Conductive organic hydrogel as well as preparation method and application thereof

Abstract

The invention relates to conductive organic hydrogel as well as a preparation method and application thereof, and belongs to the field of conductive hydrogel. Aiming at the problems of low mechanical strength, poor freezing resistance, insufficient dynamic stability, narrow sensing range and the like of the existing conductive hydrogel, the invention provides a conductive composite hydrogel with a multilevel structure prepared by a directional freezing synergistic coordination strengthening process. The hydrogel is formed by matching a polyvinyl alcohol matrix with a FeCl3 coordination cross-linking agent and a polyethylene glycol non-solvent phase, oriented molecular chain arrangement is formed through liquid-phase oriented freezing, and a three-dimensional network with a tight contraction ring structure is constructed in cooperation with the quenching strengthening effect of a polyethylene glycol / FeCl3 mixed solution. The obtained hydrogel shows the ultrahigh tensile strength of 8.25 MPa, the strain limit of 800% and the fracture toughness of 3.5 MJ / m < 3 >, and meanwhile has the low-temperature stability at the temperature of-20 DEG C, the dynamic cycle reliability of more than 104 times and the wide-range sensing response of 0-800%. The conductive hydrogel has excellent anti-freezing property (working at-20 DEG C), signal fidelity (GF = 4.37) and reusability especially in flexible sensor application, solves the technical bottleneck that mechanical properties and environmental tolerance of traditional conductive hydrogel are difficult to synergistically optimize, and provides a novel material solution for wearable equipment in an extreme environment.

Description

Technical Field

[0001] The present invention belongs to the field of conductive hydrogels, and relates to conductive organic hydrogels, their preparation methods and applications. Background Art

[0002] Conductive hydrogels are a special type of hydrogel material. In recent years, with the development of various electro-functional devices, conductive hydrogels have also received extensive attention. Due to their ability to convert tiny deformations into electrical signals and output them, as well as their soft and skin-friendly characteristics, hydrogels have potential application prospects in various fields such as wearable devices, human-computer interaction interfaces, and medical devices. Conductive hydrogels mainly achieve the change between hydrogel deformation and electrical signals in two ways: one is to add conductive fillers such as graphene, carbon nanotubes, and metal fillers during the preparation of the hydrogel. The addition of the fillers provides a conductive path for the hydrogel and can greatly improve the conductive performance of the hydrogel; the other is to mix polyelectrolytes or inorganic salts into the network structure of the hydrogel to achieve ionic conduction. However, the addition of conductive fillers often makes it difficult to balance the conductive performance and mechanical properties of the hydrogel, which poses extremely high requirements for the design of the hydrogel network structure. As a flexible electronic product, hydrogels face problems such as poor strength (<1 Mpa), poor electrical properties, insufficient antifreeze performance, weak reusability, lack of biocompatibility, and poor water retention, which cannot guarantee the stability and long-term effectiveness of hydrogels in the field of flexible electronics. Generally speaking, conductive hydrogels have very broad application prospects in the field of flexible electronics, especially in fields such as wearable devices, human-computer interaction interfaces, and medical devices.

[0003] Mechanical property defects, insufficient environmental tolerance, electrical property limitations, and process defects of traditional conductive hydrogels.

[0004] Mechanical property defects: imbalance between low strength and toughness. Traditional conductive hydrogels mainly enhance their mechanical properties through chemical cross-linking agents and nano-composite material filling. Chemical cross-linking agents such as glutaraldehyde and epichlorohydrin can construct covalent networks, but the randomly distributed cross-linking points lead to stress concentration, and the tensile strength is generally lower than 1 MPa, and the elongation at break is less than 250%. Nano-composite material filling, such as carbon nanotubes and graphene, can improve the strength, but the fracture toughness is often still lower than the level of human ligaments. In addition, some enhancement methods such as triple freeze-thaw hydrogels have problems with crack propagation sensitivity in applications, and the carbon nanotube filling system has interface debonding due to uneven dispersion, and the local stress fracture rate during stretching is as high as 57%.

[0005] Insufficient environmental tolerance: Challenges of antifreeze and long-term stability. Conductive hydrogels are prone to damage the network structure due to ice crystal formation in low-temperature environments, resulting in a significant decrease in the compressive modulus. Antifreeze additives such as glycerol or ethylene glycol can lower the freezing point, but will significantly deteriorate the conductivity and mechanical strength. At the same time, traditional hydrogels with unclosed porous structures are prone to water loss in higher humidity environments, resulting in a resistivity drift rate exceeding 50%. Hydrogels containing natural polymers are prone to biodegradation in high-temperature and high-humidity environments, losing their functional use.

