Preparation method of dual-network high-strength gel nanofiber resistance-type strain sensing material

Abstract

The invention discloses a preparation method of a dual-network high-strength gel nanofiber resistance type strain sensing material. According to the method, a two-dimensional material is synthesized through an etching method, an ionic liquid polymer monomer is prepared through an alkylation reaction, and the conductive fiber hydrogel with the adjustable mechanical property is prepared through the steps of electrostatic spinning, multi-component solvent soaking and ultraviolet in-situ polymerization. The prepared fiber hydrogel is composed of a polyvinyl alcohol polymer chain and a copolymer of acrylamide and phenylboronic acid ionic liquid, and dense crosslinking is formed through physical entanglement and physical and chemical interaction of hydrogen bonds and dynamic boric acid ester bonds. Meanwhile, MXene and carboxylated cellulose nanofibers are used as nanofillers to provide a mechanical property enhancement effect for a hydrogel network through a nano-enhancement effect, so that the hydrogel is endowed with adjustable mechanical strength and rebound resilience, and various electromyographic signals and other health signals of a human body can be monitored in real time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible wearable electronic devices, in particular to a preparation method of a double-network high-strength gel nanofiber resistive strain sensing material. BACKGROUND

[0002] With the development of information society, the demand for human health sensors is increasing. Wearable strain sensors have similar sensing functions as human skin, can realize real-time monitoring of externally applied strain, have good flexibility, resilience and high sensitivity, and thus provide a convenient and comfortable technical means for recording motion signals and health signals in life. Wearable strain sensors have great application prospects in human-computer interaction devices, smart skin, intelligent medical devices and other fields. For conductive fiber hydrogel flexible sensing materials, optimizing the internal microstructure and adjusting the cross-linking network between polymers are the key to improving their mechanical properties and sensing properties. The conductive fiber hydrogel composite resistive strain sensing material prepared by the present application is composed of a double-polymer network, the polyvinyl alcohol polymer chain is the first network of the fiber hydrogel, and the copolymer of acrylamide and phenylboric acid ionic liquid is the second network. The two networks form a dense cross-linking network through physical entanglement, hydrogen bonding, dynamic borate ester bond physical and chemical interaction. At the same time, MXene and carboxylated cellulose nanofiber as nanofiller provide mechanical property enhancement for the hydrogel network through nano-enhancement effect, giving the hydrogel adjustable mechanical strength and resilience. SUMMARY

[0003] The purpose of the present application is to solve the problems of poor air permeability and insufficient flexibility of existing flexible sensing devices, and to provide a preparation method of a double-network conductive fiber hydrogel composite resistive strain sensing material. The obtained double-network conductive fiber hydrogel has air permeability, flexibility and three-dimensional porous network structure, can realize deep surface adhesion with human tissue, and significantly reduces the interfacial stress.

[0004] To solve the above technical problems, the present application provides the following technical scheme: a preparation method of a polyacrylamide / phenylboric acid ionic liquid / polyvinyl alcohol / carboxylated cellulose nanofiber / MXene conductive fiber hydrogel composite resistive strain sensing material, comprising the following steps:

[0005] (1) First, prepare HF for etching titanium aluminum carbide, add hydrochloric acid solution to a container of polytetrafluoroethylene, add lithium fluoride and stir until completely dissolved to prepare HF. Slowly add a certain mass of titanium aluminum carbide into the HF, place the container in a 40-60℃ water bath for heating and stirring for 20-28h, centrifuge the solution at a speed of 4000-5000rpm multiple times, take the lower black solid and disperse it in deionized water. After ultrasonic treatment in an ice bath at a power of 300-400W for 1-2h, centrifuge the solution at a speed of 3000-45000rpm for 5-10min, take the upper clear liquid and place it in an environment at minus 20-80℃ for 20-28h, then place it in a freeze dryer for freeze-drying treatment, and finally obtain MXene nanosheets.

