Simple preparation method and application of high-toughness PVA conductive hydrogel

Abstract

The application relates to the technical field of high polymer material preparation, in particular to a simple preparation method and application of high-strength and high-toughness PVA conductive hydrogel, which comprises the following steps: polyvinyl alcohol is added into deionized water, and is dissolved under water bath heating to obtain a polyvinyl alcohol aqueous solution; the polyvinyl alcohol aqueous solution is cooled to room temperature, poured into a mold, sealed with a preservative film, frozen and then thawed to obtain a polyvinyl alcohol hydrogel; and the polyvinyl alcohol hydrogel is soaked in a 1 mol / L salt solution to obtain the high-strength and high-toughness PVA conductive hydrogel. The polyvinyl alcohol hydrogel prepared in the application has super-high strength, toughness and good conductivity, and can be well applied to the application of flexible sensors.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer material preparation, in particular to a simple preparation method of high-toughness PVA conductive hydrogel and application thereof. BACKGROUND

[0002] Hydrogel is a water-absorbing gel-like substance made of high polymer material, mainly composed of cross-linked polymer network. When in contact with water, the cross-linked polymer network can absorb and hold a large amount of water, thus forming a gel-like structure similar to jelly.

[0003] The polyvinyl alcohol hydrogel prepared by using polyvinyl alcohol as raw material has simple preparation method, and has advantages of flexibility, water enrichment and good biocompatibility. It is widely used in industry, agriculture, medical treatment and the like, and has wide application prospect in research of bionic electronic skin, production of wearable electronic equipment and flexible sensor and the like.

[0004] However, the polyvinyl alcohol hydrogel has the same defects as most hydrogels, i.e. poor inherent mechanical strength and easy breakage. Its low strength, toughness and weak conductivity seriously affect its application in wearable electronic equipment and flexible sensor and the like. Therefore, development of high-toughness conductive hydrogel has become a research hotspot. How to prepare high-toughness conductive hydrogel with good conductivity while maintaining the biocompatibility, non-toxicity and green environmental protection of the hydrogel has become an important research direction of the hydrogel. In view of the problems of poor mechanical property, low toughness and easy breakage and small conductivity of the polyvinyl alcohol hydrogel, the present application provides a simple and efficient preparation method of high-toughness PVA conductive hydrogel, and application of the hydrogel is shown. SUMMARY

[0005] In view of the problems in the prior art, the present application provides a preparation method of high-toughness PVA conductive hydrogel and application thereof. First, the polyvinyl alcohol aqueous solution is frozen and thawed at low temperature to form polyvinyl alcohol hydrogel, and then the polyvinyl alcohol hydrogel is soaked in various phosphate solutions to obtain high-toughness PVA conductive hydrogel. Finally, according to the high-toughness performance and good conductivity, the hydrogel is applied in the field of flexible sensor.

[0006] To achieve the above object, the present application adopts the following technical scheme:

[0007] A simple preparation method of high-toughness PVA conductive hydrogel comprises the following steps:

[0008] S1, polyvinyl alcohol is added to deionized water and dissolved under water bath heating to obtain a polyvinyl alcohol aqueous solution;

[0009] S2, pour the polyvinyl alcohol aqueous solution obtained in step S1 into a mold after cooling to room temperature, seal with plastic wrap, and then freeze in a refrigerator and thaw to obtain a polyvinyl alcohol hydrogel;

[0010] S3, the polyvinyl alcohol hydrogel obtained in step S2 is soaked in a 1 mol / L salt solution to obtain a high-toughness PVA conductive hydrogel.

[0011] Further, the water bath temperature in S1 is 95 DEG C, and the final polyvinyl alcohol aqueous solution concentration is 10wt%.

[0012] Further, the freezing temperature in S2 is -20 DEG C, and the freezing time is 12 hours.

[0013] Further, the concentration of the salt solution in S3 is 1 mol / L.

[0014] Further, the salt solution is one of sodium dihydrogen phosphate, disodium hydrogen phosphate and sodium phosphate.

[0015] Further, the soaking time in S3 is 12-60 hours.

[0016] The application also provides the application of the PVA conductive hydrogel in the field of flexible sensors.

