Underwater color-changing hydrogel with multi-layer structure as well as preparation method and application of underwater color-changing hydrogel

Abstract

The invention discloses underwater color-changing hydrogel with a multi-layer structure and a preparation method and application thereof, and belongs to the field of polymer functional materials, the color-changing hydrogel with the multi-layer structure comprises UCST type fluorescent hydrogel, LCST type fluorescent hydrogel and an electric heating control layer; the polymerization temperature of the UCST type fluorescent hydrogel is 40-80 DEG C, and the polymerization temperature of the LCST type fluorescent hydrogel is 5-25 DEG C; the electric heating control layer comprises an electric heating layer and a packaging layer, and the electric heating layer comprises an electric heating material and an electrode. Under the power-on condition, the color-changing hydrogel can achieve a wide color-changing range and a high response speed underwater, has good stability and recovers to the original shape under the power-off condition. The preparation method provided by the invention does not need complex molecular design, can realize remote color change control by cooperating with the phase change behavior of the temperature-sensitive hydrogel and fluorescent molecules, and can be widely applied to the fields of flexible wearable devices, underwater display and the like.

Description

Technical Field

[0001] The present invention belongs to the field of polymer functional materials, and particularly relates to an underwater color-changing hydrogel with a multi-layer structure, a preparation method thereof, and an application thereof. Background Art

[0002] An underwater wearable bionic skin with color-changing performance can help ocean exploration robots or divers autonomously adapt to and integrate into complex dynamic environments or conduct information exchange. However, the reported bionic color-changing skins are mainly soft materials based on intelligent structural color and pigment color, which are not suitable for environments with insufficient light such as underwater. Compared with structural color and pigment color, fluorescent color is an important medium for information exchange and body camouflage of various marine organisms. Fluorescent color has characteristics such as high color saturation and is still effective in underwater environments with insufficient light such as the ocean and rivers. Therefore, a bionic color-changing skin based on fluorescent soft materials is more suitable for underwater wearable applications.

[0003] Fluorescent hydrogels with tunable luminescence properties have become one of the hot research fields in recent years. They have many excellent properties of both solids and solutions, and the fluorescence intensity and color of multi-color fluorescent polymer hydrogels can be adjusted by controlling the superposition between the fluorescence spectra of different luminescence centers. The softness, breathability, and good biocompatibility of hydrogels enable them to be used as wearable materials. For example, the invention application with the publication number CN118955796A discloses a method for synthesizing a simulated hydrogel skin hydrogel with a skin-like touch. Applying such materials to the field of underwater visualization can endow the bionic skin with stronger luminescence performance and stability.

[0004] However, most of the reported fluorescence hydrogel color-changing methods at present are mainly induced by stimuli such as chemistry and temperature, which have problems such as stimulus residue and are not conducive to underwater or even underwater manipulation. Electrical stimulation has the advantages of no stimulus residue and remote control, and is an ideal stimulus source, which has universality with sensing systems and robot electromechanical systems. However, the design of a single-layer structure is difficult to meet the construction of an electrical stimulation and a universal underwater color-changing system. In nature, biological tissues have a multi-level structure, which can provide specific physical and chemical properties. Therefore, their micro-network structure, geometric size, thickness, composition, and mechanical properties can be finely controlled, enabling biological organisms to have complex functions. Therefore, through the design of the hydrogel layered structure, effective integration of multiple functions can be achieved.

[0005] For example, Reference 1 (Promotion of Color-Changing Luminescent Hydrogels from Thermo to Electrical Responsiveness toward Biomimetic Skin Applications, ACS Nano 2021, 15, 10415-10427) developed a multilayer hydrogel system, which was prepared by layer-by-layer assembly of thermosensitive fluorescent hydrogels, luminescent coatings, stacked graphene-based conductive papers with excellent electrothermal effects, and flexible electrodes. By selectively combining the luminescent coatings or fluorescent hydrogel layers, diverse emission color changes can be achieved within a wide color gamut range. However, the display layer and the control layer of this multilayer hydrogel system are connected by physical interactions and are easily detached underwater. The control layer is not protected underwater, the power-on response time is slow, and it lacks the ability to work stably underwater.

[0006] Therefore, it is crucial to develop a fluorescent polymer hydrogel-based intelligent bionic skin that can be used underwater, has a fast response, and a high degree of integration. Summary of the Invention

[0007] To solve the problems in the prior art, the present invention provides an underwater color-changing hydrogel with a multilayer structure, its preparation method and application. By combining electrothermal stimulation that is easy to control and has no irritating residue, and covalent interlayer adhesion, a fast response of stable fluorescence color change underwater is achieved, which is used for underwater information transmission and interaction.

