Antifreeze and anti-swelling starch-based nanocomposite hydrogel and preparation method and application thereof

Abstract

The present invention discloses a preparation method of an anti-freezing and anti-swelling starch-based nanocomposite hydrogel. The present invention includes the following steps: a) preparing a graphene oxide suspension; b) preparing a starch / polyethylene glycol / graphene oxide mixed sol; c) preparing a starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol; d) bubble treatment of the starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol; e) preparing an anti-freezing and anti-swelling starch-based nanocomposite hydrogel product. The anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in this application is a starch-based hydrogel with both anti-swelling, anti-freezing, strong stretchability and high conductivity, which can effectively solve the problem that it is difficult to balance anti-swelling property, anti-freezing property, stretchability and conductivity at present.

Description

Technical Field

[0001] It relates to the field of preparation of starch-based functional materials and the field of flexible electronics, and specifically relates to an antifreeze and anti-swelling conductive nanocomposite hydrogel, a preparation method thereof and an application thereof. Background Art

[0002] Hydrogel is a hydrophilic three-dimensional porous polymer material with good flexibility and adjustable properties, and has important application potential in the fields of flexible wearable sensors, electronic skin, tissue engineering, etc. Due to strong hydrophilicity, traditional hydrogels show obvious swelling phenomena in water, which has an adverse impact on the properties and applications of the gels; moreover, most current hydrogels are chemically cross-linked by traditional petroleum derivatives. With the increasing shortage of resources and environmental problems, it is urgent to develop "green" hydrogels with excellent properties based on biomass resources. Starch is one of the most abundant biopolymers, with characteristics such as being renewable, low-cost, biocompatible, and degradable. Starch contains a large number of hydroxyl groups, has strong hydrophilicity and cross-linking ability, and is a good material for preparing hydrogels. However, pure starch hydrogels are extremely hygroscopic and swell in water, and will freeze and become brittle at sub-zero temperatures. At the same time, their tensile properties and conductivity are very poor, which greatly limits the application of starch hydrogels in actual environments such as humid or underwater and low temperatures.

[0003] In the prior art, Zeng et al. prepared a corn starch / polyacrylamide double-network hydrogel, with its elongation at break (135%), tensile strength (about 60 kPa) and conductivity (0.27 S·m -1) are relatively low, (ShengZeng, Junyao Zhang, Guoqing Zu, Jia Huang, Transparent, flexible, and multifunctional starch-based double-network hydrogels as high-performance wearable electronics, Carbohydrate Polymers, 267 (2021) 118198); Lu et al. introduced glycerol and CaCl2 into the starch / PVA mixture to prepare a starch-based organohydrogel (J. Lu, J. Gu, O. Hu, Y. Fu, D. Ye, X. Zhang, Y. Zheng, L. Hou, H. Liu, X. Jiang, Highly tough, freezing-tolerant, healable and thermoplastic starch / poly(vinyl alcohol) organohydrogels for flexible electronic devices, J. Mater. Chem. A 9 (2021) 18406-18420.), but due to the use of organic solvents, the conductivity (1 S·m -1 ) is still very low; moreover, the above-mentioned literature does not solve the anti-swelling and anti-freezing problems of starch hydrogels. Therefore, it is very necessary to design a starch-based hydrogel with anti-swelling, anti-freezing, strong stretchability and high conductivity. Summary of the Invention

[0004] In order to make up for the deficiencies of the prior art, the present invention provides an anti-freezing, anti-swelling conductive nanocomposite hydrogel, its preparation method and application.

[0005] The technical solution of the present invention is as follows:

[0006] A preparation method of an anti-freezing, anti-swelling starch-based nanocomposite hydrogel, comprising the following steps:

[0007] a) Prepare a graphene oxide suspension: Mix graphene oxide powder, disodium hydrogen phosphate, sodium dihydrogen phosphate with deionized water, and ultrasonicate for 1 hour under sealed conditions to obtain a graphene oxide suspension;

[0008] b) Prepare a starch / polyethylene glycol / graphene oxide mixed sol: Add starch and polyethylene glycol to the graphene oxide suspension, and under sealed conditions, heat and stir in a water bath until the starch and polyethylene glycol are completely dissolved to obtain a starch / polyethylene glycol / graphene oxide mixed sol;

[0009] c) Preparation of starch / polyethylene glycol / graphene oxide / ionic liquid hybrid sol: Add ionic liquid to the starch / polyethylene glycol / graphene oxide hybrid sol, heat and stir until the two are fully mixed to obtain the starch / polyethylene glycol / graphene oxide / ionic liquid hybrid sol;

[0010] d) Bubble treatment of the starch / polyethylene glycol / graphene oxide / ionic liquid hybrid sol: Continuously heat the starch / polyethylene glycol / graphene oxide / ionic liquid hybrid sol for 1 hour, and then immediately take it out and place it in a vacuum chamber to remove bubbles;

[0011] e) Preparation of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel product: Immediately pour the starch / polyethylene glycol / graphene oxide / ionic liquid hybrid sol with removed bubbles into a mold, and then perform cyclic freeze-thawing and demoulding to obtain the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel product.

