A method for rapidly initiating the polymerization of a deep eutectic solvent to prepare a deep eutectic gel

Abstract

The present invention relates to the technical field of methods for preparing eutectic gels, and specifically discloses a method for rapidly initiating the polymerization of eutectic solvents to prepare eutectic gels, which specifically includes the following steps: Step 1, first, using industrial xylan, or cellulose, or glucomannan, or arabinoglucose, or mannan as raw materials, dialdehyde xylan (DAX) is prepared by the periodate oxidation method as follows: 20.0 g of industrial xylan is added to 800 mL of deionized water respectively, stirred until evenly dispersed to form a suspension, then 50.0 g of NaIO<subgt;4< / subgt; is weighed and added to the above suspension, and then stirred and reacted under dark at room temperature for different times. After the reaction is completed, 12 mL of ethylene glycol is slowly added to the reaction system to terminate the reaction; by using the dialdehyde xylan (DAX) solution to stabilize the LM nanodroplets, and using the DAX / LM dispersion to rapidly initiate the polymerization reaction of ChCl / AM in one step to prepare the DLPD eutectic gel, and no free radical initiator and crosslinking agent are required during the preparation process.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation method of eutectic gels, in particular to a method for rapidly initiating the polymerization of eutectic solvents to prepare eutectic gels. Background Art

[0002] In recent years, people's interest in developing high-performance flexible electronic devices has been increasing day by day. Because they can be applied to a variety of emerging fields, including electronic skin, wearable intelligent devices, soft robots, health monitoring systems, etc. Conductive hydrogels have been widely used in flexible electronic devices due to their excellent stretchability, toughness, conductivity and other characteristics. However, in order to endow conductive hydrogels with ideal mechanical properties, covalent crosslinking is usually required, and crosslinking agents, initiators and catalysts need to be added during the preparation process. Most of these reagents are cytotoxic and are not conducive to the practical application of hydrogels. In addition, another key factor restricting the application of conductive hydrogels is their poor environmental stability. Due to inevitable water evaporation or freezing, their performance is unstable and they are not suitable for extreme environments.

[0003] As a new type of green solvent, DESs have the characteristics of easy preparation, adjustable properties, low volatility and high ionic conductivity. In recent years, they have gradually been used to prepare various eutectic gel materials and have shown great advantages in the field of high-performance flexible electronic devices. Among them, polymerizable eutectic solvents containing polymerizable components are widely used in the preparation of flexible electronic devices.

[0004] The following preparation methods already exist in the prior art: A tough solvent-free ion-conductive elastomer was prepared by in-situ photoinitiated polymerization based on PDES composed of choline chloride / acrylic acid (ChCl / AA) and cellulose nanocrystals coated with tannic acid. There is also the development of a self-healing fiber optic sensor using the photoinitiated polymerization of choline chloride / acrylamide (AM) / glycerol. A remarkable characteristic of these PDES gel materials is their excellent environmental stability. Despite the obvious advantages, their gelation process still highly depends on crosslinking agents and photoinitiators. Therefore, the preparation process of PDES gel materials still needs to be further optimized. Summary of the Invention

[0005] Aiming at the technical problems proposed in the background art, the present invention provides a method for rapidly initiating the polymerization of eutectic solvents to prepare eutectic gels.

[0006] The technical solution adopted by the present invention is: A method for rapidly initiating the polymerization of eutectic solvents to prepare eutectic gels, specifically including the following steps:

[0007] Step 1: First, using industrial xylan, or cellulose, or glucomannan, or arabinoglucose, or mannan as raw materials, dialdehyde xylan (DAX) is prepared by the periodate oxidation method as follows: Add 20.0 g of industrial xylan to 800 mL of deionized water, stir until evenly dispersed to form a suspension, then weigh 50.0 g of NaIO4 and add it to the above suspension. Then, stir and react at room temperature in the dark for different times. After the reaction is completed, slowly add 12 mL of ethylene glycol to the reaction system to terminate the reaction;

[0008] Step 2: Transfer the reaction solution in Step 1 to a regenerated cellulose dialysis bag with a molecular weight cut-off of 3500 Da, dialyze in deionized water for four days, and the dialyzed aqueous solution is concentrated by rotary evaporation and freeze-dried to obtain the final product dialdehyde xylan;

[0009] Step 3: Preparation of DAX / nanodroplet (LM) dispersion: Add different masses of DAX to deionized water to prepare DAX solutions with different concentrations. Then, add different masses of LM to the DAX solutions so that the mass concentration ratio of LM in the mixed system is 1 wt%, 2 wt%, 3 wt%, and 5 wt% respectively. Use an ultrasonic reactor to process for 30 min at a power of 600 W and in an ice-water bath to obtain DAX / LM dispersions with different concentrations, denoted as DxLy respectively, where x and y refer to the concentrations of DAX and LM in the dispersion. Add liquid metal to deionized water and prepare a 3 wt% LM dispersion by ultrasonic treatment in the same method as above as a control;

[0010] Step 4: Preparation of DLPD eutectic gel: First, vacuum dry ChCl at 60 °C for 6 h to remove moisture. Mix acrylamide (AM) and choline chloride (ChCl) at a molar ratio of 2:1 in a sealed glass bottle, place it in a 60 °C water bath and stir for 1 h to form a homogeneous and transparent eutectic (DES). Then, take 2.0 mL of DES, add 1.0 mL of DAX / LM dispersion to it and mix evenly. Subsequently, quickly transfer the obtained mixture to a polytetrafluoroethylene mold, let it stand at room temperature and spontaneously polymerize to finally obtain the DLPD eutectic gel. In addition, a DLPAM hydrogel was prepared as a control sample by replacing ChCl with the same mass of water in the same method as above;

[0011] Step 5: Use a Fourier transform infrared spectrometer to collect the FT-IR spectra of xylan and DAX samples in the wavenumber range of 4000~600 cm -1 with a resolution of 4 cm -1 and the number of scans is 32 times. Use a Bruker D8 Advance X-ray diffractometer to measure the XRD spectra of xylan and DAX samples, the 2θ value range is 5~60°, and the scanning speed is -1 2°min-1 ;

[0012] Step 6: Dissolve 4 mg of DAX in 2 mL of phosphate buffer solution. After filtration using a 0.22 μm aqueous filter head, determine the molecular weight distribution of DAX by gel permeation chromatography (GPC), and determine the surface chemical composition of LM nanodroplets using an X-ray photoelectron spectrometer (XPS).

[0013] Step 7: Use a Zeiss Gemini 300 scanning electron microscope (SEM) to observe the surface morphology and elemental composition of LM nanodroplets and DLPD eutectic gels. In addition, use a transmission electron microscope (TEM) to observe the surface fine structure of LM nanodroplets, and use an infrared thermal imager to monitor the temperature change during the gelation process and record the temperature-time curve.

[0014] Step 8: Use 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a hydroxyl radical scavenger, and record the electron paramagnetic resonance (EPR) spectra of LM and DAX / LM dispersions on a Bruker spectrometer. Place the DLPD eutectic gel and DLPAM hydrogel at room temperature for 30 days for water retention testing, and evaluate their dehydration resistance by the gravimetric method.

[0015] In a further setting of the present invention, in Step 1, stir the reaction in the dark at room temperature for different times, and the times are: 24 h, 36 h, and 48 h.

[0016] In a further setting of the present invention, in Step 3, prepare DAX solutions with different concentrations, and the concentrations of the DAX solutions are: 2 wt%, 5 wt%, and 8 wt%.

