A polymer hydrogel device with electrothermal control of fluorescence color change and preparation method thereof

Abstract

The invention relates to the field of fluorescent hydrogels, and discloses a polymer hydrogel device for electrothermally regulating fluorescent color change and a preparation method thereof. The preparation method comprises the following steps: applying fluorescent paint on the non-carbon material side of a carbon-based conductive paper, and using the paint as a substrate after drying and curing; attaching a temperature-sensitive fluorescent hydrogel on the surface of the fluorescent paint, and connecting an electrode to one side of the carbon-based conductive paper of the substrate to obtain the polymer hydrogel device. When the hydrogel device is not powered on, the superimposed color of the top layer of the fluorescent polymer hydrogel and the lower layer of the fluorescent paint is displayed under ultraviolet light, and the color of the fluorescent polymer hydrogel is displayed after power is turned on, thereby achieving rich and colorful changes in the color of the device. The device can be applied to the field of intelligent display and used for information encryption and decryption, etc.

Description

Technical Field

[0001] The invention relates to the field of fluorescent hydrogels, and in particular to a polymer hydrogel device for electrothermal regulation of fluorescent color change and a preparation method thereof. Background Art

[0002] As a rising star in the field of luminescent materials, smart fluorescent polymer hydrogel is a class of polymer soft materials with adjustable luminescent properties. Unlike other classical fluorescent materials that mainly exist in solid or solution form, the three-dimensional cross-linked network of fluorescent polymer hydrogel contains a large amount of water and can exist in a highly hydrated quasi-solid form. Therefore, it has many excellent properties of both solid and solution, including modulus similar to that of biological tissues, inherent soft and wet properties, good biocompatibility, etc. Importantly, under the action of appropriate external stimuli, it is easy to exchange substances with the surrounding aqueous solution, inducing swelling or deswelling of the hydrogel, accompanied by significant changes in luminescent color or intensity, so it has great application potential in bionic drive, sensor detection, information storage encryption, etc.

[0003] For example, CN111440332A discloses a method for preparing a fluorescent hydrogel composite material, which comprises mixing a carbon source with deionized water, performing a hydrothermal reaction, adding the obtained carbon dots and glycerol to an aqueous solution of sodium alginate and gelatin, stirring, injecting the mixture into a mold, drying, spraying the mixture with a calcium chloride solution, and then removing the film. The method has the characteristics of simple operation, good repeatability, mild and easy-to-control reaction conditions, etc. The prepared fluorescent hydrogel composite material has good optical and mechanical properties and has good application prospects.

[0004] The color-changing process of most of the smart fluorescent polymer hydrogels reported so far usually relies on traditional stimulation methods such as pH, ionic strength, and temperature to regulate, which has certain limitations in application, especially in the pH or metal ion response system. The continuous alternating addition of chemical stimuli such as acids and alkalis will gradually leave inorganic salts generated by the cumulative reaction in the fluorescent polymer hydrogel, which will seriously weaken the sensitivity of its cyclic stimulation response and lead to the attenuation of color-changing performance. In addition, these external stimuli depend on the solution environment or complex and inconvenient equipment to carry. The above factors greatly limit the application of smart fluorescent polymer hydrogels. In comparison, the actual controllability of electrical stimulation is relatively strong, easy to control and adjust, and can better meet the needs of smart fluorescent polymer hydrogels in practical applications, especially in bionic soft robots, smart flexible displays and other aspects.

[0005] In recent years, some scholars have made certain attempts in the field of developing electric field stimulation responsive fluorescent polymer hydrogels. Patent CN105601955A discloses a method for preparing an electric stimulation fluorescent responsive hydrogel, which is obtained by dispersing a metal ion salt in a hyperbranched polyamide aqueous solution and heating it. The gel is very sensitive to electric field stimulation; as the electric field action time increases, the fluorescence intensity will gradually decrease. Moreover, the fluorescent electrical responsiveness of this gel is reversible; after the electric field is removed, the fluorescence intensity of the gel will gradually recover. Although there will be a decrease in fluorescence intensity under the stimulation of the electric field, rich fluorescent color changes are not achieved.

