Double-crosslinked high-strength polyeutectic fluorescent self-repairing conductive elastomer and preparation method thereof

Abstract

The present invention discloses a double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer. The present invention also discloses a method for preparing the above-mentioned conductive elastomer, comprising: mixing choline chloride and acrylic acid, and then heating and stirring the mixture at 60-70°C for 15-30min to obtain a polymerizable deep eutectic solvent DES; preparing cysteine-modified graphene quantum dots Cys-GQDs using citric acid and cysteine; adding Cys-GQDs and a photoinitiator to DES, heating and stirring at 60-70°C for 0.5-1h to obtain a prepolymer solution; casting the prepolymer solution on a horizontal glass plate, and subjecting it to in-situ polymerization by ultraviolet light irradiation to obtain a conductive elastomer. The conductive elastomer of the present invention solves the problems of insufficient tensile strength and fluorescence performance of the current poly-eutectic conductive elastomer materials that need to be further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of conductive elastic materials, and specifically relates to a double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer. The present invention also relates to a preparation method of the above conductive elastomer. Background Art

[0002] In recent years, with the development of soft robotics, flexible electronic devices, and artificial intelligence, researchers have increasingly delved into high-performance flexible sensors, and flexible conductive materials, one of their core components, have also received increasing attention. Common flexible conductive materials mainly include hydrogels and ionic liquid gels. Among them, most hydrogels have poor temperature resistance and are difficult to operate at low or high temperatures. Although ionic liquid gels have good temperature resistance, they also have problems such as high cost, complex preparation process, and poor biocompatibility. The potential risk of ionic liquid leakage further hinders their practical application. Therefore, finding a conductive elastomer with excellent comprehensive performance while being both safe and environmentally friendly remains a huge challenge.

[0003] Polyeutectic conductive elastomers (PEEs) are three-dimensional polymer networks formed by free radical polymerization of polymerizable monomers (commonly known as acrylic acid, acrylamide, itaconic acid, and maleic acid) in a high-entropy deep eutectic solvent. They are highly designable, minimally affected by ambient temperature, and pose no risk of organic solvent leakage, making them a promising candidate for research in recent years. Despite the recent progress in research on PEEs, the tensile strength of most hydrogen-bonded PEEs remains below 1 MPa. To address this issue, researchers have incorporated small molecule physical crosslinkers (such as phytic acid, tannic acid, metal halides, graphene oxide nanosheets, and MXene sheets) or polymers (such as polyethylene glycol, cellulose, polyvinyl alcohol, and starch) into PEEs to enhance their axial tensile mechanical properties by further constructing a physical crosslinking network through hydrogen bonding and physical chain entanglement. However, non-chemically bonded physical reinforcing agents partially precipitate in high humidity or underwater environments, resulting in weak bonding between the PEEs and the PEEs, and migration issues remain to be addressed. Graphene quantum dots (GQDs) are graphene sheets with lateral dimensions less than 100 nm. Unfunctionalized GQDs typically exhibit low fluorescence quantum yields and poor compatibility with polymer substrates. Currently, little research has been conducted on the doping of GQDs into polyeutectic conductive elastomers. Therefore, the rational design of modified reaction sites on the graphene quantum dot surface to enhance fluorescence quantum yields while also forming a physical / chemical dual crosslinking network with the polyeutectic substrate, thereby achieving high-strength polyeutectic fluorescent conductive elastomers, is of great research value and significance. Summary of the Invention

[0004] The purpose of the present invention is to provide a double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer, which solves the problems of insufficient tensile strength and the need to further improve the fluorescence performance of the current polyeutectic conductive elastomer materials.

[0005] Another object of the present invention is to provide a method for preparing the conductive elastomer.

[0006] The technical solution adopted by the present invention is a method for preparing a double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer, which is specifically implemented according to the following steps:

[0007] Step 1, mixing choline chloride and acrylic acid, and then heating and stirring the mixture at 60-70° C. for 15-30 minutes to obtain a polymerizable deep eutectic solvent DES;

[0008] Step 2, preparing cysteine-modified graphene quantum dots Cys-GQDs using citric acid and cysteine;

[0009] Step 3: Add the Cys-GQDs and photoinitiator obtained in step 2 to the DES prepared in step 1, and heat and stir at 60-70° C. for 0.5-1 h to obtain a prepolymer solution;

[0010] Step 4: Cast the prepolymer solution obtained in step 3 onto a horizontal glass plate and perform in-situ polymerization by ultraviolet light irradiation to obtain a conductive elastomer.

[0011] The present invention is also characterized in that:

[0012] In step 1, the molar ratio of choline chloride to acrylic acid is 1:1.8-2.4.

[0013] Step 2 is as follows:

[0014] Citric acid and L-cysteine ​​were dissolved in deionized water to form a solution, which was then heated at 180-220°C for 5-10 minutes. After the reaction was completed and the reaction solution was cooled to room temperature, the pH of the reaction solution was adjusted to 7, and then the reaction solution was purified using a dialysis bag. Finally, the purified solution was freeze-dried for 2-3 days to obtain cysteine-modified graphene quantum dots Cys-GQDs.

[0015] The molar ratio of citric acid to L-cysteine ​​is 1:1.

[0016] The molecular weight cut-off of the dialysis bag is 700~1000Da.

