Conductive hydrogel, preparation method thereof and application of conductive hydrogel in flexible resistive sensor

Abstract

The invention provides conductive hydrogel, a preparation method and application of the conductive hydrogel in a flexible resistance type sensor, and the preparation method of the conductive hydrogel comprises the following steps: adding polyvinyl alcohol and silk fibroin into water for dissolving to obtain a polyvinyl alcohol / silk fibroin solution; the preparation method comprises the following steps: adding tannic acid, borax and graphene into a sodium chloride solution for dissolving to obtain a tannic acid / borax / graphene solution; the polyvinyl alcohol / silk fibroin solution and the tannic acid / borax / graphene solution are mixed and cross-linked, and the conductive hydrogel is obtained. According to the conductive hydrogel, the preparation method and the application of the conductive hydrogel in the flexible resistance type sensor, the polyvinyl alcohol, the silk fibroin, the borax, the graphene, the tannic acid and the sodium chloride are subjected to composite crosslinking, and the high-sensitivity tensile response conductive hydrogel is prepared; the development of the flexible sensor with excellent flexibility and skin-friendly performance and excellent self-healing capability and antibacterial capability is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensors, and in particular to a conductive hydrogel, a preparation method thereof, and an application thereof in a flexible resistive sensor. Background Art

[0002] Nowadays, the rapid development of electronic skin and wearable technologies has brought great convenience to human life. Flexible sensors have been widely recognized due to their excellent bendability, stretchability, repeatability, and fast response, thus providing people with a comfortable wearing experience. Most traditional flexible wearable devices combine conductive materials with flexible substrates and act on the human skin under external forces. However, these sensors often have poor adaptability to the skin and tend to cause discomfort and unstable monitoring signals when worn.

[0003] Ideally, flexible sensors applied to wearable devices should have excellent flexibility and skin-friendliness, outstanding self-healing ability and antibacterial ability, as well as stable signal response. At present, the development of sensors with all these characteristics at low cost has become the main challenge at this stage. Summary of the Invention

[0004] Based on the technical problems existing in the background art, the present invention proposes a conductive hydrogel, a preparation method thereof, and an application thereof in a flexible resistive sensor. By compound cross-linking of polyvinyl alcohol, silk fibroin, borax, graphene, tannic acid, and sodium chloride, a highly sensitive stretch-responsive conductive hydrogel is prepared, realizing the development of a flexible sensor with excellent flexibility and skin-friendliness, outstanding self-healing ability and antibacterial ability.

[0005] A preparation method of a conductive hydrogel proposed by the present invention includes the following steps:

[0006] S1. Add polyvinyl alcohol and silk fibroin into water and dissolve to obtain a polyvinyl alcohol / silk fibroin solution;

[0007] S2. Add tannic acid, borax, and graphene into a sodium chloride solution and dissolve to obtain a tannic acid / borax / graphene solution;

[0008] S3. Mix and cross-link the polyvinyl alcohol / silk fibroin solution with the tannic acid / borax / graphene solution to obtain the conductive hydrogel.

[0009] Preferably, in step S1, add polyvinyl alcohol and silk fibroin into water, heat to 90-100 °C, and stir for 1-3 h to achieve dissolution.

[0010] Preferably, in step S1, the mass ratio of polyvinyl alcohol to silk fibroin is 1:0.5-1, preferably 1:0.6.

[0011] Preferably, in step S2, tannic acid, borax, and graphene are added to the sodium chloride solution and stirred for 0.5 - 2 h to achieve dissolution.

[0012] Preferably, in step S2, the mass ratio of tannic acid, borax, sodium chloride, and graphene is 1:0.4 - 0.6:3 - 4:0.3 - 0.5, preferably 1:0.48:3.2:0.36.

[0013] Preferably, in step S3, the content of polyvinyl alcohol in the polyvinyl alcohol / silk fibroin solution is 5 - 15 wt%, and the content of tannic acid in the tannic acid / borax / graphene solution is 1 - 10 wt%; the volume ratio of the polyvinyl alcohol / silk fibroin solution to the tannic acid / borax / graphene solution is 1 - 3:1.

[0014] The present invention also provides a conductive hydrogel prepared by the above - mentioned preparation method.

[0015] The present invention also provides an application of the above - mentioned conductive hydrogel in a flexible resistive sensor.

[0016] In the present invention, the flexible resistive sensor has a large stretching ratio, high sensitivity, short response / recovery time, small resolution, and has the advantages of skin - friendliness, self - healing property, biodegradability, etc. The degradation products are non - polluting, which conforms to the green sustainable development strategy of our country.

