Rapid-gelation tough conductive hydrogel as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to rapid-gelation tough conductive hydrogel as well as a preparation method and application thereof. The acrylic monomer, the sodium lignin sulfonate carbon dots, the ammonium persulfate and the N, N-methylene bisacrylamide are uniformly mixed and placed at room temperature, and the sodium lignin sulfonate carbon dots serve as a catalyst, so that reduction of Fe < 3 + > can be accelerated, and free radical generation can be directly participated. The sodium lignin sulfonate carbon dots promote the speed of decomposing ammonium persulfate to generate free radicals through electron transfer, excited state generation and other mechanisms, so that the polymerization reaction is accelerated, and the polymerization reaction is accelerated within extremely short time (lt; 10s) to prepare the conductive hydrogel. The conductive hydrogel prepared by the invention not only has rapid gelation ability, but also has excellent mechanical property and adhesion property, and is simple in preparation process and suitable for market popularization and application.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials and relates to a hydrogel material, in particular to a fast-gelling strong-tough conductive hydrogel and a preparation method and application thereof. Background Art

[0002] Conductive hydrogels have shown broad application potential in wearable electronics, soft robots, and flexible sensors due to their unique flexibility and stretchability. However, the preparation of traditional conductive hydrogels is time-consuming and cumbersome, and usually requires external stimulation (long-term ultraviolet irradiation, high temperature, and toxic additives). In addition, such hydrogels usually exhibit poor mechanical properties and conductivity, which are difficult to meet the needs of practical applications. Therefore, it is still a huge challenge to develop hydrogels that can be rapidly polymerized and have excellent mechanical properties and conductivity without the need for external energy stimulation and toxic additives.

[0003] Reasonable design of polymerization reaction and mechanical property enhancer is the key to achieve rapid gelation and mechanical property enhancement of conductive hydrogel. Currently, free radicals can be stimulated by autocatalytic systems based on catechol or liquid metal to achieve rapid gelation. However, these methods of rapid polymerization by simple autocatalytic systems are difficult to achieve the purpose of enhancing the mechanical properties of conductive hydrogel. Summary of the invention

[0004] In view of this, the present invention discloses a fast-gelling strong-tough conductive hydrogel and a preparation method and application thereof.

[0005] It should be noted that carbon dots, as a type of carbon nanoparticles with a size less than 10nm, have excellent optical properties, low toxicity, high biocompatibility and excellent electronic conductivity, and have attracted widespread attention in recent years. Carbon dots not only have attractive SP2 crystal nuclei, but also have unparalleled dispersibility of most nanofillers. These excellent properties can not only enhance the mechanical properties of composite materials through good interface interactions and excellent dispersibility, but more excitingly, carbon dots also have excellent catalytic properties. This is because the quantum dot characteristics of carbon dots give them excellent electron transfer capabilities, accelerating the electron transfer process in the reaction, thereby accelerating the catalytic reaction.

[0006] First, the present application prepares sodium lignin sulfonate carbon dots, and greatly enhances the mechanical properties of the hydrogel through the catalytic performance, conductivity and nano-effect of the carbon dots themselves in the hydrogel.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] The first technical purpose of the present invention is to provide a method for preparing a fast-gelling strong conductive hydrogel, which specifically comprises the following steps:

[0009] 1) Using sodium lignin sulfonate (LS) as a raw material and water as a solvent, the sodium lignin sulfonate carbon dots (LS-CDs) solution is prepared by firing and cooling;

[0010] 2) using the sodium lignin sulfonate carbon dots (LS-CDs) solution and ferric chloride as reactants, stirring evenly after ultrasonic treatment to obtain a precursor A; and stirring evenly ammonium persulfate, N,N-methylenebisacrylamide, acrylic acid monomer and deionized water to obtain a precursor B;

[0011] 3) After the precursors A and B are mixed evenly, the mixture is allowed to stand at room temperature to obtain the fast gelling hydrogel;

[0012] 4) placing the fast gelling hydrogel at a certain temperature for a certain period of time to remove unreacted acrylic acid monomers to obtain a fast gelling strong conductive hydrogel.

[0013] Furthermore, the amount of sodium lignin sulfonate (LS) is 0.25-4 g, and the amount of water is 100 mL; the firing temperature is 160° C.-180° C., preferably the firing temperature is 160° C., and the firing time is 1 hour.