[0006] (2) Dissolve 4-bromomethylphenylboronic acid with ethyl acetate, add 1-vinylimidazole after complete dissolution, use an oil bath to keep the whole system at 60-80℃, fill the inside with nitrogen, condense and reflux for 18-24h, then use ethyl acetate to rinse the unreacted substances, obtain a light yellow solid, and place it in a vacuum drying box at a range of 35-50℃ for 10-16h to obtain the final product, phenylboronic acid ionic liquid.

[0007] (3) Weigh CNF and MXene and disperse them in deionized water, place them in an ultrasonic instrument with a range of 80-150W for 5-10min, then weigh the phenylboronic acid ionic liquid (PBA-IL) and add it to the above mixed solution for storage;

[0008] (4) Weigh PVA, AM, MBA, and photoinitiator L2959 and add them to the above solution, heat and stir in a 80-120℃ water bath for 6-10h to obtain a spinning solution;

[0009] (5) Prepare the spinning solution in step (2) into a PVA / PAM(PBA-IL) / CNF / MXene fiber membrane by electrospinning technology, and store it for future use;

[0010] (6) Soak the PVA / PAM(PBA-IL) / CNF / MXene fiber membrane prepared in step (3) in a mixed solution composed of glycerol, sodium chloride, and deionized water for 18-24h to obtain a PVA / PAM(PBA-IL) / CNF / MXene fiber hydrogel;

[0011] (7) Polymerize the PVA / PAM(PBA-IL) / CNF / MXene fiber hydrogel prepared in step (4) under ultraviolet light to obtain the final fiber hydrogel.

[0012] Further, the mass of titanium aluminum carbide taken in step (1) is 0.5-2g.

[0013] Further, in step (2), the mass of 4-bromomethylphenylboronic acid is 0.75-0.95 g, the volume of ethyl acetate ranges from 20-40 mL, and the volume of 1-vinylimidazole ranges from 0.35-0.55 mL.

[0014] Further, in step (3), the addition amount of both CNF and MXene is 1-3 mg.

[0015] Further, in step (4), the concentration of PVA is 12%, the addition amount of AM is 8-12 g, the addition amount of PBA-IL is 0.2-0.6 g, the addition amount of photoinitiator L2959 is 0.5-1.2% of the mass of added AM, and the addition amount of MBA ranges from 0.5-1 mg.

[0016] Further, in step (5), the electrospinning conditions are as follows: voltage 15-20 kV, needle flow rate 0.5-2 mL / h, distance between needle and roller receiver 10-15 cm, and roller receiver rotation speed 150-200 rpm.

[0017] Further, in step (4), the mass ratio of glycerol to sodium chloride solution ranges from 1:1 to 2:1, and the concentration of the sodium chloride solution ranges from 4-8 mol / L.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] (1) The polyacrylamide / phenylboronic acid ionic liquid / polyvinyl alcohol / carboxylated cellulose nanofiber / MXene conductive fiber hydrogel composite resistive strain sensing material prepared by the present application significantly enhances the dispersion stability of MXene in water through the synergistic effect of electrostatic repulsion and steric hindrance by adding carboxylated cellulose nanofiber;

[0020] (2) The polyacrylamide / phenylboronic acid ionic liquid / polyvinyl alcohol / carboxylated cellulose nanofiber / MXene conductive fiber hydrogel composite resistive strain sensing material prepared by the present application has excellent crack propagation resistance and mechanical performance anisotropy, which is significantly superior to traditional thin film materials. Its porous structure endows it with high air permeability, meeting the long-term attachment requirements of human skin tissue;

[0021] (3) The polyacrylamide / phenylboronic acid ionic liquid / polyvinyl alcohol / carboxylated cellulose nanofiber / MXene conductive fiber hydrogel composite resistive strain sensing material prepared by the present application can achieve more precise muscle electrical signal detection, including finger movement and arm muscle movement, compared with commercial gel electrodes. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without paying creative labor, and the present application is not limited to the specific embodiments disclosed below.