[0017] Preferably, the flexible resistive sensor includes a conductive hydrogel and metal electrodes adhered to the upper and lower surfaces of the conductive hydrogel.

[0018] Preferably, the flexible resistive sensor is used in wearable devices, electronic skin, or human health monitoring.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides a conductive hydrogel, a preparation method thereof, and an application in a flexible resistive sensor. The conductive hydrogel is formed by mixing and cross - linking polyvinyl alcohol (PVA), borax (Borax), silk fibroin (SF), tannic acid (TA), sodium chloride, and graphene (GR) in a certain proportion. The borate ester bond formed between Borax and PVA polymerizes the macromolecules inside PVA, endowing the hydrogel with self - healing performance; the addition of SF can not only act as a reinforcing agent but also stabilize the non - Newtonian behavior between Borax and PVA; the combination of SF and TA enhances the self - healing ability of the hydrogel, improving the mechanical properties and viscoelasticity of the hydrogel; GR as a conductive material can greatly improve the conductivity of the hydrogel; the addition of NaCl not only improves the conductivity of the hydrogel but also enables the hydrogel to form a salt solution under low - temperature conditions, endowing it with anti - freezing ability.

[0021] The conductive hydrogel described in the present invention is applied to a flexible resistive sensor. At a low stretching level, the hydrogel mainly conducts electricity through GR. As the stretching rate increases, the main conductive component changes from GR to free ions, so that the hydrogel has higher sensitivity at a high stretching rate. Finally, the flexible resistive sensor based on the conductive hydrogel of the present invention has good stretchability (>6000%), an extremely fast response and recovery time (12.5 ms), and a wide strain sensing range (>400%); it exhibits good self-healing ability after being damaged by external forces and can be biodegradable. Description of the Drawings

[0022] Figure 1 Schematic diagram of the preparation process of the conductive hydrogel described in Example 1 of the present invention;

[0023] Figure 2 Tensile response curve of the conductive hydrogel described in Example 1 of the present invention;

[0024] Figure 3 Tensile response curves of the conductive hydrogel described in Example 1 of the present invention after different days;

[0025] Figure 4 Tensile response curves of the conductive hydrogel described in Comparative Example 1 of the present invention after different days;

[0026] Figure 5 Mass comparison curve within seven days of the conductive hydrogels described in Example 1 and Comparative Example 1 of the present invention;

[0027] Figure 6 Response curves of the conductive hydrogel described in Example 1 of the present invention after different stretching ratios at the same stretching frequency;

[0028] Figure 7 Response curves of the conductive hydrogel described in Example 1 of the present invention after different stretching frequencies at the same stretching ratio;

[0029] Figure 8 Self-healing characteristic curve of the conductive hydrogel described in Example 1 of the present invention;

[0030] Figure 9 Response time test curve of the conductive hydrogel described in Example 1 of the present invention;

[0031] Figure 10 Relative resistance change curve of the conductive hydrogel described in Example 1 of the present invention gradually stretched from 0 to 10%;

[0032] Figure 11 Tensile response curve of the conductive hydrogel described in Example 1 of the present invention at low temperature;

[0033] Figure 12 Graph showing the degradation characteristics test results of the conductive hydrogel described in Example 1 of the present invention. Detailed implementation manners

[0034] Next, the technical solutions of the present invention will be described in detail through specific examples. It should be clearly stated that these examples are for illustrative purposes only and are not construed as limiting the scope of the present invention.

[0035] Among the raw materials used in the following examples, PVA, PVA - 224, M w ~205000; SF, product number BBM1118, purchased from Bomei Laboratory; GR, purity > 98%, 1 - 3 layers, monolayer rate > 80%, D50: 7 - 12μm, D90: 11 - 15μm.

[0036] Example 1

[0037] Figure 1 Schematic diagram of the preparation process of the conductive hydrogel described in Example 1 of the present invention. Refer to Figure 1 , this example proposes a conductive hydrogel, and its preparation method specifically includes:

[0038] (1) Add PVA and SF to deionized water. The mass ratio of PVA to SF is 1:0.6. Slowly heat to 95°C and stir for 2 hours until completely dissolved to obtain a PVA / SF solution, where the content of PVA is 10wt%.

[0039] (2) Add TA, Borax, and GR to the sodium chloride solution in sequence. The mass ratio of TA, Borax, sodium chloride, and GR is 1:0.48:3.2:0.36. Stir at room temperature for 1 hour until completely dissolved to obtain a TA / Borax / GR solution, where the content of TA is 4wt%.