[0017] In a further setting of the present invention, in Step 8, the thermal stability of the gel is determined by a thermal analyzer (TA Q200), the test is carried out in a nitrogen atmosphere, the temperature range is 25 - 300 °C, and the heating rate is 10 °C min -1 , and use a differential scanning calorimeter to evaluate the anti-freezing performance of the gel; then place the gel in an aluminum pot and cool it from 20 °C to -80 °C at a cooling rate of 10 °C min -1 , keep it warm for 5 min, and then heat it to 20 °C at a rate of 10 °C min -1 , record the DSC curve. The photothermal performance of the DLPD eutectic gel is tested by a solar simulator and an infrared thermal imager, and the mechanical properties of the eutectic gel are tested by a universal testing machine. The sample size is 60 mm × 15 mm × 2.5 mm, and the tensile rate is 100 mm min -1 .

[0018] In a further setting of the present invention, it also includes a cell compatibility test, which specifically includes the following steps:

[0019] Mix MEM medium and fetal bovine serum at a volume ratio of 9:1 to prepare a cell culture medium;

[0020] Weigh 50 mg of the eutectic gel sample, sterilize both sides with ultraviolet light for 30 min, add 10 mL of the medium, and soak for 48 h to completely dissolve it;

[0021] Dilute with the medium to the required concentrations of 10, 25, and 50 μg / mL -1 , take L929 cells in the logarithmic growth phase, perform cell counting, adjust the cell concentration, and inoculate into a 96-well plate at 6×10 3 / well, and culture overnight in a constant temperature incubator at 5% CO2 and 37°C;

[0022] Add 100 μL / well of the sample solution respectively, add 100 μL / well of the medium to the control group, make 3 replicates for each treatment group, continue to culture for 24 h and 48 h, then remove the medium, wash each well three times with PBS solution, add 100 μL / well of the medium containing 10% CCK-8, culture in a constant temperature incubator at 5% CO2 and 37°C for 2 h, and use an enzyme-linked immunosorbent assay (ELISA) reader to detect the absorbance value at 450 nm. The relative cell viability is calculated according to the following formula:

[0023]

[0024] Among them, the background OD value is the absorbance of adding only the CCK-8 reagent and the medium;

[0025] After staining the cells with the live / dead cell staining method for 15 min respectively, use an inverted fluorescence microscope to observe the results and take pictures for recording.

[0026] A further setting of the present invention is that it also includes an electrochemical test, and the specific steps are as follows:

[0027] Take a eutectic gel sample with dimensions of 10 mm×10 mm×2.5 mm, use an electrochemical workstation to measure the alternating current impedance spectrum of the eutectic gel in the range of 10 5 ~1 Hz, the alternating current amplitude is 5 mV, and calculate the conductivity with the following formula;

[0028]

[0029] Among them, σ is the conductivity (S m -1 ), L is the thickness of the eutectic gel sample (cm), S is the effective contact area between the electrode and the eutectic gel sample (cm 2 ), and R is the intercept on the x-axis of the alternating current impedance spectrum (ohm).

[0030] The present invention is further configured to further include strain sensing and temperature sensing tests, and the specific steps are as follows:

[0031] The strain sensing performance of the deep eutectic gel is tested by using an electrochemical workstation in combination with a universal testing machine;

[0032] Under a constant voltage of 0.1 V, the current-time curve of the deep eutectic gel under different stretching conditions is tested, and the relative resistance change (R - R0) / R0 (%) is calculated therefrom; R0 and R are the initial resistance and the real-time resistance under the strain condition respectively. In order to monitor human movement, the deep eutectic gel is attached to the wrist, finger and knee of the human body respectively. By measuring the current-time curve during joint bending, the relative resistance change of the deep eutectic gel during human movement is calculated. In addition, the deep eutectic gel sample is placed in a polyethylene sealed bag and then placed in a water bath. In the temperature range of 30 - 90 °C, the electrochemical workstation is used to monitor the resistance change to determine the temperature response behavior of the deep eutectic gel.

[0033] The beneficial effects of the present invention are as follows:

[0034] First, in the present invention, the LM nano-droplets are stabilized by using dialdehyde xylan (DAX) solution, and the DLPD deep eutectic gel is prepared by using the DAX / LM dispersion to rapidly initiate the polymerization reaction of ChCl / AM in one step. During the preparation process, traditional radical initiators and cross-linking agents are not required. Therefore, this method is environmentally friendly and does not rely on radical initiators and cross-linking agents. DAX containing reducing aldehyde groups plays a key role in accelerating the radical polymerization reaction and improving the mechanical properties of the gel. The rich hydrogen bond network in the prepared deep eutectic gel endows it with super stretchability and self-healing properties. Since H2O participates in the strong hydrogen bond assembly, the deep eutectic gel has excellent dehydration resistance and freeze resistance. In addition, the combination of LM nano-droplets and PDES not only enhances the conductivity of the deep eutectic gel, but also endows the deep eutectic gel with excellent strain sensitivity and temperature sensitivity.

[0035] Second, in the present invention, water-soluble DAX rich in functional aldehyde groups is prepared by selective oxidation of xylan with periodate. Based on the surface anchoring effect of DAX, LM forms nano-droplets with a core-shell structure under high-frequency ultrasound and can be stably dispersed in water for a long time; a new type of deep eutectic gel is prepared by rapidly initiating the free radical polymerization of DES through the DAX / LM dispersion system at room temperature. No additional chemical initiators and cross-linking agents are required during the process. Based on the stabilizing effect and reduction characteristics of DAX, the surface reactivity of LM increases, thereby accelerating the free radical polymerization reaction rate and increasing the cross-linking density; the deep eutectic gel formed by physical cross-linking has super stretchability (2860%), self-healing performance (healing efficiency up to 87%), high conductivity (0.72 S m -1), photothermal properties and biocompatibility. Due to the participation of water molecules in the hydrogen bond network assembly of PDES, the eutectic gel exhibits excellent resistance to water loss and freezing. When used as a resistive strain sensor, the eutectic gel has high sensitivity (GF = 4.08), which can be used to identify human body movements with large deformation amplitudes and handwriting with small strains. When used as a temperature sensor, it has excellent thermal sensitivity (TCR = 5.35% K -1 ), which can be used for temperature recognition and health monitoring. Therefore, this eutectic gel has broad application prospects in the field of flexible smart wearable electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 (a) Schematic diagram of the preparation process of DAX in the present invention (including (b) oxidation degree and (c) molecular weight distribution of DAX at different reaction times; (d) infrared spectra and (e) X-ray diffraction spectra of industrial xylan and DAX; (f) changes in water solubility of xylan before and after oxidation);

[0037] Figure 2 (a) is a schematic diagram of the preparation of DAX / LM nanodroplets in the present invention (including (b) a TEM image of the DAX / LM nanodroplet and a schematic diagram of the structure of the DAX coating layer on the surface of the nanodroplet);

[0038] Figure 3 The stability photos of the LM droplets in DAX solution and pure water, the SEM image and energy spectrum of the DAX / LM nanodroplets (a), and the full scan, Ga3d and Ga2p XPS spectra of the DAX / LM nanodroplets (b);

[0039] Figure 4 (a) C for the preparation of hCl / AM DES in the present invention; (b) a flow chart for the preparation of hard PDES polymer and soft PDES eutectic gel by in situ photoinitiation and the preparation of DLPD eutectic gel by DAX / LM-initiated polymerization;

[0040] Figure 5 Schematic diagram of the preparation process of DLPD eutectic gel in the present invention (a); a photograph of the rapid gelation of DLPD eutectic gel (b); an infrared thermal imaging photograph and a self-heating rate curve of the gelation process of DLPD eutectic gel (c);

