Preparation method of self-healing hydroxyethyl cellulose-based hollow-structure hydrogel fiber strain sensing material

Abstract

The invention discloses a preparation method of a self-healing hydroxyethyl cellulose-based hollow-structure hydrogel fiber strain sensing material. The hydrogel precursor solution is injected into a mold composed of transparent polytetrafluoroethylene tubes with different diameters through a disposable syringe, the mold is put into an ultraviolet curing box to be irradiated for a certain time, the interior of the hollow fiber is coated with a certain amount of liquid metal mixture, and the final hollow-structure conductive hydrogel fiber is obtained. In a cross-linked network in the prepared hydrogel fiber, a phenylboronic acid group in the ionic liquid and a cis-diol bond on the surface of hydroxyethyl cellulose form a dynamic borate bond, and a dynamic chemical cross-linking site is provided, so that the stability of the hydrogel network is further improved. The resistance-type strain sensor assembled by using the hydrogel fiber has linear sensitivity 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 self-healing hydroxyethyl cellulose-based hollow structure hydrogel fiber strain sensing material. BACKGROUND

[0002] Emerging flexible electronics offer a promising solution to the discomfort caused by the wearing of commercial rigid sensors, thanks to their good mechanical structure, comfortable experience, tight interface integration and multifunctionality. Such flexible sensors can provide stable and intimate contact with the soft human body to record physiological signals and assess biochemical information. Hydrogel fibers are ideal candidates for in-situ monitoring of human physiological signals due to their adjustable mechanical properties, and can be divided into ionically and electronically conductive hydrogels according to the differences in conductive mechanisms. Ionically conductive hydrogels achieve electrical response through the directional migration of free ions in the electrolyte medium, and exhibit excellent linear response characteristics in a large strain range, but have high impedance. Electronically conductive hydrogels rely on conductive fillers (such as carbon nanotubes, silver nanowires and MXene) to build an electronic conductive network, although the resistance is small, but the conductive path network is easily broken due to the deformation of the matrix, leading to irreversible attenuation of the sensing performance. The self-healing polyacrylamide phenylboronic acid ionic liquid hydroxyethyl cellulose liquid metal hydrogel fiber prepared in the present application has a special hollow structure, which can well protect the liquid metal conductive coating and avoid direct contact with the measured part of the human body to cause changes in resistance under non-strain conditions. SUMMARY

[0003] The purpose of the present application is to solve the problems of poor conductivity stability of existing flexible sensing devices, and to provide a hollow structure conductive hydrogel fiber resistance strain sensing material. The hollow structure conductive hydrogel fiber obtained has a stable conductive path formed by filling the internal hollow cavity with a liquid metal conductive mixture.

[0004] To solve the above technical problems, the present application provides the following technical scheme: a preparation method of a self-healing hydroxyethyl cellulose-based hollow structure hydrogel fiber strain sensing material, comprising the following steps:

[0005] (1) First, prepare a phenylboronic acid ionic liquid polymer monomer: dissolve 0.65-0.95 g of 4-bromomethylphenylboronic acid in a range of 15-30 mL of ethyl acetate, and then add 0.40-0.55 mL of 1-vinylimidazole. Condense and reflux under nitrogen environment at a range of 70-90℃ for 20-24 hours, wash the obtained light yellow solid with ethyl acetate, and then vacuum dry at a range of 45-55℃ for 12-16 hours to obtain the product phenylboronic acid ionic liquid.