[0017] The application has the following advantages:

[0018] The application uses polyvinyl alcohol as a raw material, which has good biocompatibility and biodegradability, and can be applied in a wider range. The method for preparing the hydrogel is a freeze-thaw method of physical crosslinking, and no other chemical reagents are introduced, so it is more green and environmentally friendly, non-toxic and non-polluting.

[0019] The application does not use chemical crosslinking and does not introduce other chemical reagents, so the preparation process is simple and convenient. After the hydrogel is prepared by the freeze-thaw method, it can be soaked in a 1 mol / L phosphate salt solution to obtain a high-toughness PVA conductive hydrogel.

[0020] The polyvinyl alcohol hydrogel prepared in the application has ultra-high strength, toughness and good conductivity, and can be well applied to flexible sensors. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a preparation flowchart of the hydrogel;

[0022] Figure 2 It is a real object diagram of the PVA hydrogel after soaking in a sodium dihydrogen phosphate aqueous solution, a: before soaking, b: after soaking;

[0023] Figure 3Photographs of PVA hydrogel after immersion in sodium bisulfate aqueous solution, a: before immersion, b: after immersion;

[0024] Figure 4 Photographs of PVA hydrogel after immersion in sodium chloride aqueous solution, a: before immersion, b: after immersion;

[0025] Figure 5 Photographs of PVA hydrogel after immersion in sodium formate aqueous solution, a: before immersion, b: after immersion;

[0026] Figure 6 Photographs of PVA hydrogel after immersion in sodium hydrosulfide aqueous solution, a: before immersion, b: after immersion;

[0027] Figure 7 Photographs of PVA hydrogel after immersion in sodium nitrite aqueous solution, a: before immersion, b: after immersion;

[0028] Figure 8 Photographs of PVA hydrogel after immersion in sodium bisulfite aqueous solution, a: before immersion, b: after immersion;

[0029] Figure 9 Photographs of PVA hydrogel after immersion in sodium citrate aqueous solution, a: before immersion, b: after immersion;

[0030] Figure 10 Photographs of PVA hydrogel after immersion in sodium fluoride aqueous solution, a: before immersion, b: after immersion;

[0031] Figure 11 Photographs of PVA hydrogel after immersion in sodium acetate aqueous solution, a: before immersion, b: after immersion;

[0032] Figure 12 Photographs of PVA hydrogel after immersion in sodium nitrate aqueous solution, a: before immersion, b: after immersion;

[0033] Figure 13 Photographs of PVA hydrogel after immersion in sodium bicarbonate aqueous solution, a: before immersion, b: after immersion;

[0034] Figure 14 Photographs of PVA hydrogel after immersion in disodium hydrogen phosphate aqueous solution, a: before immersion, b: after immersion;

[0035] Figure 15 Photographs of PVA hydrogel after immersion in sodium phosphate aqueous solution, a: before immersion, b: after immersion;

[0036] Figure 16 Photographs of PVA hydrogel after immersion in deionized water solution, a: before immersion, b: after immersion;

[0037] Figure 17 Tensile graph of hydrogel soaked in different solutions;

[0038] Figure 18 Maximum stress graph of hydrogel soaked in different solutions;

[0039] Figure 19 Elastic modulus graph of hydrogel soaked in different solutions;

[0040] Figure 20 Toughness graph of hydrogel soaked in different solutions;

[0041] Figure 21 Infrared characterization graph of hydrogel after soaking in deionized water and phosphate aqueous solution;

[0042] Figure 22 TGA test graph of hydrogel after soaking in deionized water and phosphate aqueous solution;

[0043] Figure 23 Tensile stress-strain curve graph of hydrogel without soaking, soaking in deionized water, phosphate aqueous solution;

[0044] Figure 24 Maximum stress graph of hydrogel without soaking, soaking in deionized water, phosphate aqueous solution;

[0045] Figure 25 Elastic modulus graph of hydrogel without soaking, soaking in deionized water, phosphate aqueous solution;

[0046] Figure 26 Toughness graph of hydrogel without soaking, soaking in deionized water, phosphate aqueous solution;

[0047] Figure 27 Freeze resistance graph of hydrogel soaked in deionized water, phosphate aqueous solution, a: before freezing, b: after freezing;