[0041] Figure 6 (b) is an infrared thermal imaging photograph of the free radical polymerization process initiated by DAX / LM (a) and LM in the present invention;

[0042] Figure 7 The SEM image and energy spectrum of the DLPD eutectic gel of the present invention;

[0043] Figure 8 Figure (a) shows the reaction of unpaired electrons of Ga in the present invention with vinyl monomers to initiate chain growth; Figure (b) shows the mechanism of ultrasonic decomposition of H2O into ·H and ·OH and further initiation of free radical polymerization of vinyl monomers; Figure (c) shows the schematic diagram of DAX reducing Ga 3+ to Ga; Figure (d) shows the color change diagram of methyl orange (MO), congo red (CR) and methylene blue (MB) solutions after adding to the DAX / LM suspension; Figure (e) shows the EPR spectrum of free radicals captured by DMPO in LM and DAX / LM dispersions;

[0044] Figure 9 Figure shows the gelation time of DLPD eutectic gels and DLPAM hydrogels at different DAX and LM concentrations in the present invention;

[0045] Figure 10 Figure (a) shows the photograph of the DLPD eutectic gel in the tensile state in the present invention; (b) shows the schematic diagram of the structure of the eutectic gel when it is stretched; Figures (c, e) show the tensile stress-strain curves and toughness diagrams of the eutectic gel at different LM and (d, f) DAX concentrations; (g) shows the tensile stress-strain curve diagram of DLPAM hydrogel and DLPD eutectic gel; (h) shows the tensile-release curve diagram of DLPD-D5L3 eutectic gel at 100% strain for 200 consecutive times;

[0046] Figure 11 Figure (a) shows the photograph of the sticky cut surface of the eutectic gel after being immersed in water in the present invention; (b) shows the photograph of the self-healed DLPD eutectic gel with a length of about 1.5 cm stretched to more than 15 cm without breaking; (c) shows the stress-strain curve diagrams of the initial and self-healed DLPD-D5L3 eutectic gels at different healing times; (d) shows the self-healing efficiency diagrams of stress, strain and toughness of the DLPD-D5L3 eutectic gel at different healing times; (e) shows the schematic diagram of the possible self-healing mechanism;

[0047] Figure 12 Figure (a) shows the photographs of the DLPAM hydrogel placed for 48 h and the DLPD eutectic gel placed for 30 d at room temperature in the present invention; (b) shows the weight change diagrams of the DLPAM hydrogel and the DLPD eutectic gel placed in the environment for different times; (c) shows the TG curve diagrams of the DLPAM hydrogel and the DLPD eutectic gel; (d) shows the appearance photographs of the DLPAM hydrogel and the DLPD eutectic gel at -26°C; (e) shows the TG curve diagrams of the DLPAM hydrogel and the DLPD eutectic gel;

[0048] Figure 13 Figure (a) shows the infrared thermal imaging diagram and (b) shows the temperature change curve diagram of the DLPD eutectic gel under different intensities of light irradiation in the present invention;

[0049] Figure 14 Comparison diagram of L929 cell viability after 24 h and 48 h of culture with DLPD eutectic gels at different concentrations in the present invention (a); (b) Live / dead cell staining diagrams of L929 cells and the control group after co-culture with eutectic gel concentrations of 50 μg mL -1 Live / dead cell staining diagrams of L929 cells and the control group after co-culture with eutectic gels;

[0050] Figure 15 (a) EIS spectra and (b) conductivity diagrams of DLPD eutectic gels with different LM contents in the present invention; (c) Relative resistance changes of DLPD eutectic gels under cyclic stretching five times at different strains, with the inset showing the relative resistance change curve at low strain; (d) Relative resistance change diagrams at different strains;

[0051] Figure 16 (R-R0) / R0 response diagrams under different human motions in the present invention, including (a) finger bending, (b) wrist bending, (c) knee bending, (d) different gesture diagrams.

[0052] Figure 17 (a) (R-R0) / R0 response diagram during finger pressing in the present invention; (b) Schematic diagram of handwritten sensing by the DLPD strain sensor; The DLPD sensor senses specific handwritten contents, such as (c) "A" and "B", (d) "C" and "D", (e) "yes" and (f);

[0053] Figure 18 (a) Conductivity diagram, (b) resistance diagram, and (c) diagram of relative resistance change with temperature (30 - 90 °C) of the DLPD temperature sensor in the present invention; (d) Linear fitting relationship diagram of lnR and 1000 / T; (e) Diagram of thermal index, activation energy, and TCR value of the DLPD temperature sensor; (f) Comparison diagram of the TCR value of the DLPD sensor with other reported temperature sensors;

[0054] Figure 19 (a) Diagram of the DLPD temperature sensor heated by a hair dryer, (b) temperature cycle between 30 °C and 40 °C, and (c) (R-R0) / R0 response diagram to the heat generated by human breathing in the present invention; (d) Relative resistance change of the DLPD temperature sensor in the temperature range of 35 - 42 °C, shown with a temperature interval of 1 °C. Detailed implementation manners

[0055] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0056] In order to solve the problems existing in the background technology, the present application proposes the following technical solutions: A method for rapidly initiating the polymerization of a deep eutectic solvent to prepare a deep eutectic gel, specifically including the following steps:

[0057] Step 1, first, using industrial xylan, or cellulose, or glucomannan, or arabinoglucose, or mannan as raw materials, dialdehyde xylan (DAX) is prepared by the periodate oxidation method, specifically as follows: Add 20.0 g of industrial xylan to 800 mL of deionized water respectively, stir until evenly dispersed to form a suspension, then weigh 50.0 g of NaIO4 and add it to the above suspension, and then stir and react at room temperature in the dark for different times. After the reaction is completed, slowly add 12 mL of ethylene glycol to the reaction system to terminate the reaction;

[0058] In addition, in Step 1, when stirring and reacting at room temperature in the dark for different times, the times are respectively: 24 h, 36 h, and 48 h.

[0059] In Step 1, the xylan is derived from the by-product of a viscose fiber factory, extracted with 20% (w / v) concentrated alkali, and then obtained through membrane filtration and spray drying. The sugar analysis results show that xylose accounts for 97 mol% in the xylan. Choline chloride (ChCl, 98%), acrylamide (AM, 99%), and sodium periodate (NaIO4, 99%) are purchased from Shanghai Macklin Biochemical Technology Co., Ltd. The liquid metal (gallium-indium alloy EGaIn, composed of 70% Ga and 30% In, melting point 16 °C) is purchased from Dongguan Huatai Metal Materials Co., Ltd. The MEM medium is purchased from Corning Inc., USA. Fetal bovine serum and mouse fibroblasts (L929) are purchased from Wuhan Punosai Life Technology Co., Ltd. The cell counting kit is purchased from Invigentech, USA. The live / dead cell staining kit is purchased from Shanghai Beyotime Biotechnology Co., Ltd.