[0040] (3) Drop the TA / Borax / GR solution into the PVA / SF solution. The volume ratio of the TA / Borax / GR solution to the PVA / SF solution is 1:2. After stirring and mixing at room temperature and cross - linking reaction, the conductive hydrogel is obtained.

[0041] This example also proposes a flexible resistive sensor, and its preparation method specifically includes:

[0042] After cutting the copper foil into a size of 1.5×20 cm, uniformly coat the surface with silver glue solution, fold it in half and then paste it on both sides of the above - mentioned conductive hydrogel, and the flexible resistive sensor is obtained.

[0043] Comparative Example 1

[0044] This comparative example also presents a conductive hydrogel, and its preparation method specifically includes:

[0045] (1) Add PVA to deionized water, slowly heat it to 95 °C, stir for 2 h until completely dissolved to obtain a PVA solution, where the content of PVA is 10 wt%.

[0046] (2) Add TA, Borax, and GR to the sodium chloride solution in sequence. The mass ratio of TA, Borax, sodium chloride, and GR is 1:0.48:3.2:0.36. Stir at room temperature for 1 h until completely dissolved to obtain a TA / Borax / GR solution, where the content of TA is 4 wt%.

[0047] (3) Drop the TA / Borax / GR solution into the PVA solution. The volume ratio of the TA / Borax / GR solution to the PVA solution is 1:2. After stirring and mixing at room temperature and undergoing a cross-linking reaction, the conductive hydrogel is obtained.

[0048] This comparative example also simultaneously presents a flexible resistive sensor, and its preparation method specifically includes:

[0049] After cutting the copper foil into a size of 1.5×20 cm, uniformly coat the surface with a silver paste solution, fold it in half and then paste it on both sides of the above-mentioned conductive hydrogel, and the flexible resistive sensor is obtained.

[0050] Figure 2 is the tensile response curve of the conductive hydrogel described in Example 1 of the present invention. Referring to Figure 2 it can be seen that when the hydrogel is subjected to tensile stimulation, it can be divided into three response stages. When the tensile ratio is small, the distance between graphene sheets is small, and at this time, the conduction of graphene mainly dominates; as the tensile ratio increases, the distance between graphene sheets gradually increases, and at this time, the free particles and graphene in the hydrogel conduct electricity together; when the tensile ratio continues to increase, the distance between graphene sheets becomes farther, and the conductive effect is very weak. At this time, the conductive effect of the hydrogel mainly depends on the free particles ionized. The addition of SF will cause the movement of free particles to be restricted, and macroscopically, the resistance change is very obvious, and the sensitivity also increases accordingly.

[0051] Figure 3 is the tensile response curve of the conductive hydrogel described in Example 1 of the present invention after different days, Figure 4 is the tensile response curve of the conductive hydrogel described in Comparative Example 1 of the present invention after different days. Referring to Figure 3 、 4 it can be seen that the presence of SF hinders ion conduction in the conductive hydrogel in the high-tensile state, the resistance change is more obvious, and the sensitivity also increases accordingly. The comparison between the two proves that the addition of SF significantly improves the tensile sensitivity of the conductive hydrogel.

[0052] Figure 5 This is the mass comparison curve of the conductive hydrogel described in Example 1 and Comparative Example 1 of the present invention within seven days. Referring to Figure 5 It can be seen that due to the certain moisturizing effect of SF, it can be seen that the remaining mass of the conductive hydrogel every day after adding SF is higher than that of the conductive hydrogel without adding SF. However, after seven days, a lot of water still evaporates and the remaining mass is small. Therefore, the hydrogel is simply encapsulated with silicone rubber, and the mass hardly changes after seven days. With only simple encapsulation, the hydrogel can be stored for a long time.

[0053] Figure 6 This is the response curve of the conductive hydrogel described in Example 1 of the present invention after different stretching ratios at the same stretching frequency. Referring to Figure 6 It can be seen that the conductive hydrogel described in Example 1 exhibits good periodicity and reliability at stretching ratios of 5%, 20%, and 50%, highlighting the effectiveness of this conductive hydrogel in stretching applications.

[0054] Figure 7 This is the response curve of the conductive hydrogel described in Example 1 of the present invention after different stretching frequencies at the same stretching ratio. Referring to Figure 7 It can be seen that after the conductive hydrogel described in Example 1 is stretched by 50% at stretching rates of 25 mm / min, 50 mm / min, 100 mm / min, and 200 mm / min respectively, the results show that the resistance change of this conductive hydrogel remains consistent at different stretching rates and the peak fluctuation is extremely small.

