gels prepared by using Example 2, Comparative Example 1 and Comparative Example 2 during the heating process at 80℃, and the color change range is illustrated by the color change. During the heating process, the color of the fluorescent color-changing gel of Example 2 (the first row) changes from blue to green, while the color of the sample of Comparative Example 1 (the second row) and the sample of Comparative Example (the third row) changes from cyan (blue-green) to green. Obviously, the wider color change range of Example 1 is illustrated by the color change range.

[0110] Example 3

[0111] The present application provides a synergistic deformation color-changing polymer hydrogel driver with electrothermal stimulation, and the specific preparation steps comprise: after the temperature-responsive fluorescent color-changing hydrogel prepared in Example 2 is placed in a saturated carbon dioxide solution for 10 min, a swollen hydrogel is obtained, which is cut into a 2 13 mm strip, then the flexible electrothermal layer with adhesion prepared in Example 1 is also cut into a 2 13 mm strip, and then the two are overlapped and placed in contact, so that a synergistic deformation color-changing polymer hydrogel driver with electrothermal stimulation is obtained.

[0112] ReferenceFigure 3 A schematic diagram of the structure of the hydrogel driver prepared by the present embodiment. As can be seen from the figure, the hydrogel driver comprises a graphene film (carbon film) - PDMS layer (flexible layer) - adherable glue layer - fluorescent color-changing hydrogel, wherein the graphene film (carbon film), the PDMS layer (flexible layer), and the adherable glue layer constitute a flexible electrothermal layer.

[0113] As a preferred embodiment, the adherable glue layer can also be realized by double-sided tape, one side of the double-sided tape adheres to the flexible layer, and the other side adheres to the fluorescent color-changing hydrogel, bonding the fluorescent color-changing hydrogel and the flexible layer into a whole structure.

[0114] As shown in Figure 4 , the result of observing the cross-sectional morphology of the electrothermal-stimulated synergistic deformation and color-changing polymer hydrogel driver prepared in Example 3 after freeze-drying by scanning electron microscopy. As can be seen from the figure, the adherable flexible electrothermal layer and the fluorescent hydrogel driving layer are firmly combined through an interpenetrating network interface layer of about 50 microns, which ensures the stability of subsequent driving and avoids the problem of layer separation during driving.

[0115] As shown in Figure 5 , voltages of 12 V, 15 V, and 20 V are applied to the two ends of the electrothermal-stimulated synergistic deformation and color-changing polymer hydrogel driver prepared in Example 3, and the surface temperature of the flexible electrothermal layer can reach about 65 ℃, 80 ℃, and 120 ℃, respectively, as the voltage application time increases; and the higher the voltage, the faster the temperature rises. By controlling the voltage, the driving speed can be adjusted through the temperature rise rate (slope).

[0116] As shown in Figure 6 , voltages of 12 V, 15 V, and 20 V are applied to the two ends of the electrothermal-stimulated synergistic deformation and color-changing polymer hydrogel driver prepared in Example 3, and the surface temperature of the flexible electrothermal layer can reach about 65 ℃, 80 ℃, and 120 ℃, respectively, as the voltage application time increases; and the higher the voltage, the faster the temperature rises. By controlling the voltage, the driving speed can be adjusted through the temperature rise rate (slope).

[0117] Further analysis in combination with Figure 5 and Figure 6 shows that the driving speed is mainly regulated by the temperature change of the flexible electrothermal layer. The higher the temperature, the faster the hydrogel loses water, and the faster the driving speed. The thicker the carbon film, the higher the temperature of the flexible electrothermal layer under the same voltage, and the faster the corresponding driving speed. Under the same carbon film thickness, the higher the applied voltage, the higher the temperature of the flexible electrothermal layer. After investigating the appropriate number of carbon film layers (4 layers) in Example 3, the temperature is regulated by adjusting the applied voltage, thereby regulating the driving speed.