[0014] Furthermore, the mass ratio of the sodium lignin sulfonate carbon dots (LS-CDs) solution to ferric chloride is 7500:15, preferably 7.5 g and 15 mg respectively; the ultrasonic time is 10 min; and the stirring time is 30 min.

[0015] Furthermore, the mass ratio of the ammonium persulfate, N,N-methylenebisacrylamide, acrylic acid monomer and deionized water is 50:4:2500:2500, and the preferred masses are 0.05 g, 4 mg, 2.5 g and 2.5 g, respectively; and the stirring time is 30 min.

[0016] Furthermore, the room temperature standing time is 10 minutes; the monomer removal temperature is 50° C.; and the monomer removal time is 30 minutes.

[0017] The second technical purpose of the present invention is to provide a fast-gelling, strong and conductive hydrogel prepared by the method described above.

[0018] The third technical purpose of the present invention is to provide a fast-gelling strong conductive hydrogel prepared by the method as described above for use in flexible sensing.

[0019] Specifically, the fast-gelling strong conductive hydrogel is used in wearable electronic devices, smart sensors and soft robots.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] In order to improve the mechanical properties of the hydrogel, the present invention combines sodium lignin sulfonate carbon dots with Fe 3+ The self-catalytic system between sodium lignin sulfonate and polypropylene was used to prepare a conductive hydrogel that can gel quickly. Thanks to the unique quadruple role of sodium lignin sulfonate carbon dots, namely initiator, physical cross-linker, nanofiller and conductive agent, the dynamic redox between sodium lignin sulfonate and sodium persulfate serves as an initiator. In addition, because sodium lignin sulfonate carbon dots still have functional groups before carbonization, they have hydrogen bonds with polypropylene and can be used as a physical cross-linker. And because sodium lignin sulfonate itself is nano-scale, it can also be used as a carbon nanofiller. Importantly, during the carbonization process, sodium lignin sulfonate carbon dots will have sp2 crystal nuclei, which gives the hydrogel conductivity and can be used as a conductive agent. These characteristics ensure the rapid coagulation and high performance of the hydrogel. The prepared hydrogel can not only polymerize rapidly in just a few seconds (<10s), but also has the unparalleled strength, adhesion, excellent toughness and conductivity of the self-catalytic hydrogel. Thanks to these excellent properties, the hydrogel has excellent sensitivity and stability when assembled into a flexible sensor, so that it can accurately monitor human physiological signals.

[0022] In addition, the rapid gelation of the hydrogel avoids the use of high temperature, ultraviolet radiation or toxic chemical additives, showing broad application prospects. The carbon dot-metal ion self-catalytic system not only provides a new idea for the rapid preparation of conductive hydrogels, but also provides important support for the development of high-performance wearable electronic devices, smart sensors and soft robots. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0024] Figure 1 : are stress-strain curves of the hydrogels prepared in Examples 1 to 6;

[0025] Figure 2 This is the stress-strain curve of the hydrogel prepared in Comparative Example 1;

[0026] Figure 3 This is the stress-strain curve of the hydrogel prepared in Comparative Example 2;

[0027] Figure 4 The stress-strain curves of the hydrogels prepared in Examples 6 and 8 and Comparative Examples 3 to 4;

[0028] Figure 5The stress-strain curves of the hydrogels prepared in Examples 6 and 7 and Comparative Example 5;

[0029] Figure 6 The adhesion of the hydrogel prepared in Example 6 on different substrates.

[0030] Figure 7 The hydrogel prepared in Example 6 is used as a flexible sensor to measure the change in resistance signal during finger movement. DETAILED DESCRIPTION

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0034] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0035] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0036] Unless otherwise specified, the room temperature in the specific embodiments of the present invention refers to 25±5° C.; and the raw materials and reagents used in the specific embodiments of the present invention are all commercially available products.

[0037] Embodiment 1:

[0038] The preparation steps of 0.25% sodium lignin sulfonate carbon dot-based hydrogel are as follows:

[0039] S1. Add 0.25 g of sodium lignin sulfonate to 100 mL of deionized water, place the mixture in a pressure-resistant reaction bottle, heat to 160° C. and react for 1 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0040] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0041] S3, taking ammonium persulfate (0.05 g), N,N-methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0042] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0043] S5. Place the fast-gelling hydrogel obtained in step S4 in an environment of 50° C. for 30 min to obtain a fast-gelling strong hydrogel.

