A stretchable electrochromic ionic gel film and a preparation method thereof

Abstract

The present application relates to a kind of stretchable conductive structural color ion gel film and its preparation method, utilize nanogel photonic crystal in containing gel precursor ion liquid aqueous solution and carry out self-assembly, form photonic crystal, obtain the precursor liquid of the conductive structural color ion gel film;Then solidification, obtain the stretchable conductive structural color ion gel film.The conductive structural color ion gel film of the present application has good conductivity, has firm adhesion to substrate, has the response feature of visual signal and electrical signal simultaneously under mechanical movement, can be used as the monitoring sensor of human activity, and real-time feedback color and electrical signal sensing according to the change of human activity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of flexible electronic devices, and particularly relates to a stretchable conductive structural color ionic gel film and a preparation method thereof. BACKGROUND

[0002] Conductive gel films play an important role in the field of flexible electronic devices. Its excellent conductivity, adjustable mechanical flexibility and easy processing characteristics make it one of the ideal materials for flexible electronic devices. In the fields of flexible electrodes, flexible mechanical sensors, flexible displays, ionic gel films are widely used, providing reliable performance support for these devices. Especially in health monitoring, sensing skin, flexible electronic devices play an indispensable role. They can monitor physiological parameters in real time and bring revolutionary progress to the field of healthcare. Therefore, ionic gel films and flexible electronic devices together constitute a technology direction with great potential and wide application prospects. However, most of the gel electronic sensing devices in flexible electronic devices only have a single electrical signal output function, lacking visualization of data.

[0003] Structural color is a specific color phenomenon caused by the periodic arrangement of the microstructure of the surface of an object. Structural color is commonly found on the surface of biological organisms in nature, and can also be achieved through artificially manufactured nanostructured surfaces or photonic crystals. In current research, structural color units are introduced as visual signals for sensors, but the commonly used structural color building units use silica or polystyrene hard spheres as templates, which require deposition or etching operations, increasing the difficulty of preparation and still having problems such as angle dependence, affecting the accuracy of visual signal reading. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a stretchable conductive structural color ionic gel film and a preparation method thereof, which solves the problems of poor adhesion and single detection signal of existing ionic gel films, and can be used in flexible electronic devices.

[0005] The present application provides a stretchable conductive structural color ionic gel film. Nano-gel photonic crystals are self-assembled in an ionic liquid aqueous solution containing gel precursors to form photonic crystals, obtaining a precursor solution of a conductive structural color ionic gel film. Then, solidification is carried out to obtain a stretchable conductive structural color ionic gel film.

[0006] Preferably, the nano-gel photonic crystals are prepared from N-aromatic maleimide acid, N-isopropyl acrylamide and N,N'-methylene bisacrylamide.

[0007] Preferably, the N-aromatic maleimide acid is one or more of N-phenyl maleimide acid, N-naphthalene maleimide acid and N-biphenyl maleimide acid.

[0008] Preferably, the preparation method of the nanogel photonic crystal comprises the following steps:

[0009] (1) adding N-aromatic maleimide acid, N-isopropyl acrylamide and N,N'-methylene bisacrylamide and emulsifier into water, mixing uniformly and passing nitrogen, and then treating by water bath heating to obtain a mixed solution;

[0010] (2) keeping the temperature unchanged, adding initiator A to initiate the polymerization reaction, and then concentrating by dialysis after the reaction is completed to obtain nanometer hydrogel; and (3) drying the nanometer hydrogel in a freeze dryer to obtain the nanogel photonic crystal.

[0011] Preferably, in the step (1), the N-aromatic maleimide acid is 0.1-0.5wt% of the mass of water; the mass of the N-isopropyl acrylamide is 1-3wt% of the mass of water; and the molar amount of the N,N'-methylene bisacrylamide is 0.01-0.1mol% of the molar amount of the N-isopropyl acrylamide.

[0012] Preferably, in the step (1), the emulsifier is sodium dodecyl sulfonate, and the addition amount is 0.1-0.5mol% of the molar amount of the N-isopropyl acrylamide.

[0013] Preferably, in the step (2), the initiator A is potassium persulfate, and the addition amount is 1wt% of the mass of the N-isopropyl acrylamide.