[0006] Limitations in electrical properties: Low stability and limited detection range. The electrical properties of conductive hydrogels also have defects. In metal particle doping systems, the resistivity increases after bending cycles, and the irreversible ion migration leads to the degradation of the resistance change coefficient. In addition, the strain detection limit of high-modulus materials is low, while the sensitivity of highly ductile materials is insufficient. These limitations in electrical properties restrict the detection range of conductive hydrogels in applications such as strain sensors.

[0007] Process defects: Inefficient structure regulation and energy consumption limitations. The preparation processes of traditional conductive hydrogels have problems such as long time consumption, high energy consumption, and low precision in the arrangement of molecular chains. The cyclic freezing-thawing process takes as long as 12 - 24 hours, the ultraviolet light curing process has uneven surface curing problems, and although the microwave-assisted cross-linking process takes a short time, the controllable area is limited and the energy consumption is high. In addition, although the directional freezing technique can induce the arrangement of molecular chains along the temperature gradient, delamination defects occur at the millimeter scale. The conflict between efficient preparation and high cost is also a major challenge faced by the current process.

[0008] Many attempts have been made to construct hierarchically structured gel materials, such as directional freezing, nonsolvent quenching, mechanical training, etc. Through these methods, the macromolecular chains will be oriented according to the temperature gradient field, so that the molecular chains are distributed along the direction of the temperature gradient from strong to weak. At the same time, the PVA molecular chains will be distributed towards the middle and arranged more closely. A solid hydrogel with a multi-scale hierarchical structure has been prepared by freeze-casting assisted solution replacement. The anisotropic honeycomb structure shown at the microscale endows the hydrogel with strong mechanical properties. However, there are still challenges in constructing conductive organic hydrogels with excellent comprehensive properties. Summary of the Invention

[0009] In view of this, the present invention prepares a tough hydrogel by a method of substitution between directional freezing and polyethylene glycol and ferric chloride (FeCl3) solution. Polyethylene glycol (PEG) has the advantages of non-toxicity and good biocompatibility, and is widely used in the fields of cosmetics, food, medicine, etc. PEG, as an additive, regulates the polymer blend phase morphology through hydrogen bonds between molecular chains and molecules. Generally, when the molecular weight is less than 600, PEG appears in liquid form, and it is soluble in salts such as (FeCl3, KAC and LiAC). The hydrogel prepared by this method has the characteristics of taking toughness and strength into consideration, high stability, antifreeze and durability. The process of directional freezing prompts polyvinyl alcohol (PVA) to be selectively oriented along the direction of temperature gradient change. Polyethylene glycol (PEG-200) acts as a non-foaming agent to induce the in-situ phase separation of ice crystals oriented by PVA, so that the PVA molecular chains are arranged more closely, and the interaction between molecular chains is enhanced. At the same time, the coordinated coordination of ferric chloride (FeCl3) exacerbates the inward aggregation of PVA molecular chains. The present invention adopts directional freezing and non-solution quenching (DF-NSQ) to prepare an organic gel with excellent comprehensive performance. First, the PVA aqueous solution is directly frozen into ice crystals to arrange the polymer chains along the temperature gradient. Subsequently, the ice crystals are immersed in a FeCl3 / PEG200 solution for 24 hours. Since PEG200 is miscible with water but is a poor solvent for PVA, during the mutual replacement of water molecules and PEG200, due to the hydrophobic effect of the liquid-solid interface, the arranged PVA ice crystals shrink sharply, forming anisotropic multi-scale hierarchical structures in the parallel freezing direction and shrinking aggregation ring structures in the vertical freezing direction. At the same time, FeCl3 is constructed in the form of coordination enhancement. When the PVA concentration is 10%, after directional freezing for 4 hours, the conductive organic hydrogel is prepared after quenching in a 1% FeCl3 / PEG200 solution for 24 hours. The purpose of the present invention is to provide a conductive organic hydrogel, the second purpose is to provide a method for preparing a conductive organic hydrogel, and the third purpose is to use a conductive organic hydrogel in the preparation of a flexible sensor.

