A multi-network sensing hydrogel with synergistic regulation of electrical and mechanical properties, its preparation method and application

Abstract

A multi-network sensing hydrogel with synergistically modulated electrical and mechanical properties, its preparation method, and its applications are disclosed. The hydrogel is constructed using a stepwise swelling-in-situ photopolymerization method. Polyacrylic acid forms the first network, and poly(1-vinyl-3-butylimidazolium bromide) forms the conductive second network. Repeated swelling-photopolymerization processes are used to construct triple and quadruple network multi-level structures. By controlling the concentration of ionic liquid monomers in the soaking solution, the hydrogel's conductivity of 0.02–1.33 S·m is achieved. ‑1 Elongation at break: 98.40%–851.31%; Fracture stress: 32.63–211.93 kPa; Young's modulus: 63.32–150.36 kPa; Toughness: 20.62–1137.68 kJ·m ‑3 Continuous adjustment; effectively synergistically adjusts the mechanical and electrical properties of conductive hydrogels, providing a highly controllable material construction strategy for high-performance flexible sensors and wearable electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer materials technology, specifically relating to a multi-network sensing hydrogel with synergistic regulation of electrical and mechanical properties, its preparation method and application. Background Technology

[0002] Hydrogels are three-dimensional network structures formed by the physical or chemical cross-linking of hydrophilic polymer chains. They can swell in water and retain a large amount of water without dissolving. In recent years, conductive hydrogels have shown broad application prospects in fields such as flexible sensors, wearable electronic devices, energy storage devices, and biomedical engineering due to their excellent flexibility, biocompatibility, and conductivity.

[0003] However, traditional conductive hydrogels face a key technical bottleneck in practical applications: an inherent contradiction between mechanical and electrical properties. Specifically, improving the conductivity of a hydrogel usually requires increasing the content of conductive fillers or conductive polymers, but this often leads to brittleness and decreased flexibility. Conversely, improving the flexibility and ductility of the hydrogel may result in discontinuities in the conductive network, thereby reducing conductivity. This difficulty in achieving a balance between mechanical and electrical properties severely limits the application of conductive hydrogels in high-performance flexible electronic devices.

[0004] The dual-network hydrogel strategy is considered one of the effective ways to resolve the aforementioned contradictions. Dual-network hydrogels consist of two interpenetrating polymer networks: the first network typically has a high density of cross-linking points to provide strength, while the second network has a low density of cross-linking points to provide toughness. However, existing methods for preparing dual-network conductive hydrogels usually employ one-pot or sequential polymerization methods, making it difficult to precisely control the microstructure and interrelationships of the two networks. This results in a continued challenge in the synergistic regulation of electrical and mechanical properties.

[0005] Therefore, developing a method for preparing conductive hydrogels that can synergistically regulate electrical and mechanical properties, and achieving large-scale continuous adjustment of properties such as conductivity, strength, and toughness, is of great significance for promoting the development of flexible sensing materials and wearable electronic devices.

[0006] To address the inherent contradiction of simultaneously controlling the mechanical and electrical properties of functionalized hydrogels, this study introduces the structural design concept of dual-network hydrogels. A sensing hydrogel system was constructed using free radical polymerization of conductive polymers, achieving synergistic control and programmable optimization of mechanical and electrical properties. Based on this structural strategy, a combination of stepwise swelling and in-situ photopolymerization was employed to systematically construct multi-level hydrogel systems, including dual-network, triple-network, and quadruple-network systems. This allows for a wide range of continuous adjustment of the electromechanical properties of the hydrogels under controllable and repeatable conditions. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a multi-network sensing hydrogel with synergistically modulated electrical and mechanical properties, its preparation method, and its applications. This invention employs a combination of stepwise swelling and in-situ photopolymerization to construct multi-level hydrogel systems with dual, triple, and quadruple networks. This achieves synergistic regulation and programmable optimization of the hydrogel's electrical and mechanical properties without relying on complex chemical modifications.

