Water-resistant conductive hydrogels with excellent comprehensive performance, their preparation methods and applications

Abstract

This invention discloses a high-performance, water-resistant conductive hydrogel. The hydrogel is composed of water and polyvinyl alcohol, carbamate, and hydroxyethyl methyl imidazolium lactate (HMEL) fully dispersed in the water. The mass percentages of polyvinyl alcohol in the water dispersion medium are 10-15%, carbamate is 1-4%, and HMEL is 1-16%. The Young's modulus of the finished hydrogel is 0.1-0.8 MPa. This invention employs a unique raw material formulation and, through simple steps, allows the raw material components to interact without chemical reactions, producing a high-performance hydrogel with excellent water resistance, high stress, strain, and conductivity, good flexibility, and no change in appearance or performance after prolonged use in water. This expands its application range and extends its service life.

Description

Technical Field

[0001] This invention relates to the field of conductive hydrogel technology, specifically to a water-resistant conductive hydrogel of polyvinyl alcohol / carbonyl diamine / hydroxyethyl methyl imidazole lactate with excellent comprehensive performance, and its preparation and application. Background Technology

[0002] Hydrogels are gels that use water as a dispersion medium. They are water-soluble polymers with a network cross-linked structure incorporating hydrophobic groups and hydrophilic residues. The hydrophilic residues bind to water molecules, connecting them within the network, while the hydrophobic residues swell upon contact with water, resulting in a cross-linked polymer. Hydrogels are a polymeric network system that is flexible, can maintain its shape, and can absorb large amounts of water. Multifunctional conductive hydrogels have broad application prospects in future electrodes, strain sensors, wearable devices, and even the soft robotics industry (Mater. Today 2021, 50, 35; Adv. Mater. 2021, 33, 2100983; Science 2016, 353, 682). However, existing hydrogels still face significant challenges in their widespread application in these fields. The main obstacles are as follows: some existing hydrogels exhibit high stress but low strain; or high strain but low stress; or high stress and strain but low conductivity; or high stress and strain, but they swell, break, or even dissolve in water; or high stress and strain, but are hard and lack flexibility. In other words, existing hydrogels struggle to simultaneously meet the requirements of high stress, high strain, conductivity, flexibility, and high water resistance. This limitation severely restricts their application in practical tasks.

[0003] For example, 1. Some hydrogels in the prior art can be stretched to strains of 1000, 1530, 1810, 2400, 10200, or even 18000%, but their stress is very small, only 0.3, 0.16, 0.37, 0.1, 0.0016, and 0.18 MPa (Angew. Chem. Int. Ed. 2017, 56, 9141; Adv. Funct. Mater. 2022, 32, 2201846; Adv. Funct. Mater. 2022, 32, 2204565; Chem. Eng. J. 2019, 360, 334; Adv. Mater. 2022, 34, 2206904; Chem. Eng. J. 2020, 387, 1. 124105). 2. Some hydrogels, although employing innovative methods to increase the stress of traditional hydrogels (the highest stress is about 57 MPa), have very low strain, only about 18%, and almost no elasticity or flexibility (Nat. Commun. 2022, 13, 1; Adv. Funct. Mater. 2018, 29, 1806220). 3. In recent years, He's team proposed a new strategy using inorganic salt ions as gel initiators to regulate the aggregation state of polymer chains through the Hofmeister effect, thereby increasing the stress and strain of the hydrogel (Nature 2021, 590, 594). However, this hydrogel is hard and has almost no elasticity or flexibility, making it unsuitable for use as a flexible sensor, etc.

[0004] Furthermore, most existing hydrogels suffer from the following problems: poor water resistance, with mechanical properties significantly reduced after prolonged use in water; complex preparation processes, requiring product purification, resulting in pollutant emissions, necessitating specialized equipment, involving a series of chemical reactions, and hindering industrial application. Therefore, developing new hydrogels that simultaneously meet the requirements of high stress, strain, flexibility, and water resistance remains a challenge. Summary of the Invention

[0005] The technical objective of this invention is to use a unique raw material formula and simple steps to enable the interaction between the raw material components without chemical reaction, thereby preparing a high-performance hydrogel with good water resistance, high stress, strain, and electrical conductivity, good flexibility, and no change in appearance and performance after long-term use in water, so as to expand its application range and extend its service life.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a water-resistant conductive hydrogel with excellent comprehensive performance, the hydrogel being composed of water and polyvinyl alcohol, carbodiamine and hydroxyethyl methyl imidazolium lactate fully dispersed in the water, wherein the mass percentage of polyvinyl alcohol in the dispersion medium water is 10-15%, the mass percentage of carbodiamine is 1-4%, the mass percentage of hydroxyethyl methyl imidazolium lactate is 1-16%, and the Young's modulus of the finished hydrogel is 0.1-0.8 MPa.