[0012] Preferably, the graphene oxide accounts for 0.01 - 0.1% of the total weight of all components; deionized water accounts for 41.5 - 80% of the total weight of all components; the total amount of disodium hydrogen phosphate and sodium dihydrogen phosphate accounts for 1.4 - 1.6% of the total weight of all components; starch accounts for 4% - 13% of the total weight of all components; polyethylene glycol accounts for 4% - 13% of the total weight of all components; ionic liquid accounts for 4% - 41.5% of the total weight of all components; all components in this application refer to graphene oxide powder, disodium hydrogen phosphate, sodium dihydrogen phosphate, deionized water, starch, polyethylene glycol, and ionic liquid.

[0013] Preferably, in step b), the starch is potato starch, glutinous rice starch or cassava starch.

[0014] Preferably, in step b), the time for water bath heating and stirring is 2 - 3 hours.

[0015] Preferably, in step c), the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium chloride.

[0016] Preferably, in step c), the heating and stirring time is 1 - 2 hours.

[0017] Preferably, in step e), the cyclic freeze-thawing means placing the mold containing the starch / polyethylene glycol / graphene oxide / ionic liquid hybrid sol in a low-temperature freezer for a certain time, then thawing at room temperature, and repeating the processes of freezing and thawing cyclically.

[0018] Preferably, in step e), the freezing time is 2 - 5 hours; the freezing temperature is -10 - -40 °C, and the number of cyclic freeze-thawing times is 1 - 5 times.

[0019] Preferably, in step e), the freezing time is 3 hours, and the freezing temperature is -20 to -30 °C; the number of cycles of freeze-thaw is 3 to 4 times.

[0020] An anti-freezing and anti-swelling starch-based physically crosslinked hydrogel prepared by the method for preparing an anti-freezing and anti-swelling starch-based nanocomposite hydrogel as described above.

[0021] The application of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel in the fields of flexible wearable sensors, electronic skin or tissue engineering.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The purpose of this application is to prepare an anti-freezing and anti-swelling starch-based nanocomposite hydrogel with anti-swelling, anti-freezing, strong stretchability and high conductivity; in this application, an anti-freezing and anti-swelling starch-based nanocomposite hydrogel is prepared by nanocomposite methods such as double network, nanocomposite and electrostatic interaction, avoiding the disadvantages brought by chemical reactions. The anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in this application is a starch-based hydrogel with both anti-swelling, anti-freezing, strong stretchability and high conductivity, which can effectively solve the problem that it is difficult to balance anti-swelling property, anti-freezing property, stretchability and conductivity at present.