[0006] Therefore, to obtain hydrogel materials with a variety of fluorescent color changes, innovative exploration is still needed. Such a simpler, more flexible and feasible color-changing method can greatly expand its application in flexible wearable devices, flexible displays, optical devices and other fields, and is of great significance to the development of the field of smart polymer hydrogels. Summary of the invention

[0007] In view of the problem that the color-changing process of the smart fluorescent hydrogel in the prior art relies on traditional chemical stimulation, which easily leads to the accumulation of chemical substances and affects the color-changing stability, the present invention provides a method for preparing an electrothermal-regulated fluorescent color-changing polymer hydrogel device, in which the electrothermal conversion material, the electrode and the fluorescent polymer hydrogel are compounded into an integrated flexible device, and the change of a variety of fluorescent colors is achieved through electrothermal regulation. The color-changing method is simple and flexible, and can be used in the fields of flexible wearable devices, flexible displays, optical devices, etc.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing a polymer hydrogel device with electrothermal control of fluorescence color change comprises the following steps:

[0010] (1) Apply fluorescent paint on the non-carbon material side of the carbon-based conductive paper and use it as a substrate after drying and curing;

[0011] (2) A thermosensitive fluorescent hydrogel is attached to the surface of the fluorescent paint, and one side of the carbon-based conductive paper of the substrate is connected to an electrode to obtain the polymer hydrogel device.

[0012] The present invention adopts a carbon-based conductive paper with an electrothermal conversion effect to be compounded layer by layer with a fluorescent paint and a thermosensitive fluorescent hydrogel to obtain a fluorescent color-changing device that responds to electrical stimulation. The fluorescent paint and the thermosensitive fluorescent hydrogel can emit fluorescence under ultraviolet light. When not powered on, due to the high light transmittance of the polymer hydrogel, the device presents a composite color of the fluorescent color of the fluorescent paint and the superposition of the thermosensitive fluorescent hydrogel. When powered on, the carbon-based conductive paper generates Joule heat due to electrical stimulation, prompting the upper thermosensitive fluorescent hydrogel to undergo a phase change, the light transmittance decreases, the fluorescent color of the fluorescent paint is blocked, and only the color of the thermosensitive fluorescent hydrogel is presented, thereby realizing the electrostimulated fluorescent color change. By combining fluorescent paints of different colors and thermosensitive fluorescent hydrogels, the device can achieve a colorful change in color. The device can be compounded with a hard robot to realize its functions such as bionic camouflage or display under specific conditions.

[0013] The carbon-based conductive paper is prepared with reference to patent CN106409428A, and commercially available carbon fiber conductive paper with good electrothermal performance can be used.

[0014] Specifically, the preparation method of the carbon-based conductive paper is as follows: dispersing carbon materials (including graphene and carbon nanotubes) in an ethanol solution to form a carbon material ethanol dispersion and spraying the dispersion on the air / water interface to self-assemble to form a film, and using capillary force to extrude the film to obtain a dense carbon material film. The dense carbon material film is transferred from the air / water interface to the paper by an upward transfer method and dried to form the conductive paper with the electrothermal conversion effect.

[0015] The electrode is a metal electrode, including nickel cloth, copper tape or silver paste;

[0016] Since the temperature-sensitive fluorescent hydrogel used in the present invention has no self-adhesiveness, it can be bonded to the fluorescent paint layer by using PVA glue, or by using nano-clay or commercial double-sided transparent tape.

[0017] If PVA glue is used for bonding, after attaching the temperature-sensitive fluorescent hydrogel to the surface of the fluorescent paint, a freeze-thaw cycle is performed to solidify the PVA glue.