[0023] Figure 1 Preparation of hydrogel fiber and human sensing schematic diagram.

[0024] Figure 2 Dispersion performance of nanomaterials: Figure A is a TEM image of MXene; Figure B is the Zeta potential of MXene solution, CNF solution and MXene and CNF mixed solution.

[0025] Figure 3 Preparation process of conductive fiber hydrogel composite resistance strain sensing material.

[0026] Figure 4 Mechanical property characterization of PAM / PBA-IL / MXene / CNF fiber hydrogel, wherein Figure A is the stress-strain curve of PAM / PBA-IL / MXene / CNF fiber hydrogel with different amounts of PBA-IL added, and Figure B is a real picture of PAM / PBA-IL / MXene / CNF fiber hydrogel under 20, 100 and 200g load respectively.

[0027] Figure 5 Test results of human skin impedance and electromyographic signal of the double network conductive fiber hydrogel composite resistance strain sensing material prepared by the present application after being assembled into a flexible strain sensor: Figure A is the interface impedance comparison of commercial saturated silver / silver chloride electrode and double network conductive fiber hydrogel electrode on the surface of human skin; Figure B is the electromyographic signal change value tested by fiber hydrogel electrode without finger movement; Figure C is the electromyographic signal change of commercial saturated silver / silver chloride electrode and double network conductive fiber hydrogel electrode when clenching the fist; Figure D is the electromyographic signal peak value and the signal-to-noise ratio of the background when clenching the fist. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below.

[0029] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present application, therefore the present application is not limited to the specific embodiments disclosed below.

[0030] Second, the "one embodiment" or "an embodiment" referred to herein means a specific feature, structure, characteristic, or combination of features and / or characteristics described herein that can be included in at least one implementation of the present application. The various appearances of "in one embodiment" or "an embodiment" in the specification are not necessarily all referring to the same embodiment.

[0031] Example 1

[0032] The preparation of two-dimensional nanomaterial MXene is as follows:

[0033] (1) Add a hydrochloric acid solution with a concentration of 9 moles per liter into a container of polytetrafluoroethylene, add 1.6 g of lithium fluoride, stir until completely dissolved to prepare HF, and store for later use.

[0034] (2) Take 1 g of titanium aluminum carbide and slowly add it to the hydrofluoric acid, and place the polytetrafluoroethylene container in a 45°C water bath for heating and stirring for 24 h to obtain an etched MXene precursor solution.

[0035] (3) Centrifuge the obtained MXene precursor solution multiple times at a speed of 4500 rpm, and take the lower black solid and disperse it in deionized water.

[0036] (4) Disperse the black solid solution in a cell crusher (FC-650N, Nanjing Hu Chuang Scientific Instrument Co., Ltd., China) at a power of 300 W for ice bath ultrasonic treatment for 1 h, then continue to centrifuge at a speed of 4500 rpm for 5 min, and take the upper clear liquid.

[0037] (5) Place the upper clear liquid in an environment of -80°C for 24 h, then place it in a freeze dryer for freeze-drying treatment, and finally obtain a flaky MXene solid, as shown in FIG. 1. Figure 2

[0038] Example 2

[0039] The preparation of an ionic liquid polymer monomer is as follows:

[0040] (1) Dissolve 0.8594 g of 4-bromomethylphenylboronic acid in 30 mL of ethyl acetate, use an ultrasonic cleaning instrument to defoam the inside, and add 0.452 mL of 1-vinylimidazole.

[0041] (2) Place the entire system in an oil bath environment at 70°C, fill the inside of the system with nitrogen, and condense backflow for 24 h.

[0042] (3) After the reaction is completed, pour off the upper solution that has not reacted completely, use 50 mL of ethyl acetate to rinse the unreacted substances, and obtain a light yellow solid attached to the inner wall.

[0043] ​(4) The obtained light yellow solid was placed in a vacuum drying oven at 45℃ for 12h to obtain the final product, phenylboronic acid ionic liquid.