[0008] The present invention provides an underwater color-changing hydrogel with a multilayer structure, which includes a UCST-type fluorescent hydrogel, an LCST-type fluorescent hydrogel, and an electrothermal control layer; the polymerization temperature range of the UCST-type fluorescent hydrogel is 40°C - 80°C, and the polymerization temperature range of the LCST-type fluorescent hydrogel is 5°C - 25°C; the electrothermal control layer includes an electrothermal layer and a packaging layer, and the electrothermal layer includes an electrothermal material and an electrode.

[0009] In the present invention, the temperature-responsive UCST-type fluorescent hydrogel and LCST-type fluorescent hydrogel are multilayer-combined with the electrothermal control layer. When powered on underwater, the phase transition properties of the UCST-type fluorescent hydrogel and LCST-type fluorescent hydrogel are reversed, resulting in a decrease in the fluorescence intensity of the UCST-type fluorescent hydrogel and an increase in the fluorescence intensity of the LCST-type fluorescent hydrogel; after power-off, the fluorescence intensities of the two hydrogels will gradually recover. Therefore, during the power-on and power-off processes, changes in the superimposed color of the hydrogel display layer can be achieved. The UCST-type fluorescent hydrogel and the LCST-type fluorescent hydrogel are interfacially combined through covalent bonds and supramolecular interactions, effectively solving the problem of easy detachment underwater.

[0010] Preferably, the encapsulation layer is one or more of polydimethylsiloxane PDMS, Ecoflex, vulcanized silicone rubber, and silicone sealant.

[0011] Preferably, the electrothermal material is one or more of carbon nanotube fiber yarn, graphene, carbon nanotubes, and carbon black.

[0012] Preferably, the electrode is a metal electrode, including one or more of nickel cloth, conductive silver paste, copper tape, and tin bar.

[0013] A preparation method of an underwater color-changing hydrogel with a multi-layer structure provided by the present invention includes the following steps:

[0014] (1) Thoroughly mix the UCST-type hydrogel monomer, fluorescent monomer, silane coupling agent, initiator, and crosslinking agent to obtain a UCST prepolymer solution, transfer it to a silicone mold for free radical polymerization to obtain a UCST-type fluorescent hydrogel.

[0015] (2) Thoroughly mix the LCST-type hydrogel monomer, fluorescent monomer, silane coupling agent, initiator, accelerator, and crosslinking agent to obtain an LCST prepolymer solution, transfer it to a silicone mold for free radical polymerization to obtain an LCST-type fluorescent hydrogel.

[0016] (3) Connect electrodes to both ends of the electrothermal material to obtain an electrothermal layer, and then combine and seal the encapsulation layer and the electrothermal layer to obtain an electrothermal control layer.

[0017] (4) Acidify the UCST-type fluorescent hydrogel and the LCST-type fluorescent hydrogel, and perform a layer-by-layer interfacial combination of the UCST-type fluorescent hydrogel, the LCST-type fluorescent hydrogel, and the electrothermal control layer to form an underwater color-changing hydrogel with a multi-layer structure.

[0018] The multi-layer structure hydrogel prepared based on the above preparation method can achieve a wide color-changing range and a fast response speed underwater under the condition of being powered on, realize stable operation underwater, and can return to its original state when powered off.

[0019] Preferably, the UCST-type hydrogel monomer in step (1) is one or more of acrylamide, acrylic acid, N-acrylglycine amide, 2-hydroxyethyl acrylate, and methyl acrylate.

[0020] The above UCST-type hydrogel monomer endows the UCST hydrogel with an adjustable phase transition temperature through mechanisms such as hydrogen bonding, hydrophobic interaction, and electrostatic interaction.

[0021] Preferably, the LCST-type hydrogel monomer in step (2) is one or more of N,N-diethylacrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, N-ethylacrylamide, N-n-propylacrylamide, methacrylamide, 2-morpholinoethyl methacrylate, dimethylaminoethyl methacrylate, N-tert-butylacrylamide, N-isopropylmethacrylamide, N,N-diethylacrylamide, and N-ethyloxazoline.

[0022] The above LCST-type hydrogel monomers have hydrophobic groups or copolymerizable hydrophilic monomers and have precisely adjustable temperature responsiveness. Therefore, through combinatorial design, the hydrogel system can be endowed with the ability of rapid temperature-responsive phase change.

[0023] Preferably, the fluorescent monomers in step (1) and step (2) include one or more of 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthalimide, 4-(N,N-dimethylaminoethylene)amino-N-allyl-1,8-naphthamide, rhodamine b, rhodamine b methacrylamide, fluorescein, coumarin, and tetrakis(4-pyridylbiphenyl)ethylene.

[0024] Preferably, the silane coupling agent in step (1) and step (2) is 3-(methacryloyloxy)propyltrimethoxysilane.

[0025] Preferably, the initiator in step (1) and step (2) is one or more of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, α-ketoglutaric acid, ammonium persulfate, and potassium persulfate.