[0017] In step 3, the photoinitiator is photoinitiator 2959, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone or 2-hydroxy-2-methyl-1-phenylpropanone, and the mass of the added photoinitiator is 1% of the mass of DES.

[0018] In step 3, the mass of Cys-GQDs is 1–4% of the mass of DES.

[0019] In step 4, the wavelength of the ultraviolet light is 365 nm, the power is 40-60 W, the height of the ultraviolet lamp from the glass plate is 10-15 cm, and the irradiation time is 1-2 min.

[0020] Another technical solution adopted by the present invention is a double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer, which is prepared by the above-mentioned preparation method.

[0021] The beneficial effects of the present invention are:

[0022] (1) The method of the present invention designs and synthesizes cysteine-functionalized graphene quantum dots from the perspective of improving the tensile properties and self-healing properties of polyeutectic conductive elastomers. On the one hand, the rich functional group sites such as carboxyl, amino and carbonyl groups on the surface of the graphene quantum dots are used to form a rich dynamic non-covalent cross-linking network of hydrogen bonds, acid-base pairs and cation-dipole with the polyeutectic matrix. On the other hand, the modified dithiol groups can also undergo a "thiol-double bond" click reaction with acrylic acid to form a chemical covalent cross-linking network. The synergistic effect of the covalent and non-covalent double cross-linking networks increases the tensile strength of the polyeutectic conductive elastomer from 0.29 MPa to 5.64 MPa, which is 18 times higher than the tensile strength of the traditional ChCl-AA type polyeutectic conductive elastomer.

[0023] (2) The raw materials used in the method of the present invention are all common commercial chemical materials, which are low in cost and do not require further chemical treatment. The preparation method is simple and fast, and inherits the advantages of the preparation process of polymerizable deep eutectic solvents, such as simple and efficient, green and environmentally friendly, and low energy consumption of equipment;

[0024] (3) The conductive elastomer of the present invention can realize accurate signal detection in a wide temperature range (-20~60℃), a wide strain rate (100~500mm / min) and a wide strain amplitude (10%~100%), and the representative elastomer PDES-GQDs 0.04 The GF in the 10%-100% strain range is 1.19, which is twice that of the conductive elastomer PDES without Cys-GQDs. In addition, the conductive elastomer of the present invention also exhibits excellent low-temperature tensile durability (over 21,000 cycles at -20°C).

[0025] (4) The cysteine-modified graphene quantum dots prepared by the method of the present invention have a fluorescence quantum yield of up to 83.95%. The prepared double-cross-linked high-strength polyeutectic fluorescent self-healing conductive elastomer and its prepolymer have good fluorescence properties. Therefore, they can be used as anti-counterfeiting "ink". Combined with screen printing technology, they can be applied to information storage and fluorescent anti-counterfeiting, which broadens the functionality of the conductive elastomer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the principle of the method of the present invention;

[0027] Figure 2 This is the infrared spectrum of Cys-GQDs prepared in Example 1 of the present invention;

[0028] Figure 3 This is the XRD spectrum of Cys-GQDs prepared in Example 1 of the present invention;

[0029] Figure 4 The XPS spectrum of Cys-GQDs prepared in Example 1 of the present invention, wherein ad are the overall spectrum and the XPS spectra of C, N, and S elements, respectively;

[0030] Figure 5 Figure 1 is a graph of the fluorescence quantum yield of Cys-GQDs prepared in Example 1 of the present invention, wherein Figure a is the absorbance curve, Figure b is the fluorescence emission spectrum, and Figure c is the fluorescence integral area curve;

[0031] Figure 6 This is a differential scanning calorimetry graph of the DES prepared in Example 1 of the present invention;

[0032] Figure 7 This is the infrared spectrum of the DES prepared in Example 1 of the present invention;

[0033] Figure 8 This is the H NMR spectrum of the DES prepared in Example 1 of the present invention;

[0034] Figure 9 DES, PDES and PDES-GQDs prepared in Example 4 and Comparative Example 1 of the present invention 0.04 Infrared spectrum of

[0035] Figure 10 PDES-GQDs prepared in Examples 1-4 and Comparative Example 1 of the present invention x , mechanical properties comparison test chart of PDES;

[0036] Figure 11 PDES-GQDs prepared in Examples 1-4 and Comparative Example 1 of the present invention x , optical performance comparison test chart of PDES;

[0037] Figure 12 PDES-GQDs prepared in Examples 1-4 and Comparative Example 1 of the present invention x , the comparative test diagram of the thermal gravimetric performance of PDES, where Figure a is the TGA curve and Figure b is the DTG curve;

[0038] Figure 13 PDES-GQDs prepared in Example 4 of the present invention 0.04 Differential scanning calorimetry diagram of

[0039] Figure 14 PDES-GQDs prepared in Example 4 of the present invention 0.04 Self-repair process diagram;

[0040] Figure 15 PDES-GQDs prepared in Example 4 of the present invention 0.04 Electrical self-repair performance test diagram;

[0041] Figure 16 PDES-GQDs prepared in Example 4 of the present invention 0.04 Electrical self-healing rate diagram;

[0042] Figure 17 PDES-GQDs prepared in Examples 1-4 of the present invention x Strain sensing performance test diagram;

[0043] Figure 18 PDES-GQDs prepared in Example 4 of the present invention 0.04 Relative resistance change at 5% strain amplitude and 100~300mm / min strain speed;