[0018] Preferably, the mass fraction of the PVA glue is 2 to 10 wt %; the single freezing or thawing time is 15 to 120 min; and the number of freezing and thawing cycles is 2 to 10 times.

[0019] The drying and curing temperature of the fluorescent paint is 10-100° C. to ensure the curing of the fluorescent paint layer.

[0020] The fluorescent color of the thermosensitive fluorescent hydrogel includes red, green, yellow or blue, etc., and the fluorescent color of the fluorescent paint includes red, green or blue, etc. Preferably, the fluorescent color of the thermosensitive fluorescent hydrogel is different from that of the fluorescent paint, so as to achieve the change of different fluorescent colors. The color combination of the two includes red-green, green-blue, yellow-green, blue-red, etc.

[0021] The preparation process of the temperature-sensitive fluorescent hydrogel comprises the steps of: polymerizing fluorescent monomers and hydrogel monomers under the action of an initiator and a cross-linking agent, and using the hydrogel after swelling.

[0022] The fluorescent monomer is a ligand, organic dye or luminescent nanoparticle having the ability to coordinate luminescent rare earth ions; including one or more of 6-acrylamidopicolinate, 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthyl imine, fluorescein, coumarin, and tetrakis(4-pyridine biphenyl)ethylene. 6-acrylamidopicolinate is prepared according to the document [Angew.Chem.Int.Ed.2019,58,16243], and 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthyl imine is prepared according to the document [Adv.Intell.Syst.2020,DOI:10.1002 / aisy.202000239].

[0023] The hydrogel monomer is a monomer that can prepare a temperature-sensitive hydrogel (LCST), including one or more of N-isopropyl acrylamide, N-isopropyl methacryloyl, N,N-diethyl acrylamide, dimethylaminoethyl methacrylate, and N-ethyloxazoline. The light transmittance of this material changes significantly before and after the transition temperature.

[0024] The initiator includes any one or more of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, ammonium persulfate, and potassium persulfate;

[0025] The cross-linking agent includes a monomer containing multiple double bonds, preferably, any one or more of N,N′-methylenebisacrylamide, ethylene glycol diacrylate, and polyethylene glycol diacrylate.

[0026] In the preparation process of the thermosensitive fluorescent hydrogel, the content of the fluorescent monomer in each 10 ml prepolymer solution is 1-60 mg, the content of the hydrogel monomer is 1-5 g, the content of the initiator is 10-200 mg, and the content of the cross-linking agent is 2-100 mg.

[0027] In the preparation process of the thermosensitive fluorescent hydrogel, if the polymerization is a free radical polymerization initiated by light, the power of the ultraviolet light is 8 to 250 W, and the polymerization time is 2 to 120 min; if it is a free radical polymerization initiated by heat, the polymerization temperature is 10 to 25° C., and the polymerization time is 0.1 to 48 h;

[0028] When heat-induced free radical polymerization is used to prepare the thermosensitive fluorescent hydrogel, an accelerator N,N,N',N'-tetramethylethylenediamine can be added to promote the polymerization of the hydrogel. The amount of the accelerator is 2 to 20 μl per 10 ml of prepolymer solution.

[0029] During the preparation of the thermosensitive fluorescent hydrogel, the prepolymer liquid is added into the mold for polymerization reaction. If it is a light-induced free radical polymerization reaction, the mold includes two upper and lower pieces of quartz glass and a hollow mold in the middle, and the hollow mold in the middle is silicone rubber; if it is a heat-induced free radical polymerization reaction, the mold composition includes two upper and lower flat plates and a hollow mold in the middle, the upper and lower flat plates include metal and / or plastic and / or metal plates, the hollow mold in the middle is silicone rubber, and the thickness of the hollow plate in the middle is 0.5 to 10 mm.

[0030] The solution used for swelling the thermosensitive fluorescent hydrogel includes Eu 3+ Aqueous solution and / or Tb 3+ Aqueous solution and / or deionized water, swelling time is 1min to 10h.