[0026] The above photoinitiators can efficiently generate free radicals under ultraviolet light irradiation, initiate the polymerization reaction of monomers, have good water solubility and biocompatibility, and are suitable for the hydrogel system.

[0027] Preferably, the accelerator in step (2) is tetramethylethylenediamine.

[0028] Preferably, the crosslinking agent in step (1) and step (2) is one or more of N,N'-methylenebisacrylamide, polydimethyldiallylammonium chloride, ethylene glycol diacrylate, and polyethylene glycol diacrylate.

[0029] The above crosslinking agents all contain multiple polymerizable double bonds and can form a uniform three-dimensional crosslinked network with monomers in the polymerization reaction, enhancing the mechanical strength and stability of the hydrogel.

[0030] Preferably, based on the weight percentage of the UCST prepolymer solution or LCST prepolymer solution, the content of the UCST-type hydrogel monomer or LCST-type hydrogel monomer is 0.05 wt% - 35 wt%.

[0031] The content of the hydrogel monomer is regulated within the above range, so that the hydrogel network structure is formed while ensuring the UCST performance or LCST performance, thereby preparing a temperature-responsive hydrogel.

[0032] Preferably, the content of the fluorescent monomer in step (1) and step (2) is 0.01 wt %-1 wt % based on the weight percentage of the UCST type hydrogel monomer or the LCST type hydrogel monomer.

[0033] By regulating the content of the fluorescent monomer within the above range, a suitable fluorescence intensity can be obtained. When different fluorescent monomers are mixed, multicolor emission can be achieved through the content ratio, and color-changing materials can be prepared to achieve precise control of optical properties.

[0034] Preferably, based on the weight percentage of the UCST hydrogel monomer or the LCST hydrogel monomer, the content of the silane coupling agent in step (1) and step (2) is 1wt%-3.5wt%, the content of the initiator is 0.1wt%-2wt%, the content of the crosslinker is 0.05wt%-2wt%, and the content of the accelerator in step (2) is 0.05wt%-0.2wt%.

[0035] By regulating the content of the initiator or cross-linking agent, the polymerization reaction or cross-linking reaction can be ensured to proceed uniformly and efficiently, forming a stable three-dimensional network structure and enhancing the mechanical properties and functional characteristics of the hydrogel.

[0036] Preferably, step (1) and step (2) are carried out by thermally initiated or photoinitiated free radical polymerization.

[0037] Further preferably, based on thermally initiated free radical polymerization, the polymerization temperature in step (1) is 40° C.-80° C., and the polymerization time is 0.1 h-24 h.

[0038] The above-mentioned free radical polymerization temperature and time are selected to match the decomposition window of commonly used initiators to ensure rapid and complete polymerization; the UCST monomer is completely dissolved before polymerization to avoid network unevenness caused by molecular aggregation in the prepolymer solution; and the free radical polymerization reaction within this temperature range suppresses hydrogen bond interference to form a uniform cross-linked network, making the UCST behavior controllable.

[0039] Preferably, based on heat-induced free radical polymerization, the polymerization temperature in step (2) is 5° C.-25° C., and the polymerization time is 0.1 h-48 h.

[0040] Selecting the above-mentioned free radical polymerization temperature and time can ensure that the LCST monomer is completely dissolved before polymerization, avoiding hydrophobic aggregation caused by high temperature; slowing down the free radical polymerization rate, preventing uneven cross-linking, and forming a temperature-responsive network with uniform structure; avoiding destroying the hydrophilic-hydrophobic balance of the monomer, and maintaining its phase change behavior of low-temperature swelling and high-temperature shrinkage.

[0041] Preferably, based on photoinitiated free radical polymerization, the power of the ultraviolet lamp in steps (1) and (2) is 5W - 250W, and the polymerization time is 5min - 120min.

[0042] Preferably, the acid for acidification in step (4) is an organic acid or an inorganic acid.

[0043] More preferably, in step (4), the concentration of the selected acid is 0.1M - 1.5M, the volume of the selected acid is 5mL - 50mL, and the acidification time is 1h - 5h.

[0044] Application of the multi-layer structured underwater color-changing hydrogel prepared by the present invention in flexible wearable devices and underwater information display.

[0045] Preferably, the applied voltage during application is 2V - 30V.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] (1) The present invention constructs a hydrogel with a multi-layer structure, effectively covalently bonding the color-changing hydrogel and the electrothermal control layer, achieving functional integration while maintaining its stability in underwater operation.

[0048] (2) The electrothermal layer adopted by the present invention has high electrothermal efficiency in an underwater environment, can quickly heat up the hydrogel in a short time, and achieve rapid color change underwater.

[0049] (3) The underwater color-changing hydrogel prepared by the present invention is flexible, can conformally adhere to objects of different materials and shapes, such as the surface of a diving suit or a robot; and the manufacturing process is simple, without complex molecular design, and remote color change control can be achieved by coordinating the phase change behavior of the thermosensitive hydrogel and the fluorescent molecule. Description of the Drawings

[0050] Figure 1 It is the preparation flow chart of Example 1.