[0055] Figure 8 This is the self-healing characteristic curve of the conductive hydrogel described in Example 1 of the present invention. Referring to Figure 8 It can be seen that first, its initial resistance is measured and then it is cut off. The time required for it to recover to the initial resistance is the self-healing time. From Figure 8 it can be seen that the self-healing time is about 425 ms.

[0056] Figure 9 This is the response time test curve of the conductive hydrogel described in Example 1 of the present invention. Referring to Figure 9 It can be seen that in order to better simulate the impulse signal, the inventor reduced the stretching ratio of the conductive hydrogel to minimize the stretching time as much as possible. When the stretching ratio is 2%, the measured response and recovery times of the conductive hydrogel are both 12.5 ms, highlighting the excellent response and recovery speed of this conductive hydrogel.

[0057] Figure 10 This is the relative resistance change curve of the conductive hydrogel described in Example 1 of the present invention gradually stretched from 0 to 10%. Referring to Figure 10It can be seen that for each applied strain, the relative resistance change shows an obvious rising step shape, and the strain and response signal of the conductive hydrogel can remain stable within a specific time. In addition, as can be seen from Figure 10 , the conductive hydrogel can recognize a minimum strain signal of 1%.

[0058] Figure 11 This is the tensile response curve of the conductive hydrogel described in Embodiment 1 of the present invention at low temperature. Referring to Figure 11 , it can be seen that first, the tensile response curve of the conductive hydrogel at normal temperature is tested, then the conductive hydrogel is placed at -5°C for 24 h, and its response curve is tested. Finally, the conductive hydrogel is restored to room temperature and its tensile response curve is retested. It can be seen that although the performance of the conductive hydrogel decreases at low temperature, it can still be stretched normally. After being restored to room temperature, its performance is not much different from that before the test, showing excellent cold resistance.

[0059] Figure 12 This is the test result graph of the degradation characteristics of the conductive hydrogel described in Embodiment 1 of the present invention. Referring to Figure 12 , it can be seen that the conductive hydrogel is placed in a papain solution with a concentration of 0.5 g / L, and the products after 4 h and 12 h are recorded respectively. It can be seen that almost complete degradation occurs after 12 h, and the remaining products are GR and a small amount of SF, which is pollution-free to the environment.

[0060] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. A preparation method of a conductive hydrogel, characterized in that, It includes the following steps: S1. Add polyvinyl alcohol and silk fibroin into water and dissolve them to obtain a polyvinyl alcohol / silk fibroin solution; S2. Add tannic acid, borax and graphene into a sodium chloride solution and dissolve them to obtain a tannic acid / borax / graphene solution; S3. Mix and crosslink the polyvinyl alcohol / silk fibroin solution with the tannic acid / borax / graphene solution to obtain the conductive hydrogel.

2. The preparation method of the conductive hydrogel according to claim 1, characterized in that, In step S1, add polyvinyl alcohol and silk fibroin into water, heat to 90 - 100 °C and stir for 1 - 3 h to achieve dissolution.

3. The preparation method of the conductive hydrogel according to claim 1 or 2, characterized in that, In step S1, the mass ratio of polyvinyl alcohol to silk fibroin is 1:0.5 - 1, preferably 1:0.

6.

4. The preparation method of the conductive hydrogel according to any one of claims 1-3, characterized in that, In step S2, add tannic acid, borax and graphene into a sodium chloride solution and stir for 0.5 - 2 h to achieve dissolution.

5. The preparation method of the conductive hydrogel according to any one of claims 1-4, characterized in that, In step S2, the mass ratio of tannic acid, borax, sodium chloride and graphene is 1:0.4 - 0.6:3 - 4:0.3 - 0.5, preferably 1:0.48:3.2:0.

36.

6. The preparation method of the conductive hydrogel according to any one of claims 1-5, characterized in that, In step S3, the content of polyvinyl alcohol in the polyvinyl alcohol / silk fibroin solution is 5 - 15 wt%, and the content of tannic acid in the tannic acid / borax / graphene solution is 1 - 10 wt%; the volume ratio of the polyvinyl alcohol / silk fibroin solution to the tannic acid / borax / graphene solution is 1 - 3:

1.

7. A conductive hydrogel prepared by the preparation method according to any one of claims 1 - 6.

8. An application of the conductive hydrogel according to claim 7 in a flexible resistive sensor.

9. The application of the conductive hydrogel according to claim 8 in a flexible resistive sensor, characterized in that, The flexible resistive sensor includes a conductive hydrogel and metal electrodes adhered to the upper and lower surfaces of the conductive hydrogel.

10. Use of the conductive hydrogel according to claim 8 or 9 in a flexible resistive sensor, characterized in that, The flexible resistive sensor is used in wearable devices, electronic skin or human health monitoring.

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