[0010] In order to achieve the above object, the present invention provides the following technical solutions:

[0011] The present invention provides a conductive organic hydrogel, comprising the following components:

[0012] Polyvinyl alcohol is the matrix material, accounting for 5%-12.5% ​​(w / w) of the total solid content;

[0013] FeCl3 is a coordination crosslinking agent, accounting for 0.1%-1% (w / w) of the total solid content;

[0014] Polyethylene glycol 200 is the non-solvent phase;

[0015] Preferably, the solid content of the polyvinyl alcohol is 10% (w / w), and the solid content of the FeCl3 is 1% (w / w);

[0016] Furthermore, a method for preparing a conductive organic hydrogel, the steps are as follows:

[0017] (a) Melt polyvinyl alcohol in deionized water at 90 - 98 °C to form a polyvinyl alcohol hot melt solution,

[0018] (b) Pour the polyvinyl alcohol hot melt solution into a polytetrafluoroethylene mold and directionally freeze it in liquid nitrogen for 1 - 3 hours;

[0019] (c) Immerse the directionally frozen sample in a mixed solution of ferric chloride / polyethylene glycol 200 for quenching treatment, the quenching temperature is 5 - 8 °C, and the time is 24 - 72 hours;

[0020] Preferably, the polyvinyl alcohol is polyvinyl alcohol 124;

[0021] Preferably, the solid content of polyvinyl alcohol dissolved in deionized water is 2.5 - 20%;

[0022] Preferably, the solid content of ferric chloride in the ferric chloride / polyethylene glycol 200 mixed solution is 0 - 1%;

[0023] Preferably, the solid content of polyvinyl alcohol dissolved in deionized water is 10%, and the solid content of ferric chloride in the ferric chloride / polyethylene glycol 200 mixed solution is 1%;

[0024] Furthermore, the application of the conductive organic hydrogel in the preparation of a flexible sensor.

[0025] The beneficial effects of the present invention are as follows:

[0026] (1) The conductive hydrogel prepared by the present invention has various excellent characteristics. After melting polyvinyl alcohol in deionized water, it is directionally frozen. The directional freezing process promotes the orientation of polyvinyl alcohol (PVA) along the direction of the temperature gradient change. Polyethylene glycol (PEG - 200) is used as a non - foaming agent to induce in - situ phase separation of PVA - oriented ice crystals, making the PVA molecular chains arranged more closely and enhancing the interaction between molecular chains. At the same time, the synergistic coordination of ferric chloride (FeCl3) exacerbates the inward aggregation of PVA molecular chains. Therefore, the strong and conductive hydrogel prepared by the present invention has an organic hydrogel with an oriented layered structure (micrometer - scale) and a shrinkage - aggregation ring structure (sub - micrometer - scale), showing excellent toughness characteristics in the parallel freezing direction.

[0027] (2) A strong hydrogel was prepared by directional freezing and substitution between polyethylene glycol and ferric chloride (FeCl3) solution. The hydrogel showed the best mechanical properties when immersed in a ferric chloride / polyethylene glycol mixed solution with a ferric chloride solid content of 1% and a PVA content of 10%. The prepared conductive organic gel showed excellent mechanical properties (strength: 8.25 MPa, strain: 800%, toughness: 3.5 MJ / m 3 ), Young's modulus: 1.9Mpa, long-term stability (>180 days). This organogel is used as a flexible sensor with antifreeze (working at -20°C), sensing stability (100% strain loading and unloading, number of cycles >10000) and a wide working window (0% to 800%).

[0028] (3) The resulting hydrogel (DF-NSQ-PVA) used as a flexible sensor also has antifreeze properties (working at -20 °C), electrical stability (100% cycles > 10000), and a high detection range of strain (0% to 800%). Therefore, this DF-NSQ strategy enables robust mechanics and long-lasting stability, and has broad applications in the field of soft electronics with environmental tolerance.

[0029] In addition, this hydrogel exhibits super fatigue resistance in the parallel and freezing directions, and can be repeatedly stretched 80,000 times at a strain of 30%. It also exhibits excellent performance in water storage and antifreeze properties. Therefore, this method for preparing strong, antifreeze and long-lasting hydrogels exhibits excellent mechanical properties and lasting stability, and has a wide range of applications in the field of soft electronics with environmental tolerance.