[0051] Figure 2 It is the curve of the temperature change of the electrothermal control layer in Example 1 over time under the energized state.

[0052] Figure 3 It is the curve of the temperature change of the hydrogel display layer in Example 1 over time under the energized state.

[0053] Figure 4 It is the influence of different silane coupling agent ratios on the phase change ability of the UCST-type fluorescent hydrogel in Example 7.

[0054] Figure 5Effect of different silane coupling agent ratios on the phase transition ability of LCST-type fluorescent hydrogels in Example 7.

[0055] Figure 6 Fluorescence spectra of the color-changing hydrogel with a multilayer structure prepared in Detection Example 1 before and after electrification as a function of temperature.

[0056] Figure 7 Application of the color-changing hydrogel with a multilayer structure prepared in Detection Example 2 in underwater encrypted information.

[0057] Figure 8 Application of the color-changing hydrogel with a multilayer structure prepared in Detection Example 3 in fish-shaped color-changing skin.

[0058] Figure 9 Application of the color-changing hydrogel with a multilayer structure prepared in Detection Example 4 in flexible wearable devices. Detailed implementation manners

[0059] In order to more clearly illustrate the purpose, technical solutions and advantages of the present invention, the following will be described in detail with reference to the embodiments. Please note that these embodiments are only used to explain the content of the present invention and are not used to limit the scope of the present invention. Modifications or equivalent replacements made by those skilled in the art on the basis of understanding the technical solutions of the present invention are all within the protection scope of the present invention.

[0060] In the following specific implementation manners, the fluorescent monomer 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthalimide was prepared according to the literature (Adv. Intell. Syst. 2021, 3, 6, 2000239), rhodamine b methacrylamide was prepared according to the literature (Langmuir. 2014, 30, 37, 11212), and 4-(N,N-dimethylaminoethylene)amino-N-allyl-1,8-naphthamide was prepared according to the literature (ACS Macro Lett. 2019, 8, 8, 937-942).

[0061] Carbon nanotube fiber yarn was prepared according to the literature (Compos. Part B-Eng. 2023, 254, 1, 110578).

[0062] The preparation method of the encapsulation layer polydimethylsiloxane PDMS is as follows: Mix the main agent and curing agent of polydimethylsiloxane in a ratio of 10:1, stir evenly, and let it stand at room temperature to defoam; Stick a corresponding thickness of hollow silicone sheet on a glass substrate to form a mold, pour the mixed solution into the mold, scrape it flat with a scraper, and put it into an oven at 50°C - 80°C for 3h - 12h. After drying, the above-mentioned encapsulation layer is formed.

[0063] Other raw materials were purchased from the market.

[0064] Example 1

[0065] The present invention provides an underwater color-changing hydrogel with a multi-layer structure, and the preparation process is as Figure 1 shown. The specific preparation steps include:

[0066] (1) Take 0.1 mg of 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthalimide and 200 mg of acrylamide and dissolve them in 2 mL of deionized water. Add 158 μL of acrylic acid, 2.7 mg of polydimethyldiallylammonium chloride, and 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane, stir evenly, and finally add 3.5 mg of ammonium persulfate to form a UCST prepolymer solution. Then add the UCST prepolymer solution to a mold, seal it, and place it in an oven at 60 °C for 7 h. After demolding, a UCST-type fluorescent hydrogel with blue fluorescence is obtained.

[0067] (2) Take 1 mg of rhodamine b methacrylate, 300 mg of N-isopropylacrylamide, 1.7 mg of N,N'-methylenebisacrylamide, and 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane and dissolve them in 2 mL of deionized water, stir evenly, then add 3.4 mg of ammonium persulfate to form an LCST prepolymer solution. Add 5 μL of accelerator tetramethylethylenediamine, mix well, and quickly add it to a mold made of ordinary glass, seal it, and react at 10 °C for 12 h. After demolding, an LCST-type fluorescent hydrogel with red fluorescence is obtained.

[0068] (3) Cut carbon nanotube fiber yarn, wrap nickel cloth at both ends, evenly apply a layer of silver nanoslurry on the nickel cloth, then stick a layer of sticky copper tape, apply another layer of silver nanoslurry on the copper tape, and place it in an oven at 60 °C for 15 min to dry; connect wires to the copper wires at both ends and fix them with solder. Use PDMS with a thickness of 0.3 mm as the base layer, place the carbon nanotube fiber yarn with wires connected on the base, then cover a layer of PDMS on the carbon nanotube fiber yarn, and seal the edges with glue to obtain an electrothermal control layer that can be used underwater.