[0008] To achieve the above objectives, this application provides the following technical solution: A method for preparing a multi-network sensing hydrogel with synergistic regulation of electrical and mechanical properties specifically includes the following steps: The first step is to prepare a pregel solution: 20 mg of polyethylene glycol, 10 μ L of 0.1 mol / mL photoinitiator and 670 μ L of deionized water are mixed according to the mass-volume ratio to obtain mixed solution A. Mixed solution A is placed in a fume hood, and then 300 μ L of acrylic acid is added. After shaking and mixing evenly, mixed solution B is obtained. Mixed solution B is deoxygenated to obtain a pregel solution. The second step is to prepare the first network: the pregel solution is placed in a glass clamp mold and a free radical polymerization reaction is initiated under ultraviolet light to obtain polyacrylic acid gel as the first network; The third step, light-protected swelling: The polyacrylic acid gel is placed in an immersion solution containing 1-vinyl-3-butylimidazolium bromide monomer, N,N'-methylenebisacrylamide crosslinking agent and photoinitiator, and swelled in the dark for 20-28 hours. The fourth step is to prepare a double-network hydrogel: the swollen gel is subjected to in-situ photopolymerization under ultraviolet light to obtain a double-network hydrogel. Step 5: Preparation of triple network hydrogel: The double network hydrogel is placed in an immersion solution containing 1-vinyl-3-butylimidazolium bromide monomer, N,N'-methylenebisacrylamide crosslinking agent and photoinitiator, and swelled in the dark for 20-28 hours. The swollen gel is then subjected to in-situ photopolymerization under ultraviolet light to obtain triple network hydrogel. Step 6: Preparation of quadruple network hydrogel: The triple network hydrogel is placed in an immersion solution containing 1-vinyl-3-butylimidazolium bromide monomer, N,N'-methylenebisacrylamide crosslinking agent and photoinitiator, and swelled in the dark for 20-28 hours. The swollen gel is then subjected to in-situ photopolymerization under ultraviolet light to obtain the quadruple network hydrogel. In this process, the electrical and mechanical properties of the hydrogel are synergistically controlled by adjusting the concentration of 1-vinyl-3-butylimidazolium bromide monomer in the soaking solution to 50-200 mg / mL.

[0009] Further, in the first step, the amount of polyethylene glycol used is 20 mg, the photoinitiator is lithium phenyl-2,4,6-trimethylbenzoylphosphonate (Lap), the amount of photoinitiator used is 10 μL of a 0.1 mol / mL solution, the amount of deionized water used is 670 μL, the amount of acrylic acid used is 300 μL, the oscillation frequency is 40 kHz, and the oscillation time is 1-2 minutes; the deoxygenation treatment in the first step includes: inserting a syringe below the surface of mixed solution B, introducing nitrogen gas into the surface of mixed solution B for 5 minutes, and then sonicating at a frequency of 40 kHz for 10 minutes.

[0010] Furthermore, in the second step, the intensity of the ultraviolet light is 100 mW / cm². 2 The irradiation time is 5 minutes.

[0011] Further, the soaking solution in the third step is prepared as follows: 50 mg, 100 mg, 150 mg and 200 mg of 1-vinyl-3-butylimidazolium bromide monomer are weighed and placed into four centrifuge tubes, and 0.5 mg of N,N'-methylenebisacrylamide crosslinking agent and 20 μL of 0.1 mol / mL photoinitiator Lap solution are added to each tube. Deionized water is added to make the total volume 1 mL. Then, the four mixed solutions are sonicated at 40 kHz for 10 minutes to obtain four soaking solutions with different bromide concentrations.

[0012] Furthermore, in the third step, the light-protected swelling time is 24 hours; in the fourth step, the intensity of the ultraviolet light is 100 mW / cm². 2 The irradiation time is 15 minutes.

[0013] A multi-network sensing hydrogel with synergistically modulated electrical and mechanical properties prepared by any of the above preparation methods, wherein the hydrogel comprises: The first network is composed of polyacrylic acid, which is formed by free radical polymerization of acrylic acid monomers in the presence of a polyethylene glycol crosslinking agent and a photoinitiator. At least one conductive network is composed of poly(1-vinyl-3-butylimidazolium bromide), which is formed by in-situ photopolymerization after the first network is swollen in an immersion solution containing 1-vinyl-3-butylimidazolium bromide monomer, N,N'-methylenebisacrylamide crosslinking agent and photoinitiator. The conductivity of the hydrogel is achieved by adjusting the concentration of 1-vinyl-3-butylimidazolium bromide monomer and the number of network layers in the soaking solution, resulting in a conductivity ranging from 0.02 to 1.33 S·m. -1Adjustable within the specified range; elongation at break adjustable from 98.40% to 851.31%; fracture stress adjustable from 32.63 to 211.93 kPa; Young's modulus adjustable from 63.32 to 150.36 kPa; toughness adjustable from 20.62 to 1137.68 kJ·m. -3 Adjustable within the range.

[0014] Furthermore, the hydrogel is a dual-network hydrogel, comprising a first network and a layer of the conductive network, and the conductivity of the dual-network hydrogel is 0.22-1.33 S·m. -1 The fracture strain ranged from 98.40% to 275.11%, the fracture stress from 32.63 to 69.97 kPa, the Young's modulus from 63.32 to 89.89 kPa, and the toughness from 20.62 to 134.25 kJ·m. -3 .