[0044] Embodiment 2:

[0045] The preparation steps of 0.5% sodium lignin sulfonate carbon dots-based hydrogel are as follows:

[0046] S1. Add 0.5 g of sodium lignin sulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 1 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0047] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0048] S3, taking ammonium persulfate (0.05 g), N,N-methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0049] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0050] S5. Place the fast-gelling hydrogel obtained in step S4 in an environment of 50° C. for 30 min to obtain a fast-gelling strong hydrogel.

[0051] Embodiment 3:

[0052] The preparation steps of 1% sodium lignin sulfonate carbon dot-based hydrogel are as follows:

[0053] S1. Add 1 g of sodium lignin sulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 1 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0054] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0055] S3, taking ammonium persulfate (0.05 g), N,N-methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0056] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0057] S5. Place the fast-gelling hydrogel obtained in step S4 in an environment of 50° C. for 30 min to obtain a fast-gelling strong hydrogel.

[0058] Embodiment 4:

[0059] The preparation steps of 2% sodium lignin sulfonate carbon dot-based hydrogel are as follows:

[0060] S1. Add 2 g of sodium lignin sulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 1 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0061] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0062] S3, taking ammonium persulfate (0.05 g), N,N-methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0063] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0064] S5. Place the fast-gelling hydrogel obtained in step S4 in an environment of 50° C. for 30 min to obtain a fast-gelling strong hydrogel.

[0065] Embodiment 5:

[0066] The preparation steps of 3% sodium lignin sulfonate carbon dot-based hydrogel are as follows:

[0067] S1. Add 3 g of sodium lignin sulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 1 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0068] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0069] S3, taking ammonium persulfate (0.05 g), N,N-methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0070] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0071] S5. Place the fast-gelling hydrogel obtained in step S4 in an environment of 50° C. for 30 min to obtain a fast-gelling strong hydrogel.

[0072] Embodiment 6:

[0073] The preparation steps of 4% sodium lignin sulfonate carbon dot-based hydrogel are as follows:

[0074] S1. Add 4 g of sodium lignin sulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 1 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0075] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0076] S3, taking ammonium persulfate (0.05 g), N,N-methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0077] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0078] S5. The fast gelling hydrogel obtained in step S4 is placed in a 50° C. environment for 30 min to obtain a 4% sodium lignin sulfonate carbon dot-based hydrogel.

[0079] Embodiment 7:

[0080] The preparation steps of sodium lignin sulfonate carbon dot-based hydrogel fired at 180°C are as follows:

[0081] S1. Add 4 g of sodium lignin sulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 180° C. and react for 4 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0082] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0083] S3, taking ammonium persulfate (0.05 g), NN methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0084] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0085] S5. Place the fast-gelling hydrogel obtained in step S4 in an environment of 50° C. for 30 min to obtain a fast-gelling strong hydrogel.

[0086] Embodiment 8:

[0087] The preparation steps of the 2-hour fired sodium lignin sulfonate carbon dot-based hydrogel are as follows:

[0088] S1. Add 4 g of sodium lignin sulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 2 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0089] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0090] S3, taking ammonium persulfate (0.05 g), NN methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0091] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0092] S5. Place the fast-gelling hydrogel obtained in step S4 in an environment of 50° C. for 30 min to obtain a fast-gelling strong hydrogel.

[0093] In order to further demonstrate the beneficial effects of the present invention and to better understand the present invention, the following comparative examples are used to further illustrate the technical features disclosed in the present invention, but they should not be construed as limiting the present invention. Other improvements made by those skilled in the art based on the above invention content without inventive work are also considered to fall within the scope of protection of the present invention.

[0094] Comparative Example 1:

[0095] The preparation steps of polyacrylic acid hydrogel are as follows:

[0096] S1. Take ammonium persulfate (0.05 g), N,N-methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g), deionized water (7.5 g) and acrylic acid (2.5 g), stir for 30 min, place in a 60°C environment for 1 h, and form polyacrylic acid hydrogel.