[0060] Step 2, transfer the reaction solution in Step 1 to a regenerated cellulose dialysis bag with a cut-off molecular weight of 3500 Da, dialyze in deionized water for four days, and the dialyzed aqueous solution is concentrated by rotary evaporation and freeze-dried to obtain the final product dialdehyde xylan;

[0061] Step 3. Preparation of the dispersion of DAX / nanodroplets (LM): Different masses of DAX were added to deionized water to prepare DAX solutions with different concentrations. Subsequently, different masses of LM were added to the DAX solutions so that the mass concentration ratios of LM in the mixed systems were 1 wt%, 2 wt%, 3 wt%, and 5 wt% respectively. The mixtures were treated in an ultrasonic reactor at a power of 600 W and in an ice-water bath for 30 min to obtain DAX / LM dispersions with different concentrations, denoted as DxLy respectively, where x and y refer to the concentrations of DAX and LM in the dispersion. Liquid metal was added to deionized water, and an LM dispersion with a concentration of 3 wt% was prepared by ultrasonic treatment in the same manner as above as a control;

[0062] Among them, the composition of the DAX / LM dispersion is referred to Table 1;

[0063] DAX(g) LM(g) <![CDATA[H2O(g)]]> D2L3 0.6 0.9 28.5 D5L3 1.5 0.9 27.6 D8L3 2.4 0.9 26.7 D5L1 1.5 0.3 28.2 D5L2 1.5 0.6 27.9 D5L5 1.5 1.5 27.0

[0064] Table 1

[0065] In addition, in Step 3, in the DAX solutions with different concentrations prepared, the concentrations of the DAX solutions were: 2 wt%, 5 wt%

[0066] and 8 wt%.

[0067] Step 4. Preparation of DLPD eutectic gel: First, ChCl was vacuum-dried at 60 °C for 6 h to remove moisture. Acrylamide (AM) and choline chloride (ChCl) were mixed in a closed glass bottle at a molar ratio of 2:1 and placed in a 60 °C water bath and stirred for 1 h to form a homogeneous and transparent eutectic (DES). Then, 2.0 mL of DES was taken, 1.0 mL of DAX / LM dispersion was added thereto and mixed evenly. Subsequently, the obtained mixture was quickly transferred to a polytetrafluoroethylene mold and left to stand at room temperature for spontaneous polymerization, and finally a DLPD eutectic gel was obtained. In addition, a DLPAM hydrogel was prepared as a control sample in the same manner as above by using the same mass of water instead of ChCl;

[0068] Step 5. The FT-IR spectra of xylan and DAX samples were collected by a Fourier transform infrared spectrometer in the wavenumber range of 4000 - 600 cm -1 with a resolution of 4 cm -1 and the number of scans was 32 times. The XRD spectra of xylan and DAX samples were measured by a Bruker D8 Advance X-ray diffractometer, the 2θ value range was 5 - 60°, and the scanning speed was 2° min -1 ;

[0069] Step 6: Dissolve 4 mg of DAX in 2 mL of phosphate buffer solution. After filtering through a 0.22-μm hydrophilic filter, determine the molecular weight distribution of DAX by gel permeation chromatography (GPC), and determine the surface chemical composition of LM nanodroplets using an X-ray photoelectron spectrometer (XPS).

[0070] Step 7: Observe the surface morphology and elemental composition of LM nanodroplets and DLPD eutectic gels using a Zeiss Gemini 300 scanning electron microscope (SEM). In addition, observe the surface fine structure of LM nanodroplets using a transmission electron microscope (TEM), and use an infrared thermal imager to monitor the temperature change during the gelation process and record the temperature-time curve.

[0071] Step 8: Use 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a hydroxyl radical scavenger, and record the electron paramagnetic resonance (EPR) spectra of LM and DAX / LM dispersions on a Bruker spectrometer. Place the DLPD eutectic gel and DLPAM hydrogel at room temperature for 30 days for water retention testing, and evaluate their dehydration resistance by the gravimetric method.

[0072] In addition, in Step 8, the thermal stability of the gel is determined by a thermal analyzer (TA Q200). The test is carried out in a nitrogen atmosphere, the temperature range is 25–300 °C, and the heating rate is 10 °C min -1 to evaluate the antifreeze performance of the gel using a differential scanning calorimeter; then place the gel in an aluminum pot and cool it from 20 °C to -80 °C at a cooling rate of 10 °C min -1 , keep it warm for 5 min, and then heat it to 20 °C at a rate of 10 °C min -1 Record the DSC curve. The photothermal performance of the DLPD eutectic gel is tested by a solar simulator and an infrared thermal imager, and the mechanical properties of the eutectic gel are tested by a universal testing machine. The sample size is 60 mm × 15 mm × 2.5 mm, and the tensile rate is 100 mm min -1 .

[0073] In a further design, it also includes determining the degree of oxidation (DO) of DAX. The specific steps are as follows:

[0074] First, prepare NaIO4 solutions with different concentrations, measure the absorbance values of each solution at 290 nm using a UV-Vis spectrophotometer and plot a standard curve. Then, at the required reaction time points, take 2 mL of the reaction solution, measure its absorbance value at 290 nm, determine the NaIO4 concentration according to the standard curve, and further calculate the NaIO4 consumption. Finally, calculate DO according to the following formula.

[0075]

[0076] Among them, the amount of dehydrated xylose unit is 20.0 (g) / 132 (g mol -1 ) = 0.1515 mol.

[0077] In a further design, it also includes a cell compatibility test, which specifically includes the following steps:

[0078] Mix MEM medium and fetal bovine serum in a volume ratio of 9:1 to prepare a cell culture medium;

[0079] Weigh 50 mg of the eutectic gel sample, sterilize both the front and back sides by ultraviolet irradiation for 30 min, add 10 mL of the medium, and soak for 48 h to completely dissolve it;

[0080] Dilute with the medium to the required concentrations of 10, 25, and 50 μg mL -1 , take L929 cells in the logarithmic growth phase, perform cell counting, adjust the cell concentration, and inoculate into a 96-well plate at 6×10 3 / well, and culture overnight in a constant temperature incubator at 5% CO2 and 37 °C;

[0081] Respectively add 100 μL / well of the sample solution, add 100 μL / well of the medium to the control group, make 3 replicates for each treatment group, continue to culture for 24 h and 48 h, then remove the medium, wash each well three times with PBS solution, add 100 μL / well of the medium containing 10% CCK-8, culture in a constant temperature incubator at 5% CO2 and 37 °C for 2 h, use an enzyme-linked immunosorbent assay (ELISA) reader to detect the absorbance value at 450 nm, and calculate the relative cell viability according to the following formula:

[0082]

[0083] Among them, the background OD value is the absorbance of adding only the CCK-8 reagent and the medium;

[0084] After staining the cells with the live / dead cell staining method for 15 min respectively, use an inverted fluorescence microscope to observe the results and take pictures for recording.

[0085] In a further design, it also includes an electrochemical test, and the specific steps are as follows:

[0086] Take a eutectic gel sample with dimensions of 10 mm×10 mm×2.5 mm, use an electrochemical workstation to measure the alternating current impedance spectrum of the eutectic gel in the range of 10 5 ~1 Hz, the alternating current amplitude is 5 mV, and calculate the conductivity using the following formula;

[0087]

[0088] Among them, σ is the conductivity (S m -1 ), L is the thickness (cm) of the eutectic gel sample, S is the effective contact area (cm 2 ) between the electrode and the eutectic gel sample, and R is the intercept (ohm) of the AC impedance spectrum on the x-axis.

[0089] In a further design, it also includes strain sensing and temperature sensing tests, and the specific steps are as follows:

[0090] The strain sensing performance of the eutectic gel is tested by using an electrochemical workstation in combination with a universal testing machine;

[0091] Under a constant voltage of 0.1 V, the current-time curve of the eutectic gel under different stretching conditions is tested, and the relative resistance change (R - R0) / R0 (%) is calculated therefrom; R0 and R are the initial resistance and the real-time resistance under the strain condition respectively. In order to monitor human movement, the eutectic gel is attached to the wrist, finger and knee of the human body respectively. By measuring the current-time curve during joint bending, the relative resistance change of the eutectic gel during human movement is calculated. In addition, the eutectic gel sample is placed in a polyethylene sealed bag and then placed in a water bath. In the temperature range of 30 - 90 °C, the electrochemical workstation is used to monitor the resistance change to determine the temperature response behavior of the eutectic gel.