[0048] Figure 28 100 times tensile cycle graph of PVA hydrogel without soaking;

[0049] Figure 29 100 times tensile cycle graph of PVA hydrogel soaked in deionized water;

[0050] Figure 30 100 times tensile cycle graph of PVA hydrogel soaked in sodium dihydrogen phosphate aqueous solution;

[0051] Figure 31 100 times tensile cycle graph of PVA hydrogel soaked in disodium hydrogen phosphate aqueous solution;

[0052] Figure 32The tensile cycle diagram of PVA hydrogel after soaking in sodium phosphate aqueous solution for 100 times;

[0053] Figure 33 The conductivity diagram of PVA hydrogel soaked in different solutions for 12 h

[0054] Figure 34 The electron microscope diagram of hydrogel after soaking in sodium dihydrogen phosphate;

[0055] Figure 35 The electron microscope diagram of hydrogel after soaking in disodium hydrogen phosphate;

[0056] Figure 36 The electron microscope diagram of hydrogel after soaking in sodium phosphate;

[0057] Figure 37 The tensile stress-strain curve diagram of hydrogel obtained at different soaking times;

[0058] Figure 38 The electrical sensing diagram of different peak values generated by bending of fingers at different angles;

[0059] Figure 39 The electrical sensing diagram generated by bending of fingers;

[0060] Figure 40 The electrical sensing diagram generated by bending of wrist;

[0061] Figure 41 The electrical sensing diagram generated by bending of elbow;

[0062] Figure 42 The electrical sensing diagram generated by bending of knee. DETAILED DESCRIPTION

[0063] Example 1

[0064] A preparation method of a high-toughness PVA conductive hydrogel, specifically comprising the following steps:

[0065] S1, 5 parts of polyvinyl alcohol are taken into 45 parts of deionized water, covered with a plastic wrap, and dissolved in a 95℃ water bath with stirring and heating to obtain a 10wt% polyvinyl alcohol aqueous solution;

[0066] S2, the polyvinyl alcohol aqueous solution is cooled to room temperature and then poured into a mold, covered with a plastic wrap, frozen at-20℃ for 12 h, and then placed at room temperature for 4 h to thaw, to obtain a polyvinyl alcohol hydrogel;

[0067] S3, the polyvinyl alcohol hydrogel is soaked in 1mol / L sodium dihydrogen phosphate aqueous solution for 12 h to obtain a high-toughness PVA conductive hydrogel. The schematic diagram of the preparation method is shown in Figure 1 The actual photos of the hydrogel are shown in Figure 2 .

[0068] Example 2

[0069] Example 2 and Example 1 differ in that the salt solution used is sodium bisulfate, otherwise the conditions are identical. The physical photograph of the hydrogel obtained is shown in Figure 3

[0070] Example 3

[0071] Example 3 and Example 1 differ in that the salt solution used is sodium chloride, otherwise the conditions are identical. The physical photograph of the hydrogel obtained is shown in Figure 4

[0072] Example 4

[0073] Example 4 and Example 1 differ in that the salt solution used is sodium formate, otherwise the conditions are identical. The physical photograph of the hydrogel obtained is shown in Figure 5

[0074] Example 5

[0075] Example 5 and Example 1 differ in that the salt solution used is sodium bisulfide, otherwise the conditions are identical. The physical photograph of the hydrogel obtained is shown in Figure 6

[0076] Example 6

[0077] Example 6 and Example 1 differ in that the salt solution used is sodium nitrite, otherwise the conditions are identical. The physical photograph of the hydrogel obtained is shown in Figure 7

[0078] Example 7

[0079] Example 7 and Example 1 differ in that the salt solution used is sodium bisulfite, otherwise the conditions are identical. The physical photograph of the hydrogel obtained is shown in Figure 8

[0080] Example 8

[0081] Example 8 and Example 1 differ in that the salt solution used is sodium citrate, otherwise the conditions are identical. The physical photograph of the hydrogel obtained is shown in Figure 9

[0082] Example 9

[0083] Example 9 and Example 1 differ in that the salt solution used is sodium fluoride, otherwise the conditions are identical. The physical photograph of the hydrogel obtained is shown in Figure 10

[0084] Example 10 ​​​​​​​​

[0085] Example 10 and Example 1 are different in that the salt solution used is sodium acetate, and the rest of the conditions are exactly the same. The actual photos of the hydrogels obtained are shown in Figure 11 .