[0097] Comparative Example 2:

[0098] The preparation steps of sodium lignin sulfonate-based hydrogel are as follows:

[0099] S1. Sodium lignin sulfonate (75 mg) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature, and then stirred for 30 min to obtain a uniform mixed solution A;

[0100] S2, taking ammonium persulfate (0.05 g), N,N-methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0101] S3, mixing the mixed solutions A and B obtained in steps S1 and S2 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0102] S4, placing the fast gelling hydrogel obtained in step S3 in an environment of 50° C. for 30 min to obtain a sodium lignin sulfonate-based hydrogel.

[0103] Comparative Example 3:

[0104] The preparation steps of the 3-hour fired sodium lignin sulfonate carbon dot-based hydrogel are as follows:

[0105] S1. Add 4 g of sodium lignin sulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 3 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0106] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0107] S3, taking ammonium persulfate (0.05 g), NN methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0108] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0109] S5. Place the fast-gelling hydrogel obtained in step S4 in an environment of 50° C. for 30 min to obtain a fast-gelling strong hydrogel.

[0110] Comparative Example 4:

[0111] The preparation steps of the 4-hour fired sodium lignin sulfonate carbon dot-based hydrogel are as follows:

[0112] S1. Add 4 g of sodium lignin sulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 4 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0113] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0114] S3, taking ammonium persulfate (0.05 g), NN methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0115] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0116] S5. Place the fast-gelling hydrogel obtained in step S4 in an environment of 50° C. for 30 min to obtain a fast-gelling strong hydrogel.

[0117] Comparative Example 5:

[0118] The preparation steps of sodium lignin sulfonate carbon dot-based hydrogel fired at 140°C are as follows:

[0119] S1. Add 4 g of sodium lignin sulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 140° C. and react for 4 h. The reaction vessel is naturally cooled to room temperature to obtain a sodium lignin sulfonate carbon dot solution.

[0120] S2, sodium lignin sulfonate carbon dot solution (7.5 g) and ferric chloride (15 mg) were mixed, ultrasonicated for 10 min at room temperature and then stirred for 30 min to obtain a uniform mixed solution A;

[0121] S3, taking ammonium persulfate (0.05 g), NN methylenebisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stirring for 30 min to obtain a uniform mixed solution B;

[0122] S4, mixing the mixed solutions A and B obtained in steps S2 and S3 and pouring them into a mold to obtain a fast-gelling hydrogel;

[0123] S5. Place the fast-gelling hydrogel obtained in step S4 in an environment of 50° C. for 30 min to obtain a fast-gelling strong hydrogel.

[0124] The hydrogels prepared in the examples and comparative examples were subjected to mechanical property testing and toughness calculations as follows. The results are shown in Table 1.

[0125] The hydrogels prepared in the examples and comparative examples were cut into rectangular specimens (4 cm×2 mm×1 mm) and subjected to tensile property tests at room temperature. The uniaxial tensile test was performed using an electronic universal testing machine (Shenzhen Sun Technology Co., Ltd., China) at an extension speed of 80 mm / min.

[0126] Toughness is calculated based on the area under the stress-strain curve using the following formula:

[0127] ΔU=∫σdε

[0128] Where σ and ε are the stress and strain of the hydrogel, respectively.

[0129] The hydrogels prepared in the examples and comparative examples were cut into squares (2 cm×2 cm) and placed between two wooden boards, and then tested after waiting for 30 minutes.

[0130] Table 1

[0131]

[0132]

[0133] It can be seen from the data in Table 1 that the tensile strength and toughness of the hydrogel prepared in Example 6 are the highest, reaching 0.75 MPa and 2.74 MJ / m 3 From the data changes of comparative examples 1 to 5, it can be seen that the mechanical properties of the hydrogel are gradually enhanced, indicating that the sodium lignin sulfonate carbon dots used in the present invention play the role of nanofiller and physical crosslinking in the hydrogel, thereby enhancing the mechanical properties of the hydrogel.

[0134] Figure 1 is the stress-strain curve of the hydrogel prepared in Examples 1 to 6, Figure 1It can be seen that with the increase of the concentration of sodium lignin sulfonate carbon dots, the fracture strength and toughness of the hydrogel also increase. This is because:

[0135] 1. Increased cross-linking density. Sodium lignin sulfonate carbon dots not only provide redox activity during the polymerization process, but also physically or chemically cross-link with polyacrylic acid through their own chemical groups (such as hydroxyl, carboxyl, etc.). As the concentration of carbon dots increases, the cross-linking density increases, thereby enhancing the rigidity and mechanical properties of the hydrogel network.