[0024] In the present invention, after adding starch and polyethylene glycol to the graphene oxide suspension to obtain a starch / polyethylene glycol / graphene oxide hybrid sol, an ionic liquid is added to the starch / polyethylene glycol / graphene oxide hybrid sol. Through a nanocomposite method, a novel anti-freezing and anti-swelling starch-based nanocomposite hydrogel is prepared, with a simple process and good environmental friendliness. The graphene oxide and ionic liquid in this application have a synergistic anti-swelling performance. On the one hand, the ion-ion interaction between the cations and anions of the ionic liquid reduces the osmotic pressure of the gel, and the ionic liquid forms more hydrogen bonds with starch and polyethylene glycol, enhancing the internal network. On the other hand, the lamellar structure and oxygen-containing functional groups of graphene oxide interact with starch and polyethylene glycol, making the gel structure more dense, reducing the exposure degree of the molecular chains of starch and polyethylene glycol in water, and thus preventing the infiltration of a large number of water molecules. In addition, the use of graphene oxide and ionic liquid in this application also improves the compatibility of starch / polyethylene glycol, increases the hydrogen bond interaction between starch / polyethylene glycol. More importantly, the ionic liquid used in this application, 1-ethyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium chloride, belongs to molten salts with a relatively low freezing point. By interacting with water molecules, it reduces the freezing point of the hydrogel and improves the anti-freezing performance of the hydrogel. Moreover, the oxygen-containing groups on graphene oxide (i.e., hydroxyl, epoxy, and carboxyl groups), and the cations and anions of the ionic liquid (i.e., 1-ethyl-3-methylimidazolium cation, tetrafluoroborate anion, or chloride ion) connect starch and polyethylene glycol through hydrogen bonds, effectively improving the tensile properties and stability of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel. In addition, graphene oxide in this application has good electronic conductivity, and the 1-ethyl-3-methylimidazolium cation, tetrafluoroborate anion, or chloride ion in the ionic liquid also has good ionic conductivity, jointly improving the conductivity of the hydrogel. The anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in this application can sensitively and real-time monitor joint activities and has a rapid response signal for the index finger and wrist joints. Due to the excellent tensile properties and conductivity of the anti-freezing and anti-swelling conductive nanocomposite hydrogel, when using the anti-freezing and anti-swelling conductive nanocomposite hydrogel prepared in this application to prepare a wearable sensor, a wearable sensor with higher sensitivity can be obtained. That is to say, the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared by the present invention provides a basis for the development of high-performance and multifunctional flexible wearable devices, especially suitable for preparing flexible wearable sensors for monitoring requirements in underwater and low-temperature environments. In addition, the anti-freezing and anti-swelling conductive nanocomposite hydrogel prepared in this application is also suitable for applications in the fields of electronic skin or tissue engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Figure A in shows a physical photograph of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 1.Figure 1 Figure B in this is the microscopic scanning electron microscope image of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1;

[0026] Figure 2 This is the curve of the swelling rate of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1 changing with time;

[0027] Figure 3 This is the differential scanning calorimetry curve of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1;

[0028] Figure 4 Figure A in this is the physical diagram of the circuit with an LED bulb connected to the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1, Figure 4 Figure B in this is the electrochemical impedance spectroscopy diagram of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1;

[0029] Figure 5 This is the tensile curve diagram of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1;

[0030] Figure 6 This is the sensitivity curve diagram of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1;

[0031] Figure 7 This is the diagram of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1 for real-time monitoring of wrist joint movement;

[0032] Figure 8 This is the diagram of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1 for real-time monitoring of wrist joint movement underwater.

[0033] Figure 9 This is the curve of the swelling rate of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 2 changing with time;

[0034] Figure 10 This is the differential scanning calorimetry curve of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 2;

[0035] Figure 11 This is the electrochemical impedance spectroscopy diagram of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 2;

[0036] Figure 12 This is the tensile curve diagram of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 2;

[0037] Figure 13 This is the diagram of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 2 for real-time monitoring of finger joint movement underwater;

[0038] Figure 14 The change curve of the swelling ratio of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 3 with time;

[0039] Figure 15 The differential scanning calorimetry curve of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 3;

[0040] Figure 16 The electrochemical impedance spectrogram of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 3;

[0041] Figure 17 The tensile curve of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 3;

[0042] Figure 18 The real-time monitoring diagram of wrist joint movement underwater of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 3. Detailed implementation manners

[0043] The raw materials used in this application include: graphene oxide powder (purity 99%), potato starch, glutinous rice starch, 1-ethyl-3-methylimidazolium tetrafluoroborate (purity 99%), 1-ethyl-3-methylimidazolium chloride (purity 99%), polyethylene glycol (purity 99%), disodium hydrogen phosphate (analytical pure), sodium dihydrogen phosphate (analytical pure), deionized water. The mold used in this application is a laboratory polytetrafluoroethylene hydrogel test mold, namely a PTFE dumbbell tensile impact bending mold. The above-mentioned raw materials and molds are all purchased from the market and used directly.

[0044] Example 1:

[0045] A preparation method of a freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel, comprising the following steps:

[0046] Step a): Add 0.012 g of graphene oxide powder, 0.21 g of disodium hydrogen phosphate and 0.18 g of sodium dihydrogen phosphate into a conical flask containing 15 mL of deionized water, seal it with plastic wrap, and ultrasonicate for 1 hour to obtain a graphene oxide suspension;

[0047] Step b): Add 2.0 g of potato starch and 2.0 g of polyethylene glycol into the graphene oxide suspension prepared in step a), keep it at a constant temperature of 90 °C in a water bath, and stir at a stirring speed of 400 r / min for 2 hours until the mixture is completely dissolved to obtain a graphene oxide / potato starch / polyethylene glycol mixed sol;