[0044] Figure 19 PDES-GQDs prepared in Example 4 of the present invention 0.04 Relative resistance change at 10%~100% strain amplitude and 100mm / min strain speed;

[0045] Figure 20 PDES-GQDs prepared in Example 4 of the present invention 0.04 GF value in the strain range of 10% to 100%;

[0046] Figure 21 PDES-GQDs prepared in Example 4 of the present invention 0.04 Relative resistance change from -20℃ to 60℃;

[0047] Figure 22 PDES-GQDs prepared in Example 4 of the present invention 0.04 Cyclic durability test results at -20℃;

[0048] Figure 23 PDES-GQDs prepared in Example 4 of the present invention 0.04 Strain sensing diagram during human action monitoring;

[0049] Figure 24 PDES-GQDs prepared in Example 4 of the present invention 0.04 Application diagram in information storage and fluorescent anti-counterfeiting. DETAILED DESCRIPTION

[0050] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0051] The preparation method of the double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer of the present invention is based on the "one-pot" design principle. Choline chloride (ChCl) and acrylic acid (AA) are selected as hydrogen bond acceptors and hydrogen bond donors respectively. Cysteine-modified graphene quantum dots (Cys-GQDs) with thiol and rich polar functional groups (carboxyl, amino and carbonyl) sites are introduced as physical / chemical crosslinkers. After in-situ polymerization and "thiol-double bond" click reaction initiated by ultraviolet light, a double-crosslinked poly-eutectic fluorescent conductive elastomer with excellent comprehensive performance is obtained. Figure 1 As shown, the method of the present invention is specifically implemented according to the following steps:

[0052] Step 1: Preparation of polymerizable deep eutectic solvent (DES):

[0053] Choline chloride and acrylic acid are mixed in a molar ratio of 1:1.8-2.4 to obtain a mixture, and then the mixture is heated and stirred at 60-70° C. for 15-30 minutes to obtain a uniform clear and transparent solution DES;

[0054] Step 2: Preparation of Cysteine-modified Graphene Quantum Dots (Cys-GQDs):

[0055] Citric acid and L-cysteine ​​were dissolved in an appropriate amount of deionized water at a molar ratio of 1:1, wherein the total mass of citric acid and L-cysteine ​​was 40% to 60% of the mass of water. The mixed solution was then heated in an oil bath at 180 to 220°C for 5 to 10 minutes. After the reaction was completed and the reaction solution was cooled to room temperature, the reaction solution was neutralized with 1 mol / L sodium hydroxide solution to a pH of 7. The reaction solution was then purified using a dialysis bag with a molecular weight cutoff of 700 to 1000 Da. Finally, the purified solution was vacuum freeze-dried for 2 to 3 days to obtain cysteine-modified graphene quantum dots Cys-GQDs.

[0056] Step 3: Preparation of prepolymer solution:

[0057] The Cys-GQDs and photoinitiator obtained in step 2 are added to the clear and transparent solution DES prepared in step 1, and heated and stirred at 60-70° C. for 0.5-1 h to obtain a prepolymer solution; wherein the photoinitiator is photoinitiator 2959, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone or 2-hydroxy-2-methyl-1-phenylpropanone, the mass of the added photoinitiator is 1% of the mass of the solution DES, and the mass of the Cys-GQDs is 1-4% of the mass of the solution DES.

[0058] Step 4: Preparation of double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer:

[0059] The prepolymer solution prepared in step 3 was cast onto a horizontal glass plate and irradiated with ultraviolet light for in-situ polymerization to obtain a double-crosslinked, high-strength, poly-eutectic fluorescent self-healing conductive elastomer. The ultraviolet light had a wavelength of 365 nm, a power of 40-60 W, and was held 10-15 cm above the glass plate for 1-2 minutes.

[0060] Unless otherwise specified, the raw materials used in the following examples are common commercially available products.

[0061] Choline chloride (ChCl) and acrylic acid (AA) were dried under vacuum at 60 °C for 2 h before the experiment.

[0062] Example 1:

[0063] Step 1: Preparation of polymerizable deep eutectic solvent (DES):

[0064] Choline chloride and acrylic acid were mixed in a molar ratio of 1:2, and the mixture was placed in a flat-bottom flask and heated at 65°C with stirring for 15 minutes to obtain a uniform, clear, and transparent solution DES. The prepared DES was stored in a vacuum desiccator containing silica gel until use in the next step.

[0065] Step 2: Preparation of Cysteine-modified Graphene Quantum Dots (Cys-GQDs):

[0066] Cysteine-modified graphene quantum dots were synthesized using a high-temperature dry method. First, 10 g of citric acid and 6.306 g of L-cysteine ​​were dissolved in 30 mL of deionized water. The mixed solution was heated in an oil bath at 200 °C for 10 min. Then, the reaction solution was neutralized with 1 mol / L sodium hydroxide solution to a pH of 7. The reaction solution was then purified using a dialysis bag with a molecular weight cutoff of 1000 Da. Finally, the purified solution was vacuum freeze-dried for 3 days to obtain solid Cys-GQDs, which was configured into a 50 mg / mL solution for standby use.

[0067] Step 3: Preparation of prepolymer solution:

[0068] Add the Cys-GQDs solution and photoinitiator 2959 to the DES prepared in step 1. Heat and stir the mixture at 65°C for 30 minutes to obtain a uniform, clear, and transparent prepolymer solution. The photoinitiator and Cys-GQDs content are 1 wt% of the DES.

