Preparation method of low-modulus self-healing cellulose nanofiber-based hydrogel fiber strain sensing material

Abstract

The invention discloses a preparation method of a low-modulus self-healing cellulose nanofiber based hydrogel fiber strain sensing material. A hydrogel precursor solution is injected into a transparent silica gel pipeline through a wet spinning strategy, a micro sample injection pump continuously extrudes the precursor solution according to a certain propelling speed, and solution polymerization is initiated by ultraviolet light to obtain the low-modulus ionic conductive hydrogel fiber. A main network of the hydrogel fiber is composed of a three-dimensional network framework formed by polyacrylamide through covalent crosslinking, TEMPO oxidized cellulose nanofibers and polyacrylamide form an interpenetrating network, the mechanical performance of the hydrogel fiber is improved, and the self-healing effect of an internal network of hydrogel is improved through the coupling effect of dynamic hydrogen bonds and a covalent network. The resistance-type strain sensor assembled by the ionic conductive self-healing hydrogel fiber has ultralow modulus and wide strain detection range, and can realize real-time monitoring of motion states of different parts of a human body.

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 low-modulus self-healing cellulose nanofiber-based hydrogel fiber strain sensing material. BACKGROUND

[0002] In the past few decades, flexible electronics has developed at an astonishing speed and has penetrated into all aspects of modern life, covering fields such as flexible display screens, electronic skin, wearable energy devices, human-computer interaction interfaces, flexible sensors, and real-time health monitoring devices. Compared with traditional rigid and brittle silicon-based electronic devices, flexible electronic devices, with their unique characteristics of miniaturization, lightweight, portability, foldability, and stretchability, are continuously attracting the interest of researchers in the fields of materials science and chemistry. Traditional conductive functional materials generally have the disadvantages of high cost, inherent rigidity, poor biocompatibility, poor mechanical properties, and weak interfacial bonding performance, which are exactly the key parameters for evaluating the performance of flexible electronic materials. The polyacrylamide cellulose nanofiber ion-conducting self-healing hydrogel fiber prepared in the present application is based on the interpenetrating network structure of PAM and TOCNF, combined with the synergistic regulation of glycerol and sodium chloride, and prepared by a wet spinning process to obtain a flexible sensing material with low modulus and high water retention. SUMMARY

[0003] The purpose of the present application is to solve the problem of insufficient sensitivity of existing flexible sensing devices under small strain, and to provide a preparation method of a low-modulus, high-sensitivity, and good self-healing effect ion-conducting hydrogel fiber resistive strain sensing material. The internal crosslinked network of the obtained ion-conducting self-healing hydrogel fiber is crosslinked by hydrogen bonds.

[0004] To solve the above technical problems, the present application provides the following technical scheme: a preparation method of a low-modulus polyacrylamide cellulose nanofiber ion-conducting self-healing hydrogel fiber resistive strain sensing material, comprising the following steps:

[0005] (1) A certain amount of polymer monomer acrylamide (AM), TEMPO-oxidized cellulose nanofiber solution (TOCNF), sodium chloride, photoinitiator L2959, N-N-methylene bisacrylamide (MBA), and glycerol are added to 4-10 mL of deionized water, and stirred at a speed of 300-600 rpm for 8-15 min, and then subjected to ultrasonic defoaming treatment to obtain a uniform transparent solution;

[0006] (2) A simple wet spinning device is built using a medical syringe, a needle range of 15-20G, a transparent silicone tube, a micro-sampling pump, a control panel, and a UV lamp;

[0007] (3) The hydrogel precursor solution is injected into the transparent silicone tube at a certain speed by a syringe, and the tube is located directly below the ultraviolet lamp, and the ultraviolet lamp is turned on after the precursor solution is extruded from the transparent silicone hose.

[0008] (4) The prepared hydrogel fiber is received by a glass crystallizing dish.

[0009] Further, in step (1), the addition amount of AM is 1-2.5g, the addition amount of glycerol is 3g, the addition amount of TOCNF solution is 1-4g, the addition amount of photoinitiator L2959 is 0.005-0.3g, and the addition amount of MBA is 6-12mg.

[0010] Further, in step (1), the nanocellulose content of the TEMPO-oxidized cellulose nanofiber solution is 0.5-1.2%, and the solvent is water.