[0030] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0032] Figure 1 A flow chart of the preparation process of strong hydrogels prepared by directional freezing-assisted substitution between polyethylene glycol and ferric chloride (FeCl3) solution;

[0033] Figure 2Schematic diagram of the morphological structure of the hydrogel obtained after soaking in a ferric chloride / polyethylene glycol mixed solution with a ferric chloride solid content of 1% and a PVA content of 10%. a) Parallel to the freezing direction; b) Perpendicular to the freezing direction, with the same scale, both scales being 500 μm.

[0034] Figure 3 Schematic diagrams of the mechanical properties of hydrogels prepared by three different processes in different directions (the three processes are: preparing hydrogels by three cycles of freezing-thawing; preparing hydrogels by the method of directional freezing combined with the replacement between polyethylene glycol solutions; preparing hydrogels by the method of directional freezing combined with the replacement between polyethylene glycol and ferric chloride (FeCl3) solutions). a1) Stress-strain curves of three hydrogels prepared by three different processes parallel to the freezing direction; a2) Stress-strain curves of three hydrogels prepared by three different processes perpendicular to the freezing direction; b1) Schematic diagram of the stress-strain curve of hydrogels prepared by melting polyvinyl alcohol with different solid contents (2.5%, 5%, 7.5%, 10%, 12.5%) in deionized water, then performing directional freezing, and then quenching in polyethylene glycol solution parallel to the freezing direction; b2) Schematic diagram of the stress-strain curve of hydrogels prepared by melting polyvinyl alcohol with a solid content of 10% in deionized water, then performing directional freezing, and then quenching in ferric chloride / polyethylene glycol mixed solutions with ferric chloride solid contents of 0%, 0.1%, 0.5%, and 1% parallel to the freezing direction; c1) Schematic diagram of the hydrogel before stretching prepared by soaking in a ferric chloride / polyethylene glycol mixed solution with a ferric chloride solid content of 1% and a PVA content of 10%; c2) Schematic diagram of the hydrogel stretched to 300% prepared by soaking in a ferric chloride / polyethylene glycol mixed solution with a ferric chloride solid content of 1% and a PVA content of 10%; c3) Schematic diagram of the hydrogel stretched to 600% prepared by soaking in a ferric chloride / polyethylene glycol mixed solution with a ferric chloride solid content of 1% and a PVA content of 10%; c4) Schematic diagram of the hydrogel stretched to 750% prepared by soaking in a ferric chloride / polyethylene glycol mixed solution with a ferric chloride solid content of 1% and a PVA content of 10%. f1) Schematic diagram of the iron box stretched by the prepared hydrogel; f2) Schematic diagram of the weight stretched by the prepared hydrogel; g1) Schematic diagram of the heart-shaped figure of the prepared hydrogel; g2) Schematic diagram of the star-shaped figure of the prepared hydrogel.

[0035] Figure 4Schematic diagram for the electrical property analysis of a tough hydrogel prepared by the method of directional freezing in combination with the replacement between polyethylene glycol and ferric chloride (FeCl3) solution. a1) Relationship diagram of the cyclic relative resistance change of the hydrogel prepared by soaking in a ferric chloride / polyethylene glycol mixed solution with a ferric chloride solid content of 1% and a PVA content of 10% under different strains in the direction parallel to the freezing direction; a2) Relationship diagram of the cyclic relative resistance change of the prepared hydrogel under different strains in the direction perpendicular to the freezing direction; b) Schematic diagram of the relationship between the repeated stretching time and the sensitivity of the hydrogel in the parallel direction; c) Schematic diagram of the relationship between the environmental resistance and the repeated stretching cycle of the hydrogel at room temperature (25 °C) and extreme temperature (-20 °C) in the direction parallel to the freezing direction; d1) Schematic diagram of the response time and recovery time of the hydrogel in the direction parallel to the freezing direction; d2) Schematic diagram of the response time and recovery time of the hydrogel in the direction perpendicular to the freezing direction

[0036] Figure 5 Schematic diagrams for various applications of the hydrogel. a1) Say "cartoon"; a2) Say "yes"; a3) Say "me"; b) Morse code table; c) Schematic diagram of hydrogel facial contact and point touch control; d1) Schematic diagram of Morse code pressing for "CIGIT"; d2) Schematic diagram of Morse code pressing for "UCAS"; d3) Schematic diagram of Morse code pressing for "YES".

[0037] Figure 6 Schematic diagrams for the deformation demonstration of the hydrogel and the relationship between various deformations and resistance changes at high and low temperatures. a) Schematic diagrams of the stretching, bending, and twisting actions of the hydrogel; b1) Relationship diagram between wrist bending and resistance change at different temperatures; b2) Relationship diagram between finger pressing and resistance change at different temperatures; b3) Relationship diagram between finger bending and resistance change at different temperatures. Detailed implementation manners

[0038] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the diagrams provided in the following examples only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following examples and the features in the examples can be combined with each other.