[0069] Step 4: Double cross-linked high-strength polyeutectic fluorescent self-healing conductive elastomer PDES-GQDs 0.01 Preparation:

[0070] The prepolymer solution prepared in step 3 was cast on a leveled glass plate and polymerized under ultraviolet light. The wavelength of the ultraviolet light was 365 nm, the power was 40 W, the height of the ultraviolet lamp from the glass plate was 10 cm, and the irradiation time was 1 min to obtain a double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer PDES-GQDs. 0.01 .

[0071] Example 2:

[0072] This example is basically the same as Example 1, except that the amount of Cys-GQDs is used. In step 3 of this example, the amount of Cys-GQDs used is 2 wt % of DES, and the reaction yields a double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer PDES-GQDs. 0.02 .

[0073] Example 3:

[0074] This example is basically the same as Example 1, except that the amount of Cys-GQDs is used. In step 3 of this example, the amount of Cys-GQDs used is 3wt% of DES, and the reaction yields a double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer PDES-GQDs. 0.03 .

[0075] Example 4:

[0076] This example is basically the same as Example 1, except that the amount of Cys-GQDs is used. In step 3 of this example, the amount of Cys-GQDs used is 4 wt% of DES, and the reaction yields a double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer PDES-GQDs. 0.04 .

[0077] Example 5:

[0078] Step 1: Choline chloride and acrylic acid were mixed in a molar ratio of 1:1.8, and the mixture was placed in a flat-bottom flask and heated and stirred at 70° C. for 20 minutes to obtain a uniform, clear, transparent solution DES. The prepared DES was stored in a vacuum desiccator containing silica gel until use in the next step.

[0079] Step 2: Synthesize cysteine-modified graphene quantum dots using a high-temperature dry method. First, dissolve 10 g of citric acid and 6.306 g of L-cysteine ​​in 40 mL of deionized water. Heat the mixed solution in an oil bath at 220 ° C for 5 min. Then, neutralize the reaction solution with 1 mol / L sodium hydroxide solution to a pH of 7. Then, purify the reaction solution using a dialysis bag with a molecular weight cutoff of 800 Da. Finally, freeze-dry the purified solution in vacuum for 2 days to obtain solid Cys-GQDs, which are configured into a 50 mg / mL solution for standby use.

[0080] Step 3: Add the Cys-GQDs solution and the photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone to the DES prepared in Step 1. Heat and stir the mixture at 70°C for 1 hour to obtain a uniform, clear, and transparent prepolymer solution. The photoinitiator and Cys-GQDs are present in an amount of 1 wt% of the DES.

[0081] Step 4: Cast the prepolymer solution prepared in step 3 onto a leveled glass plate and polymerize it under ultraviolet light, wherein the ultraviolet light wavelength is 365 nm, the power is 50 W, the height of the ultraviolet lamp from the glass plate is 15 cm, and the irradiation time is 2 min to obtain a double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer PDES-GQDs.

[0082] Example 6:

[0083] Step 1: Choline chloride and acrylic acid were mixed in a molar ratio of 1:2.4, and the mixture was placed in a flat-bottom flask and heated and stirred at 60° C. for 30 minutes to obtain a uniform, clear, transparent solution DES. The prepared DES was stored in a vacuum desiccator containing silica gel until use in the next step.

[0084] Step 2: Use a high-temperature dry method to synthesize cysteine-modified graphene quantum dots. First, dissolve 10 g of citric acid and 6.306 g of L-cysteine ​​in 50 mL of deionized water. Heat the mixed solution in an oil bath at 180 ° C for 8 min. Then, neutralize the reaction solution with 1 mol / L sodium hydroxide solution to a pH of 7. Then, purify the reaction solution using a dialysis bag with a molecular weight cutoff of 700 Da. Finally, the purified solution is vacuum freeze-dried for 3 days to obtain solid Cys-GQDs, which is configured into a 50 mg / mL solution for standby use.

[0085] Step 3: Add the Cys-GQDs solution and the photoinitiator 1-hydroxycyclohexylphenyl ketone to the DES prepared in Step 1. Heat and stir the mixture at 60°C for 1 hour to obtain a uniform, clear, and transparent prepolymer solution. The photoinitiator and Cys-GQDs are present in an amount of 1% by weight of the DES, and 1% by weight of the DES.

[0086] Step 4: Cast the prepolymer solution obtained in step 3 onto a leveled glass plate and polymerize it under ultraviolet light, wherein the ultraviolet light wavelength is 365 nm, the power is 60 W, the height of the ultraviolet lamp from the glass plate is 15 cm, and the irradiation time is 2 min to obtain a double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer PDES-GQDs.

[0087] Comparative Example 1:

[0088] In this comparative example, Cys-GQDs were not added, and the rest was the same as in Example 1, and the reaction obtained a polyeutectic conductive elastomer PDES.

[0089] The following performance tests were performed on various substances prepared in the Examples and Comparative Examples:

[0090] (1) Fourier-transform infrared spectroscopy (FT-IR): A Thermo Scientific Nicolet iS20 FT-IR spectrometer manufactured by Thermo Fisher Scientific was used to measure characteristic parameters such as wave number, intensity, and shape of functional groups in the molecular structure. The scanning range was 4000–400 cm -1 , with a resolution of 16cm -1 , the number of scans is 32.