[0086] Example 11

[0087] Example 11 and Example 1 are different in that the salt solution used is sodium nitrate, and the rest of the conditions are exactly the same. The actual photos of the hydrogels obtained are shown in Figure 12 .

[0088] Example 12

[0089] Example 12 and Example 1 are different in that the salt solution used is sodium bicarbonate, and the rest of the conditions are exactly the same. The actual photos of the hydrogels obtained are shown in Figure 13 .

[0090] Example 13

[0091] Example 13 and Example 1 are different in that the salt solution used is disodium hydrogen phosphate, and the rest of the conditions are exactly the same. The schematic diagram of the preparation method is shown in Figure 1 , and the actual photos of the hydrogels obtained are shown in Figure 14 .

[0092] Example 14

[0093] Example 14 and Example 1 are different in that the salt solution used is sodium phosphate, and the rest of the conditions are exactly the same. The schematic diagram of the preparation method is shown in Figure 1 , and the actual photos of the hydrogels obtained are shown in Figure 15 .

[0094] Example 15

[0095] Example 15 and Example 1 are different in that the time of soaking in 1 mol / L sodium dihydrogen phosphate aqueous solution is 12 hours, and the rest of the conditions are exactly the same.

[0096] Example 16

[0097] Example 16 and Example 1 are different in that the time of soaking in 1 mol / L sodium dihydrogen phosphate aqueous solution is 24 hours, and the rest of the conditions are exactly the same.

[0098] Example 17

[0099] Example 17 and Example 1 are different in that the time of soaking in 1 mol / L sodium dihydrogen phosphate aqueous solution is 36 hours, and the rest of the conditions are exactly the same.

[0100] Example 18

[0101] Example 18 and Example 1 are different in that the soaking time in 1 mol / L aqueous sodium dihydrogen phosphate solution is 60 hours, and the rest of the conditions are exactly the same.

[0102] Comparative Example 1

[0103] Comparative Example 1 and Example 1 are different in that the salt solution used is replaced by deionized water, and the rest of the conditions are exactly the same. The preparation method is shown in Figure 1 , and the physical photos of the hydrogels obtained are shown in Figure 16 .

[0104] Examples 1-12 and Comparative Example 1 explore the effect of salt solution on hydrogel,

[0105] The stress, strain, elastic modulus and toughness of the hydrogels obtained in Examples 1-12 and Comparative Example 1 are tested, and the stress and strain calculation formulas are as follows:

[0106] δ = F / A

[0107] Where δ is the stress, Kpa

[0108] F is the pulling force, N

[0109] A is the cross-sectional area, m 3

[0110] ε = ΔL / L0

[0111] ε is the strain, %

[0112] ΔL is the deformation length, mm

[0113] L0 is the original length, mm

[0114] The tensile stress-strain curve test results of the hydrogels obtained in Examples 1-12 and Comparative Example 1 are shown in Figure 17 , and the tensile test of the hydrogels is carried out by a mechanical instrument to obtain the maximum stress, elastic modulus and toughness data of the hydrogels. The maximum stress bar chart is shown in Figure 18 , and from the figure it can be seen that different anions improve the mechanical properties of the hydrogels differently, and among them, NaH2PO4 solution improves the stress of the hydrogels the most. This may be due to the strong ionic strength of sodium dihydrogen phosphate, which can cause salting-out effect, reduce the solubility of PVA chain, and cause the polymer to shrink. This dehydration effect can increase the crystallinity or physical crosslinking density of PVA chain, thereby improving the mechanical properties.

[0115] The elastic modulus results of the hydrogels obtained in Examples 1-12 and Comparative Example 1 are shown in Figure 19It can be seen from the figure that different anions have different effects on the elastic modulus of the hydrogel, among which sodium dihydrogen phosphate solution has the greatest effect on the elastic modulus of the hydrogel. This is because sodium dihydrogen phosphate has strong hydration ability, which can compete for free water in the PVA network, forcing the chain segments to pack more closely, forming a more compact cross-linked structure, thereby increasing the elastic modulus.