[0044] Example 3

[0045] A preparation method of a polyacrylamide / phenylboronic acid ionic liquid / polyvinyl alcohol / carboxylated cellulose nanofiber / MXene conductive fiber hydrogel composite resistive strain sensing material, as shown in Figure 3 , comprises the following steps:

[0046] (1) Configure the spinning solution of the nanofiber membrane, wherein the concentration of PVA is 12%, the addition amount of AM is 2g (in 10mL deionized water), the addition amount of PBA-IL is 0.4g (in 10mL deionized water), the addition amount of the photoinitiator L2959 is 1% of the added AM mass, and the addition amount of MBA is 1mg.

[0047] (2) Adjust the spinning process parameters: receiving distance is 15cm, injection speed is constant at 1mL h-1, voltage is 16KV, air humidity is 50-60%, and environmental temperature is 24-28℃, to obtain the nanofiber membrane.

[0048] (3) Immersing the nanofiber membrane in a ternary mixed solution of glycerol and sodium chloride solution, wherein the mass ratio of glycerol to sodium chloride solution is 1:1, and the concentration of the sodium chloride solution is 5mol / L. Soak for about 12h.

[0049] (4) Irradiating the fiber membrane with primary crosslinking under 20W ultraviolet light for 10min to improve the connection strength between the crosslinking points of the fibers, and finally obtaining the fiber hydrogel.

[0050] Comparative Example 1

[0051] The same raw materials and preparation parameters as used in Example 3 are used to prepare a conductive fiber hydrogel sensing material, but the addition amount of phenylboronic acid ionic liquid is changed, and the mechanical properties of the material are compared with the material applied in the present application, comprising the following steps:

[0052] (1) Configure the spinning solution of the nanofiber membrane, wherein the concentration of PVA is 12%, the addition amount of AM is 2g (in 10mL deionized water), the addition amount of PBA-IL is 0.1, 0.2, 0.3g (in 10mL deionized water), the addition amount of the photoinitiator L2959 is 1% of the added AM mass, and the addition amount of MBA is 1mg.

[0053] (2) Adjust the spinning process parameters: receiving distance is 15cm, injection speed is constant at 1mL h -1 , voltage is 16KV, air humidity is 50-60%, and environmental temperature is 24-28℃, to obtain the nanofiber membrane.

[0054] (3) The nanofiber membrane is immersed in a ternary mixed solution of glycerol and sodium chloride solution, wherein the mass ratio of glycerol to sodium chloride solution is 1:1, and the concentration of the sodium chloride solution is 5 mol / L. The immersion time is about 12 h.

[0055] (4) The fiber membrane with initial cross-linking is irradiated under ultraviolet light of 20 W for 10 min to improve the connection strength between the cross-linking points of the fibers, and finally the fiber hydrogel with different ionic liquid contents is obtained, as shown in Figure 4 .

[0056] Test Example:

[0057] Mechanical performance test: The parameters of the conductive fiber hydrogel prepared in Example 3 and the comparative example are recorded, and the tensile properties are tested by using a universal testing machine (UTM6502, Shenzhen Sanechips Technology Co., Ltd., China) at a speed of 10 mm / min, and the stress-strain curve is tested, and each sample is tested at least 3 times.

[0058] Human sensing performance test: The electrochemical workstation (model CHI660E) of Shanghai Chenhua Company is used to test the electrochemical impedance spectrum of the commercial gel electrode and the fiber hydrogel electrode in the IMPAC mode, and a three-electrode system is used, the working electrode and the counter electrode are attached to the surface of the skin to be tested, the reference electrode is attached to the surface of the distal skin, and the test frequency range is 100-10000000 Hz. The electromyography test module (Chip Future) is used to test the electromyography of the muscle, and a three-electrode system is used, the working electrode and the counter electrode are attached to the muscle to be tested, and the reference electrode is attached to the distal muscle to prevent the interference of the active electromyography signal.