[0048] Step c): Add 5 g of 1-ethyl-3-methylimidazolium tetrafluoroborate to the graphene oxide / potato starch / polyethylene glycol mixed sol, and continue to stir at a stirring speed of 400 r / min at 90 °C for 1 hour to fully mix and interact 1-ethyl-3-methylimidazolium tetrafluoroborate with starch / polyethylene glycol / graphene oxide, obtaining a starch / polyethylene glycol / graphene oxide / 1-ethyl-3-methylimidazolium tetrafluoroborate sol;

[0049] Step d): Continue to heat the starch / polyethylene glycol / graphene oxide / 1-ethyl-3-methylimidazolium tetrafluoroborate sol for 1 hour without stirring, and then immediately take it out and place it in a vacuum box to remove the bubbles in the sol;

[0050] Step e): Immediately pour the starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol with removed bubbles into a mold, freeze it at -30 °C for 3 hours, and then thaw it at room temperature for 1 hour. Repeat this freeze-thaw cycle process 3 times to strengthen the interaction between the gel components, and finally demold to obtain an antifreeze and anti-swelling starch-based nanocomposite hydrogel. This antifreeze and anti-swelling starch-based nanocomposite hydrogel consists of a dumbbell-shaped part and two square parts. Among them, the two square parts are respectively fixedly connected at both ends of the dumbbell-shaped part, and the two square parts and the dumbbell-shaped part are integrally formed. The size of the dumbbell-shaped part is 12 cm in length, 1 cm in width, and 0.3 cm in thickness. The sizes of the two square parts are the same, and the size of each square part is 2 cm in width and 0.4 cm in thickness, as Figure 1 shown in Figure A.

[0051] Characterize and analyze the microscopic morphology, anti-swelling performance, antifreeze performance, conductivity and tensile performance of the antifreeze and anti-swelling starch-based nanocomposite hydrogel prepared in Example 1. The results are as follows:

[0052] Analysis of the microscopic morphology of the antifreeze and anti-swelling starch-based nanocomposite hydrogel: Brittle fracture the antifreeze and anti-swelling starch-based nanocomposite hydrogel in liquid nitrogen, then freeze-dry it, sputter gold, and then observe its microscopic morphology using a scanning electron microscope, as Figure 1 shown in Figure B. As can be seen from Figure 1 Figure B, the antifreeze and anti-swelling starch-based nanocomposite hydrogel is macroscopically intact and plastic, and microscopically composed of a dense structure.

[0053] Analysis of the anti-swelling performance of the antifreeze and anti-swelling starch-based nanocomposite hydrogel: Immerse the antifreeze and anti-swelling starch-based nanocomposite hydrogel in water, weigh it after taking it out at different times, and then use the formula SR = (W t -W i ) / W i ×100% to calculate the swelling ratio of the hydrogel, where Wt is the mass of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel taken out after being immersed in water for different times, W i is the initial mass of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel without being immersed in water. In this application, the change in the swelling rate of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel within the time range of 0 to 310 hours of immersion in water was analyzed, and the analysis results are as follows Figure 2 shown. From Figure 2 , it can be seen that the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel has a very fast water absorption rate in the first 2 hours. However, after 4 hours, the swelling rate of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel begins to decline. By the end of 310 hours, the swelling rate of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1 is only 4.3%. Therefore, the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1 has excellent swelling resistance performance

[0054] Analysis of the freeze resistance of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel: Figure 3 is the differential scanning calorimetry curve of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel. As can be seen from Figure 3 , the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel starts to freeze at -10°C, reaches the freezing point at -15°C, and completes the freezing process at -24°C Figure 3 , which fully demonstrates that the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1 has excellent freeze resistance performance

[0055] Analysis of the conductivity of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel: The conductivity of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1 was measured using an electrochemical workstation. The test method is as follows: The square part of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel was tightly clamped with two copper sheets, and the copper sheets were connected to the electrochemical workstation with the wires of the conductive clip. First, the open circuit potential of the circuit was measured to be 0V. Then, the electrochemical impedance spectroscopy function was turned on, the potential was set to 0V, and the frequency change range was 1 - 10 6 Hz, and a scan was performed to obtain the electrochemical impedance spectroscopy diagram, as shown in Figure B of Figure 4 . From the curve B in Figure 4 , the intersection point of the curve and the abscissa is read as the resistance R. Then, the conductivity of the hydrogel was calculated using the formula σ = L / RA, where L is the thickness of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel in meters, and A is the contact area between the copper sheet and the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel in square meters 2 . In addition, from the curve B in Figure 4 , it can also be seen that the resistance of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel is 5.0Ω. Then, according to the above formula, the conductivity σ of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel prepared in Example 1 can be calculated to be 2.0 S·m-1 In addition, in order to visually verify that the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel has electrical conductivity, this application specifically connects it to a circuit with an LED bulb, as Figure 4 shown in Figure A of Figure 4 Figure A, it can be seen that connecting the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel to a circuit with an LED bulb can light up the LED bulb, which also proves that the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel has electrical conductivity.