[0069] (4) After placing the fluorescent hydrogels prepared in steps (1) and (2) in deionized water for 3 min, swollen hydrogels are obtained. Cut them into blocks of 1*1 cm 2 , acidify the two for 1 h and then stack them in contact. Then stack and contact them with the electrothermal control layer prepared in step (3) to obtain a color-changing hydrogel with a multi-layer structure. Then place it in seawater at 5 °C and apply electricity.

[0070] As Figure 2 and Figure 3As shown, the underwater color-changing hydrogel of the multi-layer structure in this embodiment is electrified, and the temperature change sensitivity of the electrothermal control layer and the hydrogel display layer is observed. It can be observed that the flexible electrothermal control layer made of carbon nanotube fiber yarn has a fast temperature change and high sensitivity, and the temperature of the hydrogel display layer above it also increases significantly.

[0071] Example 2

[0072] The preparation method of this example is the same as that of Example 1, except that the fluorescent monomers used are different, specifically as follows:

[0073] (1) Take 0.1 mg of 4-(N,N-dimethylaminoethylene)amino-N-allyl-1,8-naphthalimide amide and 200 mg of acrylamide and dissolve them in 2 mL of deionized water. Add 158 μL of acrylic acid, 2.7 mg of polydimethyldiallylammonium chloride, and 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane and stir evenly. Finally, add 3.5 mg of ammonium persulfate to form a UCST prepolymer solution. Then, add the UCST prepolymer solution to a mold, seal it, and place it in an oven at 60 °C for 7 h. After demolding, a UCST-type fluorescent hydrogel with yellow-green fluorescence is obtained.

[0074] (2) Take 1 mg of 4-(N,N-dimethylaminoethylene)amino-N-allyl-1,8-naphthalimide amide, 300 mg of N-isopropylacrylamide, 1.7 mg of N,N'-methylenebisacrylamide, and 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane and dissolve them in 2 mL of deionized water. Stir evenly, then add 3.4 mg of ammonium persulfate to form an LCST prepolymer solution. Add 5 μL of the accelerator tetramethylethylenediamine, mix well, and quickly add it to a mold made of ordinary glass, seal it, and react at 10 °C for 12 h. After demolding, an LCST-type fluorescent hydrogel with yellow-green fluorescence is obtained.

[0075] Example 3

[0076] The preparation method of this example is the same as that of Example 1, except that the UCST-type hydrogel monomers used are different, specifically as follows:

[0077] (1) Take 0.1 mg of 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthalimide and 340 mg of N-acryloylglycine amide and dissolve them in 2 mL of deionized water. Add 2.7 mg of polydimethyldiallylammonium chloride and 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane and stir evenly. Finally, add 3.5 mg of ammonium persulfate to form a UCST prepolymer solution. Then, add the UCST prepolymer solution to a mold, seal it, and place it in an oven at 60 °C for 7 h. After demolding, a UCST-type fluorescent hydrogel with blue fluorescence is obtained.

[0078] Example 4

[0079] The preparation method of this example is the same as that of Example 1, except that the LCST-type hydrogel monomers used are different, specifically as follows:

[0080] (1) Take 1 mg of rhodamine b methacrylate, 300 mg of N,N-diethylacrylamide, 1.7 mg of N,N'-methylenebisacrylamide, and 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane, dissolve them in 2 mL of deionized water, stir evenly, finally add 3.4 mg of ammonium persulfate to form a prepolymer solution, add 5 μL of accelerator tetramethylethylenediamine, mix well and quickly add it to a common glass mold and seal it, and react at 10 °C for 12 h. After demolding, an LCST-type fluorescent hydrogel with red fluorescence is obtained.

[0081] Example 5

[0082] The preparation method of this example is the same as that of Example 1, except that the crosslinking agent used is different, specifically as follows:

[0083] (1) Take 0.1 mg of 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthalimide and 200 mg of acrylamide, dissolve them in 2 mL of deionized water, add 158 μL of acrylic acid, 1 mg of N,N'-methylenebisacrylamide, and 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane, stir evenly, finally add 3.5 mg of ammonium persulfate to form a UCST prepolymer solution, then add the UCST prepolymer solution to the mold and seal it, and place it in an oven at 60 °C for 7 h. After demolding, a UCST-type fluorescent hydrogel with blue fluorescence is obtained.

[0084] (2) Take 1 mg of rhodamine b methacrylate, 300 mg of N-isopropylacrylamide, 1.7 mg of ethylene glycol diacrylate, and 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane, dissolve them in 2 mL of deionized water, stir evenly, then add 3.4 mg of ammonium persulfate to form a prepolymer solution, add 5 μL of accelerator tetramethylethylenediamine, mix well and quickly add it to a common glass mold and seal it, and react at 10 °C for 12 h. After demolding, an LCST-type fluorescent hydrogel with red fluorescence is obtained.