[0031] During the preparation process, the temperature-sensitive fluorescent hydrogel can be cut into a desired shape.

[0032] The present invention also provides a polymer hydrogel device with electrothermal controlled fluorescence color change obtained according to the preparation method, which shows fluorescence color under ultraviolet irradiation, realizes electrostimulated fluorescence color change after the electrode is energized, and the electrode energization voltage is 5 to 30 V. It uses 254nm or 365nm ultraviolet irradiation to display corresponding colors and patterns, and the specific wavelength depends on the experimental situation or the selected fluorescent monomer.

[0033] The preferred voltage for the current supply is 10 to 20V.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The fluorescent polymer hydrogel and fluorescent paint in the polymer hydrogel device of the present invention can emit fluorescence under ultraviolet light. When the power is not turned on, the superimposed color of the top layer of fluorescent polymer hydrogel and the bottom layer of fluorescent paint of the device is displayed under ultraviolet light. After the power is turned on, the temperature of the device rises, the transmittance of the fluorescent polymer hydrogel decreases significantly, the color of the bottom layer of fluorescent paint is blocked, and the fluorescent color changes. By using fluorescent polymer hydrogels with different colors, a rich and colorful change of the device color can be achieved.

[0036] (2) The polymer hydrogel device of the present invention has good electrical conductivity and high electrothermal efficiency, and the polymer hydrogel device can complete color changes in a short time.

[0037] (3) By selecting the color and designing the shape of the fluorescent polymer hydrogel and fluorescent paint in the polymer hydrogel device, patterned display can be achieved with the assistance of external voltage and the light source used, which can be applied to the field of smart display for information encryption and decryption.

[0038] (4) The electrothermally regulated fluorescent color-changing polymer hydrogel device of the present invention has a certain flexibility and can be conformally bonded to a hard robot. In a specific environment, it can realize the bionic camouflage and display of the robot, avoiding the liquid environment required by ordinary color-changing hydrogel-based bionic robots.

[0039] (5) The preparation process of the polymer hydrogel device of the present invention is simple and easy to operate. It does not require expensive preparation instruments, high temperature and catalysts, is time-saving, has low requirements on environmental factors, and does not cause any impact. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the preparation process of the polymer hydrogel device of the present invention;

[0041] Figure 2 is a curve showing the temperature change over time of the polymer hydrogel device prepared in Example 1 at different voltages;

[0042] Figure 3 The fluorescence spectrum of the polymer hydrogel device prepared in Example 2 before and after power-on and the actual image under 254nm ultraviolet light;

[0043] Figure 4 This is a fluorescence change diagram of the polymer hydrogel device in Example 3 when the power is turned on and off five times under ultraviolet light;

[0044] Figure 5 This is a fluorescence color change image of the cherry tree prepared by the polymer hydrogel device in Example 4 after being powered on under ultraviolet light;

[0045] Figure 6 This is a graph showing the fluorescent color change of the functional robot obtained in Example 5 after turning the power on and off under ultraviolet light. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

[0047] In the following specific embodiments, the fluorescent monomer 6-acrylamidopyridine carboxylate is prepared according to the document [Angew.Chem.Int.Ed.2019,58,16243], and 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthaleneimine is prepared according to the document [Adv.Intell.Syst.2020,DOI:10.1002 / aisy.202000239].

[0048] The preparation method of carbon-based conductive paper refers to patent CN106409428A. The specific preparation method is as follows: disperse the carbon material (including graphene and carbon nanotubes) in an ethanol solution to form a carbon material ethanol dispersion and spray it on the air / water interface for self-assembly to form a film, and use capillary force to extrude the film to obtain a dense carbon material film. The dense carbon material film is transferred from the air / water interface to the paper by an upward transfer method and dried to form the conductive paper with the electrothermal conversion effect.

[0049] Other raw materials were purchased from the market.