[0015] Furthermore, the hydrogel is a triple-network hydrogel, comprising a first network and two conductive network layers, and the conductivity of the triple-network hydrogel is 0.07-0.38 S·m. -1 The elongation at break ranges from 316.57% to 851.31%, the fracture stress ranges from 83.30 to 211.93 kPa, the Young's modulus ranges from 73.04 to 150.36 kPa, and the highest toughness can reach 1137.68 kJ·m. -3 .

[0016] Furthermore, the hydrogel is a quadruple network hydrogel, comprising a first network and three conductive network layers, and the conductivity of the quadruple network hydrogel is 0.02-0.51 S·m. -1 The elongation at break ranges from 314.58% to 681.48%, the fracture stress ranges from 80.88 to 143.79 kPa, the Young's modulus ranges from 85.85 to 141.86 kPa, and the toughness ranges from 177.99 to 595.84 kJ·m. -3 .

[0017] This application also discloses the application of multi-network sensing hydrogels with synergistic regulation of electrical and mechanical properties prepared by any of the above preparation methods in flexible sensors, wearable electronic devices, human-computer interaction interfaces, health monitoring devices or soft robots.

[0018] Explanation of the principle: The design principle of this invention is based on the synergistic enhancement mechanism of dual-network hydrogels and the controllable construction strategy of stepwise swelling-in-situ photopolymerization. The first network, namely the polyacrylic acid network, serves as the skeleton network, providing basic structural support and swelling capacity. The carboxyl groups in the polyacrylic acid network endow the gel with pH responsiveness and ion exchange capacity, while the cross-linking points formed by the polyethylene glycol cross-linking agent ensure the stability of the network. The second network, the poly(1-vinyl-3-butylimidazolium bromide) network, serves as a conductive network, providing ionic conductivity channels. 1-vinyl-3-butylimidazolium bromide is a cationic salt, and the imidazole cations and free bromide ions in its molecular structure can dissociate. The directional movement of these ions enables the material to conduct ionic currents, thereby endowing the hydrogel with excellent ionic conductivity. By controlling the concentration of this monomer in the soaking solution, the crosslinking density and the number of conductive pathways of the second network can be controlled, thereby achieving continuous adjustment of conductivity. The core innovation of this invention is the stepwise swelling-in-situ photopolymerization strategy. The advantages of this strategy are: 1. The construction of each network layer is carried out independently, avoiding mutual interference between different network formation processes; 2. The swelling process allows monomers to fully penetrate the existing network, ensuring full interpenetration between the new and old networks; 3. The photopolymerization reaction conditions are mild and controllable, and can be completed rapidly at room temperature, which is beneficial for maintaining the network's microstructure; 4. By repeating the swelling-photopolymerization process, the number of network layers can be precisely controlled, achieving gradient regulation of performance. Synergistic enhancement mechanism of multiple network structures: When the material is subjected to stress, the relative slippage and energy dissipation between different networks improve the toughness of the material; at the same time, the multiple interpenetrating network structure ensures the continuity of the conductive path, and can maintain stable electrical performance even under large deformation. This synergistic optimization of structure and performance is the fundamental reason why the present invention can achieve both electrical and mechanical performance control. The initial network was prepared by free radical polymerization using acrylic acid as monomer, polyethylene glycol as crosslinking agent, and Lap as photoinitiator. Subsequently, the initial hydrogel was immersed in an aqueous solution containing 1-vinyl-3-butylimidazolium bromide, N,N′-methylenebisacrylamide, and Lap for 24 h, and a second network layer was introduced through in-situ photopolymerization. Further, by repeating the "swelling-absorption-polymerization" process, conductive network structures of different levels were constructed stepwise to finally obtain a multi-network hydrogel system. For the same set of samples, the composition of the immersion solution used in each swelling stage was kept consistent to ensure that the changes in hydrogel performance mainly came from the evolution of network layers themselves, rather than differences in chemical composition.