[0085] Example 6

[0086] The preparation method of this example is the same as that of Example 1, except that the initiator and free radical polymerization method used are different, specifically as follows:

[0087] (1) 0.1 mg of 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthalimide and 200 mg of acrylamide were dissolved in 2 mL of deionized water. 158 μL of acrylic acid, 2.7 mg of polydimethyldiallylammonium chloride, and 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane were added and stirred evenly. Finally, 3.5 mg of α-ketoglutaric acid was added to form a UCST prepolymer solution. Then, the UCST prepolymer solution was added to a mold, sealed, and placed under a UV lamp (50 W) for reaction for 3 h. After demolding, a UCST-type fluorescent hydrogel with blue fluorescence was obtained.

[0088] (2) 1 mg of rhodamine b methacrylate, 300 mg of N-isopropylacrylamide, 1.7 mg of N,N′-methylenebisacrylamide, and 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane were dissolved in 2 mL of deionized water and stirred evenly. Then, 3.4 mg of α-ketoglutaric acid was added to form an LCST prepolymer solution. After mixing evenly, it was quickly added to a mold of ordinary glass, sealed, and reacted under a UV lamp for 3 h. After demolding, an LCST-type fluorescent hydrogel with red fluorescence was obtained.

[0089] Example 7

[0090] The preparation method of this example is the same as that of Example 1, except that the content of the silane coupling agent used is different, specifically as follows:

[0091] (1) 200 mg of acrylamide was dissolved in 2 mL of deionized water. 158 μL of acrylic acid, 2.7 mg of polydimethyldiallylammonium chloride, and 3.5 / 5.3 / 7 / 8.8 / 10.5 / 12.3 μL of 3-(methacryloyloxy)propyltrimethoxysilane were added and stirred evenly. Finally, 3.5 mg of ammonium persulfate was added to form a prepolymer solution. Then, the prepolymer solution was added to a mold, sealed, and placed in an oven at 60 °C for reaction for 7 h. After demolding, 7 UCST-type hydrogels with different ratios of silane coupling agent were obtained.

[0092] (2) 300 mg of N-isopropylacrylamide, 1.7 mg of N,N′-methylenebisacrylamide, and 3.5 / 5.3 / 7 / 8.8 / 10.5 / 12.3 μL of 3-(methacryloyloxy)propyltrimethoxysilane were dissolved in 2 mL of deionized water and stirred evenly. Then, 3.4 mg of ammonium persulfate was added to form a prepolymer solution. 5 μL of accelerator tetramethylethylenediamine was added. After mixing evenly, it was added to a mold of ordinary glass, sealed, and reacted at 10 °C for 12 h. After demolding, LCST-type hydrogels with different ratios of silane coupling agent were obtained.

[0093] (3) The hydrogels prepared in step (1) and step (2) were placed in deionized water for 3 min, and then the swollen hydrogels were obtained and cut into 1*1 cm 2in the form of a block

[0094] As Figure 4 and Figure 5 shown, UCST-type hydrogels and LCST-type hydrogels with different proportions of silane coupling agents were placed at different temperatures, and their phase transition degrees were observed and recorded. It can be seen that with the increase in the content of the silane coupling agent, the phase transition ability of UCST-type hydrogels and LCST-type hydrogels gradually weakens.

[0095] Comparative Example 1

[0096] The preparation method of this comparative example was the same as that of Example 7, except that the content of the silane coupling agent used was different, specifically as follows:

[0097] (1) 200 mg of acrylamide was dissolved in 2 mL of deionized water, 158 μL of acrylic acid, 2.7 mg of polydimethyldiallylammonium chloride, and 1.8 μL of 3-(methacryloyloxy)propyltrimethoxysilane were added and stirred evenly. Finally, 3.5 mg of ammonium persulfate was added to form a prepolymer solution. Then, the prepolymer solution was added to a mold, sealed, and placed in an oven at 60 °C for 7 h. After demolding, 7 UCST-type hydrogels with different proportions of silane coupling agents were obtained.

[0098] (2) 300 mg of N-isopropylacrylamide, 1.7 mg of N,N'-methylenebisacrylamide, and 1.8 μL of 3-(methacryloyloxy)propyltrimethoxysilane were dissolved in 2 mL of deionized water, stirred evenly, and then 3.4 mg of ammonium persulfate was added to form a prepolymer solution. 5 μL of accelerator tetramethylethylenediamine was added, and after mixing evenly, it was added to a mold of ordinary glass, sealed, and reacted at 10 °C for 12 h. After demolding, LCST-type hydrogels with different proportions of silane coupling agents were obtained.

[0099] As Figure 4 and Figure 5 shown, when the proportion of the silane coupling agent is less than 1%, the hydrogel cannot be formed.

[0100] Detection Example 1

[0101] Under an ultraviolet lamp at 365 nm, the color change of the multi-layered structure hydrogel prepared in Example 1 with temperature change after being energized underwater was observed. As Figure 6 shown, the fluorescence significantly changed from blue to pink, and the corresponding fluorescence spectrum test results also showed different fluorescences in the energized and de-energized states.