[0050] Example 1

[0051] Preparation process Figure 1 As shown:

[0052] (1) 1 mg of 6-acrylamidopicolinate, 2 g of N-isopropylacrylamide, 5 mg of N,N'-methylenebisacrylamide and 200 mg of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone were dissolved in 10 ml of deionized water to form a prepolymer solution, the prepolymer solution was added to a mold and sealed, and irradiated with 250 W 365 nm ultraviolet light for 60 min to obtain a thermosensitive fluorescent hydrogel; the obtained hydrogel was placed in a 0.1 mol L -1 Eu(NO 3 ) 3 After soaking in the solution for 50 minutes to swell, it was rinsed with deionized water to obtain a swollen hydrogel with red fluorescence, which was cut into 20mm*20mm squares for later use.

[0053] (2) Apply fluorescent paint with green fluorescence on the side of the carbon-based conductive paper where the carbon material film has not been transferred, dry and solidify at 35°C to obtain a base layer, trim the base layer appropriately and perform hot pressing to make it flat; apply 2 wt% PVA on the surface of the fluorescent paint, adhere the hydrogel prepared in step (1) to the fluorescent paint, freeze at low temperature for 15 minutes, thaw at room temperature for 30 minutes, and repeat 7 times to fix the hydrogel on the fluorescent paint; connect an electrode on the side of the carbon-based conductive paper containing the carbon material to obtain a polymer hydrogel device with certain flexibility and electrothermal controllable fluorescence color change.

[0054] Different voltages were applied to the hydrogel device to observe the temperature sensitivity of the hydrogel device. The results are as follows: Figure 2 As shown, it can be observed that when the voltage is 15V, the temperature of the hydrogel device changes faster and has higher sensitivity.

[0055] Example 2

[0056] (1) Take 5 mg of 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthaleneimine, 1.5 g of N-isopropylacrylamide, 2 mg of N,N'-methylenebisacrylamide and 75 mg of ammonium persulfate and dissolve them in 10 ml of deionized water to form a prepolymer solution, quickly add 2 μl of accelerator N,N,N',N'-tetramethylethylenediamine, mix quickly and add the prepolymer solution into a common glass mold and seal it, and react at 10°C for 24 hours. After demolding, a polymer hydrogel with blue fluorescence is obtained, which swells in deionized water for 2 hours.

[0057] (2) A fluorescent paint with red fluorescence is scraped on the side of the carbon-based conductive paper where the carbon material film has not been transferred, and the paint is dried and cured at 80°C to obtain a base layer, and the base layer is appropriately trimmed and hot-pressed to make it flat; the hydrogel prepared in step (1) is cut into circles with a diameter of 15 mm using a laser cutting machine (using a power of 90 W), and PVA with a mass fraction of 8 wt% is coated on the surface of the fluorescent paint and the fluorescent polymer hydrogel, each coating only half of the surface area, and the two halves of the surface coated with PVA glue are pasted to each other, frozen at low temperature for 40 minutes, thawed at room temperature for 45 minutes, and the cycle is repeated twice, so that the fluorescent polymer hydrogel can be bonded to the surface of the fluorescent paint; an electrode is connected to the side of the carbon-based conductive paper containing the carbon material to obtain a polymer hydrogel device with a certain flexibility and electrothermal control of fluorescent color change.

[0058] like Figure 3 As shown, the color change of the device before and after power-on is observed under a 254nm ultraviolet lamp, and the fluorescence obviously changes from purple to blue. The corresponding fluorescence spectrum test results also show the different fluorescence displayed in the power-on and power-off states.