[0136] 2. Uniform free radical generation. As the core of the redox reaction, sodium lignin sulfonate carbon dots can improve the efficiency of free radical generation in the reaction system. A higher concentration of carbon dots means more free radicals participating in the polymerization reaction, resulting in a more uniform and dense network structure, thereby improving the tensile strength and fracture toughness of the hydrogel.

[0137] 3. Enhancement of energy dissipation mechanism

[0138] Sodium lignin sulfonate carbon dots have excellent interfacial interaction capabilities. They can form dynamic non-covalent bonds (such as hydrogen bonds, electrostatic effects, etc.) through physical adsorption or chemical bonding with the polyacrylic acid network. Under the action of external forces, these weak interactions can play a role in energy dissipation and improve the toughness of the hydrogel.

[0139] 4. Filling effect of carbon dots

[0140] Sodium lignin sulfonate carbon dots themselves act as a nanofiller and have a reinforcing effect. The addition of carbon dots can not only increase the hardness and modulus of the hydrogel, but also improve the uniformity and crack resistance of the entire network. This physical reinforcement effect becomes more significant with the increase of carbon dot concentration.

[0141] 5. Multiple network effects In the system of high-concentration sodium lignin sulfonate carbon dots, a structure similar to multiple networks will be formed. One of the networks is a chemical cross-linking network based on polyacrylic acid, and the other is an auxiliary network formed by the physical or chemical interaction between carbon dots and polyacrylic acid. This multiple network can provide more energy dissipation paths when the hydrogel is stretched, thereby improving toughness.

[0142] Figure 2 is the stress-strain curve of comparative example 1. By comparing Figure 1-2 It can be seen that the mechanical properties of pure polyacrylic acid hydrogel are much lower than those of hydrogel prepared based on sodium lignin sulfonate carbon dots. This is because although pure polyacrylic acid hydrogel is a uniform whole, there is no other cross-linking method, so it is far lower than any of the hydrogels prepared based on sodium lignin sulfonate carbon dots.

[0143] Figure 3The stress-strain curve of the hydrogel prepared in Comparative Example 2 is shown in FIG. Figure 1 and Figure 3 It can be seen that the hydrogel prepared based on sodium lignin sulfonate carbon dots is much higher than sodium lignin sulfonate hydrogel. This is because:

[0144] 1. Strengthening effect of sodium lignin sulfonate carbon dots

[0145] Sodium lignin sulfonate carbon dots (LS-CDs) not only have the chemical functionality of sodium lignin sulfonate, but also introduce the physical enhancement properties of nano carbon dots. Carbon dots can form stronger physical and chemical cross-linked networks with polyacrylic acid and ferric chloride, such as strengthening the network structure of the gel through hydrogen bonds, π-π interactions or electrostatic attraction. The nano size and high specific surface area of ​​carbon dots help to disperse the load and improve the tensile properties and toughness of the hydrogel.

[0146] 2. Optimization of the cross-linking network

[0147] Sodium lignin sulfonate carbon dots increase the cross-linking point density, forming a more uniform cross-linking network, enabling the hydrogel to more effectively disperse and absorb external forces, thereby improving mechanical properties and toughness.

[0148] 3. Promotion of ionic crosslinking by carbon nanodots

[0149] Effect of carbon dots on ferric chloride (Fe 3+ ) ionic crosslinking behavior. For example, the surface functional groups of carbon dots (such as hydroxyl or carboxyl) and Fe 3+ It forms more stable coordination bonds, enhances the stability of ionic cross-linking, and further improves the strength and toughness of the hydrogel.

[0150] 4. Improvement of energy dissipation mechanism

[0151] The introduction of carbon dots provides additional energy dissipation mechanisms, such as molecular chain slippage or reversible interactions between nanocarbon dots and polyacrylic acid, which can absorb more external force energy and thus improve toughness.

[0152] The lack of this additional dissipation path in sodium lignin sulfonate hydrogels causes them to break easily under stress.

[0153] 5. Differences in microstructure

[0154] Carbon dots improve the uniformity and overall strength of the material by limiting the aggregation of polyacrylic acid chains or forming a denser network structure.