[0039] Among them, the attached drawings are only for illustrative purposes, showing only schematic diagrams rather than physical diagrams, and should not be construed as limiting the present invention; for better illustration of the embodiments of the present invention, some components in the attached drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the attached drawings may be omitted.

[0040] In the attached drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the attached drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the attached drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0041] The manufacturers and models of the raw materials used in the embodiments of the present invention are as follows:

[0042] Polyvinyl alcohol (PVA), PVA 124 from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0043] Polyethylene glycol (PEG), PEG 200 from Shanghai Macklin Biochemical Co., Ltd.;

[0044] Anhydrous ferric chloride, from Shanghai Macklin Biochemical Co., Ltd.

[0045] Example 1: Morphology and structure of an organic hydrogel containing 10% PVA after directional freezing and PEG200 quenching

[0046] First, melt PVA (97 °C) in deionized water (PVA solid content: 10%). Pour the melted PVA solution into a square mold and place it in a cold field chamber (-19 °C - -17 °C) for freezing for 12 hours. Then take out the frozen sample and thaw it at room temperature (25 °C), and repeat this operation three times to prepare a cyclic freeze-thaw hydrogel.

[0047] PVA Number of cyclic freeze-thaw times Example 1 10％ Three times

[0048] The hydrogel prepared in Example 1 has a strain of about 300% and a stress of 0.2 MPa, showing the characteristics of low toughness and low strain capacity macroscopically and a uniform distribution microscopically.

[0049] Examples 2 - 6: Mechanical properties of organic hydrogels under different process parameters

[0050] First, PVA was melted (at 97 °C) in deionized water (PVA solid content: 2.5%, 5%, 7.5%, 10%, 12.5%). The melted PVA solution was poured into a self-made polytetrafluoroethylene mold and placed in liquid nitrogen for directional freezing for 2 h. Then, the frozen sample was taken out and immersed in a polyethylene glycol solution and stored in an environment of 5 - 8 °C for 10 - 15 h to prepare a hydrogel.

[0051]

[0052]

[0053] The hydrogels prepared by the process of Examples 2 - 6 showed better mechanical properties compared to the hydrogels prepared by cyclic freezing - thawing. Microscopically, the temperature gradient field promoted the alignment of PVA molecular chains along the direction of temperature gradient change, making the prepared directionally frozen hydrogel anisotropic. Moreover, the replacement of polyethylene glycol with the aqueous solution changed the aggregated state structure of PVA molecular chains, and the crystal structure was reshaped, enabling the hydrogel to exhibit different mechanical properties perpendicular and parallel to the freezing direction. Among them, when the PVA solid content was 10%, the strain could reach 700% and the stress could reach 5 MPa in the direction parallel to the freezing direction.

[0054] Performance testing:

[0055] (1) Tensile test

[0056] The prepared hydrogel was cut into dumbbell - shaped splines along the parallel and perpendicular freezing directions. Then, the specimens were tested on a universal testing machine (produced by Instron, series 3360) at a crosshead speed of 50 mm / min.

[0057] (2) SEM morphology observation

[0058] The prepared hydrogel was freeze - dried in vacuum for 24 h and immersed in liquid nitrogen to cause brittle fracture along the parallel and perpendicular directions to the freezing direction. Then, the fracture surface was analyzed by scanning electron microscopy (SEM, S4300, Hitachi). The surface morphologies of the hydrogels prepared with different PVA contents (2.5%, 5%, 7.5%, 10%, 12.5%) and different ferric chloride solid contents (0%, 0.1%, 0.5%, 1%) were studied.

[0059] (3) Force - stimulated electrical response test

[0060] A self - made stretching device was combined with an electrochemical workstation to analyze the electrical response of the force - stimulated behavior under different strains and fixed - strain cyclic loads.

[0061] (4) Mechanical sensing test under low - temperature environment

[0062] The conductive hydrogel was placed in a high-temperature and a low-temperature chamber at -20 °C for 12 h respectively. Then, the samples were tested using an electrochemical workstation and a low-temperature chamber at -20 °C.

[0063] Examples 7 - 10: Mechanical properties of hydrogels with different parameters.