[0006] (2) A certain amount of polymer monomer acrylamide (AM), phenylboronic acid ionic liquid (PBA-IL), hydroxyethyl cellulose (HEC), photoinitiator L2959, N-N-methylene bisacrylamide (MBA) and glycerol (Gly) are added to deionized water, heated and stirred for 10-15 minutes, and finally placed in an ultrasonic cleaning instrument for defoaming treatment to obtain a uniform transparent solution;

[0007] (3) The solution is injected into a mold composed of transparent polytetrafluoroethylene (PTFE) tubes of different diameters through a disposable syringe, and then the mold is placed in a UV curing box for irradiation for a period of time to form a hydrogel fiber;

[0008] (4) The hollow structure hydrogel fiber removed from the tube is placed at room temperature for a period of time to achieve a balance between water loss and water absorption of the hydrogel;

[0009] (5) A certain amount of nickel powder and liquid metal (gallium-indium alloy, 16°) are stirred on an evaporating dish until they are uniformly mixed to obtain a liquid metal mixed conductive material for storage;

[0010] (6) The liquid metal mixed conductive material is coated on the inner wall and both ends of the hollow structure hydrogel using a stainless steel wire, and a soft conductive fabric is used to connect the two ends to form a conductive device.

[0011] Further, in step (2), the amount of HEC added is in the range of 0.05-1 g, the amount of AM added is in the range of 1-2.5 g, the amount of Gly added is in the range of 2-4 g, the amount of PBA-IL added is in the range of 0.05-1 g, the amount of photoinitiator L2959 added is in the range of 0.05-0.2 g, and the amount of MBA added is in the range of 5-10 mg.

[0012] Further, in step (3), the mold is composed of 4 PTFE tubes and a stainless steel wire, the outer PTFE tube has a length range of 8-10 cm, an inner diameter range of 1-2 mm, and a wall thickness range of 0.5-1.5 mm, the core PTFE tube has a length range of 5-10 cm, an inner diameter range of 0.5-0.8 mm, and a wall thickness range of 0.1-0.3 mm, the two end support PTFE tubes have a length range of 2-5 cm, an inner diameter range of 1-2 mm, and a wall thickness range of 1.0-3.0 mm, and the iron wire has a length range of 5-10 cm and a diameter range of 0.5-1.0 mm.

[0013] Further, in step (3), the UV light intensity is in the range of 80-100 W, and the irradiation time is in the range of 15-30 min.

[0014] Further, in step (4), the placement environment of the hollow structure hydrogel fiber is in the range of 20-40°C and 60-80% RH.

[0015] Further, in step (5), the mass ratio of liquid metal to nickel powder ranges from 8:1 to 10:1, and the diameter of the nickel powder ranges from 10 to 20 microns.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] (1) The self-healing polyacrylamide-benzeneboronic acid ionic liquid-hydroxyethyl cellulose-liquid metal hollow structure conductive hydrogel fiber resistive strain sensing material prepared by the present application can form a stable conductive path in the hollow cavity of the fiber and a physical isolation layer formed by the hydrogel shell. This structure effectively solves the problem of direct contact between the conductive coating and the human body surface, and significantly improves the resistance stability of the strain sensor.

[0018] (2) The self-healing polyacrylamide-benzeneboronic acid ionic liquid-hydroxyethyl cellulose-liquid metal hollow structure conductive hydrogel fiber resistive strain sensing material prepared by the present application has a double-network system formed by PAM (PBA-IL) and HEC, which endows the hydrogel fiber with excellent tensile properties. In terms of electrical properties, the combination of strain sensing sensitivity and wide strain range exhibits good strain response performance. In terms of self-healing performance, the self-healing performance of the hydrogel fiber is significantly enhanced based on the synergistic effect of dynamic borate ester bonds and multiple hydrogen bonds. Specifically, in terms of mechanical properties, the strain recovery efficiency of the broken fiber can be as high as 75% after healing for 120 minutes. In terms of electrical properties, the healing process is faster, and the conductivity recovery efficiency approaches complete recovery, reaching 99%, after only 30 minutes.

[0019] (3) The polyacrylamide-benzeneboronic acid ionic liquid-hydroxyethyl cellulose-liquid metal hollow structure conductive hydrogel fiber resistive strain sensing material prepared by the present application can be used in real-time detection devices for human body movement, including wrist movement, finger bending, knee movement, etc. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiment description. 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 creative labor. Among them:

[0021] Figure 1 Schematic diagram for the preparation of hydrogel fiber and human body sensing.