[0019] This application provides a multi-network sensing hydrogel with synergistic regulation of electrical and mechanical properties, its preparation method, and its application. Compared with the prior art, it has the following advantages: 1. Achieved synergistic regulation of electrical and mechanical properties: This invention constructs a multi-network hydrogel through a stepwise swelling-in-situ photopolymerization strategy, achieving an electrical conductivity ranging from 0.02 to 1.33 S·m. -1The range can be continuously adjusted, and the elongation at break can reach 98.40%-851.31%, while the fracture stress can reach 32.63-211.93 kPa, which effectively solves the contradiction between electrical and mechanical properties in traditional conductive hydrogels. 2. The preparation method is simple, controllable, and highly reproducible: This invention uses photopolymerization, which has mild reaction conditions (room temperature is sufficient) and a fast reaction rate (from several minutes to tens of minutes). Furthermore, the performance of the product can be precisely controlled by adjusting the swelling time and monomer concentration. The same set of samples uses the same soaking solution at each swelling stage, ensuring that the performance changes mainly come from the evolution of the network hierarchy itself, rather than differences in chemical composition, resulting in excellent experimental reproducibility. 3. Wide range and fine gradient of performance control: By adjusting the concentration of ionic liquid monomers in the soaking solution (50-200mg / mL) and the number of network layers (two to four networks), the electrical and mechanical properties of hydrogels can be controlled in a wide range and with fine gradients to meet the needs of different application scenarios. 4. Good biocompatibility of materials: The monomers (acrylic acid, 1-vinyl-3-butylimidazolium bromide) and crosslinking agents (polyethylene glycol, N,N'-methylenebisacrylamide) used in this invention are all materials with good biocompatibility. The hydrogel prepared is suitable for wearable devices and biomedical devices that come into direct contact with the human body. 5. Broad application prospects: The hydrogel of this invention has excellent conductivity, flexibility, strength and toughness, and is suitable for a variety of application scenarios such as flexible strain sensors, pressure sensors, bioelectric signal detection electrodes, and wearable health monitoring devices, providing a general and scalable solution for the material design of high-performance flexible electronic devices; 6. Low process cost and easy to scale up production: The raw materials used in this invention are all commercial products with low prices; the preparation process is simple and does not require special equipment, which is conducive to industrial production and practical application. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the synthesis process and structure of the multi-network hydrogel of this application, where a is the process of synthesizing multi-network hydrogel from polyacrylic acid hydrogel through repeated soaking, and b is a schematic diagram of four hierarchical hydrogel network structures. Figure 2 The figures are tensile stress-strain curves of the multi-network hydrogels of this application, where a is the tensile stress-strain curve of the initial hydrogel and the dual-network hydrogel soaked in four different concentrations of 1-vinyl-3-butylimidazolium bromide, b is the tensile stress-strain curve of the tri-network hydrogel, and c is the tensile stress-strain curve of the tetra-network hydrogel. Figure 3The graphs show the maximum tensile stress and elongation at break of the multi-network hydrogels of this application. In graph a, the maximum tensile stress and elongation at break of the bi-network hydrogel vary with the concentration of 1-vinyl-3-butylimidazolium bromide; in graph b, the maximum tensile stress and elongation at break of the tri-network hydrogel vary with the concentration of 1-vinyl-3-butylimidazolium bromide; and in graph d, the maximum tensile stress and elongation at break of the tetra-network hydrogel varies with the concentration of 1-vinyl-3-butylimidazolium bromide. Figure 4 The diagrams show the Young's modulus and toughness of the multi-network hydrogels of this application. In diagram a, the Young's modulus and toughness of the bi-network hydrogel change with the concentration of 1-vinyl-3-butylimidazolium bromide in the soaking solution; in diagram b, the Young's modulus and toughness of the tri-network hydrogel change with the concentration of 1-vinyl-3-butylimidazolium bromide in the soaking solution; and in diagram c, the Young's modulus and toughness of the tetra-network hydrogel change with the concentration of 1-vinyl-3-butylimidazolium bromide in the soaking solution. Figure 5 This is a diagram illustrating the synergistic control of the mechanical and electrical properties of the multi-network hydrogel in this application. In diagram a, the elongation at break and electrical conductivity of the hydrogel are controlled by adjusting the concentration of 1-vinyl-3-butylimidazolium bromide in the soaking solution and the number of network layers. In diagram b, the Young's modulus and electrical conductivity of the hydrogel are controlled by adjusting the concentration of 1-vinyl-3-butylimidazolium bromide in the soaking solution and the number of network layers. In diagram c, the toughness and electrical conductivity of the hydrogel are controlled by adjusting the concentration of 1-vinyl-3-butylimidazolium bromide in the soaking solution and the number of network layers. Figure 6 The following are the sensing performance test graphs of the multi-network hydrogel of this application: a) is the sensing curve of the dual-network hydrogel soaked in 200 mg / mL bromide concentration, the triple-network hydrogel soaked in 50 mg / mL bromide concentration, and the quadruple-network hydrogel soaked in 150 mg / mL bromide concentration; b) is the GF size of the three hydrogels in a; c) is the stability graph of the hydrogel sensor under small strain (5%, 10%, 20%) with 5-8 consecutive tensile cycles at each strain to evaluate the stability of the sensor; d) is the stability graph of the hydrogel sensor under large strain (50%, 100%, 200%) with 5-8 consecutive tensile cycles at each strain to evaluate the stability of the sensor; e) is the sensing performance of the hydrogel sensor for speech recognition; and f) is the sensing performance of the hydrogel sensor for different degrees of finger bending. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading this disclosure, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0022] Example 1, Preparation of a first network (polyacrylic acid gel): Place 20 mg of polyethylene glycol (PEG, molecular weight 20000) into a 1.5 mL centrifuge tube, add 10 μL of lithium phenyl-2,4,6-trimethylbenzoylphosphonate (Lap) photoinitiator solution (concentration 0.1 mol / mL) and 670 μL of deionized water, and shake to dissolve at room temperature. Place the centrifuge tube in a fume hood, add 300 μL of acrylic acid (AA) monomer, and shake at 40 kHz for 1–2 minutes to obtain a homogeneous pregel solution.