[0102] Detection Example 2

[0103] Based on the application of the underwater color-changing hydrogel with a multi-layered structure prepared in Example 1 in underwater encrypted information:

[0104] (1) Dissolve 300 mg of acrylamide and 1.7 mg of N,N′-methylenebisacrylamide in 2 mL of deionized water, add 1 mg of rhodamine b methacrylate and stir evenly. Finally, add 3.4 mg of ammonium persulfate to form a prepolymer solution. Add 5 μL of accelerator tetramethylethylenediamine, mix well and add it to a mold made of ordinary glass and seal it. React at 10 °C for 12 h. After demolding, a hydrogel with red fluorescence is obtained.

[0105] (2) Place the UCST fluorescent hydrogel with blue fluorescence prepared in Example 1 in deionized water for 3 min to obtain a swollen hydrogel, and cut it into 25 pieces of 1*1 cm 2 blocks; Place the LCST fluorescent hydrogel with red fluorescence prepared in Example 1 in deionized water for 3 min to obtain a swollen hydrogel, and cut it into 16 pieces of 1*1 cm 2 blocks;

[0106] (3) Place the fluorescent hydrogel prepared in step (1) in deionized water for 3 min to obtain a swollen hydrogel, and cut it into 9 pieces of 1*1 cm 2 blocks. Acidify the gel for 1 h and then stack them in contact. Then stack and contact them with the electrothermal control layer prepared in step (3) of Example 1 to obtain an underwater fluorescent color-changing display with a multi-layer structure.

[0107] As Figure 7 shown, combine different block hydrogels together and observe under a 365 nm ultraviolet lamp to achieve information encryption and display. When not powered on, the hydrogel area shows a whole block of blue fluorescence; when the electrothermal control layer is powered on, after power-on, obvious changes in fluorescence color and fluorescence intensity occur in the hydrogel area, and the obvious number "21" appears; after power-off, the hydrogel area quickly returns to a whole block of blue fluorescence, and information encryption and display are achieved throughout the process.

[0108] Detection Example 3

[0109] Place the UCST hydrogel with blue fluorescence and the LCST hydrogel with red fluorescence prepared in Example 1 in deionized water for 3 min to obtain swollen hydrogels, cut them into fish shapes, acidify both for 1 h and then stack them in contact. Then stack and contact both with the electrothermal control layer prepared in step (3) of Example 1 to obtain a color-changing skin with different shapes. Then place it in seawater at 5 °C and power it on.

[0110] As Figure 8 shown, after powering on the fluorescent color-changing skin with different shapes and placing it in water, observe it under a 365 nm ultraviolet lamp, and obvious changes in fluorescence color and fluorescence intensity occur in the color-changing skin.

[0111] Detection Example 4

[0112] (1) After placing the UCST-type fluorescent hydrogel prepared in step (1) of Example 7 and added with 3.5 μL of 3-(methacryloyloxy)propyltrimethoxysilane in deionized water for 3 min, a swollen hydrogel was obtained, and it was cut into 3 circles with a diameter of 1 cm;

[0113] (2) After placing the LCST-type fluorescent hydrogel with red fluorescence prepared in Example 1 in deionized water for 3 min, a swollen hydrogel was obtained, and it was cut into 2 circles with a diameter of 1 cm;

[0114] (3) After placing the yellow-green fluorescent UCST-type fluorescent hydrogel prepared in step (1) of Example 2 in deionized water for 3 min, a swollen hydrogel was obtained, and it was cut into 1 circle with a diameter of 1 cm;

[0115] (4) After placing the green fluorescent LCST-type fluorescent hydrogel prepared in step (2) of Example 2 in deionized water for 3 min, a swollen hydrogel was obtained, and it was cut into 1 circle with a diameter of 1 cm;

[0116] (5) After acidifying the fluorescent hydrogels prepared in steps (1)-(4) for 1 h and then overlapping and contacting them, and then overlapping and contacting them with the electrothermal control layer prepared in step (3) of Example 1, a bionic skin capable of performing fluorescent color change display underwater can be obtained.

[0117] As Figure 9 shown, the bionic skin was combined with a prosthetic arm to obtain an interactive skin display, and it was observed under a 365 nm ultraviolet lamp. After connecting the power supply and energizing, obvious fluorescent color changes occurred in the area with the bionic skin, realizing the functions of early warning and exploration.

[0118] In addition, in the manner of referring to Examples 1-7, experiments were carried out with other raw materials and conditions listed in this specification, and a multi-layer structured underwater wearable hydrogel color-changing skin was also prepared. From the above examples, comparative examples and the corresponding test results, it can be seen that the multi-layer structured color-changing hydrogel provided by the present invention effectively covalently binds the color-changing hydrogel and the electrothermal control layer, realizes function integration while maintaining its stability in underwater operation, and can quickly heat the hydrogel in a short time to achieve rapid color change underwater, and can be applied to underwater bionic devices.