[0155] Figure 4 The stress-strain curves of the hydrogels prepared in Examples 6 and 8 and Comparative Examples 3 to 4 are shown in FIG. Figure 4It can be seen that the hydrogel prepared based on carbon dots fired for 1-2 hours has the highest mechanical strength and toughness. This is because the long firing time (>2 hours) leads to excessive removal or chemical rearrangement of the functional groups on the surface of the carbon dots, weakening the number or quality of its active sites, reducing the initiation efficiency and interaction with the polymer. Secondly, the carbon dots fired in a short time have a suitable size distribution, electron transfer ability and rigidity-flexibility balance at the same time. These factors work together to make them the most efficient in initiating polymerization and enhancing the performance of hydrogels. Therefore, the hydrogel initiated by carbon dots fired for 1-2 hours exhibits the best mechanical properties and toughness.

[0156] Figure 5 The stress-strain curves of the hydrogels prepared in Examples 6 and 7 and Comparative Example 5 are shown in FIG. Figure 5 It can be seen that the hydrogel prepared by sintering carbon dots at 160°C has the highest mechanical properties and toughness. At 140°C, the temperature is low, the carbonization reaction of sodium lignin sulfonate is incomplete, and the generated carbon dots have fewer surface active groups, resulting in low free radical generation efficiency, poor crosslinking density and mechanical properties of the hydrogel. At 160°C, the pyrolysis and functional group modification of sodium lignin sulfonate reach the best balance, and the generated carbon dots have abundant and appropriately distributed active groups (such as carboxyl and hydroxyl), which promotes free radical generation and uniform crosslinking network formation. However, 180°C leads to excessive decomposition of surface functional groups or excessive graphitization of carbon dots, a reduction in surface active sites, and reduced interaction ability with polyacrylic acid.

[0157] Figure 6 The adhesion of the hydrogel prepared in Example 6 on different substrates is shown in FIG. Figure 6 It can be seen that the hydrogel still has excellent adhesion to different substrates, even to hydrophobic PTFE, it still has an adhesion of more than 10kPa. Importantly, the hydrogel can still show an adhesion of more than 20kPa on pig skin, which shows that the hydrogel also has good adhesion to human skin.

[0158] Figure 7 The resistance signal change of the hydrogel prepared in Example 6 as a flexible sensor during finger movement. It can be seen from the figure that when the finger is bent, the relative resistance will increase accordingly, and when it is straightened, the relative resistance will return to the initial state, and during the cyclic bending process, the peak value of the resistance hardly changes, which indicates that the hydrogel flexible sensor has high stability and repeatability.

[0159] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a fast-gelling strong conductive hydrogel, characterized in that the steps include: 1) Using sodium lignin sulfonate (LS) as a raw material and water as a solvent, the sodium lignin sulfonate carbon dots (LS-CDs) solution is prepared by firing and cooling; 2) using the sodium lignin sulfonate carbon dots (LS-CDs) solution and ferric chloride as reactants, stirring evenly after ultrasonic treatment to obtain a precursor A; 3) stirring ammonium persulfate, N,N-methylenebisacrylamide, acrylic acid monomer and deionized water to obtain precursor B; 4) After the precursors A and B are mixed evenly, the mixture is allowed to stand at room temperature to obtain the fast gelling hydrogel; 5) placing the fast-gelling hydrogel at a certain temperature for a certain period of time to remove unreacted acrylic acid monomers to obtain a fast-gelling strong conductive hydrogel.

2. The preparation method according to claim 1, characterized in that: The dosage ratio of sodium lignin sulfonate (LS) to water is 0.25-4:100; the firing temperature is 160° C.-180° C., and the firing time is 1-2 hours.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the sodium lignin sulfonate carbon dots (LS-CDs) solution to ferric chloride is 7500:

15.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the ammonium persulfate, N,N-methylenebisacrylamide, acrylic acid monomer and deionized water is 50:4:2500:2500.

5. The preparation method according to claim 1, characterized in that: The room temperature standing time is 10 minutes; the monomer removal temperature is 50° C., and the monomer removal time is 30 minutes.

6. A fast-gelling, strong and conductive hydrogel prepared by the method according to any one of claims 1 to 5.

7. Use of the fast-gelling strong and tough conductive hydrogel prepared by the method according to any one of claims 1 to 5 or the fast-gelling strong and tough conductive hydrogel according to claim 6 in flexible sensing.

Images