[0059] Example 3

[0060] (1) 60 mg of 6-acrylamidopicolinate, 5 g of N-isopropylacrylamide, 100 mg of N,N'-methylenebisacrylamide and 10 mg of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone were dissolved in 10 ml of deionized water to form a prepolymer solution 1, the prepolymer solution 1 was added to a mold and sealed, irradiated with 8W 365nm ultraviolet light for 8 min, and demolded to obtain a hydrogel 1. The hollow pattern in the middle was cut into a lantern shape using a laser cutting machine;

[0061] Take 60 mg of 6-acrylamidopicolinate, 5 g of N-isopropylacrylamide, 100 mg of N,N'-methylenebisacrylamide and 10 mg of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone and dissolve them in 10 ml of deionized water to form prepolymer 2. Place a square mold with a hollowed-out size larger than the shape of hydrogel 1 on the quartz glass sheet where hydrogel 1 has been placed, pour prepolymer 2 into the mold, and seal it with another quartz glass sheet. Irradiate with 200 W 365 nm ultraviolet light for 70 min. After demolding, hydrogel 2 is obtained. The obtained hydrogel 2 is placed in 0.005 mol L -1 Eu(NO 3 ) 3 After soaking in the solution for 2 minutes and then rinsing with deionized water, a polymer hydrogel with built-in patterning and red fluorescence was obtained.

[0062] (2) Fluorescent paint with green fluorescence is scraped on the side of the carbon-based conductive paper where the carbon material film has not been transferred, and the base layer is obtained by drying and curing at 10°C. The base layer is properly trimmed and hot-pressed to make it flat; PVA with a mass fraction of 7wt% is coated on the surface of the fluorescent paint and the fluorescent polymer hydrogel, and the two surfaces are pasted to each other, frozen at low temperature for 60 minutes, thawed at room temperature for 60 minutes, and the cycle is repeated 4 times. The fluorescent polymer hydrogel can be bonded to the surface of the fluorescent paint; an electrode is connected to the side of the carbon-based conductive paper containing the carbon-based material to obtain a polymer hydrogel device with a certain flexibility and electrothermal controllable fluorescence color change.

[0063] like Figure 4 As shown, the hydrogel device was placed under a 254nm ultraviolet lamp and powered on. After a period of time, the color of the hydrogel 1 area changed and the lantern pattern became clear. After the power was disconnected for a period of time, the color of the hydrogel 1 area was restored and the pattern gradually disappeared. After repeated power on and off for 5 times, the lantern pattern was still clear and the color change was obvious, indicating that the prepared electrothermal control color-changing device based on fluorescent polymer hydrogel has good repeatability.

[0064] Example 4

[0065] (1) 45 mg of 6-acrylamidopicolinate, 1.0 g of N-isopropylacrylamide, 50 mg of N,N′-methylenebisacrylamide and 33 mg of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone were dissolved in 10 ml of deionized water to form a prepolymer solution, which was added to a quartz glass mold and sealed, and irradiated with 50 W 365 nm ultraviolet light for 2 min. The above steps were repeated to obtain three hydrogels. The obtained hydrogel 1 was placed in a 0.07 mol L -1 Eu(NO 3 )3 After soaking in the solution for 10 h and then rinsing with deionized water, a high molecular weight hydrogel with red fluorescence was obtained. -1 Tb(NO 3 ) 3 The obtained hydrogel 3 was placed in 1.0 mol L -1 Eu(NO 3 ) 3 and Tb(NO 3 ) 3 After being immersed in the mixed solution for 55 min and then rinsed with deionized water, a polymer hydrogel with yellow fluorescence was obtained.

[0066] (2) Place the mold on the side of the carbon-based conductive paper where the carbon material film has not been transferred, place fluorescent paint with blue fluorescence in the mold, apply it evenly, and dry it at 45°C to obtain base layer 1. Use a laser cutter to cut a hollow pattern in the shape of a crown from silicone, place the mold on base layer 1, pour fluorescent paint with green fluorescence, apply it evenly, and dry it at 32°C to obtain base layer 2. Use a laser cutter to cut a hollow pattern in the shape of a branch from silicone, place the mold at a suitable position on base layer 2, pour fluorescent paint with reddish-brown fluorescence, apply it evenly, and dry it at 47°C to obtain base layer 3. Trim the base layer appropriately and perform hot pressing to make it flat.