[0056] Analysis of the tensile properties of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel: The tensile properties of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel were measured using a digital tensile tester. Specifically, the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel was fixed in the middle of the clips of the tensile tester, and the tensile rate was set to 100 mm / min to obtain a tensile curve, as Figure 5 shown. From Figure 5 it can be seen that the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel has excellent tensile properties. Among them, the tensile strength of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel is 647 kPa, and the elongation at break is 658%.

[0057] Analysis of the sensitivity of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel:

[0058] This application combines a digital tensile tester and an electrochemical workstation to analyze the sensitivity of the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel and calculate the gauge factor (GF). Specifically:

[0059] ① Fix the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel in the middle of the clips of the tensile tester, and connect the tensile tester and the electrochemical workstation with a wire with a conductive clip. Set the working voltage to 1.0 V, and start the tensile tester and the electrochemical workstation at the same time to measure the tensile curve and the resistance-time curve, as Figure 6 shown. From Figure 6 it can be seen that the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel has a high sensitivity, and the maximum gauge factor GF value is as high as 6.04.

[0060] ② Fix the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel on the wrist, connect it to the electrochemical workstation with a wire with a conductive clip, set the working voltage to 1.0 V, move the wrist joint, and measure the resistance-time curve in real time. The test results are as Figure 7 shown. From Figure 7 it can be seen that the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel has a rapid response signal to bending and straightening the wrist, proving that the freeze-resistant and swelling-resistant starch-based nanocomposite hydrogel can sensitively and real-time monitor joint activities, and is very suitable for application in flexible wearable sensors, electronic skin or tissue engineering fields.

[0061] Analysis of the underwater sensing performance of antifreeze and anti-swelling starch-based nanocomposite hydrogels:

[0062] Fix the antifreeze and anti-swelling starch-based nanocomposite hydrogel prepared in Example 1 on the wrist, connect it to an electrochemical workstation with a wire equipped with a conductive clip, set the working voltage to 1.0 V, place the hand underwater, move the wrist joint, and measure the resistance-time curve in real time. The test results are as Figure 8 shown. As can be seen from Figure 8 it, the antifreeze and anti-swelling starch-based nanocomposite hydrogel has a rapid response signal to the bending and straightening of the wrist underwater, proving that the antifreeze and anti-swelling starch-based nanocomposite hydrogel prepared in Example 1 can sensitively and real-time monitor underwater joint activities and is very suitable for application in the field of flexible wearable sensors used in underwater environments.

[0063] Example 2:

[0064] A preparation method of an antifreeze and anti-swelling starch-based nanocomposite hydrogel, comprising the following steps:

[0065] Step a): Add 0.0072 g of graphene oxide powder, 0.18 g of disodium hydrogen phosphate, and 0.16 g of sodium dihydrogen phosphate into a conical flask containing 13 mL of deionized water, seal it with plastic wrap, and ultrasonicate for 1 hour to obtain a graphene oxide suspension;

[0066] Step b): Add 3.0 g of potato starch and 1.0 g of polyethylene glycol into the graphene oxide suspension prepared in step a), keep it at a constant temperature of 90 °C in a water bath, and stir at a stirring speed of 400 r / min for 2 hours until the mixture is completely dissolved to obtain a graphene oxide / potato starch / polyethylene glycol mixed sol;

[0067] Step c): Add 7 g of 1-ethyl-3-methylimidazolium tetrafluoroborate to the graphene oxide / potato starch / polyethylene glycol mixed sol, and continue to stir at a stirring speed of 400 r / min at 90 °C for 1 hour to fully mix and interact 1-ethyl-3-methylimidazolium tetrafluoroborate with starch / polyethylene glycol / graphene oxide to obtain a starch / polyethylene glycol / graphene oxide / 1-ethyl-3-methylimidazolium tetrafluoroborate sol;

[0068] Step d): Continue to heat the starch / polyethylene glycol / graphene oxide / 1-ethyl-3-methylimidazolium tetrafluoroborate sol for 1 hour without stirring, and then immediately take it out and place it in a vacuum box to remove the bubbles in the sol;

[0069] Step e): Immediately pour the starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol without bubbles into a mold, place it at -30°C for freezing for 3 hours, and then thaw it at room temperature for 1 hour. Repeat this freeze-thaw cycle process 3 times to strengthen the interaction between gel components. Finally, demold to obtain an anti-freezing and anti-swelling starch-based nanocomposite hydrogel. The anti-freezing and anti-swelling starch-based nanocomposite hydrogel consists of a dumbbell-shaped part and two square parts. Among them, the two square parts are fixedly connected to both ends of the dumbbell-shaped part respectively, and the two square parts and the dumbbell-shaped part are integrally formed. The size of the dumbbell-shaped part is 12 cm in length, 1 cm in width, and 0.3 cm in thickness. The two square parts have the same size, and the size of each square part is 2 cm in width and 0.4 cm in thickness.