[0014] Preferably, the water bath heating treatment temperature in the step (1) is 50-80℃.

[0015] Preferably, the gel precursor comprises hydroxyethyl acrylate and a crosslinking agent. The crosslinking agent is one of N,N'-methylene bisacrylamide and ethylene glycol bisacrylate.

[0016] Preferably, the ionic liquid is one of 1-ethyl-3-methyl imidazole trifluoromethane sulfonate, 1-ethyl-3-methyl imidazole bis-trifluoromethane sulfonimide and 1-ethyl-3-methyl imidazole tetrafluoroborate, and the concentration of the ionic liquid aqueous solution is 10wt%-90wt%.

[0017] The application further provides a preparation method of a stretchable conductive structural color ionic gel film, comprising the following steps:

[0018] (1) performing self-assembly of the nanogel photonic crystal in an ionic liquid aqueous solution containing a gel precursor to form a photonic crystal, so as to obtain a precursor solution of the conductive structural color ionic gel film;

[0019] (2) pouring the precursor solution of the conductive structural color ionic gel film into a mold for solidification to obtain a stretchable conductive structural color ionic gel film.

[0020] Preferably, the amount of the nanogel photonic crystal in step (1) is 4-5 wt%. The amount of hydroxyethyl acrylate in the gel precursor is 10-20 wt%, and the amount of the crosslinking agent is 1.5 wt% of the amount of hydroxyethyl acrylate.

[0021] Preferably, the gel precursor further comprises an initiator B. The amount of the initiator B is 1 wt% of the amount of hydroxyethyl acrylate, and the initiator B is selected from ammonium persulfate or 2-hydroxy-2-methyl-1-phenylpropanone.

[0022] Preferably, the solidification method in step (2) is ultraviolet irradiation or oven heating.

[0023] The principle of the present application is:

[0024] Based on the construction of the conductive ionic gel with a polymer network of hydroxyethyl acrylate (HEA) as a monomer, the present application introduces nanogel obtained by copolymerization of N-isopropyl acrylamide (NIPAm) monomer and N-aromatic maleimide acid monomer as a structural color basic unit to prepare a stretchable conductive structural color ionic gel film. Due to the strong interaction between the ionic liquid and the PHEA polymer network, the prepared conductive structural color ionic gel film has good mechanical properties and conductivity. When the conductive structural color ionic gel is subjected to external mechanical stimulation (such as compression, stretching or twisting), the internal structure (such as the polymer network) will be deformed, affecting the migration path and speed of the internal ions, and then changing the conductivity of the gel; at the same time, the change of the internal microstructure also changes the spacing between the periodically arranged nanogel structural units, affecting the ability of the gel to reflect light of a specific wavelength, so as to achieve the simultaneous output of electrical signals and optical signals under mechanical stimulation, and has the potential to be used as a visual sensor for human activity.

[0025] Advantageous effects

[0026] (1) The conductive structural color ionic gel film of the present application has good conductivity, strong adhesion to the substrate, and the characteristics of simultaneously responding to visual signals and electrical signals under mechanical movement, and can be used as a monitoring sensor for human activity to real-time feedback color and electrical signal sensing according to the change of human activity.

[0027] (2) The preparation of the conductive structural color ionic gel film of the present application is simple, controllable, low in cost, reusable, and convenient to carry.

[0028] (3) The prepared stretchable conductive structural color ionic gel film can be used as a double signal sensor for human motion, on the one hand, when the human body moves, due to the change of the structural color unit spacing, real-time color sensing is fed back, on the other hand, the electrical conductivity can realize the monitoring of the electrical signal, double signal transmission, so that the data can be visualized.

[0029] (4) The structural color produced by the prepared stretchable conductive structural color ionic gel film has non-angle dependence, which is more conducive to observation and detection. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a preparation schematic diagram of the stretchable conductive structural color ionic gel film, wherein a is a preparation schematic diagram of nanogel, and b is a preparation schematic diagram of the conductive structural color ionic gel film.