[0119] The above-described embodiments have elaborated on the technical solutions of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, or substitutions in a similar manner within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An underwater color-changing hydrogel with a multi-layer structure, characterized in that, It includes a UCST type fluorescent hydrogel, a LCST type fluorescent hydrogel and an electrothermal control layer; the polymerization temperature of the UCST type fluorescent hydrogel is 40°C-80°C, and the polymerization temperature of the LCST type fluorescent hydrogel is 5°C-25°C; the electrothermal control layer includes an electrothermal layer and a packaging layer, and the electrothermal layer includes an electrothermal material and an electrode.

2. The underwater color-changing hydrogel with a multi-layer structure according to claim 1, characterized in that, The encapsulation layer is one or more of polydimethylsiloxane PDMS, Ecoflex, vulcanized silicone rubber, and silicone sealant; The electric heating material is one or more of carbon nanotube fiber yarn, graphene, carbon nanotube, and carbon black; The electrode is a metal electrode, including one or more of nickel cloth, conductive silver paste, copper tape, and tin strip.

3. The preparation method of the underwater color-changing hydrogel with a multi-layer structure according to claim 1 or 2, characterized in that The following steps are involved: (1) A UCST-type hydrogel monomer, a fluorescent monomer, a silane coupling agent, an initiator and a cross-linking agent are fully mixed to obtain a UCST prepolymer solution, which is then transferred to a silicone mold for free radical polymerization to obtain a UCST-type fluorescent hydrogel. (2) The LCST hydrogel monomer, fluorescent monomer, silane coupling agent, initiator, promoter and cross-linking agent are fully mixed to obtain an LCST prepolymer solution, which is then transferred to a silicone mold for free radical polymerization to obtain an LCST fluorescent hydrogel. (3) Electrodes are connected to both ends of the electric heating material to obtain an electric heating layer, and then the packaging layer and the electric heating layer are combined and sealed to obtain an electric heating control layer. (4) The UCST-type fluorescent hydrogel and the LCST-type fluorescent hydrogel are acidified, and the UCST-type fluorescent hydrogel, the LCST-type fluorescent hydrogel and the electrothermal control layer are combined layer by layer to form an underwater color-changing hydrogel with a multilayer structure.

4. The preparation method according to claim 3, characterized in that, The UCST type hydrogel monomer described in step (1) is one or more of acrylamide, acrylic acid, N-acryloylglycine amide, hydroxyethyl acrylate, and methyl acrylate; The LCST type hydrogel monomer described in step (2) is one or more of N,N-diethylacrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, N-ethylacrylamide, N-n-propylacrylamide, methacrylamide, 2-morpholinylethyl methacrylate, dimethylaminoethyl methacrylate, N-tert-butylacrylamide, N-isopropylmethacrylamide, N,N-diethylacrylamide, and N-ethyloxazoline.

5. The preparation method according to claim 3, wherein The fluorescent monomers described in step (1) and step (2) are one or more of 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthyl imine, 4-(N,N-dimethylaminoethylene)amino-N-allyl-1,8-naphthylamide, rhodamine b, rhodamine b methacrylamide, fluorescein, coumarin, and tetrakis(4-pyridylbiphenyl)ethylene.

6. The preparation method according to claim 4, characterized in that, Calculated by weight percentage of the UCST prepolymer solution or the LCST prepolymer solution, the content of the UCST type hydrogel monomer or the LCST type hydrogel monomer is 0.05wt%-35wt%.

7. The preparation method according to claim 5, wherein, Calculated as a percentage by weight of the UCST-type hydrogel monomer or the LCST-type hydrogel monomer, the content of the fluorescent monomer in step (1) and step (2) is 0.01 wt % to 1 wt %.

8. The preparation method according to claim 3, wherein Steps (1) and (2) are carried out by thermal-initiated or photo-initiated free radical polymerization; Based on thermal-initiated free radical polymerization, in step (1), the polymerization temperature is 40°C - 80°C and the polymerization time is 0.1 h - 24 h; in step (2), the polymerization temperature is 5°C - 25°C and the polymerization time is 0.1 h - 48 h; Based on photo-initiated free radical polymerization, in steps (1) and (2), the power of the ultraviolet lamp is 5 W - 250 W and the polymerization time is 5 min - 120 min.

9. The preparation method according to claim 3, characterized in that In step (4), the acid for acidification is an organic acid or an inorganic acid; the concentration of the selected acid is 0.1 M - 1.5 M, the volume of the selected acid is 5 mL - 50 mL, and the acidification time is 1 h - 5 h.

10. Use of the underwater color-changing hydrogel with a multilayer structure according to claim 1 or 2 in flexible wearable devices and underwater information display.

11. The application according to claim 10, wherein The applied power-on voltage is 2 V - 30 V.

Images