[0118] AsFigure 7 As shown in the figure, when a voltage of 15 V is applied to both ends of the hydrogel actuator prepared in Example 3, the color change of the hydrogel actuator during deformation is observed by thermal imaging. As can be seen from the figure, the actuator changes color from blue to green as the energizing time increases.

[0119] like Figure 8 As shown, this is the actuator with a special cross-shaped pattern prepared in Example 3. The temperature-responsive fluorescent hydrogel prepared in Example 3 was placed in a saturated carbon dioxide solution for 10 min to obtain a swollen hydrogel, which was then cut into 2... A 2 mm square; then, the flexible electrothermal layer with adhesion prepared in Example 1 is also cut into a cross shape; subsequently, 2 A 2 mm hydrogel sheet is attached to the four corners of the edge of the cross-shaped flexible heating layer. Under these conditions, the initial shape of the actuator is a cross shape with the four corners pointing downwards.

[0120] like Figure 9 As shown, after being powered on, the four corners of the aforementioned actuator begin to gradually bend upwards. Clearly, under energized conditions, as the temperature of the flexible heating layer increases, the bending direction of the flexible heating layer changes, causing the hydrogel to deform and its color to change accordingly. Obviously, after being powered on, the hydrogel actuator can achieve simultaneous color change and deformation.

[0121] This invention introduces two fluorophores capable of fluorescence resonance energy transfer (FRET) at a distance of less than 10 nm into a hydrogel. When a voltage is applied to the flexible electrothermal layer of the actuator, the carbon film with an electrothermal effect converts electrical energy into Joule heat, which is then transferred to the fluorescent hydrogel layer, inducing the hydrogel to lose water and shrink in volume. This volume shrinkage process, on the one hand, induces the actuator, and on the other hand, gradually reduces the distance between the two fluorophores in the fluorescent hydrogel, triggering FRET and thus achieving a color change.

[0122] The above are merely preferred embodiments of the present invention and do not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by achieving the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A hydrogel driver of synergistic deformation and discoloration driven by electrothermal stimulation, the hydrogel driver being a composite structure consisting of a flexible electrothermal layer and a fluorescent discoloring hydrogel; the flexible electrothermal layer being a driving layer with electrothermal conversion effect; the fluorescent discoloring hydrogel having temperature response effect and being driven by the temperature of the flexible electrothermal layer to synchronously deform and discolor; when powered, the flexible electrothermal layer is heated and expands, and the fluorescent discoloring hydrogel is heated and shrinks in volume, causing the flexible electrothermal layer to bend to one side of the fluorescent discoloring hydrogel; at the same time, the volume shrinkage causes fluorescence resonance energy transfer between two fluorophores in the fluorescent discoloring hydrogel, realizing the change of fluorescent color of the fluorescent discoloring hydrogel, and then the hydrogel driver realizes the synergistic deformation and discoloration; the flexible electrothermal layer comprises a flexible layer and a carbon material layer; the flexible layer comprises a first side and a second side; the carbon material layer is attached to the first side to form the flexible electrothermal layer; the fluorescent discoloring hydrogel is attached to the second side; the second side has an adhesive ability, which can adhere the flexible electrothermal layer and the fluorescent discoloring hydrogel to form an integrated structure; the adhesive ability of the flexible layer is obtained by the adhesive glue layer provided on the second side; the adhesive glue layer can produce an adhesive effect by surface contact with the fluorescent discoloring hydrogel; the adhesive glue layer is a network interpenetrating interface structure formed by the reaction of the photopolymerization product between the flexible layer and the fluorescent discoloring hydrogel.

2. The electrothermally stimulated synergistic shape-changing hydrogel actuator of claim 1, wherein, the carbon material layer is a carbon film obtained by self-assembly of carbon-based materials at the water / air interface and then pressing.