[0007] Furthermore, the polyvinyl alcohol has a weight-average molecular weight of 105,000-110,000 and a degree of alcoholysis of 99%.

[0008] A method for preparing a water-resistant conductive hydrogel with excellent comprehensive performance includes the following steps:

[0009] S1. Weigh 10-15 parts of polyvinyl alcohol, 1-4 parts of carbodiamine and 1-16 parts of hydroxyethyl methyl imidazole lactate according to the weight ratio, mix them with 100 parts of deionized water, stir thoroughly and then stir at 90-100℃ for 1-4 hours to obtain a mixed solution for later use.

[0010] S2. The mixed solution obtained in step S1 is subjected to ultrasonic degassing treatment, and then poured into a mold for later use.

[0011] S3. Place the mold containing the mixed solution from step S2 into a refrigerator and freeze it at -18 to -22°C for 2 to 8 hours. After removing it, place it at room temperature for 3 to 4 hours to obtain the finished hydrogel.

[0012] Furthermore, in step S1, the stirring speed is 1000-1800 r / min.

[0013] Furthermore, in step S2, the power of the ultrasonic degassing treatment is 120-200W, and the time is 20-40min.

[0014] Furthermore, in step S2, the mold used is a standard dumbbell-shaped mold.

[0015] The strain sensor made using the aforementioned water-resistant conductive hydrogel with excellent comprehensive performance includes a long strip-shaped hydrogel body, with copper foil connecting strips wrapped around both ends of the hydrogel body along its length, and the copper foil connecting strips being connected to wires.

[0016] The aforementioned high-performance water-resistant conductive hydrogel has applications in conductive materials, smart screen touchscreen materials, and wearable flexible materials.

[0017] The beneficial effects of this invention are:

[0018] (1) The present invention provides a water-resistant conductive hydrogel with excellent comprehensive performance, which has high strain (500%), high stress (25MPa), high elasticity, anti-swelling, and water resistance. It does not swell or deform after being continuously immersed in water for 6 months, and its mechanical properties do not decrease. It has the potential to be used in aquatic environments for a long time. At the same time, it also has good elasticity, with a Young's modulus not exceeding 0.8 MPa, and has a wide range of applications.

[0019] (2) The present invention provides a water-resistant conductive hydrogel with excellent comprehensive performance. The conductive component in the finished hydrogel is hydroxyethyl methyl imidazole lactate. It does not require pre-modification like the conductive components of traditional hydrogels such as nano-metals and nano-carbon, nor does it require complex polymerization reactions like the conductive components of polymers. Therefore, the preparation process is simple and the application effect is good.

[0020] (3) Due to the strong hydrogen bonding between polyvinyl alcohol and carbodiamine and hydroxyethyl methyl imidazole lactate in the raw materials, the mixed solution of polyvinyl alcohol / carbodiamine / hydroxyethyl methyl imidazole lactate can be frozen once to obtain a hydrogel with excellent comprehensive performance. This overcomes the defects of traditional hydrogel preparation processes, which require multiple preparation steps, are cumbersome, time-consuming, require special equipment, and have pollutant emissions. It is suitable for large-scale industrial production.

[0021] (4) The hydrogel preparation process of the present invention is simple and easy to operate. The product does not require purification, there is no pollutant emission, no special equipment is required, and no chemical reaction is involved, thus solving the problem of the complexity of traditional hydrogel preparation processes. The raw materials are inexpensive and readily available, the investment cost is low, the applicability is strong, and it is easy to realize industrial application.

[0022] (5) The present invention provides a water-resistant conductive hydrogel with excellent comprehensive performance, which can be used in wearable flexible materials, conductive materials, smart screen touch screen materials, etc. Attached Figure Description

[0023] Figure 1 This is a scanning electron microscope image of pure polyvinyl alcohol hydrogel;

[0024] Figure 2 This is a scanning electron microscope image of the hydrogel prepared in Example 1 of the present invention;

[0025] Figure 3 This is a schematic diagram of the strain sensor fabricated using the hydrogel obtained in Example 1;

[0026] Figure 4 This is a test diagram of a hydrogel strain sensor used in a wearable sensor for the finger.