[0023] Using a syringe inserted below the liquid surface, nitrogen gas was bubbled into the pre-gelation solution for 5 minutes to remove dissolved oxygen, followed by sonication at 40 kHz for 10 minutes for further deoxygenation. The deoxygenated pre-gelation solution was then injected into a mold consisting of two glass plates (1 mm apart) and a silicone gasket, and sonicated at 100 mW / cm². 2 Polymerization was carried out under ultraviolet light (wavelength 365 nm) for 5 minutes to obtain polyacrylic acid (PAA) gel as the first network.

[0024] The resulting PAA gel is transparent and has good swelling properties, providing an ideal framework structure for the subsequent introduction of conductive networks.

[0025] Example 2, the preparation of the soaking solution, specifically includes the following steps: Step 1, Immersion Solution A (low concentration): Weigh 50 mg of 1-vinyl-3-butylimidazolium bromide monomer [VBIM]Br monomer, 0.5 mg of N,N'-methylenebisacrylamide (MBAA) crosslinking agent and 20 μL of Lap photoinitiator solution (concentration 0.1mol / mL), add 929.5 μL of deionized water, shake at 40 kHz for 5 minutes, and then sonicate for 10 minutes to obtain a homogeneous immersion solution A; Step 2, Immersion Solution B (medium to low concentration): Weigh 100 mg of 1-vinyl-3-butylimidazolium bromide monomer [VBIM]Br monomer, 0.5 mg of N,N'-methylenebisacrylamide MBAA crosslinking agent and 20 μL of Lap photoinitiator solution, add 879.5 μL of deionized water, and prepare immersion solution B in the same way; Step 3, Immersion solution C (medium to high concentration): Weigh 150 mg [VBIM]Br monomer, 0.5 mg MBAA crosslinking agent and 20 μL Lap photoinitiator solution, add 829.5 μL deionized water, and prepare immersion solution C in the same way; Step 4, Immersion Solution D (high concentration): Weigh 200 mg [VBIM]Br monomer, 0.5 mg MBAA crosslinking agent and 20 μL Lap photoinitiator solution, add 779.5 μL deionized water, and prepare immersion solution D in the same way.

[0026] Example 3, the preparation of a dual-network hydrogel, specifically includes the following steps: The PAA gel prepared in Example 1 was cut into small pieces (2 cm × 1 cm) and immersed in four soaking solutions (A, B, C, and D) prepared in Example 2, respectively, and swollen for 24 hours under light-protected conditions. During the swelling process, the [VBIM]Br monomer, MBAA crosslinking agent, and photoinitiator diffused fully into the interior of the PAA network.

[0027] The swollen gel was removed and placed on a glass plate, then heated at 100 mW / cm². 2 Polymerization was carried out under ultraviolet light for 15 minutes to allow the [VBIM]Br monomer to polymerize in situ into a poly(1-vinyl-3-butylimidazolium bromide) (P[VBIM]Br) network, resulting in a double-network (DN) hydrogel. These were designated DN-A, DN-B, DN-C, and DN-D, corresponding to samples with different [VBIM]Br concentrations.

[0028] The performance of the obtained dual-network hydrogel was tested, and the results are shown in Table 1: Table 1 Performance data of dual-network hydrogels .

[0029] As shown in Table 1, with the increase of [VBIM]Br concentration in the soaking solution, the conductivity of the dual-network hydrogel decreased from 0.22 S·m. -1 Increased to 1.33 S·m -1 However, the fracture strain decreased from 275.11% to 98.40%, and the toughness decreased from 134.25 kJ·m. -3 Reduced to 20.62 kJ·m -3 This indicates that there is a certain trade-off between electrical conductivity and mechanical properties in the dual-network structure, but the present invention achieves synergistic regulation of the two within a certain range by adjusting the monomer concentration.

[0030] Example 4, Preparation of triple network hydrogel: The dual-network hydrogels (DN-A, DN-B, DN-C, DN-D) prepared in Example 3 were immersed again in soaking solutions with the same components as those used in the first immersion (i.e., DN-A was immersed in soaking solution A, DN-B was immersed in soaking solution B, and so on), and swollen again for 24 hours under light-protected conditions.