[0116] The toughness test results of the hydrogels obtained in Examples 1-12 and Comparative Example 1 are shown in Table 1, which shows that different anions have different effects on the toughness of PVA hydrogel, among which dihydrogen phosphate ions have the most obvious effect on the toughness of PVA hydrogel. This is because dihydrogen phosphate forms more hydrogen bonds with PVA hydrogel, and the increase in the number of hydrogen bonds enhances the dynamic cross-linking ability of the hydrogel, thereby enhancing the toughness of the hydrogel. The enhancement of the toughness of the hydrogel makes the hydrogel more resistant to damage and less prone to breakage. Figure 20

[0117] It is found by comparison that when the salt solution is sodium dihydrogen phosphate, the performance of the material is the best. On this basis, further attempts are made on other phosphates, and tests of Examples 13 and 14 are carried out.

[0118] The hydrogel materials obtained in Examples 1, 13, 14 and Comparative Example 1 are characterized by infrared, as shown in Table 2. Figure 21 With the introduction of salt ions, the shift of the hydroxyl peak in PVA hydrogel becomes more obvious. PVA gel shows a typical hydroxyl stretching vibration peak at 3440 cm -1 -1. After soaking in phosphate solution, the blue shift of the hydroxyl stretching vibration peak becomes more obvious with the increase of the concentration of sodium ions in the salt solution. The hydroxyl peak of PVA hydrogel soaked in sodium dihydrogen phosphate is shifted to 3430 cm -1 -1, the hydroxyl peak of PVA hydrogel soaked in sodium hydrogen phosphate is shifted to 3426 cm -1 -1, and the hydroxyl peak of PVA hydrogel soaked in sodium phosphate is shifted to 3420 cm -1 -1. The shift gradually becomes obvious. This indicates that the introduction of phosphate will affect the hydrogen bond interaction between PVA hydrogel chains, thereby affecting the mechanical properties of PVA hydrogel.

[0119] The hydrogel materials obtained in Examples 1, 13, 14 and Comparative Example 1 are characterized by thermogravimetric test (TGA), as shown in Table 3. Figure 22 ​As can be seen from the figure, with the increase of the sodium ion content in the soaked salt solution, the residual material at the end of the TGA test gradually increases. It shows that: during the soaking process, sodium ions penetrate into the PVA hydrogel network, and under the condition of the same concentration of phosphate solution, the more sodium ions that can enter the PVA hydrogel crosslinking network in the phosphate solution that can dissociate more sodium ions, the more salt ions that can enter the PVA hydrogel crosslinking network, resulting in the increase of the residual material in the thermogravimetric analysis results with the increase of the number of sodium ions. The more sodium ions that enter the PVA hydrogel crosslinking network, the stronger the hydrogen bond or ion-dipole interaction between the polymer chains, and the better the mechanical properties of the hydrogel.

[0120] The stress, strain, elastic modulus and toughness tests were carried out on the hydrogel materials obtained in Example 1, Example 13, Example 14, Comparative Example 1 and the original polyvinyl alcohol hydrogel without soaking treatment. The tensile stress-strain curve test results are shown in Figure 23 The maximum stress bar chart is shown in Figure 24 As can be seen from the figure, with the increase of the sodium ion content in the soaked salt solution, the residual material at the end of the TGA test gradually increases. It shows that: during the soaking process, sodium ions penetrate into the PVA hydrogel network, and under the condition of the same concentration of phosphate solution, the more sodium ions that can enter the PVA hydrogel crosslinking network in the phosphate solution that can dissociate more sodium ions, the more salt ions that can enter the PVA hydrogel crosslinking network, resulting in the increase of the residual material in the thermogravimetric analysis results with the increase of the number of sodium ions. The more sodium ions that enter the PVA hydrogel crosslinking network, the stronger the hydrogen bond or ion-dipole interaction between the polymer chains, and the better the mechanical properties of the hydrogel. The more sodium ions, the stronger the crosslinking density inside the PVA hydrogel and the ion-dipole interaction between Na ions and the hydrogel, resulting in the increase of the maximum stress of the hydrogel.