3. The electrothermally stimulated synergistic shape-changing hydrogel actuator of claim 1, wherein, The preparation method of the carbon material layer comprises: ultrasonic dispersion of carbon-based materials in an ethanol solution to obtain a carbon material ethanol dispersion; the carbon material ethanol dispersion is sprayed onto the surface of the static water to self-assemble into a carbon film at the water / air interface; the carbon film is extruded to obtain the carbon material layer with a dense structure.

4. The electrothermally stimulated synergistic shape-changing hydrogel actuator of claim 1, wherein, The carbon material layer is transferred to the first side of the flexible layer and dried to obtain the flexible electrothermal layer.

5. The electrothermally stimulated, synergistic, shape-changing, hydrogel-driven color changer of claim 2, wherein, The carbon-based materials include graphene or carbon nanotubes.

6. The electrothermally stimulated, synergistic deformation and color-changing hydrogel actuator of claim 1, wherein, The method of interfacial polymerization comprises: immersing the flexible layer in a first initiator solution to make the first initiator swell into the material of the flexible layer; dissolving the polymerization monomer, the second initiator and the first crosslinking agent respectively to obtain a pre-polymerization solution, and then performing photopolymerization of the pre-polymerization solution on the second side to obtain a photopolymerization product; the photopolymerization product and the fluorescent discoloring hydrogel covalently react and interact with each other after contact to form a network interpenetrating interface structure, forming the adhesive glue layer, and adhering the fluorescent discoloring hydrogel to the surface of the flexible layer; the material of the flexible layer is PDMS.

7. The electrothermally stimulated, synergistic, shape-changing, hydrogel-driven color changer of claim 6, wherein, The first initiator is benzophenone; the polymerization monomer includes acrylamide, acrylic acid and acrylic acid-N-succinimidyl ester; the second initiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone; the first crosslinking agent is N,N-methylene bisacrylamide; and the photopolymerization product is polyacrylic acid-N-succinimidyl ester.

8. The electrothermally stimulated, syneresis-induced color-changing hydrogel actuator of claim 1, wherein, The preparation method of the fluorescent color-changing hydrogel comprises the following steps: forming a prepolymer solution of a fluorescent monomer, ethyl methacrylate and dimethylaminoethyl methacrylate, and then performing photopolymerization under the action of a third initiator and a second crosslinking agent, and then swelling in a CO2 saturated solution and then using.

9. The electrothermally stimulated, syneresis-induced color-changing hydrogel actuator of claim 8, wherein, The preparation method of the fluorescent monomer comprises the following steps: reacting 4-bromo-1,8-naphthalide and propylamine or allylamine at 75-85 DEG C for 7-10 hours under ethanol conditions, and then performing suction filtration to obtain an intermediate; or, directly reacting the intermediate with a substituent under the protection of an inert atmosphere, or, reacting the intermediate with the substituent after alkalization treatment, and then performing post-treatment to obtain the fluorescent monomer.

10. The electrothermally stimulated, synergistic deformation and color-changing hydrogel actuator of claim 8, wherein, The fluorescent monomer comprises at least yellow fluorescent molecules and blue fluorescent molecules, and the yellow fluorescent molecules and the blue fluorescent molecules can occur fluorescent resonance energy transfer at a distance of <10 nm under a power-on state.

11. The electrothermally stimulated, synergistic, shape-changing, hydrogel-driven coloration actuator of claim 10, wherein, The power-on voltage under the power-on state is 6-20 V.

12. The electrothermally stimulated, synergistic, shape-changing, hydrogel-driven color changer of claim 9, wherein, When the intermediate and the substituent directly react under the protection of an inert atmosphere to obtain a suspension, and then performing post-treatment to obtain blue fluorescent molecules, the reaction conditions comprise a temperature of 105-115 DEG C and a reaction time of 6-7 hours; and the post-treatment comprises washing the suspension with deionized water, filtering and vacuum drying.

13. The electrothermally stimulated, synergistic, shape-changing, hydrogel-driven color changer of claim 9, wherein, When the intermediate and the substituent directly react under the protection of an inert atmosphere to obtain a suspension, and then performing post-treatment to obtain blue fluorescent molecules, the reaction conditions comprise a temperature of 105-115 DEG C and a reaction time of 6-7 hours; and the post-treatment comprises washing the suspension with deionized water, filtering and vacuum drying.