[0022] Figure 2 Preparation process of hollow structure hydrogel fiber.

[0023] Figure 3 Preparation process of the hollow structure hydrogel fiber, Figure A is the preparation process of the liquid metal mixed conductive material; Figure B is the state of the material with different mass ratios of liquid metal and nickel powder.

[0024] Figure 4 Sensing performance characterization of the hollow structure hydrogel fiber, Figure A is the strain sensitivity coefficient of the hollow structure hydrogel conductive fiber; Figure B is the relative resistance change of the hollow structure hydrogel conductive fiber under a small strain condition of 10-50%; Figure C is the relative resistance change of the hollow structure hydrogel conductive fiber under different stretching speeds under a strain condition of 50%; Figure D is the instantaneous resistance response of the hollow structure hydrogel conductive fiber under a strain condition of 20%.

[0025] Figure 5 Self-healing performance characterization of the hollow structure hydrogel fiber, Figure A is the real object figure of the hollow structure hydrogel conductive fiber re-lighting the bulb after self-healing; Figure B is the stress-strain curve of the hollow structure hydrogel fiber under different self-healing times; Figure C is the self-healing efficiency of the maximum strain and the maximum stress of the hollow structure hydrogel fiber; Figure C is the current change of the hollow structure hydrogel conductive fiber under the condition of repeated cutting.

[0026] Figure 6 The test results of the polyacrylamide phenylboronic acid ionic liquid hydroxyethyl cellulose liquid metal hollow structure conductive hydrogel fiber resistance strain sensing material prepared by the present application after being assembled into a flexible strain sensor to test the movement of each part of the human body: Figure A is a schematic diagram of the parts of the human body that can be tested by the flexible sensor; Figure B is the relative resistance value change of the flexible strain sensor when testing the finger bending at different angles; Figure C is the relative resistance value change of the flexible strain sensor when testing the wrist bending at different angles. DETAILED DESCRIPTION

[0027] 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.

[0028] In the following description, a large number of 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 scope of the present application, therefore the present application is not limited to the specific embodiments disclosed below.

[0029] 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 present 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.

[0030] Example 1

[0031] The preparation of an ionic liquid polymer monomer, the steps are as follows:

[0032] (1) 0.8594 g of 4-bromomethylphenylboronic acid was dissolved in 30 mL of ethyl acetate, the interior was defoamed using an ultrasonic cleaning instrument, and 0.452 mL of 1-vinylimidazole was added.

[0033] (2) The whole system was placed in an oil bath environment at 70°C, the inside of the system was filled with nitrogen, and the condensation reflux was carried out for 24 h.

[0034] (3) After the reaction was completed, the unreacted upper solution was poured off, and 50 mL of ethyl acetate was used to rinse the unreacted material to obtain a light yellow solid attached to the inner wall.

[0035] (4) The obtained light yellow solid was placed in a vacuum drying box at 45°C for 12 h to obtain the final product, phenylboronic acid ionic liquid.

[0036] Example 2

[0037] The assembly of the self-made PTFE mold, the steps are as follows:

[0038] (1) Four tubes and stainless steel wires were cut according to the following dimensions: outer PTFE tube length 8 cm, core PTFE tube length 7 cm, PTFE tube length at both ends 2 cm, and stainless steel wire length 9 cm.

[0039] (2) To ensure that the hollow part of the hollow hydrogel fiber is in the middle of the fiber, the PTFE tube was immersed in water at 90°C for about 10 min, and then cooled by immersing in cold water, ensuring that the PTFE tube maintains a certain degree of flatness.

[0040] (3) The stainless steel wire with a diameter of 0.5 mm was combined with the core PTFE tube, and finally it was sleeved inside the outer PTFE tube, and the PTFE tube with a length of 2 cm, an inner diameter of 1 mm, and a wall thickness of 1.5 mm was used as support on both sides.

[0041] Example 3

[0042] The preparation of a liquid metal mixture, the steps are as follows:

[0043] (1) First, weigh 1 g of liquid metal, then weigh 0.1 g of nickel powder, and place the weighed substances in a crystallizing dish for later use.