[0067] (3) Connect the substrate obtained in step (2) to the electrode, and cut the red fluorescent polymer hydrogel obtained in step (1) into the shape of a cherry using a laser cutter. Cut the yellow fluorescent polymer hydrogel obtained in step (1) into the shape of a cherry using a laser cutter. Cut the green fluorescent polymer hydrogel obtained in step (1) into the shape of a leaf using a laser cutter. Coat 5 wt% PVA on the surface of the green fluorescent paint and the multicolor fluorescent polymer hydrogel, and stick the multicolor fluorescent polymer hydrogel to the appropriate position on the crown-shaped green fluorescent paint, freeze at low temperature for 50 minutes, thaw at room temperature for 80 minutes, and repeat 8 times. The fluorescent polymer hydrogel can be bonded to the surface of the fluorescent paint to obtain an electrothermal control color-changing device with a certain flexibility.

[0068] like Figure 5 As shown, when the device is connected to a power source and observed under a 254nm ultraviolet lamp, the area loaded with the fluorescent polymer hydrogel undergoes obvious changes in fluorescence color and fluorescence intensity, which can simulate the ripening process of cherry tree fruits.

[0069] Example 5

[0070] (1) Dissolve 10 mg of 6-acrylamidopicolinate, 2.5 g of N-isopropylacrylamide, 30 mg of N,N′-methylenebisacrylamide and 15 mg of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone in 10 ml of deionized water to form a prepolymer solution, add the prepolymer solution into a quartz glass mold and seal it, and irradiate it with 100 W 365 nm ultraviolet light for 4 min. Repeat the above steps to obtain three hydrogels. The obtained hydrogel 1 is placed in 0.15 mol L -1 Eu(NO 3 ) 3 The obtained hydrogel 2 was placed in 0.01 mol L -1 Tb(NO 3 ) 3 The obtained hydrogel 3 was placed in 0.08 mol L -1 Eu(NO 3 ) 3 and Tb(NO 3 ) 3 After being immersed in the mixed solution for 30 min and then rinsed with deionized water, a polymer hydrogel with yellow fluorescence was obtained.

[0071] (2) Place the mold on the side of the carbon-based conductive paper where the carbon material film has not been transferred, place fluorescent paint with green fluorescence in the mold, apply it evenly, and dry and solidify it at 48°C to obtain a base layer. The base layer is appropriately trimmed and hot-pressed to make it flat.

[0072] (3) Connect the substrate obtained in step (2) to the electrode, and cut the red fluorescent polymer hydrogel obtained in step (1) into 9 10mm*10mm squares using a laser cutter. Cut the yellow fluorescent polymer hydrogel obtained in step (1) into 8 10mm*10mm squares using a laser cutter. Cut the green fluorescent polymer hydrogel obtained in step (1) into 8 10mm*10mm squares using a laser cutter. Coat 9wt% PVA on the surface of the green fluorescent paint and the multicolor fluorescent polymer hydrogel, and stick the multicolor fluorescent polymer hydrogel to the appropriate position on the green fluorescent paint, freeze at low temperature for 15min, thaw at room temperature for 66min, and repeat 6 times. The fluorescent polymer hydrogel can be bonded to the surface of the fluorescent paint to obtain an electrothermal control color-changing device with a certain flexibility.

[0073] like Figure 6As shown, the electrothermal color-changing device based on fluorescent polymer hydrogel is combined with a hard robot to obtain a functional robot, which is placed under a 254nm ultraviolet lamp for observation. In certain scenarios, the robot can be camouflaged. When the device is connected to a power source, the area loaded with fluorescent polymer hydrogel undergoes obvious changes in fluorescence color and fluorescence intensity, which can realize the display of the robot.