[0031] The gel after secondary swelling was removed and heated at 100 mW / cm. 2 The gels were polymerized again under ultraviolet light for 15 minutes, and a third layer of P[VBIM]Br network was introduced to obtain triple network (TN) hydrogels. These were designated as TN-A, TN-B, TN-C, and TN-D, respectively.

[0032] The performance of the obtained triple network hydrogel was tested, and the results are shown in Table 2: Table 2 Performance data of triple network hydrogel .

[0033] As shown in Table 2, compared with the double-network hydrogel, the triple-network hydrogel exhibits a significantly higher elongation at break (up to 851.31%), and its fracture stress and toughness also increase substantially (reaching a maximum of 211.93 kPa and 1137.68 kJ·m, respectively). -3 This indicates that increasing the network hierarchy can effectively improve the mechanical properties of materials, especially their energy dissipation capacity under large deformation conditions. Although the electrical conductivity decreased somewhat, it remained within the range of 0.07–0.38 S·m. -1 Within the available range.

[0034] Example 5, Preparation of a quadruple network hydrogel: The triple network hydrogels (TN-A, TN-B, TN-C, TN-D) prepared in Example 4 were immersed again in the same soaking solution with the same components as in the previous two soakings, and swollen for a third time for 24 hours under light-protected conditions.

[0035] The gels after three swelling cycles were removed and subjected to a third polymerization under 100 mW / cm² UV light for 15 minutes to introduce a fourth layer of P[VBIM]Br network, resulting in a quadruple network (QN) hydrogel. These were designated QN-A, QN-B, QN-C, and QN-D, respectively.

[0036] The performance of the obtained quadruple network hydrogel was tested, and the results are shown in Table 3: Table 3 Performance data of the quadruple network hydrogel .

[0037] As can be seen from Table 3, the quadruple network hydrogel maintains a high tunable conductivity (0.02-0.51 S·m). -1 While maintaining excellent mechanical properties (elongation at break 314.58%-681.48%, toughness 177.99-595.84 kJ·m), it also maintains excellent mechanical properties (elongation at break 314.58%-681.48%, toughness 177.99-595.84 kJ·m). -3 Compared to triple networks, quadruple networks offer improved mechanical properties and a wider range of conductivity control, demonstrating the flexibility of multi-network structure design.

[0038] Example 6, Performance Testing Method: Conductivity testing: The conductivity of the hydrogel was tested using the four-probe method. The hydrogel sample to be tested was cut into 10 mm × 10 mm × 1 mm pieces, placed in a four-probe test fixture, and the AC impedance spectrum was measured at room temperature using an electrochemical workstation (CHI660E) with a frequency range of 0.1 Hz-100 kHz. The conductivity was calculated based on the impedance data.

[0039] Mechanical property testing: The tensile properties of the hydrogel were tested using a universal testing machine (Instron 5944). The hydrogel samples were cut into dumbbell shapes (gauge length: 20 mm × 5 mm × 1 mm) and subjected to uniaxial tensile testing at a tensile rate of 10 mm / min. The stress-strain curves were recorded. The fracture stress, fracture strain, Young's modulus (secant modulus at 15% strain), and toughness (area under the stress-strain curve) were calculated based on the stress-strain curves.

[0040] Sensing performance testing: A hydrogel sample was connected to a copper electrode to form a strain sensor. A universal testing machine was used to apply periodic tensile strain to the sample, while an electrochemical workstation recorded the resistance change in real time. The sensitivity coefficient GF = (ΔR / R0) / ε was calculated based on the relationship between the rate of change of resistance (ΔR / R0) and strain, where R0 is the initial resistance, ΔR is the change in resistance, and ε is the strain. The response time and recovery time were tested using square wave strain loading.

[0041] Example 7, Application of dual-network hydrogel in strain sensors: The dual-network hydrogel DN-D (with an electrical conductivity of 1.33 S·m) prepared in Example 3 was used. -1 The hydrogel (with a fracture strain of 98.40%) was used to fabricate a flexible strain sensor. The hydrogel was cut into strips of 20 mm × 10 mm × 1 mm, with copper foil at both ends as electrodes, and connected to an electrochemical workstation by wires.

[0042] The sensor performance test results are as follows: (1) Strain response range: The sensor can detect 0-90% strain. The sensitivity coefficient GF is about 1.8 in the 0-90% strain range, showing good strain response characteristics.

[0043] (2) Cyclic stability: The resistance signal remained stable and no obvious drift was observed during continuous tensile cycle tests at strains of 5%, 10% and 20%, indicating that the sensor has good durability.

[0044] (3) Speech recognition test: The sensor was attached to the human vocal cords and could clearly detect different pronunciations of the experimenter. The signal was stable and repeatable, which proved its application potential in wearable devices.