[0121] The elastic modulus results of the hydrogel materials obtained in Example 1, Example 13, Example 14, Comparative Example 1 are shown in Figure 25 As can be seen from the figure, with the increase of the sodium ion content in the soaked salt solution, the elastic modulus gradually increases. That is, the elastic modulus from small to large is in the order of NaH2PO4< Na2HPO4< Na3PO4. This may be due to the high pH of trisodium phosphate, which promotes the deprotonation of PVA, promotes the chain arrangement, and increases the crystalline region. At the same time, the crosslinking effect of PO4³ - will increase the crosslinking points of the network inside the hydrogel, making the network more rigid.

[0122] The toughness test results of the hydrogel materials obtained in Example 1, Example 13, Example 14, Comparative Example 1 are shown in Figure 26 As can be seen from the figure, with the increase of the sodium ion content in the soaked salt solution, the toughness gradually increases. That is, the toughness from small to large is in the order of NaH2PO4< Na2HPO4< Na3PO4. 4。 It shows that: with the increase of the number of sodium ions, the number of hydrogen bonds and ion-dipole interactions inside the PVA hydrogel increases, which enhances the dynamic crosslinking ability of the hydrogel, and the toughness of the PVA hydrogel is enhanced. The increase of the toughness of the hydrogel makes the hydrogel more resistant to damage and less prone to breakage.

[0123] The hydrogel materials obtained from Example 1, Example 13, Example 14, Comparative Example 1 were subjected to anti-freezing test, i.e. the mechanical properties of the hydrogel were tested after the materials were respectively placed at room temperature for 24 h and frozen at -20℃ for 24 h, and the results are shown in Table 1, Table 2 and Table 3. Figure 27 It is shown that the PVA hydrogel soaked by the phosphate solution has certain anti-freezing property, and the anti-freezing property of the PVA hydrogel is better as the amount of sodium ions contained in the phosphate solution increases, i.e. NaH2PO4< Na2HPO4< Na3PO4. The anti-freezing property of the hydrogel can reflect that the PVA hydrogel has good mechanical properties at low temperature, and can avoid brittle fracture. It also shows that the PVA hydrogel can maintain conductivity and flexibility in cold, has good stability, and can be better applied to wearable flexible sensors.

[0124] The hydrogel materials obtained from Example 1, Example 13, Example 14, Comparative Example 1 and not soaked by the phosphate solution were subjected to cyclic stability test, and the results are shown in Table 4 and Table 5. Figures 28-32 The images of the PVA hydrogel soaked by the phosphate solution are relatively stable after 100 stretching cycles, and the cyclic stability is good. It is shown that the PVA hydrogel soaked by the phosphate solution has good stability and low hysteresis, which reflects the superiority of the mechanical properties of the hydrogel and the reliability of the actual application. It is embodied that the PVA hydrogel soaked by the phosphate solution can be applied to the application of flexible sensors that need to be repeatedly deformed.

[0125] Electrical performance test:

[0126] The hydrogel materials obtained from Example 1, Example 13, Example 14, Comparative Example 1 and not soaked by the phosphate solution were subjected to conductivity test, and the results are shown in Table 6 and Table 7. Figure 33 It can be seen from the figure that the conductivity of the hydrogel soaked by the sodium hydrogen phosphate solution is the highest, and the conductivity of the PVA hydrogel soaked by the sodium phosphate solution with the most sodium ions is reduced. This may be due to that the high concentration of sodium ions in the hydrogel can increase the internal cross-linking density and ion-dipole interaction in the hydrogel, so as to make the channel aperture for transporting salt ions small (electron microscope Figures 34-36 ), and the migration path of the ions is blocked, thereby reducing the number of free-moving ions, resulting in the decrease of the conductivity of the hydrogel.

[0127] Effect of soaking time on the hydrogel in Example 1, 15-18

[0128] The hydrogel obtained from Example 1, 15-18 was subjected to tensile stress-strain curve test, and the results are shown in Table 8 and Table 9. Figure 37As shown, it can be seen that when the PVA hydrogel is soaked in 1 mol / L phosphate aqueous solution, with the increase of soaking time, the ion diffusion in the hydrogel is more uniform, and the crosslinked network of the hydrogel is also more uniform and dense. The increase of crosslinking between the hydrogel and ions increases the number of hydrogen bonds between polymer chains, which increases the crosslinking density of the hydrogel, thereby improving the mechanical properties of the hydrogel. However, if the soaking time in the salt solution is too long (≥60 h), the internal structure of the hydrogel will be destroyed, the crosslinking of ions will be excessive, the crosslinked network will be too dense, the polymer chains of the hydrogel will be broken, the hydrogel will change from toughness to brittleness, and the fracture energy will decrease, thereby reducing the mechanical properties of the PVA hydrogel.