[0064] First, PVA was melted (at 97 °C) in deionized water (PVA solid content: 10%). The melted PVA solution was poured into a self-made polytetrafluoroethylene mold and placed in liquid nitrogen for directional freezing for 2 h. Then, the frozen samples were taken out and immersed in a ferric chloride / polyethylene glycol solution (ferric chloride solid content: 0%, 0.1%, 0.5%, 1%) and stored in an environment at 5 - 8 °C for 10 - 15 h to prepare the hydrogel.

[0065]

[0066]

[0067] The hydrogels prepared by the process of Examples 7 - 10 showed better performance in mechanical properties compared to the hydrogels prepared by cyclic freeze - thawing and the hydrogels prepared by directional freezing with polyethylene glycol quenching. As described in the process method of Examples 2 - 6, after the aggregate structure of the PVA molecular chains changed and the crystal structure was reshaped, the introduction of iron salt ions made the PVA molecular chains arrange more closely inward, further enhancing the mechanical properties of the hydrogel in the direction parallel to the freezing direction (the strain can reach 1000% and the stress is 8.25 MPa).

[0068] Example 11: Preparation process of the flexible sensor.

[0069] First, the hydrogel prepared by the process method of Examples 2 - 6 was cut into a spline with a size of 2 cm × 1 cm, and then copper foils were connected to both ends of the spline as electrodes.

[0070] Performance test:

[0071] (1) Tensile test.

[0072] The prepared hydrogel was cut into dumbbell - shaped splines along the parallel and perpendicular freezing directions. Then, the specimens were tested on a universal testing machine (produced by Instron Corporation, series 3360) at a crosshead speed of 50 mm / min.

[0073] (2) SEM morphological observation.

[0074] The prepared hydrogel was freeze-dried in vacuum for 24 hours and immersed in liquid nitrogen to cause brittle fracture along directions parallel and perpendicular to the freezing direction. Then, the fracture surface was analyzed using a scanning electron microscope (SEM, S4300, Hitachi). The surface morphologies of hydrogels prepared with different PVA contents (2.5%, 5%, 7.5%, 10%, 12.5%) and different ferric chloride solid contents (0%, 0.1%, 0.5%, 1%) were studied.

[0075] (3) Force-stimulated electrical response test

[0076] The self-made stretching device was combined with an electrochemical workstation to analyze the electrical response of the force-stimulated behavior under different strains and fixed-strain cyclic loads.

[0077] (4) Mechanical sensing test under low-temperature environment

[0078] The conductive hydrogel was placed in a high-temperature and low-temperature chamber at -20 °C for 12 h respectively. Then, the sample was tested using an electrochemical workstation and a low-temperature chamber at -20 °C.

[0079] (5) Sensing test

[0080] Figures 4-6 The sensing tests were all carried out using the hydrogel prepared according to the scheme of Example 10. Under this condition, the hydrogel exhibited excellent electrical response performance and also had the ability to maintain long-term stable operation in various temperature environments.

[0081] (6) Sensing performance

[0082] As Figure 5 shown, the hydrogel prepared by quenching PVA with a solid content of 10% in a ferric chloride / polyethylene glycol mixed solution with a ferric chloride content of 1% exhibited wide inspection range and stability in the direction parallel to the freezing direction. The inspection range of the sensor in the direction parallel to the freezing direction could stably perform 5 cycles from 200% to 800%. ΔR / R0 increased with the increase of strain ( Figure 5 a1). Due to the significant structural differences between the parallel and perpendicular freezing directions, the detection range perpendicular to the freezing direction varied from 10% to 100% and had a relatively low ΔR / R0 value ( Figure 5 a2). Sensitivity is an important indicator to measure the sensing performance of flexible sensors. It can be calculated by the following formula:

[0083]

[0084] where GF is the gauge factor, ΔR is the relative resistance change rate, and R0 is the initial resistivity. The comparative analysis of the variation of GF with strain shows that the hydrogel prepared according to the scheme of Example 10 has anisotropy ( Figure 4a1, a2). The gel is more sensitive to the strain parallel to the freezing direction, with a maximum of 1.5( Figure 4 b). For hydrogels, the ability to work in extreme weather is also an important indicator to measure whether a hydrogel is excellent. The prepared hydrogel can maintain a stable electrical response in the environment from -20°C to 20°C Figure 4 c). For the response / recovery time, the prepared hydrogel can respond quickly. In the direction perpendicular to the freezing direction, at a strain of 30%, its response / recovery time can be as fast as less than 100 ms Figure 4 d1). It shows the characteristics of fast response / reply both in the parallel and perpendicular freezing directions Figure 4 d1, d2).