[0027] Figure 5This is a test diagram of a hydrogel strain sensor used in a wearable sensor at the elbow.

[0028] Figure 6 This is a test diagram of a hydrogel strain sensor used in a wearable sensor for the knee.

[0029] Figure 7 These are conductive test photos of hydrogel strain sensors used in electrically powered circuits;

[0030] Figure 8 These are test photos taken at 300% strain after the hydrogel prepared in Example 1 was perforated.

[0031] Figure 9 These are comparison photos of the hydrogel before and after soaking in water for six months.

[0032] Attached image labels: 1. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0034] A water-resistant conductive hydrogel with excellent comprehensive performance is disclosed. The hydrogel is composed of water and polyvinyl alcohol, carbodiamine, and hydroxyethyl methyl imidazolium lactate fully dispersed in the water. The polyvinyl alcohol has a weight-average molecular weight of 105,000-110,000 and a degree of alcoholysis of 99%. The mass percentage of polyvinyl alcohol in the dispersion medium water is 10-15%, the mass percentage of carbodiamine is 1-4%, and the mass percentage of hydroxyethyl methyl imidazolium lactate is 1-16%. The Young's modulus of the finished hydrogel is 0.1-0.8 MPa.

[0035] A method for preparing a water-resistant conductive hydrogel with excellent comprehensive performance includes the following steps:

[0036] S1. Weigh 10-15 parts of polyvinyl alcohol, 1-4 parts of carbodiamine and 1-16 parts of hydroxyethyl methyl imidazole lactate according to the weight ratio, mix them with 100 parts of deionized water, stir thoroughly and then stir at 90-100℃ for 1-4 hours to obtain a mixed solution for later use.

[0037] S2. The mixed solution obtained in step S1 is subjected to ultrasonic degassing treatment at 120-200W for 20-40 minutes. After that, it is poured into a standard dumbbell-shaped mold for later use.

[0038] S3. Place the mold containing the mixed solution from step S2 into a refrigerator and freeze it at -18 to -22°C for 2 to 8 hours. After removing it, place it at room temperature for 3 to 4 hours to obtain the finished hydrogel.

[0039] The strain sensor made using the aforementioned water-resistant conductive hydrogel with excellent comprehensive performance includes a long strip-shaped hydrogel body, with copper foil connecting strips wrapped around both ends of the hydrogel body along its length, and the copper foil connecting strips being connected to wires.

[0040] The aforementioned high-performance water-resistant conductive hydrogel has applications in conductive materials, smart screen touchscreen materials, and wearable flexible materials.

[0041] Example 1:

[0042] Preparation of a water-resistant conductive hydrogel of polyvinyl alcohol / carbonyl diamine / hydroxyethyl methyl imidazole lactate:

[0043] (1) By weight percentage (based on the mass of water), the concentration of polyvinyl alcohol is 10%, the concentration of carbodiamine is 4%, and the concentration of hydroxyethyl methyl imidazolium lactate is 1%. Weigh 5 g of polyvinyl alcohol, 2 g of carbodiamine, and 0.5 g of hydroxyethyl methyl imidazolium lactate, add 50 g of deionized water, and stir at 95 °C for 4 h to obtain a mixed solution of polyvinyl alcohol / carbodiamine / hydroxyethyl methyl imidazolium lactate for later use.

[0044] (2) At room temperature, the polyvinyl alcohol / carbonyl diamine / hydroxyethyl methyl imidazole lactate mixed solution prepared in step (1) was subjected to ultrasonic degassing treatment at 150W for 30 minutes. After that, the degassed polyvinyl alcohol / carbonyl diamine / hydroxyethyl methyl imidazole lactate mixed solution was poured into a standard dumbbell mold.

[0045] (3) Place the mold containing the mixed solution from step (2) into a refrigerator and freeze it at -20 ℃ for 7 h. Then take it out and let it stand at room temperature for 3 h to obtain the finished hydrogel.