[0129] The PVA hydrogel soaked in deionized water solution will swell, which reduces the crosslinking density between the polymer chains of the hydrogel due to the entry of water molecules, reduces the number of hydrogen bonds, and thus reduces the maximum stress of the hydrogel, which is equivalent to reducing the percentage concentration of polyvinyl alcohol in the PVA hydrogel. The swelling of the hydrogel reduces the crosslinking density of the hydrogel, and the crosslinked network in the hydrogel becomes loose, which leads to a decrease in the rigidity of the hydrogel. The originally curled segments stretch, making it easier for the polymer chains in the hydrogel to orient along the external force direction during stretching, thereby increasing the elongation at break of the hydrogel.

[0130] The polyvinyl alcohol hydrogel obtained by soaking in 1 mol / L sodium phosphate aqueous solution in Example 1 was used as the experimental object to explore its application in flexible sensors.

[0131] Figure 38 is the different peak electrical sensing diagram generated by the bending of the finger at different angles, and the bending angles are 30°, 60° and 90°. Figure 39 、 Figure 40 、 Figure 41 、 Figure 42 is the electrical sensing diagram formed by the bending of different parts of the body, and the different parts of the body are the finger, wrist, elbow and knee, which shows that the PVA hydrogel sensor soaked in sodium phosphate solution is fixed on the finger of a person, and when the finger is bent at different degrees (30°, 60° and 90°), the electrical signal changes significantly, as shown in FIG. 38. The greater the degree of finger bending, the greater the resistance of the PVA hydrogel due to the narrowing of the ion channel, making the peak value of the electrical signal more obvious. After verifying that different peak electrical signals can be obtained when the finger is bent at different degrees, the sensor detection capability of other parts of the body was also tested, i.e. the transmission capability of the PVA hydrogel sensor to large human movements such as wrist bending, elbow bending and knee bending was tested. Figures 39-42The electrical signal sensing maps respectively representing the bending of human finger, wrist, elbow and knee are shown in the figures, from which it can be seen that the peak shapes of the electrical signals generated by the movements of different parts of human body are different, and the greater the movement amplitude, the greater the relative resistance change, and the higher the peak value of the electrical signal peak, wherein the peak value of the electrical signal peak generated in the bending process of the knee is obviously higher than that of the electrical signal peak formed in the bending movement of other parts. It can be illustrated from this that the hydrogel can produce stable, reliable and repeatable electrical signals when applied to a flexible sensor, and the movement conditions of the joints of each part of the human body can be more accurately monitored by observing the peak shape of the electrical signal peak and the size of the electrical signal peak value.

Claims

1. An application of a high-strength and tough PVA conductive hydrogel in the field of flexible sensors, characterized in that, By observing the peak shape and peak value of the electrical signal, the movement of joints in various parts of the human body can be monitored. The preparation method of the hydrogel includes the following steps: S1. Polyvinyl alcohol is added to deionized water and dissolved under water bath heating at 95°C to obtain a 10wt% polyvinyl alcohol aqueous solution. S2. After cooling the polyvinyl alcohol aqueous solution obtained in step S1 to room temperature, pour it into a mold, seal it with plastic wrap, freeze it in the refrigerator, and then thaw it to obtain polyvinyl alcohol hydrogel. S3. Soak the polyvinyl alcohol hydrogel obtained in step S2 in a 1 mol / L salt solution for 12-60 hours to obtain a high-strength and tough PVA conductive hydrogel; the salt solution is one of sodium dihydrogen phosphate and disodium hydrogen phosphate.

2. The application of the high-strength and tough PVA conductive hydrogel according to claim 1 in the field of flexible sensors, characterized in that, The freezing temperature in S2 is -20℃, and the freezing time is 12 hours.

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