[0044] (2) Take a portion of the nickel powder into the liquid metal using a micro spatula, mix and stir until completely mixed.

[0045] Example 4

[0046] A polyacrylamide phenylboronic acid ionic liquid hydroxyethyl cellulose liquid metal hollow structure conductive hydrogel fiber resistive strain sensing material, as shown in Figure 2 comprises the following steps:

[0047] (2) 2 g of AM, 0.5 g of PBA-IL, 0.05 g of HEC, 0.01 g of photoinitiator L2959, 10 mg of MBA, and 3 g of Gly were added to deionized water, heated and stirred for 10 minutes, and finally placed in an ultrasonic cleaning instrument for defoaming treatment to obtain a uniform transparent solution;

[0048] (3) The solution was injected into a mold composed of transparent polytetrafluoroethylene (PTFE) tubes of different diameters by a disposable syringe, and then the mold was placed in a UV curing box for irradiation for a period of time to form a hydrogel fiber;

[0049] (4) The hollow structure hydrogel fiber removed from the tube was placed in a condition of 25°C, 80% RH for 24h to reach the water loss and water absorption state balance of the hydrogel;

[0050] (5) Liquid metal and nickel powder with a mass ratio of 10:1 were weighed and stirred on an evaporating dish until they were evenly mixed to obtain a liquid metal mixed conductive substance for storage;

[0051] (6) The liquid metal mixed conductive substance was coated on the inner wall and both ends of the hollow structure hydrogel fiber using a stainless steel wire, and a soft conductive fabric was used to connect the two ends to form a conductive device.

[0052] Comparative Example 1

[0053] The same raw materials and preparation parameters as in Example 2 were used, but the mass ratio of liquid metal to nickel powder was changed to prepare a liquid metal conductive mixture for comparison of the form, as shown in Figure 3 comprises the following steps:

[0054] (1) First, weigh 1 g of liquid metal, then weigh 1 g, 0.2 g, and 0 g of nickel powder, and place the weighed substances in a crystallizing dish for storage.

[0055] (2) Use a micro spatula to take a portion of the nickel powder into the liquid metal, mix and stir until completely mixed.

[0056] Test Example:

[0057] Substance form comparison: compare the substance form of the liquid metal mixed conductive substance prepared in Example 3 with that of the comparative example, and take pictures of the liquid metal mixed conductive substance prepared in different proportions on a cover glass.

[0058] Electrical performance test: fix the assembled hollow structure conductive hydrogel fiber sensor on both sides of the probe of the universal tensile testing machine (UTM6502, Shenzhen SMI, China), use conductive fabric to lead out both ends and connect with the LCR digital bridge, the length of the conductive hydrogel fiber is 30 mm, and the distance between the two probes is 10 mm. Test the relative strain of 10%-50% and 100%-500% for 3 cycles, the small strain tensile speed is 50 mm / min, and the large strain tensile speed is 100 mm / min. Test the instantaneous resistance response under the condition of a tensile speed of 500 mm / min and a relative strain of 40%, as shown in Figure 4 .

[0059] Self-healing performance test: use the universal material testing machine to test the stress-strain curve and resistance value of the conductive hydrogel fiber under different self-healing times, calculate the relative mechanical performance and self-healing efficiency of the electrical performance, and the test parameters are as follows: for mechanical performance, select the fiber sample length of 30 mm, and test the stress-strain curve at a tensile speed of 50 mm / min; for electrical performance, select the sample length of 20 mm, and measure the resistance change before and after self-healing at a voltage of 1 V, as shown in Figure 4 .

[0060] Human body sensing performance test: use the LCR digital bridge (TH2830, Changzhou Tonghui Electronics Co., Ltd.) to test the resistance change of the conductive hydrogel fiber under the movement condition of part of the human body, the conductive hydrogel fiber has an inner diameter of 1 mm, an outer diameter of 2 mm, and a length of 20 mm, and the conductive hydrogel fiber is led out at both ends with conductive fabric for measurement. The resistance value is directly measured in the DCR mode of the LCR digital bridge, the voltage is 1 V, and the frequency is 1 KHz, as shown in Figure 6 .