[0031] Figure 2 It is a material performance characterization diagram of the stretchable conductive structural color ionic gel film of Example 1, wherein a is a photo of color change of the stretchable conductive structural color ionic gel film under gradual stretching, b is a reflection wavelength change diagram of the stretchable conductive structural color ionic gel film gradually stretched to 100%, and c is a relative resistance change of the stretchable conductive structural color ionic gel film gradually stretched to 200% tension;

[0032] Figure 3 It is a diagram of the material of the stretchable conductive structural color ionic gel film of Example 1 used as a double signal sensor for human motion, wherein a and c are photos of different motion states of the stretchable conductive structural color ionic gel film adhered to different parts of the human body, and a and c correspond to fingers and wrists respectively; b and d are relative resistance changes of the stretchable conductive structural color ionic gel film in response to human finger and wrist motion. DETAILED DESCRIPTION

[0033] The application will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. In addition, it should be understood that after reading the content taught by the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope of the appended claims of the application.

[0034] Example 1

[0035] A stretchable conductive structural color ionic gel film based on 1-ethyl-3-methyl imidazole trifluoromethane sulfonate is prepared according to the following method:

[0036] The first step, preparation of nano-gel photonic crystal with structural color: (1) adding 1wt% of N-isopropyl acrylamide, 0.1wt% of N-phenyl maleamic acid, 0.01mol% of N,N'-methylene bisacrylamide and 0.1mol% of sodium dodecyl sulfate to water, mixing uniformly and purging nitrogen, then heating treatment in water bath at 70℃, obtaining a mixed solution; (2) keeping the temperature unchanged, adding 1wt% of potassium persulfate to initiate polymerization, and then dialysis and concentration to obtain a color nano-hydrogel with structural color; drying the nano-hydrogel dispersion in the freeze dryer to obtain a dehydrated nano-gel lyophilizate.

[0037] The second step, preparation of stretchable conductive structural color ionic gel film: (1) adding 4wt% of dehydrated nano-gel lyophilizate, 15wt% of hydroxyethyl acrylate monomer, 1.5wt% of N,N'-methylene bisacrylamide crosslinking agent and 1wt% of 2-hydroxy-2-methyl-1-phenylpropanone initiator to 60wt% of 1-ethyl-3-methyl imidazole trifluoromethane sulfonate ionic liquid aqueous solution; (2) placing the stretchable conductive structural color ionic gel precursor prepared in step (2) into a forming mold and degassing in a vacuum environment for 15min; (3) placing the mixed film under ultraviolet light with a wavelength of 365nm for 3h, and finally obtaining a stretchable conductive structural color ionic gel film.

[0038] It can be seen from Figure 2 a that with the increase of strain, the structural color of the ionic gel gradually changes from red in the natural state to green, and when the strain reaches 100%, the color of the gel finally changes to blue. The main reason for this phenomenon is that the distance between the nano-gels with periodic structure in the cross section of the ionic gel decreases with the increase of strain, resulting in a decrease in the wavelength of light diffraction, showing a blue shift behavior. Figure 2 The reflection spectrum of the ionic gel in b corresponds to the stretching result, and with the increase of strain, the thickness of the cross section of the gel after stretching decreases, resulting in a gradual decrease in the intensity of the reflection spectrum. At the same time, due to the conductive behavior of the ionic gel, when the area of the cross section after stretching decreases, the flow capacity of ions also decreases, and the Figure 2 The relative resistance of the ionic gel in c is observed to increase with the increase of strain. These two characteristics endow the ionic gel with the ability to monitor mechanical movement in visual and electrical signals.

[0039] It can be seen from Figure 3 that the structural color ionic gel can feedback the visual and electrical signals under the actual movement of the joint. Figure 3a is the color change of the ionic gel which is green in natural state after bending at the finger joint. After bending the finger joint, the strain of the ionic gel increases, which makes its color change from green to blue, and its relative resistance becomes larger, see Figure 3 b. Figure 3 In c, after the structural color ionic gel is attached to the wrist joint, the color of the ionic gel changes from green to red due to the compression of the wrist joint. At the same time, due to the increase of the cross-sectional area of the gel after compression, the ionic flow increases Figure 3 In d, the change of its relative resistance is observed to be smaller.