[0092] The above technical solution is explained as follows: The industrial xylan obtained from the viscose fiber factory is extracted by strong alkali, and most of the branched chains are removed and mostly present a linear structure. There are dense hydrogen bond interactions between these molecular chains, forming a large number of crystalline regions in the xylan, resulting in its insolubility in water;

[0093] The specific experimental examples of the present invention are as follows:

[0094] In the prior art, previous studies have confirmed that industrial xylan only undergoes partial dissolution in strong alkaline solvents (such as aqueous tetraethylammonium hydroxide) and organic solvents of dimethyl sulfoxide / tetrabutylammonium fluoride;

[0095] Based on the above considerations, the present invention modifies industrial xylan at room temperature by the NaIO4 oxidation method ( Figure 1 a), to improve the solubility of xylan and endow it with new functionalities, such as Figure 1 b shows that the oxidation reaction rate is the largest within the initial 12 h, and the DO value of xylan increases with the extension of the reaction time and can reach 92.9% at 48 h;

[0096] At the same time, compared with the original xylan (molecular weight is about 38000 g mol -1) Compared with [specific comparison object], the molecular weight of DAX decreased significantly. After oxidation for 24 h, 36 h, and 48 h, the molecular weights were 11510, 9940, and 9500 g / mol respectively. -1 (such as Figure 1 )

[0097] DAX after 48 h of oxidation was selected for subsequent studies. The structure of DAX was analyzed by FT-IR. The results showed that new signal peaks appeared at 1730 and 860 cm -1 , which originated from the stretching vibration of the carbonyl group (ν C＝O ) and the hemiacetal vibration formed by the dialdehyde group (ν C-O ) (such as Figure 1 d), indicating that NaIO4 oxidized the hydroxyl groups in xylan to aldehyde groups;

[0098] In addition, the XRD results showed that the crystallization peak of xylan disappeared after oxidation (such as Figure 1 e), indicating that the prepared DAX had a highly disordered structure. The amorphous DAX had good water solubility (such as Figure 1 f).

[0099] In further design, as Figure 2 shown, DAX / LM nano-droplets were prepared by high-frequency ultrasonic decomposition of large pieces of EGaIn in the DAX solution. DAX with flexible molecular chains was anchored on the surface of spherical nano-droplets. The TEM image confirmed the core-shell structure of the DAX / LM nano-droplets, and the nano-droplets in the D5L3 dispersion had a DAX thin layer with a thickness of about 9.1 nm on the surface (such as Figure 2 b)

[0100] Among them, as Figure 3 shown in a, the DAX / LM dispersion remained stable after being placed for 24 h, mainly due to the stabilizing effect of DAX. It could be observed by SEM that the diameters of the DAX / LM nano-droplets in the dispersion ranged from dozens of nanometers to hundreds of nanometers. At the same time, the uniformly distributed C element on the surface of these nano-droplets also confirmed the existence of the DAX layer;

[0101] However, the stability of the H2O / LM dispersion without DAX was poor, and obvious precipitation was observed after being placed for 4 h. The surface element composition of the prepared DAX / LM nano-droplets was further characterized by XPS ( Figure 3 b-d);

[0102] The characteristic peaks in the XPS full spectrum confirmed the existence of C, O, Ga, and In elements on the surface of the DAX / LM nano-droplets. The diffraction peaks at binding energies of 1118.03 eV and 1115.97 eV in the Ga2p spectrum were attributed to Ga 3+ and Ga 0, Ga can also be observed in the Ga 3d spectrogram 3+ and Ga 0 diffraction peaks, indicating the presence of a Ga2O3 oxide layer on the surface of the DAX / LM nano-droplets. This oxide layer plays an important role in anchoring DAX on the LM surface, which is beneficial to improving the dispersion stability of the LM nano-droplets in the DAX solution;

[0103] In further designs, regarding the preparation of DLPD eutectic gels under the DAX / LM initiating system, the details are as follows: Due to the ionic conductivity and rich hydrogen bond interactions of DES, in this invention, two solid components, ChCl and AM, are mixed and stirred at 60 °C to prepare DES (as Figure 4 a);

[0104] First of all, if DES is directly mixed with a photoinitiator (1.0 wt% of AM) and in-situ polymerized under 365 nm ultraviolet light, a hard glassy PDES polymer can be obtained (as Figure 4 b). Although this polymer has high mechanical strength, it lacks adaptability and sensitivity to bending and strain. Therefore, the application of this polymer is greatly limited. If water (1 / 2 of the volume of DES) is added to DES and polymerized by ultraviolet light initiation, a soft PDES eutectic gel can be obtained. However, the disadvantage is that the mechanical properties of this eutectic gel are poor and it lacks versatility;

[0105] Based on the above considerations, using the prepared DAX / LM dispersion as an initiator, a DLPD eutectic gel with a dense hydrogen bond network was prepared by one-pot rapid radical polymerization ( Figure 5 a); This method avoids the use of toxic photoinitiators and energy-consuming ultraviolet light irradiation, and can complete gelation within 2 min ( Figure 5 b), and the prepared eutectic gel has excellent comprehensive properties;

[0106] To further understand the gelation process, an infrared thermal imager was used to monitor the heat distribution during gelation, as Figure 5 shown in c. After adding the DAX / LM dispersion, radical polymerization occurs rapidly within 11 s and releases a large amount of heat. Due to the exothermic characteristics of radical polymerization, the surface temperature of the reaction system rises to 45.7 °C at 152 s, indicating that the DAX / LM system has an extremely fast initiation rate. At the same time, based on the stabilizing effect of DAX, the radical polymerization reaction of DES proceeds uniformly under the initiation of DAX / LM ( Figure 6 a). It can be observed from the SEM image that the elements C, O, N, Ga, In, and Cl are evenly distributed in the eutectic gel matrix ( Figure 7)。Conversely, when using the LM aqueous dispersion to initiate the free radical polymerization of DES, the exothermic reaction starts from the bottom of the reaction system ( Figure 6 b), which is mainly related to the rapid fusion and precipitation of LM nanodroplets with poor stability, ultimately leading to the non-uniform polymerization of DES.

[0107] Among them, the free radical polymerization mechanism of PDES can be attributed to two aspects;

[0108] First, the unpaired electrons of gallium can react with the π bond of acrylamide monomer to form a carbonyl radical, and the carbonyl radical continues to react with the adjacent acrylamide monomer, ultimately forming polyacrylamide ( Figure 8 a);

[0109] Second, under the action of high-frequency ultrasound, water can be split into hydroxyl radicals (·OH) and hydrogen radicals (·H) ( Figure 8 b); usually, the generated free radicals can quickly recombine to form H2O2, H2 and H2O, resulting in low efficiency of ·OH-initiated polymerization.