[0045] Example 8, Application of quadruple network hydrogel in strain sensors: The quadruple network hydrogel QN-C (conductivity 0.23 S·m) prepared in Example 5 was used. -1 The hydrogel (with a fracture strain of 484.89%) was used to prepare a bioelectric signal detection electrode. The hydrogel was cut into strips of 20 mm × 10 mm × 1 mm, and the ends of the hydrogel were attached to the skin surface of the finger as detection electrodes.

[0046] (1) Strain response range: The sensor can detect strain from 0 to 480%. The sensitivity coefficient GF is about 6.4 in the strain range of 0 to 480%, which shows good strain response characteristics.

[0047] (2) Cyclic stability: The resistance signal remained stable and did not drift significantly during continuous tensile cycle tests at 50%, 100% and 200% strain, indicating that the sensor has good durability.

[0048] (3) Finger bending test: The sensor was attached to the index finger joint. Different degrees of finger bending of the experimenter could be clearly fed back as electrical signals. The signals were stable and repeatable, which proved its application potential in wearable devices.

[0049] This invention provides a multi-network sensing hydrogel with synergistic regulation of electrical and mechanical properties, its preparation method, and its applications. Through a stepwise swelling-in-situ photopolymerization strategy, dual-network, triple-network, and quadruple-network hydrogel systems were successfully constructed, achieving a wide range of continuous adjustment of properties such as conductivity, elongation at break, fracture stress, Young's modulus, and toughness.

[0050] The core innovations of this invention are: 1. The stepwise swelling-in-situ photopolymerization method is used to achieve precise and controllable construction of multiple network structures; 2. By controlling the concentration of ionic liquid monomers and the number of network layers in the soaking solution, the synergistic optimization of electrical and mechanical properties is achieved; 3. The preparation method is simple, the conditions are mild, the repeatability is good, and it is easy to scale up production.

[0051] The hydrogel of this invention has broad application prospects in fields such as flexible sensors, wearable electronic devices, human-computer interfaces, and health monitoring equipment. Examples demonstrate that this hydrogel can be used in high-sensitivity strain sensors, pressure sensors, and bioelectrical signal detection electrodes, exhibiting excellent overall performance.

[0052] The above description is only a preferred embodiment of the present invention. It should be noted that, under the premise of following the principles of the present invention, improved experimental schemes should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-network sensing hydrogel with synergistically modulated electrical and mechanical properties, characterized in that, Specifically, the steps include the following: The first step is to prepare a pregel solution: 20 mg of polyethylene glycol, 10 μ L of 0.1 mol / mL photoinitiator and 670 μ L of deionized water are mixed according to the mass-volume ratio to obtain mixed solution A. Mixed solution A is placed in a fume hood, and then 300 μ L of acrylic acid is added. After shaking and mixing evenly, mixed solution B is obtained. Mixed solution B is deoxygenated to obtain a pregel solution. The second step is to prepare the first network: the pregel solution is placed in a glass clamp mold and a free radical polymerization reaction is initiated under ultraviolet light to obtain polyacrylic acid gel as the first network; The third step, light-protected swelling: The polyacrylic acid gel is placed in an immersion solution containing 1-vinyl-3-butylimidazolium bromide monomer, N,N'-methylenebisacrylamide crosslinking agent and photoinitiator, and swelled in the dark for 20-28 hours. The fourth step is to prepare a double-network hydrogel: the swollen gel is subjected to in-situ photopolymerization under ultraviolet light to obtain a double-network hydrogel. Step 5: Preparation of triple network hydrogel: The double network hydrogel is placed in an immersion solution containing 1-vinyl-3-butylimidazolium bromide monomer, N,N'-methylenebisacrylamide crosslinking agent and photoinitiator, and swelled in the dark for 20-28 hours. The swollen gel is then subjected to in-situ photopolymerization under ultraviolet light to obtain triple network hydrogel. Step 6: Preparation of quadruple network hydrogel: The triple network hydrogel is placed in an immersion solution containing 1-vinyl-3-butylimidazolium bromide monomer, N,N'-methylenebisacrylamide crosslinking agent and photoinitiator, and swelled in the dark for 20-28 hours. The swollen gel is then subjected to in-situ photopolymerization under ultraviolet light to obtain the quadruple network hydrogel. Specifically, by adjusting the concentration of 1-vinyl-3-butylimidazolium bromide monomer in the soaking solution to 50-200 mg / mL and the number of network layers, the electrical and mechanical properties of the hydrogel can be synergistically controlled.