[0011] Further, in step (2), the size of the transparent silicone tube is 1-5mm in diameter and 2-10mm in diameter, and the total power of the ultraviolet lamp is 8-15W.

[0012] Further, in step (3), the injection speed of the micro-injection pump is 1.5-2.5mL / h, and the length of the transparent silicone tube is 30-50mm.

[0013] Further, in step (3), the transparent silicone tube is located 1-5cm below the ultraviolet lamp, and the irradiation power of the ultraviolet lamp is 8-15W.

[0014] Compared with the prior art, the present application has the following advantages:

[0015] (1) The low modulus polyacrylamide cellulose nanofiber ion conductive self-healing hydrogel fiber resistance strain sensing material prepared by the present application forms an interpenetrating structure through hydrogen bonding crosslinking between TOCNF and PAM network, and the synergistic effect of this dynamic hydrogen bonding network cooperates to give the fiber high ductility, and the strain recovery efficiency after self-healing at room temperature for 6 hours can reach 78%;

[0016] (2) The low modulus polyacrylamide cellulose nanofiber ion conductive self-healing hydrogel fiber resistance strain sensing material prepared by the present application significantly improves the water retention performance of the hydrogel fiber by adjusting the addition amount of glycerol, ensuring the stability of the fiber moisture content; at the same time, by introducing sodium chloride, excellent conductivity is achieved, and the fiber is given excellent sensing performance. The hydrogel fiber shows high sensitivity and fast response, so that it can produce relatively stable sensing signals to 1% to 5% of the small strain and 100% to 500% of the large strain;

[0017] (3) The low-modulus polyacrylamide cellulose nanofiber ion-conducting self-healing hydrogel fiber resistive strain sensing material prepared by the application can detect the movement state of the human body at multiple parts, including wrist movement, finger bending, knee movement, etc. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Wherein:

[0020] Figure 1 Preparation of hydrogel fiber and schematic diagram of human application thereof; Figure 2 Preparation of ion-conducting hydrogel fiber, wherein figure a is a preparation flowchart of wet spinning hydrogel fiber; figure b is a physical diagram of hydrogel fiber wound on a glass rod.

[0021] Figure 3 Mechanical properties of ion-conducting hydrogel fiber, figure a is a stress-strain curve of hydrogel fiber with different glycerol contents; figure b is a stress-strain curve of hydrogel fiber with different TOCNF contents; figure c is a stress-strain curve of hydrogel fiber with different NaCl contents.

[0022] Figure 4 Electrical properties and sensing properties of ion-conducting hydrogel fiber, wherein figure a is the change of electrical conductivity of ion-conducting hydrogel fiber with different amounts of added sodium chloride, figure b is the strain sensitivity coefficient of ion-conducting hydrogel fiber; figure c is the relative resistance change of ion-conducting hydrogel fiber under a small degree of strain of 1-5%; figure d is the relative resistance change of ion-conducting hydrogel fiber under a large degree of strain of 50-200%.

[0023] Figure 5 Self-healing properties of ion-conducting hydrogel fiber, wherein figure a is a physical diagram of the self-healing process of hydrogel fiber dyed with malachite green and congo red respectively; figure b is a stress-strain curve of hydrogel fiber healed for 1h, 2h and 3h respectively; figure c is the change of bulb brightness before and after self-healing of hydrogel.

[0024] Figure 6The test results of the flexible strain sensor assembled by the low modulus polyacrylamide cellulose nanofiber ion conductive self-healing hydrogel fiber resistive strain sensing material prepared by the application for detecting the movement of multiple parts of the human body are shown in Figure a, which is the relative resistance value change of the flexible strain sensor for testing different angles of finger bending; Figure b is a schematic diagram of the parts of the human body that can be tested by the flexible strain sensor; Figure c is the relative resistance value change of the flexible strain sensor for testing wrist bending; Figure d is the relative resistance value change of the low modulus hydrogel fiber flexible strain sensor for testing ankle bending; and Figure e is the relative resistance value change of the flexible strain sensor for testing knee bending. DETAILED DESCRIPTION

[0025] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below.

[0026] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the application, but the 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 concept of the application, so the application is not limited by the specific embodiments disclosed below.

[0027] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the application. "In one embodiment" appearing in different places in the description does not mean the same embodiment, nor is it an independent or alternative embodiment that excludes other embodiments.