[0110] Free radicals often have high oxidizing properties and can degrade and fade dyes such as methyl orange, congo red and methylene blue. When a small amount of DAX / LM dispersion is dropped into the three dye solutions respectively, the solution color quickly disappears, indicating that free radicals are generated in the ultrasonic dispersion ( Figure 8 d);

[0111] In addition, EPR spectroscopy was used to detect the free radicals in the dispersion, and obvious quartet signals with a relative intensity of 1:2:2:1 were shown in the spectrum, indicating that ·OH exists in both LM and DAX / LM dispersions;

[0112] Comparative findings show that the signal intensity of ·OH in the DAX / LM dispersion is significantly higher than that in the LM dispersion, and this result indicates that DAX plays an important role in the formation and stabilization of free radicals;

[0113] However, unoxidized LM (Ga 0 ) can reduce H2O2 back to ·OH, thereby increasing the free radical polymerization rate. On the one hand, as mentioned above, the presence of DAX promotes the stable dispersion of LM nanodroplets, increasing the surface area of LM, which is beneficial to the reduction of H2O2 on the LM surface. On the other hand, DAX containing aldehyde groups can reduce Ga 3+ to Ga 0

[31] , further accelerating the reduction of H2O2 by Ga to ·OH, thus promoting the free radical polymerization reaction.

[0114] According to the above polymerization mechanism, the gelation time of the eutectic gel is related to the concentrations of both DAX and LM in the DAX / LM dispersion. As Figure 9As shown, as the DAX concentration increased from 2 wt% to 8 wt%, the gelation time shortened from 98 s to 44 s, confirming that the redox reaction between DAX and LM played an important role in accelerating free radical polymerization. Similarly, the higher the LM concentration, the shorter the gelation time. In addition, it can be observed that the average gelation time of DES under the initiation of the D5L3 system was only 57 s, while the gelation time required for the same proportion of AM aqueous solution was as long as 198 s, which was mainly attributed to the good hydrogen bond accepting ability of the ChCl molecules in DES.

[0115] The further explanations are as follows:

[0116] As Figure 10 a shows, the DLPD eutectic gel with a length of about 1 cm can be stretched to more than 10 cm, showing excellent tensile properties. To quantify the mechanical properties of the DLPD eutectic gel, the stress-strain curve was detected by a universal testing machine and systematically analyzed. As Figure 10 c shows, the concentration of LM has a significant effect on the mechanical strength and strain of the DLPD eutectic gel. At a DAX concentration of 5 wt%, when the LM concentration increased from 1 wt% to 3 wt%, the tensile strength and elongation at break of the eutectic gel increased to 95.8 kPa and 2860% respectively, mainly due to the energy dissipation effect of LM nanodroplets and the increase in physical cross-linking sites provided by LM nanodroplets inside the eutectic gel;

[0117] Among them, LM presents a flowing state under stress ( Figure 10 b), which helps to improve the toughness and ductility of the eutectic gel. However, when the LM concentration is further increased to 5 wt%, the mechanical properties of the eutectic gel decrease significantly;

[0118] The specific reasons can be attributed to:

[0119] 1) High concentrations of LM will generate excessive free radicals, resulting in shorter polymer chains or less cross-linking, thus reducing the binding strength;

[0120] 2) Excessive LM concentration in the eutectic gel matrix is prone to phase separation;

[0121] In addition, the mechanical properties of the DLPD eutectic gel are also affected by the DAX concentration. As Figure 10 d shows, with the LM concentration fixed at 3 wt%, as the DAX concentration increased from 2 wt% to 8 wt%, the tensile strength of the eutectic gel increased significantly from 62.1 kPa to 130.7 kPa, which was mainly because DAX to Ga 3+The reduction effect is enhanced, promoting the stabilization of Ga to ·OH and its reaction with double bonds, thus accelerating the rate of free radical polymerization reaction and increasing the crosslinking density. The elongation at break of the DLPD eutectic gel shows a trend of increasing first and then decreasing with the increase of DAX concentration, and the elongation at break reaches 2860% when the DAX concentration is 5 wt%.

[0122] Therefore, by adjusting the DAX concentration, the mechanical properties of the DLPD eutectic gel can be adjusted within a wide range. When the DAX and LM concentrations are 5 wt% and 3 wt% respectively, the toughness of the DLPD eutectic gel reaches 2.38 MJ m -3 ( Figure 10 e,f), which is significantly higher than that of the DLPAM hydrogel ( Figure 10 g);

[0123] In addition, at 100% strain, a 200-cycle continuous tensile-release test was carried out on the DLPD-D5L3 eutectic gel to test its fatigue resistance ( Figure 10 h), and the results show that except for the first cycle, the offset of the remaining cycle curves during the cyclic tensile-release process is extremely small, indicating that the eutectic gel has excellent fatigue resistance.

[0124] In summary, the DLPD eutectic gel prepared in the present invention exhibits excellent self-healing performance due to the existence of a large number of hydrogen bond interactions. As shown in Figure 11 a, after cutting the eutectic gel sample in half from the middle, the cut interface was re-spliced, and it was left at room temperature for a period of time to spontaneously heal. The self-healing performance of the eutectic gel was evaluated in terms of mechanical properties. The results show that for the sample that was directly re-spliced and self-healed for 24 h after cutting, its tensile strength almost completely recovered, but the strain only recovered to about 20% of the initial state ( Figure 11 c), indicating that its self-healing effect is not ideal;

[0125] In the present invention, it was found that the DLPD eutectic gel rich in physical connections is easily affected by water. After soaking the cut of the gel in water, due to the hydrogen bond competition of water, the hydrogen bond network in the eutectic gel matrix becomes loose, and then the cut surface becomes sticky, which is beneficial to the self-healing of the eutectic gel. Therefore, water was used as an additive to further study its synergistic effect on the self-healing performance of the eutectic gel. The results show that the water-assisted self-healing eutectic gel exhibits excellent mechanical properties ( Figure 11 b), and both the tensile stress and strain increase with the prolongation of the healing time;

[0126] In addition, after 24 h of healing, the strain of the eutectic gel reaches 2480% (self-healing efficiency 87%) ( Figure 11d). Moreover, the toughness has almost recovered to its original state. The self-healing behavior of the eutectic gel can be attributed to the abundant interfacial hydrogen bonding in the gel network. When the fractured eutectic gel is re-docked, due to the diffusion and interaction of polymer chains and free ions on the contact surface, the hydrogen bond network can be reconstructed. Figure 11 e).

[0127] In addition, in the examples, the weight change of the DLPD eutectic gel exposed to room temperature environment was also monitored to evaluate its water retention property.

[0128] As Figure 12 shown in a, the DLPD eutectic gel can still maintain the same morphology and flexibility as the initial state after being exposed to air for 30 days. At the same time, the eutectic gel only lost 9.8% of its initial weight after being placed for 12 h. Figure 12 b);

[0129] The water resistance of the DLPD eutectic gel is mainly attributed to the participation of water molecules in the hydrogen bond network assembly of PDES. Figure 5 a), which makes it difficult for water to lose. However, with the extension of the exposure time, the weight of the eutectic gel gradually increases and returns to 99.7% of the initial weight after 30 days, which is mainly related to the hygroscopicity of the ChCl component in PDES.

[0130] In contrast, due to the inevitable water volatilization, the weight of the DLPAM hydrogel decreased by 63.6% after being exposed for 12 h, and its appearance shrank significantly and lost flexibility. Therefore, it does not have long-term usability. In addition, TG was used to further study the thermal stability of the DLPD eutectic gel.

[0131] As ​ shown in c, at 150 °C, the weight loss of the DLPD eutectic gel is only 13%, while the weight loss of the DLPAM hydrogel reaches 35%, indicating that the DLPD eutectic gel has excellent thermal stability and applicability in a wide temperature range. Therefore, based on the rich hydrogen bond network and hydration properties of PDES, the DLPD eutectic gel has higher environmental stability than the DLPAM hydrogel.

[0132] In further designs, it also includes putting the prepared gel in the refrigerator overnight to evaluate its antifreeze performance.