[0070] Characterize and analyze the anti-swelling performance, anti-freezing property, conductivity, tensile property, and underwater sensing property of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 2. The results are as follows:

[0071] Analysis of the anti-swelling performance of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel: Immerse the anti-freezing and anti-swelling starch-based nanocomposite hydrogel in water, weigh it after taking it out at different times, and then use the formula SR=(W t -W i ) / W i ×100% to calculate the swelling ratio of the hydrogel, where W t is the mass of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel after taking it out at different times when immersed in water, and W i is the initial mass of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel without being immersed in water. This application analyzed the change of the swelling ratio of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 2 in the time range of 0 to 310 hours when immersed in water. The analysis results are as Figure 9 shown. It can be seen from Figure 9 that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 2 has a very fast water absorption rate in the first 4 hours. After 6 hours, the swelling ratio of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel begins to decrease. By 310 hours, the swelling ratio of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 2 is only 8.2%. This shows that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in this Example 2 also has excellent anti-swelling performance.

[0072] Analysis of the anti-freezing property of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel: Figure 10 is the differential scanning calorimetry curve of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel. From Figure 10It can be seen that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 2 starts to freeze at -3°C, reaches the freezing point at -12°C, and completes the freezing process at -26°C. Figure 10 This fully demonstrates that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 2 has excellent anti-freezing performance.

[0073] Analysis of the conductivity of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel: The conductivity of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in this Example 2 was measured using an electrochemical workstation. The test method is as follows: The square part of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel was tightly clamped with two copper sheets, and the copper sheets were connected to the electrochemical workstation with the wires of the conductive clip. First, the open-circuit potential of the circuit was measured to be 0V. Then, the electrochemical impedance spectroscopy function was turned on, the potential was set to 0V, and the frequency change range was 1-10 6 Hz, and a scan was performed to obtain the electrochemical impedance spectrogram, as Figure 11 shown. From Figure 10 it, the intersection point of the curve and the abscissa was read as the resistance R. The conductivity of the hydrogel was calculated using the formula σ = L / RA, where L is the thickness of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel in m, and A is the contact area between the copper sheet and the anti-freezing and anti-swelling starch-based nanocomposite hydrogel in m 2 . In addition, from Figure 11 it can also be seen that the resistance of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 2 is 6.3Ω. Then, according to the above formula, the conductivity σ of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 2 can be calculated to be 1.6 S·m -1 .

[0074] Analysis of the tensile properties of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel: The tensile properties of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel were measured using a digital tensile tester. Specifically, the anti-freezing and anti-swelling starch-based nanocomposite hydrogel was fixed in the middle of the clips of the tensile tester, and the tensile rate was set to 100 mm / min to obtain the tensile curve, as Figure 12 shown. From Figure 12 it can be seen that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel has excellent tensile properties. Among them, the tensile strength of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel is 571 kPa, and the elongation at break is 570%.

[0075] Analysis of the underwater sensing performance of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel:

[0076] Fix the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 2 on the index finger, connect it to an electrochemical workstation with a wire equipped with a conductive clip, set the working voltage to 1.0 V, place the hand underwater, move the index finger joint, and measure the resistance-time curve in real time. The test results are as Figure 13 shown. It can be seen from Figure 13 that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel has a rapid response signal to the bending and straightening of the finger underwater, proving that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 2 can sensitively and real-time monitor the underwater joint activities, and is very suitable for being applied to the field of flexible wearable sensors in the underwater environment.