[0040] Example 2

[0041] A stretchable conductive structural color ionic gel film based on 1-ethyl-3-methyl imidazole bistrifluoromethanesulfonylimide salt is prepared according to the following method:

[0042] First step, preparation of nanogel photonic crystal with structural color: (1) add N-isopropyl acrylamide with a mass of 2wt% of water, N-naphthalene maleic amide acid with a mass of 0.3wt% of water, N,N'-methylene bisacrylamide with a mole of 0.05mol% of N-isopropyl acrylamide, and 0.3mol% of sodium dodecyl sulfate into water, mix uniformly and introduce nitrogen, then heat treatment in water bath at 70℃ to obtain a mixed solution; (2) keep the temperature unchanged, add potassium persulfate with a dosage of 1wt% of N-isopropyl acrylamide to initiate polymerization, and after the reaction is completed, dialysis and concentration to obtain a color nanogel with structural color; dry the nanogel dispersion in (1) in a freeze dryer to obtain a dehydrated nanogel lyophilizate.

[0043] Second step, preparation of stretchable conductive structural color ionic gel film: (1) add dehydrated nanogel with a dosage of 4.5wt%, hydroxyethyl acrylate monomer with a dosage of 10wt%, ethylene glycol bisacrylate with a dosage of 1.5wt% of hydroxyethyl acrylate monomer, and 2-hydroxy-2-methyl-1-phenylpropanone initiator with a dosage of 1wt% of hydroxyethyl acrylate monomer into 70wt% of 1-ethyl-3-methyl imidazole bistrifluoromethanesulfonylimide salt ionic liquid aqueous solution; (2) place the stretchable conductive structural color ionic gel precursor prepared in step (1) into a forming mold and degas in a vacuum environment for 15min; (3) place the mixed film in an oven at a temperature of 75℃ for 3h to finally prepare a stretchable conductive structural color ionic gel film.

[0044] Example 3

[0045] A stretchable conductive structural color ionic gel film based on 1-ethyl-3-methyl imidazole tetrafluoroborate is prepared according to the following method:

[0046] The first step is to prepare a nano-gel photonic crystal with structural color: (1) adding N-isopropyl acrylamide with a mass of 3wt% of water, N-biphenyl maleamic acid with a mass of 0.5wt% of water, N,N'-methylene bisacrylamide with a mole of 0.05mol% of N-isopropyl acrylamide, and 0.5mol% of sodium dodecyl sulfate into water, mixing uniformly and passing nitrogen, and then heating treatment in a water bath at 70℃ to obtain a mixed solution; (2) keeping the temperature unchanged, adding potassium persulfate with a dosage of 1wt% of N-isopropyl acrylamide to initiate the polymerization reaction, and after the reaction is completed, the color nano-hydrogel with structural color is obtained by dialysis and concentration; the nano-hydrogel dispersion liquid in (1) is dried in a freeze dryer to obtain a dehydrated nano-gel lyophilizate.

[0047] The second step is to prepare a stretchable conductive structural color ionic gel film: (1) adding a dosage of 5wt% of dehydrated nano-gel, a dosage of 20wt% of hydroxyethyl acrylate monomer, a dosage of 1.5wt% of N,N'-methylene bisacrylamide crosslinking agent of the hydroxyethyl acrylate monomer, and a dosage of 1wt% of 2-hydroxy-2-methyl-1-phenylpropanone initiator of the dosage of the hydroxyethyl acrylate monomer into a 50wt% aqueous solution of 1-ethyl-3-methyl imidazole tetrafluoroborate ionic liquid; (2) placing the stretchable conductive structural color ionic gel precursor liquid prepared in step (2) into a forming mold and degassing in a vacuum environment for 15min; (3) placing the mixed film under ultraviolet light with a wavelength of 365nm for 3h to finally prepare a stretchable conductive structural color ionic gel film.