[0133] As ​ shown in d, due to the formation of ice crystals, the DLPAM hydrogel loses flexibility at -26 °C; while at this temperature, no ice crystals appear on the surface of the DLPD eutectic gel, and it can still maintain good flexibility. This antifreeze property is attributed to the participation of water molecules in the hydrogen bond network assembly in the eutectic gel. The antifreeze performance of the gel was further studied by DSC, as ​As shown in e, the DSC curve of the DLPAM hydrogel showed an obvious exothermic peak at -17.3 °C, indicating that the hydrogel was frozen at this temperature. However, no peak was observed in the DSC curve of the DLPD eutectic gel, indicating that the eutectic gel did not freeze in the temperature range of -80 to 20 °C, confirming its excellent anti-freezing performance. Traditional anti-freezing hydrogels usually require the replacement of most of the water with organic solvents to inhibit freezing under low-temperature conditions. However, the DLPD eutectic gel prepared in this study does not require a solvent replacement step, and its inherent anti-freezing performance is beneficial to its application in extreme environments;

[0134] In further design, in the present invention, based on the ability of LM nanodroplets to convert light energy into heat energy, the prepared DLPD eutectic gel exhibits excellent photothermal performance;

[0135] As ​ shown in a, under the simulated sunlight irradiation of 1000 W m -2 , the temperature of the DLPD eutectic gel containing LM nanodroplets gradually increased from 27.5 °C to 44.6 °C within 5 min. When the light intensity was increased to 2000 W m -2 , the heating rate of the eutectic gel increased significantly due to the absorption of more light energy ( ​ b), and the surface temperature could rise to 54.4 °C within 5 min. Therefore, the DLPD eutectic gel exhibits excellent photothermal characteristics, making it promising in the fields of photothermal therapy, solar energy storage and utilization, etc.

[0136] In further design, in the present invention, the DLPD eutectic gel was co-cultured with mouse fibroblasts (L929) at concentrations of 10, 25, and 50 μg mL -1 for 24 h and 48 h to further explore its biocompatibility. As ​ shown in a, all sample groups at different concentrations showed a cell survival rate of more than 95%. According to the grading standard, the cytotoxicity of the DLPD eutectic gel was grade 0, indicating no cytotoxicity; the live / dead cell double staining method (Calcein-AM / PI) was used to further determine the cell survival rate, and the results are as ​ shown in b. After co-culture at a eutectic gel concentration of 50 μg mL -1 for 24 h and 48 h, no PI-stained positive cells were observed, and the cell density was almost the same as that of the control group, indicating that the DLPD eutectic gel has no effect on cell proliferation and has excellent in vitro biocompatibility.

[0137] In further design, in the present invention, the combination of LM and DES endows the DLPD eutectic gel with excellent electrical conductivity and strain sensitivity;

[0138] The details are as follows: First, the conductivity of DLPD eutectic gels with different concentrations of LM was studied by electrochemical impedance spectroscopy (EIS) ​ a), and the results showed that the impedance value of the eutectic gel decreased with the increase of LM concentration; further, the conductivity of each eutectic gel was calculated, and the results are as ​ shown in b. When the LM concentration was 1 wt%, the conductivity was only 0.18 S m -1 , mainly because fewer conductive networks were formed inside the eutectic gel, and at this time, the conductivity mainly depended on the mobility of chloride ions and choline cations;

[0139] As the LM concentration increased from 1 wt% to 5 wt%, the conductivity of the eutectic gel increased significantly to 1.46 S m -1 , mainly because a denser conductive network and a stronger quantum tunneling effect were formed inside the eutectic gel. Based on the excellent mechanical properties and high conductivity, the DLPD-D##L3 eutectic gel was selected for the sensing performance test. As ​ shown in c, in the strain range of 1% - 500%, the relative resistance change of the eutectic gel changed with the increase of the tensile strain during the cyclic tensile - release process;

[0140] Among them, when the external stress was released, the resistance of the eutectic gel almost completely returned to the initial state, and significant stability and reversibility were shown in both the small - strain and large - strain ranges. It could be clearly observed that the relative resistance change of the DLPD eutectic gel showed a monotonically increasing trend during uniform stretching ​ d). On this basis, the strain sensitivity was calculated by piece - wise linear fitting, denoted by GF (the slope of the relative resistance change - tensile strain curve);

[0141] The results showed that the GF values of the eutectic gel were 1.54, 2.88, and 4.08 in the strain ranges of 0% - 600%, 600% - 1200%, and 1200% - 2000% respectively, indicating that the DLPD eutectic gel had the characteristics of a wide sensing range and high strain sensitivity. As shown in Table 2, comparing the DLPD eutectic gel with other reported gel sensors in terms of conductivity and strain sensitivity, it can be seen that the overall performance of the DLPD eutectic gel sensor is more excellent; Table 5.2 Comparison of the conductivity and GF values of the DLPD eutectic gel with other reported gel materials.

[0142]

[0143]

[0144] Table 2

[0145] In a further design, in the present invention, based on the high sensitivity of DLPD low eutectic gel, it is further applied to human motion monitoring.

[0146] like ​ As shown in Figure a, the DLPD eutectic gel-based strain sensor can accurately monitor bending and stretching behaviors and respond to different bending angles in real time through changes in relative resistance. Similarly, the sensor can accurately monitor the cyclic bending of the wrist and knee ( ​ b,c). In addition, DLPD sensors can also be used to recognize complex gestures ( ​ d). The relative resistance change-time curve shows regular and stable signals for different hand gestures (counting down from 5 to 0). When making the "3" gesture, the signal strength of the middle finger, ring finger, and pinky finger remains unchanged, while the signal strength of the remaining two fingers increases due to joint bending. Therefore, the DLPD eutectic gel sensor shows excellent application prospects in human motion monitoring and wearable electronics.

[0147] In a further design, the present invention not only detects large tensile mechanical deformation, but also monitors small pressure effects. When the finger repeatedly presses on the surface, the DLPD sensor shows a stable response signal ( ​ a). At the same time, the DLPD sensor can also identify pressure changes during handwriting ( ​ b). When different letters such as "A", "B", "C" and "D" are written on the sensor surface, different signal patterns are generated ( ​ c, d), and the regularity and reversibility of the relative resistance change signal during repeated handwriting indicate that the DLPD strain sensor has excellent writing recognition ability; ​ As shown in Figures e and f, the DLPD sensor can also recognize words (such as "xylan" and "yes"). Therefore, by monitoring the tiny changes in the electrical signal caused by changes in writing force and direction, the sensor can identify the written content, making it potentially applicable in the field of handwriting anti-counterfeiting.

[0148] In a further design, the present invention also includes further studying the temperature sensing performance of the DLPD eutectic gel in view of its physical cross-linking characteristics;

[0149] First, the effect of temperature on conductivity was studied using EIS. The results showed that the conductivity increased almost linearly with increasing temperature ( ​ a). Among them, the conductivity of the DLPD-D5L3-based sensor increased most significantly, from 0.74S m -1 (30℃) increased to 4.01S m -1 (90℃).

[0150] The increase in conductivity is mainly attributed to the following two reasons:

[0151] 1) The increase in temperature leads to an increase in the mobility of ions;

[0152] 2) The increase in temperature causes the hydrogen bond crosslinking to loosen, thereby expanding the spatial migration range of ions. Meanwhile, the resistance of the DLPD temperature sensor decreases with the increase in temperature ( ​ b), and the resistance decreases significantly by one order of magnitude as the temperature increases from 30 °C to 90 °C.