[0046] The hydrogel prepared in this embodiment was measured to have a stress of 25 MPa, a strain of 500%, a Young's modulus of 0.6 MPa, an electrical conductivity of 16 S / m, and good flexibility.

[0047] Example 2:

[0048] Preparation of a water-resistant conductive hydrogel of polyvinyl alcohol / carbonyl diamine / hydroxyethyl methyl imidazole lactate:

[0049] (1) By weight percentage (based on the mass of water), the concentration of polyvinyl alcohol is 12%, the concentration of carbodiamine is 2%, and the concentration of hydroxyethyl methyl imidazolium lactate is 5%. Weigh 6 g of polyvinyl alcohol, 1 g of carbodiamine, and 2.5 g of hydroxyethyl methyl imidazolium lactate, add 50 g of deionized water, and stir at 90 °C for 3 h to obtain a polyvinyl alcohol / carbodiamine / hydroxyethyl methyl imidazolium lactate mixed solution for later use.

[0050] (2) At room temperature, the polyvinyl alcohol / carbonyl diamine / hydroxyethyl methyl imidazole lactate mixed solution prepared in step (1) was subjected to ultrasonic degassing treatment at 120W for 40 min. After that, the degassed polyvinyl alcohol / carbonyl diamine / hydroxyethyl methyl imidazole lactate mixed solution was poured into a standard dumbbell mold.

[0051] (3) Place the mold containing the mixed solution from step (2) into a refrigerator and freeze it at -18 ℃ for 8 h. Then take it out and let it stand at room temperature for 4 h to obtain the finished hydrogel.

[0052] The hydrogel prepared in this embodiment was measured to have a stress of 31 MPa, a strain of 600%, a Young's modulus of 0.4 MPa, an electrical conductivity of 21 S / m, and good flexibility.

[0053] Example 3:

[0054] Preparation of a water-resistant conductive hydrogel of polyvinyl alcohol / carbonyl diamine / hydroxyethyl methyl imidazole lactate:

[0055] (1) By weight percentage (based on the mass of water), the concentration of polyvinyl alcohol is 15%, the concentration of carbodiamine is 1%, and the concentration of hydroxyethyl methyl imidazolium lactate is 16%. Weigh 7.5 g of polyvinyl alcohol, 0.5 g of carbodiamine, and 8 g of hydroxyethyl methyl imidazolium lactate, add 50 g of deionized water, and stir at 100 °C for 1 h to obtain a polyvinyl alcohol / carbodiamine / hydroxyethyl methyl imidazolium lactate mixed solution for later use.

[0056] (2) At room temperature, the polyvinyl alcohol / carbonyl diamine / hydroxyethyl methyl imidazole lactate mixed solution prepared in step (1) was subjected to ultrasonic degassing treatment at 200W for 20 min. After that, the degassed polyvinyl alcohol / carbonyl diamine / hydroxyethyl methyl imidazole lactate mixed solution was poured into a standard dumbbell mold.

[0057] (3) Place the mold containing the mixed solution from step (2) into a refrigerator and freeze it at -22 ℃ for 2 hours. Then take it out and let it stand at room temperature for 3.5 hours to obtain the finished hydrogel.

[0058] The hydrogel prepared in this embodiment was measured to have a stress of 29 MPa, a strain of 500%, a Young's modulus of 0.3 MPa, an electrical conductivity of 19 S / m, and good flexibility.

[0059] Performance test

[0060] 1. Comparison of internal structural characterization

[0061] To demonstrate the superior effects of this invention, as a comparison, this invention prepared pure polyvinyl alcohol hydrogel (following the same steps as in Example 1, except without the addition of carbodiamine and hydroxyethyl methyl imidazole lactate), and measured the polyvinyl alcohol hydrogel (as shown in the attached figure). Figure 1 (as shown) and the hydrogel prepared in Example 1 (as shown in the attached document). Figure 2 The scanning electron microscope (SEM) shown. From Figure 1 and Figure 2 It is evident that the pure polyvinyl alcohol hydrogel has a porous internal structure, while the hydrogel prepared in Example 1 has a dense structure. This is mainly because the strong hydrogen bonding between polyvinyl alcohol, carbodiamine, and hydroxyethyl methyl imidazole lactate makes the hydrogel prepared in Example 1 more dense, thereby significantly improving its mechanical properties.