14. The electrothermally stimulated, synergistic, morphing, hydrogel-driven color changer of claim 9, wherein, The inert atmosphere comprises a rare gas atmosphere or a nitrogen atmosphere.

15. The electrothermally stimulated, synergistic, morphing, hydrogel-driven color changer of claim 9, wherein, When the substituent is N,N-dimethylethanolamine or N,N-dimethylpropanolamine, blue fluorescent molecules are prepared.

16. The electrothermally stimulated, synergistic, morphological and chromic, hydrogel actuator of claim 9, wherein, When the substituent is N,N'-dimethylethylenediamine, yellow fluorescent molecules are prepared.

17. The electrothermally stimulated, synergistic, morphing, hydrogel-driven color changer of claim 9, wherein, The third initiator comprises any one of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, ammonium persulfate and potassium persulfate.

18. The electrothermally stimulated, synergistic, morphing, hydrogel-driven color changer of claim 9, wherein, The second crosslinking agent comprises any one of N,N'-methylenebisacrylamide, ethylene glycol diacrylate and polyethylene glycol diacrylate.

19. The electrothermally stimulated, synergistic, morphing, hydrogel-driven color changer of claim 10, wherein, The adding amount of the yellow fluorescent molecules and the blue fluorescent molecules is 2-20 mg per 10 mL of the prepolymer solution; the adding amount of the third initiator is 60-240 mg; the adding amount of the second crosslinking agent is 30-120 mg; and the adding amount of ethyl methacrylate and dimethylaminoethyl methacrylate is 1-5 g.

20. The electrothermally stimulated, syneresis-induced color-changing hydrogel actuator of claim 9, wherein, The molar ratio of 4-bromo-1,8-naphthalide and propylamine or allylamine is 1:1.5-2.

21. The electrothermally stimulated, syneresis-induced color-changing hydrogel actuator of claim 9, wherein, The molar ratio of the intermediate and the substituent is 1:30-60.

22. A method of making an electrothermally stimulated, synergistic, morphological and color changing hydrogel actuator according to any one of claims 1-21, characterized in that, The specific steps comprise: S1. providing a fluorescent monomer The intermediate is obtained by reacting 4-bromo-1,8-naphthalic anhydride and propylamine or allylamine in ethanol at 75-85°C for 7-10h, and then filtering; the intermediate is reacted with a substituent under the protection of inert atmosphere, or the substituent treated by alkaline is reacted with the intermediate, and then treated to obtain two different fluorescent monomers respectively; S2. Preparation of the fluorescent color-changing hydrogel The fluorescent monomer, ethyl methacrylate, dimethylaminoethyl methacrylate, a third initiator and a second crosslinking agent are polymerized to obtain the fluorescent color-changing hydrogel; S3. Preparation of the carbon film The carbon-based material is ultrasonically dispersed in an ethanol solution to obtain a carbon material ethanol dispersion; the carbon material ethanol dispersion is sprayed onto a static water surface to self-assemble into a carbon film at the water / air interface; and the carbon film is extruded to obtain the carbon material layer with a dense structure; S4. Preparation of the flexible electrothermal layer The carbon material layer prepared in S3 is transferred to the first side of the flexible layer for affixing and drying to form the flexible electrothermal layer; S5. Preparation of the polymer hydrogel actuator The fluorescent color-changing hydrogel prepared in S2 is placed in a CO2 saturated solution for swelling, and the adhesive layer of the flexible electrothermal layer is stacked and contacted with the swollen fluorescent color-changing hydrogel to obtain the polymer hydrogel actuator.

23. Application of the electrothermal stimulation synergistic deformation color-changing hydrogel actuator of any one of claims 1-21 in a bionic camouflage soft robot to realize co-mingling with the environment.

Images