[0153] Among them, the relative resistance change of the temperature sensor is significantly affected by temperature ( ​ d), and the largest resistance change amplitude is observed especially in the temperature range of 30 - 40 °C, indicating the highest sensitivity to temperature in this range. Based on this, the relationship between resistance and temperature was further studied and can be expressed by the following formula:

[0154]

[0155] where, R is the resistance at temperature T, R0 is the resistance at T = ∞, Ea is the activation energy, k is the Boltzmann constant, and B is the thermal index. Formula (5 - 4) can be further evolved into

[0156]

[0157] It can be seen that there is a linear relationship between ln(R) and 1 / T. As ​ shown in c, by linearly fitting the measured data, it is found that there is a good linear relationship between ln(R) and 1 / T for all samples. And the slope of the fitting straight line (corresponding to the B value) changes slightly with the increase in the LM concentration.

[0158] According to the formula the Ea can be calculated using the following formula:

[0159] E a = 2kB

[0160] The temperature coefficient of resistance (TCR) can be defined as:

[0161]

[0162] Combining formula (5 - 5) and formula (5 - 7), the relationship between TCR and the thermal index is:

[0163]

[0164] The TCR value of the DLPD temperature sensor was calculated at room temperature (300K). The negative sign of the TCR value indicates that the temperature sensor has a negative temperature coefficient characteristic, as ​As shown in Figure e, when the LM concentration is 1wt%, the B value reaches 4811K; when the LM concentration is 5wt%, the B value decreases to 4370K. At the same time, Ea and TCR also show the same trend as the thermal index. TCR is usually used to evaluate the thermal response sensitivity of temperature sensors. The results show that the TCR value of DLPD temperature sensor is 4.80%K -1 ~5.35%K -1 , exceeding the TCR values of most reported temperature sensors ( ​ f);

[0165] In summary, the responsiveness and stability of the DLPD temperature sensor during continuous use were further studied through cyclic testing. ​ As shown in the figure, the DLPD sensor can sense the alternating hot and cold air generated by the hair dryer in real time. Subsequently, the low-melting gel was placed in an alternating temperature environment of 30℃ and 40℃. The results showed that the relative resistance change had excellent repeatability and stability within three cycles ( ​ b), confirming the reliability of the DLPD temperature sensor. In addition, the DLPD sensor has an obvious real-time resistance response to the heat generated by human breathing, indicating that it has excellent instantaneous temperature recognition capability (19c). At the same time, the DLPD temperature sensor shows extremely high sensitivity and can quickly identify small temperature changes, such as ​ As shown in Figure d, within a small range of 35 to 42°C, the relative resistance change signal of the DLPD sensor can reflect small temperature changes in real time (temperature interval is 1°C), so it has application potential in the field of human health monitoring.

[0166] In the present invention, water-soluble DAX rich in functional aldehyde groups is prepared by selective oxidation of xylan with periodate. Based on the surface anchoring effect of DAX, LM forms nanodroplets with a core-shell structure under the action of high-frequency ultrasound and can be stably dispersed in water for a long time.

[0167] In the present invention, a novel eutectic gel is prepared by rapidly initiating DES free radical polymerization at room temperature through a DAX / LM dispersion system. No additional chemical initiator or cross-linking agent is required during the process. Due to the stabilizing effect and reducing properties of DAX, the surface reactivity of LM is increased, thereby accelerating the free radical polymerization reaction rate and improving the cross-linking density.

[0168] In the present invention, the eutectic gel formed by physical crosslinking has super stretchability (2860%), self-healing properties (healing efficiency of 87%), high conductivity (0.72S m -1 ), photothermal properties and biocompatibility. Due to the participation of water molecules in the hydrogen bond network assembly of PDES, the eutectic gel exhibits excellent resistance to water loss and freezing.

[0169] In the present invention, when the eutectic gel is used as a resistive strain sensor, it has high sensitivity (GF = 4.08), and can be used to identify large-amplitude human movements and the writing strokes of minute strains; when used as a temperature sensor, it has excellent thermosensitivity (TCR = 5.35% K -1 ), and can be used for temperature identification and health monitoring. Therefore, the eutectic gel has broad application prospects in the field of flexible intelligent wearable electronic devices.

[0170] In addition, in the present invention, by using dialdehyde xylan (DAX) solution to stabilize LM nano-droplets, and using the DAX / LM dispersion to rapidly initiate the polymerization reaction of ChCl / AM in one step to prepare the DLPD eutectic gel, there is no need to use traditional radical initiators and cross-linking agents during the preparation process. Therefore, this method is environmentally friendly. DAX containing reducing aldehyde groups plays a key role in accelerating the radical polymerization reaction and improving the mechanical properties of the gel. The rich hydrogen bond network in the prepared eutectic gel endows it with super stretchability and self-healing properties. Since H2O participates in the strong hydrogen bond assembly, the eutectic gel has excellent dehydration resistance and freeze resistance. In addition, the combination of LM nano-droplets and PDES not only enhances the conductivity of the eutectic gel, but also endows the eutectic gel with excellent strain sensitivity and temperature sensitivity, making it have application potential as a multifunctional sensor in human movement recognition and health monitoring.

[0171] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for rapidly initiating the polymerization of a deep eutectic solvent to prepare a deep eutectic gel, characterized in that, Specifically, it includes the following steps: Step 1: First, using industrial xylan as the raw material, dialdehyde xylan DAX is prepared by the periodate oxidation method as follows: Add 20.0 g of industrial xylan to 800 mL of deionized water, stir until evenly dispersed to form a suspension, then weigh 50.0 g of NaIO4 and add it to the above suspension. Then, stir and react at room temperature in the dark for different times. After the reaction is completed, slowly add 12 mL of ethylene glycol to the reaction system to terminate the reaction; Step 2: Transfer the reaction solution in Step 1 to a regenerated cellulose dialysis bag with a molecular weight cut-off of 3500 Da, dialyze in deionized water for four days, and the dialyzed aqueous solution is concentrated by rotary evaporation and freeze-dried to obtain the final product, dialdehyde xylan; Step 3: Preparation of the DAX / nanodroplet dispersion: Add different masses of DAX to deionized water to prepare DAX solutions with different concentrations. Then, add different masses of nanodroplets to the DAX solutions so that the mass concentration ratios of the nanodroplets in the mixed system are 1 wt%, 2 wt%, 3 wt%, and 5 wt% respectively. Use an ultrasonic reactor to treat for 30 min at a power of 600 W and in an ice-water bath to obtain DAX / nanodroplet dispersions with different concentrations. The nanodroplets are a gallium-indium alloy of liquid metal; Step 4: Preparation of the DLPD eutectic gel: First, vacuum dry choline chloride at 60 °C for 6 h to remove moisture. Mix acrylamide and choline chloride in a closed glass bottle at a molar ratio of 2:1, place it in a 60 °C water bath and stir for 1 h to form a homogeneous and transparent eutectic DES. Then, take 2.0 mL of DES, add 1.0 mL of the DAX / nanodroplet dispersion and mix evenly. Subsequently, quickly transfer the obtained mixture to a polytetrafluoroethylene mold, let it stand at room temperature and spontaneously polymerize to finally obtain the DLPD eutectic gel.

2. A method for rapidly initiating the polymerization of a deep eutectic solvent to prepare a deep eutectic gel according to claim 1, characterized in that, In Step 1, stir and react at room temperature in the dark for different times, and the times are: 24 h, 36 h, and 48 h respectively.

3. A method for rapidly initiating the polymerization of a deep eutectic solvent to prepare a deep eutectic gel according to claim 1, characterized in that, In Step 3, in the DAX solutions with different concentrations prepared, the concentrations of the DAX solutions are: 2 wt%, 5 wt%, and 8 wt% respectively.

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