[0091] (2) H NMR spectroscopy ( 1 H-Nuclear magnetic resonance, 1 H-NMR: A Bruker 400M nuclear magnetic resonance spectrometer produced by Bruker Instruments of Germany was used to measure the chemical shift of protons in the molecular structure and characteristic peak areas. According to the polarity of the test molecule, a suitable deuterated reagent was selected, using deuterated dimethyl sulfoxide (DMSO- d 6) The single peak at 2.50 ppm is the standard reference peak.

[0092] (3) X-ray diffraction (XRD): The crystal phase of the samples was analyzed using an X-ray diffractometer (Rigaku SmartLabSE, Japan) with Cu-Ka rays as the incident light source, an acceleration voltage of 40 kV, a scanning angle of 5°–80°, and a scanning speed of 5° / min.

[0093] (4) X-ray photoelectron spectroscopy (XPS): The surface charge of the sample was obtained using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha). 5 × 5 mm 2 The sample of different sizes is attached to the sample plate and placed into the sample chamber of the Thermo Scientific K-Alpha XPS instrument. The pressure in the sample chamber is less than 2.0×10 -7 When the pressure was 1000 mbar, the sample was sent into the analysis chamber, and monochromatic AlKa rays with 1486.6 eV photons were used as the excitation source, with a spot size of 400 μm, an operating voltage of 12 kV, and a filament current of 6 mA; the full spectrum scan energy was 150 eV with a step size of 1 eV; the narrow spectrum scan energy was 50 eV with a step size of 0.1 eV.

[0094] (5) Fluorescence quantum yield (FLQY): Quinine sulfate, which has a similar wavelength range, was selected as a reference. The slope method was used to determine the fluorescence quantum yield of Cys-GQDs. The fluorescence quantum yield of quinine sulfate at an excitation wavelength of 360 nm was 0.54. The specific operation was as follows: Quinine sulfate was dissolved in 0.1 mol / L H2SO4 to prepare solutions of different concentrations. The absorbance was measured to make it less than 0.1. Similarly, Cys-GQDs were prepared into dispersions of different concentrations. The fluorescence spectra were measured to make the absorbance close to the absorbance measured at each concentration of quinine sulfate. Then, using 360 nm as the excitation wavelength, the fluorescence spectra of each sample at the corresponding concentration were measured. The emission peak area of ​​each fluorescence spectrum was calculated by integration. A graph was drawn with the absorbance of quinine sulfate and each graphene quantum dot as the horizontal axis and the fluorescence peak area as the vertical axis. The fluorescence quantum yield of each graphene quantum dot was calculated using the following formula.

[0095]

[0096] Among them, Y and Y r are the fluorescence quantum yields of each analyte and reference substance quinine sulfate, m s and m r are the ratios (slopes) of the integrated fluorescence peak areas of each analyte and reference substance to the absorbance; n s and nr is the refractive index of each analyte and quinine sulfate solution, generally 1.33.

[0097] (6) Thermal properties: The thermal stability of the conductive elastomer was measured using a TG 209F3 thermogravimetric analyzer (NETZSCH Instrument Manufacturing Co., Ltd., Germany) in the temperature range of 100-800°C at a heating rate of 20°C / min. The entire heating process was carried out under nitrogen protection. The melting point of the deep eutectic solvent was measured using a DSC 200F3 differential scanning calorimeter (NETZSCH Instrument Manufacturing Co., Ltd., Germany). The test atmosphere was nitrogen, the heating rate was 10°C / min, and the total test temperature range was -80°C to 90°C.

[0098] (7) Optical properties: The optical transmittance and absorptivity of the conductive elastomer were obtained by testing using an ultraviolet spectrophotometer (V-700).

[0099] (8) Mechanical properties: The mechanical properties of the composite film were tested using an AI-7000-NGD electronic universal testing machine (Gautwell (Dongguan) Co., Ltd.). The self-healing efficiency was characterized by the ratio of the tensile area of ​​the self-healed sample to the original sample. The self-healing temperature was room temperature, the self-healing time was 24 h, and the sample rectangular size was 40 × 10 mm. 2 , the loading rate is 100mm / min.

[0100] (9) Resistance-time signal measurement: The electrical signal changes of the conductive elastomer were measured using an electrochemical workstation (CHI660E) in the IT mode. The test environment was 25°C and the relative humidity was 30%-35%.

[0101] (10) Optical image capture: Use a camera to capture optical images of the conductive elastomer.

[0102] The test results are as follows:

[0103] (1) The test results of Cys-GQDs prepared in Example 1 are as follows:

[0104] In order to characterize the successful synthesis of cysteine-modified graphene quantum dots, FT-IR spectroscopy was used to characterize the chemical structure of the product. Figure 2 The infrared spectra of citric acid, cysteine ​​and Cys-GQDs are shown. It can be seen that the FT-IR spectrum of Cys-GQDs is at 3548 cm -1 and 3440cm -1 The stretching vibration peak of -OH and the asymmetric stretching vibration peak of -NH2 appeared at 2547 cm -1 The peak at 1586 cm is attributed to the stretching vibration of -SH. -1 and 1706cm-1 The peaks at 1074 cm-1 are attributed to the -C=O stretching vibration of the carboxylic acid and amide bonds, respectively. -1 and 1398cm -1 The characteristic absorption peaks of -COC and -C-NH-C are respectively located at the bottom and the successful grafting of functional groups such as thiol and amino groups indicates the successful preparation of cysteine-modified quantum dots. Figure 3 ) It can be seen that Cys-GQDs has a broad diffraction peak at 2θ=23°, corresponding to an interlayer spacing of 0.385nm, which indicates that Cys-GQDs have a disordered graphene structure, slightly larger than the interlayer spacing of 0.335nm of original graphene. This is also due to the presence of many functional groups on its surface, further proving the presence of rich functional groups on the surface of quantum dots. In order to further study the surface chemistry of Cys-GQDs, XPS spectroscopy was used to characterize the types of elements and the chemical environment of each element, such as Figure 4 As shown in a, the XPS spectrum of Cys-GQDs shows four peaks at 163, 284.38, 399.56 and 531.22 eV, corresponding to the four elements C, O, N and S, respectively, which indicates that Cys-GQDs are composed of these four elements. 1s The XPS graph also shows three peaks at 284.31, 285.62 and 287.75 eV ( Figure 4 b), respectively, are attributed to C=C, CO / CS / CN and C=O bonds; N 1s The XPS graph of the pyridine-type nitrogen and pyrrolic-type nitrogen have two obvious peaks at 399.00 and 399.65 eV, respectively. Figure 4 c); S 2p The XPS graph shows two peaks at 162.84 and 164.03 eV ( Figure 4 The presence of the CSC group is confirmed by the d-type fluorescence spectra, further demonstrating the successful preparation of Cys-GQDs. The luminescence performance of fluorescent materials is typically evaluated by their fluorescence quantum yield, with a high fluorescence quantum yield indicating high luminescence efficiency. Figure 5 a shows the absorbance curves of quinine sulfate and Cys-GQDs at different concentrations. Figure 5 The fluorescence emission spectra of quinine sulfate and Cys-GQDs with different absorbances are given in b, and then we can get Figure 5 The fluorescence integrated area curve at different absorbances is shown in c. The fluorescence quantum yield of Cys-GQDs is 83.95% calculated from the slope of the curve.

[0105] (2) The test results of the DES prepared in Example 1 are as follows:

[0106] like Figure 6As shown in the figure, the melting point of DES was determined to be -7.6 °C by differential scanning calorimetry, which is lower than that of its component ChCl (T m =305℃) and AA (T m =14℃) melting point, which directly proves the successful synthesis of DES. The chemical structure of DES was analyzed by FT-IR spectroscopy, such as Figure 7 As shown, except for 1481cm -1 and 1087cm -1 The peaks correspond to the bending vibration peaks of -CH2 and CN in choline chloride. + In addition to the asymmetric stretching vibration peak at 1722 cm -1 The stretching vibration peak of C=O of the carboxyl group in the acrylic acid component was observed at 2680 cm, proving that it still exists in the form of carboxylic acid rather than molten salt, indicating that DES is connected by hydrogen bonds; -1 and 3660cm -1 The broad band between corresponds to the stretching vibration peak of the OH bond, which also verifies the above inference. 1 H-NMR spectrum ( Figure 8 ), the chemical shifts and integral ratios of the characteristic peaks of all characteristic protons match well with those of ChCl and AA, and the continuous shift to low field further confirms the formation of hydrogen bonds in DES.

[0107] (3) Conductive elastomer PDES-GQDs prepared in Example 4 0.04 The infrared characterization test results of the conductive elastomer PDES prepared in Example 1 are as follows:

[0108] like Figure 9 As shown in a, in the PDES elastomer without the introduction of Cys-GQDs, after in situ photopolymerization, the 1427 cm -1 C=C and 951cm -1 =CH-related stretching vibration peaks are significantly weakened, and the peak of PAA at 1719 cm -1 The carboxyl group at the position remains intact and the red shift to 1717 cm after polymerization -1 ( Figure 9 b), indicating its successful polymerization. After the introduction of Cys-GQDs, the -1 The stretching vibration peak belonging to the thiol group in Cys-GQDs was significantly reduced, indicating that the thiol group on Cys-GQDs and the olefin on the acrylic acid in DES successfully underwent a "thiol-double bond" click reaction.

[0109] (4) Conductive elastomer PDES-GQDs prepared in Examples 1-4 xThe results of the comparative tests on the mechanical properties, optical transmittance and thermal properties of the conductive elastomer PDES prepared in Comparative Example 1 are as follows:

[0110] The mechanical properties of the double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer prepared by the present invention are as follows: Figure 10 As shown in the figure, as the Cys-GQDs content gradually increases from 0wt% to 4wt%, the strain of the conductive elastomer decreases from the initial 1200% to 525%, and the elastomer PDES-GQDs x The strength of PDES-GQDs increased from 0.29MPa to 5.64MPa. 0.04 The strength of the conductive elastomer is 19.4 times that of the blank sample. This is because the introduction of Cys-GQDs further enriches the hydrogen bond density in the conductive elastomer, and the thiol groups on the quantum dots successfully undergo a "thiol-double bond" click reaction with the double bonds on the acrylic monomer. The chemical and physical double cross-linked network greatly improves its mechanical strength. In addition, although the introduction of Cys-GQDs during the polymerization process will react with the double bonds on the acrylic acid in DES to generate new carbon-sulfur covalent bonds, thereby affecting the optical transmittance of the conductive elastomer, the conductive elastomer still has good optical transmittance when 4wt% of Cys-GQDs is added in the experiment. PDES-GQDs was quantified using a UV / visible spectrophotometer. 0.04 The optical transmittance in the visible light range is still greater than 60% ( Figure 11 ). Using TGA ( Figure 12 a) and DTG curve ( Figure 12 b) Thermal properties of the samples were tested at a heating rate of 20°C / min under N2 atmosphere. In the temperature range of 100~700°C, the pre-dried PDES and PDES-GQDs x Elastomers exhibit a typical two-step degradation upon heating. The first step of thermal degradation occurs at 170-280°C, which is due to the decarboxylation of the carboxyl groups in the polyacrylic acid component. The second step of thermal decomposition occurs at 280-500°C ( Figure 12 b), which is due to the decomposition of CC bonds in PAA and ChCl components. After adding Cys-GQDs, PDES-GQDs 0.04The first-stage initial degradation temperature of the elastomer was 20°C higher than that of the control PDES elastomer, and the weight loss was reduced by 7%. This result can be attributed to the formation of high-density hydrogen bonds, cation dipoles and other non-covalent interactions between Cys-GQDs and the low eutectic solvent. In addition, in the presence of Cys-GQDs, the initial thermal degradation temperature of the second stage increased by 70°C, which confirms that after the introduction of Cys-GQDs, a "thiol-double bond" click reaction occurred, and new carbon-sulfur covalent bonds were generated. In addition, the PDES-GQDs in the range of -100~80°C were measured by differential scanning calorimetry. 0.04 Thermal behavior of elastomers. PDES-GQDs 0.04 There is no obvious crystallization peak in the DSC curve of the elastomer ( Figure 13 ), and its glass transition temperature is -23.17℃, showing an amorphous structure and good low-temperature resistance.

[0111] (5) Conductive elastomer PDES-GQDs prepared in Examples 1-4 x The test results of the self-healing performance, fluorescence performance and strain sensing performance are as follows:

[0112] The double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer prepared by the present invention also has excellent self-healing and fluorescence properties. Its fluorescence phenomenon can be clearly observed under 365nm ultraviolet light. Two pieces of conductive elastomer are cut flatly with a blade, and then the two flat sections are spliced ​​together under gentle pressure. When a certain force is manually applied and stretched to 100% deformation, it still does not break, and it can still return to its original shape after the force is removed, indicating its excellent room temperature self-healing performance ( Figure 14 ); At the same time, in order to characterize the electrical self-healing properties of the conductive elastomer, a small light bulb was used for intuitive detection ( Figure 15 ), after being cut off, the small bulb turns from bright to dark, and after being spliced ​​together again, the electrical performance can be quickly restored to make the bulb glow, indicating its excellent room temperature electrical self-repair performance. Figure 16 As shown, in order to accurately measure the electrical self-healing rate, the IT mode of the electrochemical workstation was used to track the current in real time. The results showed that once the two fracture interfaces came into contact, the PDES-GQDs 0.04 The elastomer quickly recovered from 0 A to the original current signal within 0.04 s.

[0113] The double-crosslinked high-strength poly-eutectic fluorescent self-healing conductive elastomer prepared by the present invention has excellent strain sensing performance. 0.04 Good mechanical properties, electrical self-healing and conductive properties of elastomers using PDES-GQDs 0.04 The elastomer is assembled with high performance strain sensors. Figure 17As shown in Figure 2, under a strain rate of 100 mm / min and a strain amplitude of 5%, PDES-GQDs 0.04 The relative resistance change (ΔR / R0) value of the sensor increases with the addition of Cys-GQDs, showing an overall linear growth trend. In particular, when the Cys-GQDs content reaches 4wt%, the relative resistance change reaches the highest, which is about twice that of PDES elastomer, which also shows that the addition of Cys-GQDs improves the response sensitivity of the strain sensor. Figure 18 As shown, the elastic PDES-GQDs were further observed under a fixed strain of 5%. 0.04 The relative resistance change value remained almost unchanged at different stretching speeds of 100~300mm / min, except for the rebound hysteresis phenomenon at 300mm / min. At stretching speeds of 400mm / min and above, the response of the strain sensor decreased slightly, proving the response stability of the elastomer under high-speed strain (200mm / min). In the practical application of strain sensors assembled with elastomers, they are often significantly affected by their sensitivity to small strains. In order to characterize the sensitivity of the elastomer to strain, the PDES-GQDs elastomer was tested at a strain speed of 100mm / min. 0.04 The assembled strain sensor was tested in the strain range of 10% to 100%, and the results showed that its ΔR / R0 value gradually increased ( Figure 19 The sensitivity of the tensile strain sensor was evaluated using the strain sensitivity factor (GF), which is defined as the rate of change of resistance with applied strain. Figure 20 As shown, PDES-GQDs 0.04 The GF value in the strain range of 10%~100% is 1.19, which is more than twice that of PDES. This is attributed to the 0.04 The Cys-GQDs component introduced into the elastomer has good electrical conductivity. Figure 21 It can be seen that at temperatures of -20℃ and 60℃, PDES-GQDs 0.04 The relative resistance change of the elastomer is close to that at 25℃, indicating that it has high and low temperature resistant sensing performance. Taking into account the outstanding low temperature tolerance mentioned above, the PDES-GQDs 0.04 Cyclic durability of the elastomer sensor at a strain rate of 100 mm / min and a strain amplitude of 3% at -20°C. Figure 22 The PDES-GQDs showed a fast and stable response during the stretching cycle, and the residual strain after 21,000 cycles was negligible, indicating that the PDES-GQDs 0.04 Elastomers have remarkable low-temperature fatigue sensing properties.