[0048] Example 4

[0049] A stretchable conductive structural color ionic gel film based on 1-ethyl-3-methyl imidazole trifluoromethane sulfonate is prepared according to the following method:

[0050] The first step is to prepare a nano-gel photonic crystal with structural color: (1) adding N-isopropyl acrylamide with a mass of 2wt% of water, N-phenyl maleamic acid with a mass of 0.2wt% of water, N,N'-methylene bisacrylamide with a mole of 0.03mol% of N-isopropyl acrylamide, and 0.1mol% of sodium dodecyl sulfate into water, mixing uniformly and passing nitrogen, and then heating treatment in a water bath at 70℃ to obtain a mixed solution; (2) keeping the temperature unchanged, adding potassium persulfate with a dosage of 1wt% of N-isopropyl acrylamide to initiate the polymerization reaction, and after the reaction is completed, the color nano-hydrogel with structural color is obtained by dialysis and concentration; the nano-hydrogel dispersion liquid in (1) is dried in a freeze dryer to obtain a dehydrated nano-gel lyophilizate.

[0051] Second step, preparation of stretchable conductive structural color ionogel film: (1) to 60wt% of 1-ethyl-3-methyl imidazole trifluoromethane sulfonate ionic liquid aqueous solution, add the amount of 5wt% of dehydrated nanogel freeze-dried material, the amount of 15wt% of hydroxyethyl acrylate monomer, the amount of 1.5wt% of N,N'-methylene bisacrylamide crosslinking agent of hydroxyethyl acrylate monomer, the amount of 1wt% of 2-hydroxy-2-methyl-1-phenylpropanone initiator of the amount of hydroxyethyl acrylate monomer; (2) the stretchable conductive structural color ionogel precursor liquid prepared in step (2) is placed in a forming mold and degassed in a vacuum environment for 15 min; (3) the mixed film is placed under a wavelength of 365nm ultraviolet light for 3h, and finally a stretchable conductive structural color ionogel film is prepared.

[0052] Example 5

[0053] A stretchable conductive structural color ionogel film based on 1-ethyl-3-methyl imidazole bis-trifluoromethane sulfonimide salt is prepared according to the following method:

[0054] First step, preparation of nanogel photonic crystal with structural color: (1) add N-isopropyl acrylamide with a mass of 3wt% of water, N-naphthalene maleic amide with a mass of 0.3wt% of water, 0.05mol% of N,N'-methylene bisacrylamide with a mole amount of 0.05mol% of N-isopropyl acrylamide, and 0.3mol% of sodium dodecyl sulfate with a mole amount of 0.3mol% of N-isopropyl acrylamide to water, mix uniformly and introduce nitrogen, then heat treat in a water bath at 70℃ to obtain a mixed solution; (2) keep the temperature unchanged, add 1wt% of potassium persulfate of N-isopropyl acrylamide to initiate polymerization, and after the reaction is completed, dialysis and concentration are carried out to obtain a colored nanohydrogel with structural color; the nanohydrogel dispersion liquid in (1) is dried in a freeze dryer to obtain dehydrated nanogel freeze-dried material.

[0055] Second step, preparation of stretchable conductive structural color ionogel film: (1) to 75wt% of 1-ethyl-3-methyl imidazole bis-trifluoromethane sulfonimide ionic liquid aqueous solution, add the amount of 5wt% of dehydrated nanogel, the amount of 10wt% of hydroxyethyl acrylate monomer, the amount of 1.5wt% of ethylene glycol bisacrylate of hydroxyethyl acrylate monomer, and the amount of 1wt% of 2-hydroxy-2-methyl-1-phenylpropanone initiator of the amount of hydroxyethyl acrylate monomer; (2) the stretchable conductive structural color ionogel precursor liquid prepared in step (2) is placed in a forming mold and degassed in a vacuum environment for 15 min; (3) the mixed film is placed in an oven at a temperature of 75℃ for 3h, and finally a stretchable conductive structural color ionogel film is prepared.

[0056] Example 6

[0057] A stretchable conductive structural color ionic gel film based on 1-ethyl-3-methyl imidazole tetrafluoroborate is prepared according to the following method:

[0058] First, prepare a nano-gel photonic crystal with structural color: (1) add N-isopropyl acrylamide with a mass of 1wt% of water, N-biphenyl maleamic acid with a mass of 0.1wt% of water, N,N'-methylene bisacrylamide with a mole of 0.01mol% of N-isopropyl acrylamide, and 0.5mol% of sodium dodecyl sulfate into water, mix well and pass nitrogen, then heat treat in a water bath at 70℃, to obtain a mixed solution; (2) keep the temperature unchanged, add potassium persulfate with a dosage of 1wt% of N-isopropyl acrylamide to initiate polymerization, and after the reaction is completed, dialysis and concentration are carried out to obtain a colored nano-hydrogel with structural color; the nano-hydrogel dispersion in (1) is dried in a freeze dryer to obtain a dehydrated nano-gel lyophilizate.