2. The method for preparing the multi-network sensing hydrogel with synergistically regulated electrical and mechanical properties according to claim 1, characterized in that: In the first step, the amount of polyethylene glycol used is 20 mg, the photoinitiator is lithium phenyl-2,4,6-trimethylbenzoylphosphonate (Lap), the amount of photoinitiator used is 10 μL of a 0.1 mol / mL solution, the amount of deionized water used is 670 μL, the amount of acrylic acid used is 300 μL, the oscillation frequency is 40 kHz, and the oscillation time is 1-2 minutes; the deoxygenation treatment in the first step includes: inserting a syringe below the surface of mixed solution B, introducing nitrogen gas into the surface of mixed solution B for 5 minutes, and then sonicating at a frequency of 40 kHz for 10 minutes.

3. The method for preparing the multi-network sensing hydrogel with synergistically regulated electrical and mechanical properties according to claim 1, characterized in that, In the second step, the intensity of the ultraviolet light is 100 mW / cm². 2 The irradiation time is 5 minutes.

4. The method for preparing a multi-network sensing hydrogel with synergistically regulated electrical and mechanical properties according to claim 1, characterized in that, The soaking solution in the third step is prepared as follows: 50 mg, 100 mg, 150 mg and 200 mg of 1-vinyl-3-butylimidazolium bromide monomer are weighed and placed into four centrifuge tubes, and 0.5 mg of N,N'-methylenebisacrylamide crosslinking agent and 20 μL of 0.1 mol / mL photoinitiator Lap solution are added to each tube. Deionized water is added to make the total volume 1 mL. The four mixed solutions are then sonicated at 40 kHz for 10 minutes to obtain four soaking solutions with different bromide concentrations.

5. The method for preparing a multi-network sensing hydrogel with synergistically regulated electrical and mechanical properties according to claim 1, characterized in that, In the third step, the light-protected swelling time is 24 hours; in the fourth step, the intensity of the ultraviolet light is 100 mW / cm². 2 The irradiation time is 15 minutes.

6. The multi-network sensing hydrogel with synergistically regulated electrical and mechanical properties prepared by the preparation method according to any one of claims 1-5, characterized in that, The hydrogel comprises: The first network is composed of polyacrylic acid, which is formed by free radical polymerization of acrylic acid monomers in the presence of a polyethylene glycol crosslinking agent and a photoinitiator. At least one conductive network is composed of poly(1-vinyl-3-butylimidazolium bromide), which is formed by in-situ photopolymerization after the first network is swollen in an immersion solution containing 1-vinyl-3-butylimidazolium bromide monomer, N,N'-methylenebisacrylamide crosslinking agent and photoinitiator. The conductivity of the hydrogel is achieved by adjusting the concentration of 1-vinyl-3-butylimidazolium bromide monomer and the number of network layers in the soaking solution, resulting in a conductivity ranging from 0.02 to 1.33 S·m. -1 Adjustable within the specified range; elongation at break adjustable from 98.40% to 851.31%; fracture stress adjustable from 32.63 to 211.93 kPa; Young's modulus adjustable from 63.32 to 150.36 kPa; toughness adjustable from 20.62 to 1137.68 kJ·m. -3 Adjustable within the range.

7. The multi-network sensing hydrogel with synergistically modulated electrical and mechanical properties according to claim 6, characterized in that, The hydrogel is a dual-network hydrogel, comprising a first network and a conductive network layer, and the conductivity of the dual-network hydrogel is 0.22-1.33 S·m. -1 The fracture strain ranged from 98.40% to 275.11%, the fracture stress from 32.63 to 69.97 kPa, the Young's modulus from 63.32 to 89.89 kPa, and the toughness from 20.62 to 134.25 kJ·m. -3 .

8. The multi-network sensing hydrogel with synergistic regulation of electrical and mechanical properties according to claim 6, characterized in that, The hydrogel is a triple-network hydrogel, comprising a first network and two conductive network layers, and the conductivity of the triple-network hydrogel is 0.07-0.38 S·m. -1 The elongation at break ranges from 316.57% to 851.31%, the fracture stress ranges from 83.30 to 211.93 kPa, the Young's modulus ranges from 73.04 to 150.36 kPa, and the highest toughness can reach 1137.68 kJ·m. -3 .

9. The multi-network sensing hydrogel with synergistic regulation of electrical and mechanical properties according to claim 6, characterized in that, The hydrogel is a quadruple network hydrogel, comprising a first network and three conductive network layers, and the conductivity of the quadruple network hydrogel is 0.02-0.51 S·m. -1 The elongation at break was 314.58%-681.48%, the fracture stress was 80.88-143.79 kPa, the Young's modulus was 85.85-141.86 kPa, and the toughness was 177.99-595.84 kJ·m. -3 .

10. The application of a multi-network sensing hydrogel with synergistically regulated electrical and mechanical properties prepared by the preparation method according to any one of claims 1-5 in flexible sensors, wearable electronic devices, human-computer interaction interfaces, health monitoring devices or soft robots.

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