[0061] 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, those skilled in the art should understand 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, which should be covered in the scope of the claims of the present application.

Claims

1. A method for preparing a self-healing hydroxyethylcellulose-based hollow-structured hydrogel fiber strain sensing material, characterized in that, The preparation method comprises the following steps: (1) A certain amount of polymer monomer acrylamide (AM), phenylboronic acid ionic liquid (PBA-IL), hydroxyethyl cellulose (HEC), photoinitiator L2959, N-N-methylene bisacrylamide (MBA) and glycerol (Gly) are added to a range of 5-10 mL of deionized water, heated and stirred for 10-15 minutes, and finally placed in an ultrasonic cleaning instrument for defoaming treatment to obtain a uniform transparent solution; (2) The solution is injected into a mold composed of different diameter transparent polytetrafluoroethylene (PTFE) tubes through a disposable syringe, and then the mold is placed in a ultraviolet curing box for irradiation for a period of time to form a hydrogel fiber; (3) The hollow structure hydrogel fiber taken out from the tube is placed in a room temperature environment for 20-24 hours to achieve the water loss and water absorption state balance of the hydrogel; (4) A certain amount of nickel powder and liquid metal are stirred on a crystallizing dish until they are evenly mixed to obtain a liquid metal mixed conductive material for storage; (5) The liquid metal mixed conductive material is coated on the inner wall and both ends of the hollow structure hydrogel using a stainless steel wire, and a soft conductive fabric is used to connect both ends to form a conductive device.

2. The production method according to claim 1, characterized by, The preparation process of PBA-IL in step (1) is as follows: 0.65-0.95 g of 4-bromomethylphenylboronic acid is dissolved in a range of 15-30 mL of ethyl acetate, and after complete dissolution, 0.40-0.55 mL of 1-vinylimidazole is added. Under a nitrogen environment, condensation reflux is carried out at a range of 70-90°C for 20-24 hours. The obtained light yellow solid is washed with ethyl acetate, and then vacuum dried at a range of 45-55°C for 12-16 hours to obtain the product phenylboronic acid ionic liquid.

3. The preparation method according to claim 1, characterized in that, In step (1), the addition amount of HEC ranges from 0.05 to 1 g, the addition amount of AM ranges from 1 to 2.5 g, the addition amount of Gly ranges from 2 to 4 g, the addition amount of PBA-IL ranges from 0.2 to 0.8 g, the addition amount of photoinitiator L2959 ranges from 0.05 to 0.2 g, and the addition amount of MBA ranges from 5 to 10 mg.

4. The method of claim 1, wherein, In step (2), the mold is composed of four PTFE tubes and one stainless steel wire, the outer PTFE tube has a length range of 8-10 cm, an inner diameter range of 1-2 mm, and a wall thickness range of 0.5-1.5 mm, the core PTFE tube has a length range of 5-10 cm, an inner diameter range of 0.5-0.8 mm, and a wall thickness range of 0.1-0.3 mm, the two end supporting PTFE tubes have a length range of 2-5 cm, an inner diameter range of 1-2 mm, and a wall thickness range of 1.0-3.0 mm, and the iron wire has a length range of 5-10 cm and a diameter range of 0.5-1.0 mm.

5. The preparation method according to claim 1, characterized in that, In step (2), the ultraviolet light intensity ranges from 80 to 100 W, and the irradiation time ranges from 15 to 30 min.

6. The method of claim 1, wherein, In step (3), the hollow structure hydrogel fiber is placed in an environment with a temperature range of 20-40°C and a relative humidity range of 60-80%.

7. The preparation method according to claim 1, characterized in that, In step (4), the mass ratio of liquid metal to nickel powder ranges from 8:1 to 10:1, and the diameter of the nickel powder ranges from 10 to 20 microns.

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