[0077] Example 3:

[0078] A preparation method of an anti-freezing and anti-swelling starch-based nanocomposite hydrogel, comprising the following steps:

[0079] Step a): Add 0.012 g of graphene oxide powder, 0.19 g of disodium hydrogen phosphate and 0.16 g of sodium dihydrogen phosphate into a conical flask containing 13 mL of deionized water, seal it with plastic wrap, and ultrasonicate for 1 hour to obtain a graphene oxide suspension;

[0080] Step b): Add 1.0 g of potato starch and 3.0 g of polyethylene glycol into the graphene oxide suspension prepared in step a), keep it at a constant temperature of 90 °C in a water bath, and stir at a stirring speed of 400 r / min for 2 hours until all the mixture is dissolved to obtain a graphene oxide / potato starch / polyethylene glycol mixed sol;

[0081] Step c): Add 7 g of 1-ethyl-3-methylimidazolium chloride into the graphene oxide / potato starch / polyethylene glycol mixed sol, and continue to stir at a stirring speed of 400 r / min at 90 °C for 1 hour to make 1-ethyl-3-methylimidazolium chloride fully mixed and interact with starch / polyethylene glycol / graphene oxide to obtain a starch / polyethylene glycol / graphene oxide / 1-ethyl-3-methylimidazolium chloride sol;

[0082] Step d): Continue to heat the starch / polyethylene glycol / graphene oxide / ionic liquid sol for 1 hour without stirring, and then immediately take it out and place it in a vacuum box to remove the bubbles in the sol;

[0083] Step e): Immediately pour the starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol that has been defoamed into a mold, place it in a freezer at -10°C for 3 hours, and then thaw it at room temperature for 1 hour. Repeat this freeze-thaw cycle 4 times to strengthen the interaction between the gel components. Finally, demold to obtain an anti-freezing and anti-swelling starch-based nanocomposite hydrogel. The anti-freezing and anti-swelling starch-based nanocomposite hydrogel consists of a dumbbell-shaped part and two square parts. Among them, the two square parts are fixedly connected to both ends of the dumbbell-shaped part respectively, and the two square parts and the dumbbell-shaped part are integrally formed. The size of the dumbbell-shaped part is 12 cm in length, 1 cm in width, and 0.3 cm in thickness. The sizes of the two square parts are the same, and the size of each square part is 2 cm in width and 0.4 cm in thickness.

[0084] Characterize and analyze the anti-swelling performance, conductivity, tensile performance, and underwater sensing performance of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3. The results are as follows:

[0085] Analysis of the anti-swelling performance of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel: Immerse the anti-freezing and anti-swelling starch-based nanocomposite hydrogel in water, weigh it after taking it out at different times, and then use the formula SR=(W t -W i ) / W i ×100% to calculate the swelling ratio of the hydrogel, where W t is the mass of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel after being taken out at different times of immersion in water, and W i is the initial mass of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel without being immersed in water. This application analyzed the change of the swelling ratio of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3 within the time range of 0-310 hours of immersion in water. The analysis results are as Figure 14 shown. From Figure 14 it can be seen that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3 has a very fast water absorption rate in the first 1.5 hours. After 6 hours, the swelling ratio of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel begins to decline. By 310 hours, the swelling ratio of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3 is only 7.9%. This shows that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in this Example 3 also has excellent anti-swelling performance.

[0086] Analysis of the anti-freezing performance of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel: Figure 15 is the differential scanning calorimetry curve of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel. From Figure 14It can be seen that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3 starts to freeze at -5°C, reaches the freezing point at -12°C, and completes the freezing process at -33°C. Therefore, Figure 15 it also fully demonstrates that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3 has excellent anti-freezing performance.

[0087] Analysis of the electrical conductivity of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel: The electrical conductivity of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in this Example 3 was measured using an electrochemical workstation. The test method is as follows: The square part of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel was tightly clamped with two copper sheets, and the copper sheets were connected to the electrochemical workstation with the wires of the conductive clips. First, the open-circuit potential of the circuit was measured to be 0V. Then, the electrochemical impedance spectroscopy function was turned on, the potential was set to 0V, and the frequency change range was 1 - 10 6 Hz, and a scan was performed to obtain an electrochemical impedance spectrogram, as Figure 16 shown. The intersection point of the curve and the abscissa was read from Figure 16 as the resistance R, and then the electrical conductivity of the hydrogel was calculated using the formula σ = L / RA, where L is the thickness of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel in m, and A is the contact area between the copper sheet and the anti-freezing and anti-swelling starch-based nanocomposite hydrogel in m 2 . In addition, it can also be seen from Figure 16 that the resistance of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3 is 7.5Ω. Then, according to the above formula, the electrical conductivity σ of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3 can be calculated to be 1.3S·m -1 .

[0088] Analysis of the tensile properties of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel: The tensile properties of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel were measured using a digital tensile tester. Specifically, the anti-freezing and anti-swelling starch-based nanocomposite hydrogel was fixed in the middle of the clips of the tensile tester, and the tensile rate was set to 100mm / min to obtain a tensile curve, as Figure 17 shown. It can be seen from Figure 17 that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel has excellent tensile properties. Among them, the tensile strength of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel is 496kPa, and the elongation at break is 436%.