[0028] Example 1

[0029] The simple wet spinning transfer station is built, as shown in Figure 2 , the steps are as follows:

[0030] (1) The sample injection device is composed of a 1 mL medical syringe, an 18G needle, and a transparent silicone tube with an inner diameter of 1 mm and an outer diameter of 2 mm. First, the medical syringe is combined with the 18G needle, then one end of the transparent silicone tube is inserted into the outside of the 18G needle, and the silicone tube and needle connection part is fixed using transparent tape.

[0031] (2) The control system is composed of a micro-injection pump and a control panel, and a 10W ultraviolet lamp is used as a curing device. The lamp head is irradiated from the top of the transparent silicone tube with a distance of 2 cm, and a fan is used for cooling at the same time.

[0032] Example 2

[0033] A preparation method of a low modulus polyacrylamide cellulose nanofiber ion conductive self-healing hydrogel fiber resistive strain sensing material, as shown in Figure 2 , the steps are as follows:

[0034] (1) 2 g of polymer monomer acrylamide, 2 g of TEMPO oxidized cellulose nanofiber solution with a mass concentration of 1%, 0.5 g of sodium chloride, 0.01 g of photoinitiator L2959, 10 mg of N-N-methylene bisacrylamide, and 3 g of glycerol were added to 5 mL of deionized water, and after stirring at a speed of 500 rpm for 10 min, ultrasonic defoaming treatment was performed to obtain a uniform transparent solution;

[0035] (2) A simple wet spinning device was built using a 1 mL medical syringe, an 18G needle, a transparent plastic silica gel tube with an inner diameter of 1 mm and an outer diameter of 2 mm, a micro-injection pump, a control panel, and a 10W ultraviolet lamp;

[0036] (3) The hydrogel precursor solution was injected into the silica gel tube with a length of 50 mm at a speed of 2 mL / h, and the tube was located 2 cm below the ultraviolet lamp. The power of the ultraviolet lamp was 10W. After the precursor solution was extruded from the transparent silica gel hose, the ultraviolet lamp was turned on;

[0037] (4) The hydrogel fibers prepared were received using a glass crystallizing dish.

[0038] Comparative Example 1

[0039] Ion-conducting hydrogel fibers were prepared using the same raw materials and preparation parameters as in Example 2, but changing the addition amount of glycerol, TOCNF, and NaCl, including the following steps:

[0040] (1) 2 g of polymer monomer acrylamide, 0 / 1 / 3 g of TEMPO oxidized cellulose nanofiber solution with a mass concentration of 1%, 0.1 / 0.3 / 0.7 g of sodium chloride, 0.01 g of photoinitiator L2959, 10 mg of N-N-methylene bisacrylamide, and 0 / 1 / 2 g of glycerol were added to 5 mL of deionized water, and after stirring at a speed of 500 rpm for 10 min, ultrasonic defoaming treatment was performed to obtain a uniform transparent solution;

[0041] (2) A simple wet spinning device was built using a 1 mL medical syringe, an 18G needle, a transparent plastic silica gel tube with an inner diameter of 1 mm and an outer diameter of 2 mm, a micro-injection pump, a control panel, and a 10W ultraviolet lamp;

[0042] (3) The hydrogel precursor solution was injected into the silica gel tube with a length of 50 mm at a speed of 2 mL / h, and the tube was located 2 cm below the ultraviolet lamp. The power of the ultraviolet lamp was 10W. After the precursor solution was extruded from the transparent silica gel hose, the ultraviolet lamp was turned on;

[0043] (4) The hydrogel fibers prepared were received using a glass crystallizing dish.

[0044] Test Example:

[0045] Mechanical property test: The ion-conductive hydrogel fibers prepared in Example 2 and the comparative examples were recorded for parameters, and then a universal testing machine (UTM6502, Shenzhen SANS Test Machines Co., Ltd.) was used to stretch the hydrogel fiber sample at a speed of 100 mm / min to test the stress-strain curve, and each sample was tested at least 3 times. As shown in Figure 3 .

[0046] Electrical property test: The resistance and conductivity of the conductive hydrogel fiber were tested using an LCR digital bridge, and the sample parameters were that the diameter of the ion-conductive hydrogel fiber was 1 mm and the length was 20 mm, and a flat conductive clamp was used to directly clamp the fiber at both ends for measurement. The resistance value was directly measured in the DCR mode of the LCR digital bridge, with a voltage of 1 V and a frequency of 1 KHz.