[0074] In summary, by means of the above technical solution of the present invention, the present invention prepares an electrothermal controllable color-changing device based on fluorescent polymer hydrogel by a simple method. In addition, the inventor of this case also conducted experiments with other raw materials and conditions listed in this specification with reference to the methods of Examples 1 to 5, and also prepared an electrothermal controllable color-changing device based on fluorescent polymer hydrogel.

[0075] It should be noted that, in this article, in general, the elements defined by the sentence "including..." do not exclude the existence of other identical elements in the steps, processes, methods or experimental equipment including the elements.

[0076] It should be understood that the above embodiments are preferred embodiments of the present invention. The above examples are only for illustrating the technical concept and features of the present invention. The purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly. However, the implementation of the present invention is not limited to the above embodiments. Any other changes, modifications, substitutions, and combinations made under the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a polymer hydrogel device with electrothermal control of fluorescence color change, It is characterized in that The steps include: (1) Apply fluorescent paint on the non-carbon material side of the carbon-based conductive paper and use it as a substrate after drying and curing; (2) attaching a temperature-sensitive fluorescent hydrogel on the surface of the fluorescent paint, and connecting an electrode to one side of the carbon-based conductive paper of the substrate to obtain the polymer hydrogel device; The fluorescent paint and the temperature-sensitive fluorescent hydrogel have different fluorescent colors; The preparation process of the temperature-sensitive fluorescent hydrogel comprises the steps of: polymerizing fluorescent monomers and hydrogel monomers under the action of an initiator and a cross-linking agent, and using the hydrogel after swelling.

2. The method for preparing the polymer hydrogel device with electrothermal control of fluorescence color change according to claim 1, It is characterized in that The fluorescent paint and the temperature-sensitive fluorescent hydrogel are bonded by using PVA glue, nano clay or commercial double-sided transparent tape.

3. The method for preparing the polymer hydrogel device with electrothermal control of fluorescence color change according to claim 2, It is characterized in that When PVA glue is used for bonding, after the temperature-sensitive fluorescent hydrogel is attached to the surface of the fluorescent paint, a freeze-thaw cycle is performed to solidify the PVA glue.

4. The method for preparing the polymer hydrogel device with electrothermal control of fluorescence color change according to claim 1, It is characterized in that The drying and curing temperature of the fluorescent paint is 10-100°C.

5. The method for preparing the polymer hydrogel device with electrothermal control of fluorescence color change according to claim 1, It is characterized in that The fluorescent monomer includes any one or more of 6-acrylamidopicolinate, 4-(2-dimethylaminoethoxy)-N-allyl-1,8-naphthaleneimide, fluorescein, coumarin, and tetrakis(4-pyridylbiphenyl)ethylene; The hydrogel monomer includes any one or more of N-isopropyl acrylamide, N-isopropyl methacryloyl, N,N-diethyl acrylamide, dimethylaminoethyl methacrylate, and N-ethyloxazoline.

6. The method for preparing the polymer hydrogel device with electrothermal control of fluorescence color change according to claim 1, It is characterized in that The initiator includes any one or more of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, ammonium persulfate, and potassium persulfate; the crosslinking agent includes any one or more of N,N'-methylenebisacrylamide, ethylene glycol diacrylate, and polyethylene glycol diacrylate.

7. The method for preparing the polymer hydrogel device with electrothermal control of fluorescence color change according to claim 1, It is characterized in that In every 10 ml of prepolymer solution, the content of the fluorescent monomer is 1-60 mg, the content of the hydrogel monomer is 1-5 g, the content of the initiator is 10-200 mg, and the content of the cross-linking agent is 2-100 mg.

8. A polymer hydrogel device with electrothermal controllable fluorescence color change obtained by the preparation method according to any one of claims 1 to 7, It is characterized in that When the electrode is powered on, the electro-stimulated fluorescence color change is achieved, and the voltage of the electrode is 5 to 30V.

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