[0089] Analysis of the underwater sensing performance of the anti-freezing and anti-swelling starch-based nanocomposite hydrogel:

[0090] Fix the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3 on the wrist, then connect it to an electrochemical workstation with a wire equipped with a conductive clip. Set the working voltage to 1.0 V, place the hand underwater, move the wrist joint, and measure the resistance-time curve in real time. The test results are as Figure 18 shown. As can be seen from Figure 18 , the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3 has a rapid response signal to the bending and straightening of the wrist underwater, proving that the anti-freezing and anti-swelling starch-based nanocomposite hydrogel prepared in Example 3 can sensitively and real-time monitor underwater joint activities and is very suitable for application in the field of flexible wearable sensors in underwater environments.

Claims

1. A preparation method of an antifreeze and anti-swelling starch-based nanocomposite hydrogel, characterized in that: It includes the following steps: a) Preparing a graphene oxide suspension: Mix graphene oxide powder, disodium hydrogen phosphate, sodium dihydrogen phosphate and deionized water, and ultrasonicate for 1 hour under sealed conditions to obtain a graphene oxide suspension; b) Preparing a starch / polyethylene glycol / graphene oxide mixed sol: Add starch and polyethylene glycol to the graphene oxide suspension, and under sealed conditions, heat and stir in a water bath until the starch and polyethylene glycol are completely dissolved to obtain a starch / polyethylene glycol / graphene oxide mixed sol; c) Preparing a starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol: Add an ionic liquid to the starch / polyethylene glycol / graphene oxide mixed sol, where the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium chloride, and heat and stir, until the two are fully mixed to obtain a starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol; d) Bubble treatment of the starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol: Continuously heat the starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol, and then perform bubble removal treatment; e) Preparing an antifreeze and anti-swelling starch-based nanocomposite hydrogel product: Immediately pour the degassed starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol into a mold, and then perform cyclic freezing and thawing, and demold to obtain an antifreeze and anti-swelling starch-based nanocomposite hydrogel product.

2. The preparation method of the antifreeze and anti-swelling starch-based nanocomposite hydrogel according to claim 1, characterized in that: The graphene oxide accounts for 0.01-0.1% of the total weight of all components; the deionized water accounts for 41.5-80% of the total weight of all components; the total amount of disodium hydrogen phosphate and sodium dihydrogen phosphate accounts for 1.4-1.6% of the total weight of all components; the starch accounts for 4%-13% of the total weight of all components; the polyethylene glycol accounts for 4%-13% of the total weight of all components; the ionic liquid accounts for 4%-41.5% of the total weight of all components.

3. The preparation method of the antifreeze and anti-swelling starch-based nanocomposite hydrogel according to claim 1, characterized in that: In step b), the starch is potato starch, glutinous rice starch or cassava starch.

4. The preparation method of the antifreeze and anti-swelling starch-based nanocomposite hydrogel according to claim 1, characterized in that: In step b), the time for heating and stirring in a water bath is 2-3 hours.

5. The preparation method of the antifreeze and anti-swelling starch-based nanocomposite hydrogel according to claim 1, characterized in that: In step c), the heating and stirring time is 1-2 hours.

6. The preparation method of the antifreeze and anti-swelling starch-based nanocomposite hydrogel according to claim 1, characterized in that: In step e), the cyclic freezing and thawing means placing the mold containing the starch / polyethylene glycol / graphene oxide / ionic liquid mixed sol in a low-temperature freezer for a certain time, then thawing at room temperature, and repeating the freezing and thawing process cyclically.

7. The preparation method of the antifreeze and anti-swelling starch-based nanocomposite hydrogel according to claim 1, characterized in that: In step e), the freezing time is 2-5 hours; the freezing temperature is -10 to -40 °C, and the number of cyclic freezing and thawing times is 1-5 times.

8. An antifreeze and anti-swelling starch-based nanocomposite hydrogel prepared by the preparation method of the antifreeze and anti-swelling starch-based nanocomposite hydrogel according to any one of claims 1 to 7.

9. An application of an antifreeze and anti-swelling starch-based nanocomposite hydrogel in the fields of flexible wearable sensors, electronic skin or tissue engineering; the antifreeze and anti-swelling starch-based nanocomposite hydrogel is the antifreeze and anti-swelling starch-based nanocomposite hydrogel according to claim 8.

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