[0059] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that a number of improvements and refinements can be made without departing from the spirit and scope of the technical solutions of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for preparing a dual-network high-strength gel nanofiber resistive strain sensing material, characterized in that, The preparation method includes the following steps: (1) Weigh carboxylated cellulose nanofibers (CNF) and MXene, disperse them in deionized water, and place them in an ultrasonic instrument with a range of 80-150W for 5-10 minutes. Then weigh phenylboronic acid ionic liquid (PBA-IL) and add it to the above mixed solution. Store for later use. (2) Weigh out polyvinyl alcohol (PVA), acrylamide (AM), NN-methylenebisacrylamide (MBA) and photoinitiator L2959 and add them to the above solution. Heat and stir in a water bath at 80-120℃ for 6-10 hours to obtain a spinning solution. (3) The spinning solution in step (2) is prepared into a PVA / PAM(PBA-IL) / CNF / MXene fiber membrane by electrospinning technology and stored for later use; (4) The PVA / PAM(PBA-IL) / CNF / MXene fiber membrane prepared in step (3) is immersed in a mixed solution of glycerol, sodium chloride and deionized water for 18-24 hours to obtain PVA / PAM(PBA-IL) / CNF / MXene fiber hydrogel. (5) The PVA / PAM(PBA-IL) / CNF / MXene fiber hydrogel obtained in step (4) is polymerized under ultraviolet light to obtain the final fiber hydrogel.

2. The preparation method according to claim 1, characterized in that, The preparation process of MXene in step (1) is as follows: First, hydrofluoric acid (HF) is prepared for etching titanium aluminum carbide. Hydrochloric acid solution is added to a polytetrafluoroethylene container, and lithium fluoride is added and stirred until completely dissolved to prepare HF. 0.5-2g of titanium aluminum carbide is slowly added to HF, and the container is placed in a water bath at 40-60℃ and heated and stirred for 20-28h. The solution is centrifuged multiple times at a speed of 4000-5000rpm, and the lower layer of black solid is dispersed in deionized water. The solution is ultrasonicated in an ice bath at a power of 300-400W for 1-2h, and then centrifuged at a speed of 3000-4500rpm for 5-10min. The supernatant is placed in an environment of -20-80℃ for 20-28h and then freeze-dried in a freeze dryer to finally obtain MXene nanosheet solid.

3. The preparation method according to claim 1, characterized in that, The preparation process of PBA-IL in step (1) is as follows: Dissolve 0.75-0.95 g of 4-bromomethylphenylboronic acid in 20-40 mL of ethyl acetate. After complete dissolution, add 0.35-0.55 mL of 1-vinylimidazole. The reaction temperature is 60-80℃, and the interior is filled with nitrogen. After reflux for 18-24 h, wash the unreacted substances with ethyl acetate to obtain a pale yellow solid. Dry the solid in a vacuum drying oven at 35-50℃ for 10-16 h to obtain the final product, phenylboronic acid ionic liquid.

4. The preparation method according to claim 1, characterized in that, In step (1), the amount of both CNF and MXene added is 1-3 mg.

5. The preparation method according to claim 1, characterized in that, In step (2), the concentration range of PVA is 8-12%, the amount of AM added is 1-2g, the amount of PBA-IL added is 0.2-0.6g, the amount of photoinitiator L2959 added is 0.5-1.2% of the mass of AM added, the amount of MBA added is 0.5-1mg, and the amount of deionized water added is 6-12mL.

6. The preparation method according to claim 1, characterized in that, In step (3), the conditions for electrospinning are: voltage 15-20kV, needle flow rate 0.5-2mL / h, distance between needle and roller receiver 10-15cm, and roller receiver rotation speed 150-200rpm.

7. The preparation method according to claim 1, characterized in that, In step (4), the mass ratio of glycerol to sodium chloride solution is in the range of 1:1 to 2:1, and the concentration of sodium chloride solution is in the range of 4-8 mol / L.

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