[0062] 2. Fabrication of strain sensors

[0063] The strain sensor was assembled and prepared using the hydrogel obtained in Example 1 of this invention, as shown in the structural attachment. Figure 3 As shown in the figure, a long strip of hydrogel (70 mm × 10 mm × 1.2 mm) was wrapped at both ends with copper foil connecting strips, and then the copper foil connecting strips were connected to copper wires to assemble the hydrogel strain sensor. This hydrogel strain sensor was fixed to the fingers, elbows, and knees to detect the electrical output signals of the fingers, elbows, and knees. The results are shown in the attached figure. Figure 4 Appendix Figure 5 and attached Figure 6 As shown. By Figure 4 , Figure 5 and Figure 6 It can be seen that the hydrogel strain sensor has good flexibility and strong conductivity, that is, the hydrogel of the present invention can be used in wearable sensors.

[0064] 3. Demonstration of electrical conductivity

[0065] The hydrogel prepared in Example 1 of this invention was connected to a circuit, and the brightness of an LED bulb was tested when the strain of the hydrogel was 200%. The results are attached. Figure 7 As shown, by Figure 7 It can be seen that when the strain of the hydrogel is 200%, the LED bulb still maintains a high brightness, proving that it has good conductivity.

[0066] 4. Mechanical property demonstration

[0067] The mechanical properties of the hydrogel prepared in Example 1 of this invention are demonstrated, as shown in the attached figure. Figure 8 As shown, the hydrogel with the central pore was stretched by 300% without breaking. This demonstrates that the hydrogel possesses excellent mechanical properties.

[0068] 5. Anti-swelling and water resistance tests

[0069] The hydrogel prepared in Example 1 of this invention was immersed in water under polar conditions for 6 months, and its volume hardly changed. Figure 9 As shown: the left image is the gel before soaking in water, and the right image is the gel after soaking in water for six months. Therefore, the hydrogel sensor of this invention can be used in water for a long time, significantly improving its practicality.

Claims

1. A water-resistant conductive hydrogel having excellent comprehensive properties, characterized by: The hydrogel is composed of water and polyvinyl alcohol, carbamide and hydroxyethyl methyl imidazole lactate fully dispersed in water, and the mass percentage of polyvinyl alcohol in the dispersion medium water is 10-15%, the mass percentage of carbamide is 1-4%, and the mass percentage of hydroxyethyl methyl imidazole lactate is 1-16%, and the Young's modulus of the finished hydrogel is 0.1-0.8 Mpa. The preparation method of the water-resistant conductive hydrogel with excellent comprehensive performance comprises the following steps: S1, according to the weight fraction, 10-15 parts of polyvinyl alcohol, 1-4 parts of carbamide and 1-16 parts of hydroxyethyl methyl imidazole lactate are respectively taken, and 100 parts of deionized water is mixed, fully stirred and uniformly mixed, and then stirred at 90-100℃ environmental conditions for 1-4h to prepare a mixed solution for standby; S2, the mixed solution prepared in step S1 is treated by ultrasonic defoaming, and then poured into a mold for standby; S3, the mold containing the mixed solution in step S2 is placed in a refrigerator and treated at-18 to-22℃ for 2-8h, and then placed at room temperature for 3-4h to obtain the finished product hydrogel.

2. The water-resistant conductive hydrogel having excellent comprehensive properties according to claim 1, characterized by: The weight average molecular weight of the polyvinyl alcohol is 105000-110000, and the alcoholysis degree is 99%.

3. The water-resistant conductive hydrogel having excellent comprehensive properties according to claim 1, characterized by: In step S1, the stirring speed is 1000-1800r / min.

4. The water-resistant conductive hydrogel having excellent comprehensive properties according to claim 1, characterized by: In step S2, the power of the ultrasonic defoaming treatment is 120-200W, and the time is 20-40min.

5. The water-resistant conductive hydrogel having excellent comprehensive properties according to claim 1, characterized by: In step S2, the mold used is a standard dumbbell mold.

6. A strain sensor made of the water-resistant conductive hydrogel having excellent comprehensive properties according to claim 1, characterized by: It comprises an elongated hydrogel body, and copper foil connecting bands are respectively arranged at both ends of the hydrogel body in the length direction, and the copper foil connecting bands are connected with wires.

7. The application of the water-resistant conductive hydrogel with excellent comprehensive performance in claim 1 in conductive materials, smart screen touch materials and wearable flexible materials.

Images