[0114] The application of the conductive elastomer prepared by the present invention in human motion monitoring is as follows: Figure 23 As shown, the elastomer PDES-GQDs 0.04 Captured the frown ( Figure 23 a) and mouth opening and closing ( Figure 23 b) and other micro-expressions or facial movements related to tension changes, which lays the foundation for designing facial recognition technology in combination with human-computer interaction. In addition to detecting small facial movements, PDES-GQDs 0.04 When elastic bodies are assembled at different joints of the human body, they can also sense other larger-scale human movements and motions. For example, tracking the nodding of the head at the neck joint ( Figure 23 c), knuckle bending ( Figure 23 d), wrist joint and hand up and down movement ( Figure 23 e), elbow joint arm bending ( Figure 23 f), knee and ankle walking ( Figure 23 g and Figure 23 i) and chest expansion exercises ( Figure 23 h), the corresponding regular ΔR / R0 values ​​and similar electrical signal curves are obtained. In particular, Figure 23 As shown in Figure c, the relative resistance change of the elastomer can be used to determine the bending angle of the neck. When it is made into a wearable device, the ΔR / R0 generated by bending at a certain angle is set as the warning line. Once the warning line is exceeded for a long time, a reminder will be issued, ultimately playing a role in intelligently protecting the health of the user. Overall, these results highlight that PDES-GQDs 0.04 Wearable strain sensors assembled with elastomers effectively collect somatosensory motion signals from different body regions, have consistent real-time reproducibility and stability, and have the potential to be made into smart wearable devices, which may provide new inspiration for the improvement of flexible electronic devices.

[0115] In addition, given the conductive elastomer PDES-GQDs x Possessing good fluorescence performance and strain sensing performance, Figure 24 The application of its prepolymer in fluorescent anti-counterfeiting performance and tamper-evident (tamper-evident) function. Figure 24 As shown in the figure, since Cys-GQDs have good fluorescence properties, conductive elastomer prepolymer is used as ink for screen printing, and coated paper is selected as the substrate. In order to enrich its application in information storage and anti-counterfeiting, a barcode and QR code with embedded information of XAUT are designed ( Figure 24 a) and screen printed to obtain Figure 24 The state shown in b shows that good fluorescent anti-counterfeiting can still be performed even after drying and curing. At the same time, the results also show that the QR code recognition effect is stronger than the barcode, which is attributed to the richer information in the QR code and easier positioning during recognition.

Claims

1. A method for preparing a double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer, characterized in that: Please follow the steps below to implement it: Step 1, mixing choline chloride and acrylic acid, and then heating and stirring the mixture at 60-70° C. for 15-30 minutes to obtain a polymerizable deep eutectic solvent DES; Step 2, preparing cysteine-modified graphene quantum dots Cys-GQDs using citric acid and cysteine; Step 3: Add the Cys-GQDs and photoinitiator obtained in step 2 to the DES prepared in step 1, and heat and stir at 60-70° C. for 0.5-1 h to obtain a prepolymer solution; Step 4: Cast the prepolymer solution obtained in step 3 onto a horizontal glass plate and perform in-situ polymerization by ultraviolet light irradiation to obtain a conductive elastomer.

2. The preparation method of the double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer according to claim 1, characterized in that: In step 1, the molar ratio of choline chloride to acrylic acid is 1:1.8-2.

4.

3. The preparation method of the double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer according to claim 1, characterized in that: Step 2 is as follows: Citric acid and L-cysteine ​​were dissolved in deionized water to form a solution, which was then heated at 180-220°C for 5-10 minutes. After the reaction was completed and the reaction solution was cooled to room temperature, the pH of the reaction solution was adjusted to 7, and then the reaction solution was purified using a dialysis bag. Finally, the purified solution was freeze-dried for 2-3 days to obtain cysteine-modified graphene quantum dots Cys-GQDs.

4. The preparation method of the double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer according to claim 3, characterized in that: The molar ratio of the citric acid to L-cysteine ​​is 1:

1.

5. The method for preparing the double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer according to claim 3, characterized in that: The molecular weight cut-off of the dialysis bag is 700~1000Da.

6. The method for preparing a double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer according to claim 1, characterized in that: In step 3, the photoinitiator is photoinitiator 2959, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone or 2-hydroxy-2-methyl-1-phenylpropanone, and the mass of the added photoinitiator is 1% of the mass of DES.

7. The method for preparing a double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer according to claim 1, characterized in that: In step 3, the mass of Cys-GQDs is 1–4% of the mass of DES.

8. The method for preparing a double-crosslinked high-strength polyeutectic fluorescent self-healing conductive elastomer according to claim 1, characterized in that: In step 4, the wavelength of the ultraviolet light is 365 nm, the power is 40-60 W, the height of the ultraviolet lamp from the glass plate is 10-15 cm, and the irradiation time is 1-2 min.

9. Double cross-linked high-strength polyeutectic fluorescent self-healing conductive elastomer, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 8.

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