[0085] (7) Sensing applications and antifreeze performance

[0086] The hydrogel prepared by the method of directional freezing combined with the replacement between polyethylene glycol and ferric chloride (FeCl3) solution has excellent mechanical properties and sensing properties. Its excellent properties enable the sensor to detect weak deformation and shape deformation, and can become a catcher for technologies such as speech recognition. The sensor can stably identify the same word with different accents Figure 5 a1, a2, a3). The sensor can also identify two different contact methods: facial contact and point contact Figure 5 c). According to the Morse code table, different information can be output through the point and surface contacts of the hydrogel Figure 5 d1, d2, d3). The hydrogel also exhibits excellent flexibility and antifreeze properties. The hydrogel can return to its original shape after performing actions such as stretching, bending, and twisting Figure 6 a). At the same time, the hydrogel shows stable electrical properties in the environment of -20°C and 20°C Figure 6 b1, b2, b3).

[0087] In summary, we prepared a strong hydrogel by directional freezing and substitution between polyethylene glycol and ferric chloride (FeCl3) solution. The hydrogel prepared by this method has the characteristics of toughness and strength, high stability, antifreeze and durability. The directional freezing process causes polyvinyl alcohol (PVA) to be oriented along the direction of temperature gradient change. Polyethylene glycol (PEG-200) acts as a non-solvent to induce in-situ phase separation of PVA ice crystals, and the hydrophobic effect promotes the PVA molecular chains to be arranged more closely, and the interaction between molecular chains is enhanced. At the same time, the synergistic coordination of ferric chloride (FeCl3) enhances the aggregation of PVA molecular chains. The obtained hydrogel (DF-NSQ-PVA) shows excellent mechanical properties (strength: 8.25Mpa, strain: 800%, toughness: 3.5MJ / m3), Young's modulus: 1.9MPa, and long-term stability (>180 days) in 10% PVA and 1% FeCl3 / Peg200 solution. This hydrogel used as a flexible sensor also has antifreeze resistance (operating at -20 °C), electrical stability (100% cycles >10000), and a high detection range of strain (0% ~ 800%). Therefore, this DF-NSQ strategy enables robust mechanics and long-lasting stability, and has broad applications in soft electronics with environmental tolerance.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A conductive organic hydrogel, characterized in that, It contains the following components: Polyvinyl alcohol is the matrix material, accounting for 5%-12.5% ​​(w / w) of the total solid content; FeCl3 is a coordination crosslinking agent, accounting for 0.1%-1% (w / w) of the total solid content; Polyethylene glycol 200 is the non-solvent phase.

2. The conductive organic hydrogel according to claim 1, wherein The solid content of the polyvinyl alcohol is 10% (w / w), and the solid content of the FeCl3 is 1% (w / w).

3. The preparation method of the conductive organic hydrogel according to claim 1 or 2, characterized in that, The steps are as follows: (a) melting polyvinyl alcohol in deionized water at 90-98° C. to form a polyvinyl alcohol hot melt solution, (b) pouring the polyvinyl alcohol hot melt solution into a polytetrafluoroethylene mold and directionally freezing it in liquid nitrogen for 1-3 hours; (c) The sample after directional freezing is immersed in a mixed solution of ferric chloride / polyethylene glycol 200 for quenching at a temperature of 5-8° C. for a time of 24-72 hours.

4. The preparation method of the conductive organic hydrogel according to claim 3, characterized in that: The polyvinyl alcohol is polyvinyl alcohol 124.

5. The preparation method of the conductive organic hydrogel according to claim 4, characterized in that: The solid content of polyvinyl alcohol dissolved in deionized water is 2.5-20%.

6. The preparation method of the conductive organic hydrogel according to claim 5, wherein: The solid content of ferric chloride in the ferric chloride / polyethylene glycol 200 mixed solution is 0-1%.

7. The preparation method of the conductive organic hydrogel according to claim 6, characterized in that: The solid content of polyvinyl alcohol dissolved in deionized water is 10%, and the solid content of ferric chloride in the ferric chloride / polyethylene glycol 200 mixed solution is 1%.

8. Use of the conductive organic hydrogel according to claim 1 or 2 in preparing a flexible sensor.

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