[0047] Sensing performance test: The ion-conductive hydrogel fiber was fixed on both sides of the universal tensile testing machine (UTM6502, Shenzhen SANS Test Machines Co., Ltd.) probe, and copper tape was used to lead out both ends and directly connected to the LCR digital bridge, the length of the ion-conductive hydrogel fiber was 30 mm, and the distance between the two probes was 10 mm. The relative strain of 1 / 3 / 5%, 50%-200% was tested for 3 cycles, and the stretching speed of small strain was 50 mm / min and the stretching speed of large strain was 100 mm / min. As shown in Figure 4 .

[0048] Self-healing performance test: The universal material testing machine was used to test the stress-strain curve and resistance value of the ion-conductive hydrogel fiber under different self-healing times, and the relative mechanical property and electrical property self-healing efficiency were calculated, and the test parameters were as follows: for mechanical property, the fiber sample length was 30 mm and the stretching speed was 100 mm / min for stress-strain curve test. For electrical property, the sample length was 20 mm, the voltage was 1 V, and the resistance change before and after self-healing was measured.

[0049] Human sensing performance test: The LCR digital bridge (TH2830, Changzhou Tonghui Electronics Co., Ltd.) was used to test the resistance change of the ion-conductive hydrogel fiber under different human body part movement conditions, and the diameter of the ion-conductive hydrogel fiber was 1 mm and the length was 20 mm, and a conductive clamp was used at both ends of the conductive hydrogel fiber. The human body parts tested were fingers, wrists, ankles, and knees. The resistance value was directly measured in the DCR mode of the LCR digital bridge, with a voltage of 1 V and a frequency of 1 KHz.

[0050] It should be noted that the above examples are only used to illustrate the technical solutions of the present application but not to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that there are still many improvements and modifications that can be made without departing from the spirit and scope of the technical solutions of the present application, and all these improvements and modifications should be encompassed in the scope of the claims of the present application.

Claims

1. A method for preparing a low-modulus self-healing cellulose nanofiber-based hydrogel fiber strain sensing material, characterized by, The preparation method comprises the following steps: (1) a certain mass of polymer monomer acrylamide (AM), TEMPO oxidized cellulose nanofiber solution (TOCNF), sodium chloride, photoinitiator L2959, N-N-methylene bisacrylamide (MBA) and glycerol are added into a range of 4-10 mL of deionized water, and after stirring at a speed of 300-600 rpm for 8-15 min, ultrasonic defoaming treatment is performed to obtain a uniform transparent solution; (2) a simple wet spinning device is built using a medical syringe, a needle with a range of 15-20G, a transparent silicone tube, a micro-injection pump, a control panel and a UV lamp; (3) the hydrogel precursor solution is injected into the transparent silicone tube at a certain speed, the tube is located directly below the UV lamp, and the UV lamp is turned on after the precursor solution is extruded from the transparent silicone hose; (4) a glass crystallizing dish is used to receive the prepared hydrogel fiber.

2. The production method according to claim 1, characterized by, In step (1), the cellulose nanofiber content of the TEMPO oxidized cellulose nanofiber solution ranges from 0.5 to 1.2%, and the solvent is water.

3. The preparation method according to claim 1, characterized in that, In step (1), the addition amount of AM ranges from 1 to 2.5 g, the addition amount of glycerol ranges from 2 to 6 g, the addition amount of TOCNF solution ranges from 1 to 4 g, the addition amount of photoinitiator L2959 ranges from 0.005 to 0.3 g, and the addition amount of MBA ranges from 6 to 12 mg.

4. The method of claim 1, wherein, In step (2), the size of the transparent silicone tube is 1-5 mm in inner diameter and 2-10 mm in outer diameter, and the total power of the UV lamp is 8-15 W.

5. The preparation method according to claim 1, characterized in that, In step (3), the injection speed of the micro-injection pump ranges from 1.5 to 2.5 mL / h, and the length of the transparent silicone tube ranges from 30 to 50 mm.

6. The method of claim 1, wherein, In step (3), the transparent silicone tube is located 1-5 cm below the UV lamp, and the irradiation power of the UV lamp is 8-15 W.

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