[0059] Second, prepare a stretchable conductive structural color ionic gel film: (1) add dehydrated nano-gel with a dosage of 5wt% to 50wt% of 1-ethyl-3-methyl imidazole tetrafluoroborate ionic liquid aqueous solution, hydroxyethyl acrylate monomer with a dosage of 20wt%, N,N'-methylene bisacrylamide crosslinking agent with a dosage of 1.5wt% of hydroxyethyl acrylate monomer, and 2-hydroxy-2-methyl-1-phenylpropanone initiator with a dosage of 1wt% of hydroxyethyl acrylate monomer; (2) place the stretchable conductive structural color ionic gel precursor prepared in step (2) into a forming mold and degas in a vacuum environment for 15min; (3) place the mixed film under ultraviolet light with a wavelength of 365nm for 3h, to finally prepare a stretchable conductive structural color ionic gel film.

[0060] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application should not be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be considered as falling within the protection scope of the present application.

Claims

1. A stretchable electrochromic ionic gel thin film, characterized in that: The nanogel photonic crystal is self-assembled in an ionic liquid aqueous solution containing a gel precursor to form a photonic crystal, so that a precursor solution of a conductive structural color ionic gel film is obtained; then solidification is performed to obtain a stretchable conductive structural color ionic gel film; the gel precursor comprises hydroxyethyl acrylate and a crosslinking agent; and the preparation method of the nanogel photonic crystal comprises the following steps: (1) adding N-aromatic maleamic acid, N-isopropyl acrylamide and N,N'-methylene bisacrylamide and an emulsifier into water, uniformly mixing and introducing nitrogen, and then performing water bath heating treatment to obtain a mixed solution; (2) keeping the temperature unchanged, adding an initiator A to initiate a polymerization reaction, and performing dialysis and concentration after the reaction is completed to obtain nanowater gel; (3) drying the nanowater gel in a freeze dryer to obtain nanogel photonic crystal.

2. The electrochromic ionogel thin film according to claim 1, wherein: The N-aromatic maleamic acid is one or more of N-phenyl maleamic acid, N-naphthalene maleamic acid and N-biphenyl maleamic acid.

3. The electrochromic ionogel thin film according to claim 1, wherein: In step (1), the mass of the N-aromatic maleamic acid is 0.1-0.5wt% of the mass of water; the mass of the N-isopropyl acrylamide is 1-3wt% of the mass of water; and the molar amount of the N,N'-methylene bisacrylamide is 0.01-0.1mol% of the molar amount of the N-isopropyl acrylamide.

4. The electrochromic ionogel thin film of claim 1, wherein: In step (1), the emulsifier is sodium dodecyl sulfonate, and the addition amount is 0.1-0.5mol% of the molar amount of the N-isopropyl acrylamide.

5. The electrochromic ionogel thin film of claim 1, wherein: In step (2), the initiator A is potassium persulfate, and the addition amount is 1wt% of the mass of the N-isopropyl acrylamide.

6. The electrochromic ionogel thin film of claim 1, wherein: The ionic liquid is one of 1-ethyl-3-methyl imidazole trifluoromethane sulfonate, 1-ethyl-3-methyl imidazole bis-trifluoromethane sulfonimide and 1-ethyl-3-methyl imidazole tetrafluoroborate, and the concentration of the ionic liquid aqueous solution is 10wt%-90wt%.

7. A preparation method of the stretchable conductive structural color ionic gel film according to any one of claims 1-6, comprising the following steps: (1) using nanogel photonic crystal to self-assemble in an ionic liquid aqueous solution containing a gel precursor to form a photonic crystal, so that a precursor solution of a conductive structural color ionic gel film is obtained; (2) pouring the precursor solution of the conductive structural color ionic gel film into a mold to perform solidification, so that a stretchable conductive structural color ionic gel film is obtained.

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