A fast-gelling strong and tough conductive hydrogel as well as a preparation method and application thereof

Abstract

The application belongs to the technical field of high polymer materials, and particularly relates to a kind of fast gelation strong and tough conductive hydrogel and its preparation method and application.The application uniformly mixes acrylic monomer, sodium lignosulfonate carbon dots, ammonium persulfate and N,N-methylene bisacrylamide, places in room temperature, and through sodium lignosulfonate carbon dots as catalyst, not only can accelerate the reduction of Fe 3+ , but also can directly participate in free radical generation.Sodium lignosulfonate carbon dots promote the speed of free radical generation generated by ammonium persulfate decomposition through electron transfer and excited state generation mechanism, thereby accelerating the polymerization reaction to prepare conductive hydrogel in a very short time (<10s).The conductive hydrogel prepared by the application not only has fast gelation capacity, but also has excellent mechanical properties and adhesion properties, and the preparation process is simple, suitable for market promotion and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and relates to a hydrogel material, in particular to a fast-gelation tough conductive hydrogel and a preparation method and application thereof. BACKGROUND

[0002] Conductive hydrogels exhibit a wide range of 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 tedious, and usually requires external stimuli (long-term ultraviolet irradiation, high temperature and toxic additives). In addition, such hydrogels usually exhibit poor mechanical properties and conductivity, which is difficult to meet the needs of practical applications. Therefore, it is still a great challenge to develop a hydrogel that can be rapidly polymerized without external energy stimulation and toxic additives and has excellent mechanical properties and conductivity.

[0003] Rational design of polymerization reaction and mechanical property enhancer is the key to realizing fast gelation and enhanced mechanical properties of conductive hydrogel. At present, free radicals can be excited by self-catalytic systems based on catechol or liquid metal to achieve fast gelation. However, these simple self-catalytic systems for rapid polymerization are difficult to achieve the purpose of enhancing the mechanical properties of conductive hydrogel. SUMMARY

[0004] Therefore, the application discloses a fast-gelation tough conductive hydrogel and a preparation method and application thereof.

[0005] It should be noted that carbon dots, as a kind of carbon nanoparticles with a size of less than 10 nm, have excellent optical properties, low toxicity, high biocompatibility and excellent electronic conductivity, and have attracted much attention in recent years. Carbon dots not only have an attractive SP2 crystal core, but also have unparalleled dispersibility of most nano-fillers. These excellent properties not only enhance the mechanical properties of the composite through good interfacial interaction and excellent dispersibility, but more excitingly, carbon dots also have excellent catalytic properties. This is because the quantum dot characteristics of carbon dots enable them to have excellent electron transfer ability, accelerating the electron transfer process in the reaction and thus accelerating the catalytic reaction.

[0006] Firstly, the application prepares sodium lignosulfonate carbon dots, and the mechanical properties of the hydrogel are greatly enhanced through the catalytic properties, conductivity and nano effect of the carbon dots in the hydrogel.

[0007] In order to achieve the above purpose, the application adopts the following technical solutions:

[0008] The first technical purpose of the application is to provide a preparation method of a fast-gelation tough conductive hydrogel, which specifically comprises the following steps:

[0009] 1) taking sodium lignosulfonate (LS) as raw material, taking water as solvent, and preparing sodium lignosulfonate carbon dots (LS-CDs) solution through calcination and cooling;

[0010] 2) taking the sodium lignosulfonate carbon dots (LS-CDs) solution and ferric chloride as reactants, stirring uniformly after ultrasonic treatment to obtain precursor A; stirring uniformly ammonium persulfate, N,N-methylene bisacrylamide, acrylic monomer and deionized water to obtain precursor B;

[0011] 3) mixing the precursors A and B uniformly, and then standing at room temperature to obtain the rapid-gelation hydrogel;

[0012] 4) placing the rapid-gelation hydrogel at a certain temperature for a certain time to remove unreacted acrylic monomer to obtain the rapid-gelation tough and conductive hydrogel.

[0013] Further, the amount of sodium lignosulfonate (LS) is 0.25-4g, and the amount of water is 100mL; the calcination temperature is 160-180℃, and the preferred calcination temperature is 160℃, and the time is 1h.

[0014] Further, the mass ratio of the sodium lignosulfonate carbon dots (LS-CDs) solution and ferric chloride is 7500:15, and the preferred mass of the two is 7.5g and 15mg respectively; the ultrasonic treatment time is 10min; and the stirring time is 30min.

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

[0016] Further, the standing time at room temperature is 10min; the monomer removal temperature is 50℃; and the monomer removal time is 30min.

[0017] The second technical purpose of the present application is to provide a rapid-gelation tough and conductive hydrogel prepared by the above method.

[0018] The third technical purpose of the present application is to provide an application of the rapid-gelation tough and conductive hydrogel prepared by the above method in flexible sensing.

[0019] Specifically, the application of the rapid-gelation tough and conductive hydrogel in wearable electronic devices, intelligent sensors and soft robots.

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

[0021] The present application is to improve the mechanical properties of hydrogel, and a conductive hydrogel capable of rapid gelation is prepared by a self-catalytic system based on sodium lignosulfonate carbon dots and Fe 3+ The sodium lignosulfonate carbon dots have four unique functions, namely initiator, physical crosslinking agent, nanofiller and conductive agent. The dynamic oxidation-reduction between sodium lignosulfonate and sodium persulfate acts as an initiator. In addition, the sodium lignosulfonate carbon dots also have functional groups before carbonization, which can form hydrogen bonds with polypropylene and act as a physical crosslinking agent. Moreover, the sodium lignosulfonate itself is at the nanoscale and can also act as a carbon nanofiller. Importantly, during the carbonization process, the sodium lignosulfonate carbon dots have sp2 crystal nuclei, which endow the hydrogel with conductivity and can act as a conductive agent. These characteristics ensure the rapid aggregation and high performance of the hydrogel. The prepared hydrogel not only can rapidly polymerize in a short time (<10s), but also has unparalleled strength, adhesion, excellent toughness and conductivity, which is beneficial to the excellent performance. When the hydrogel is assembled into a flexible sensor, it has excellent sensitivity and stability, so as to accurately monitor the physiological signals of the human body.

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

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without creative labor.

[0024] Figure 1 The stress-strain curve of the hydrogel prepared for Example 1-6;

[0025] Figure 2 The stress-strain curve of the hydrogel prepared for Comparative Example 1;

[0026] Figure 3 The stress-strain curve of the hydrogel prepared for Comparative Example 2;

[0027] Figure 4 The stress-strain curve of the hydrogel prepared for Example 6, 8 and Comparative Example 3-4;

[0028] Figure 5Stress-strain curves of the hydrogels prepared for Examples 6, 7 and Comparative Example 5;

[0029] Figure 6 Adhesion of the hydrogels prepared for Example 6 on different substrates.

[0030] Figure 7 Resistance signal change of the hydrogels prepared for Example 6 as flexible sensors upon finger movement. DETAILED DESCRIPTION

[0031] Various illustrative embodiments of the present application are described in detail herein below with reference to the attached drawings. These embodiments are listed by way of example only, and should not be construed as limiting the present application. It should be understood that numerous other embodiments can be devised by those skilled in the art which fall within the scope of the present application. Accordingly, the detailed description of the present application is not intended to limit the scope of the present application as described in the claims.

[0032] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. In addition, where particular ranges of values are given, understand that each intervening value, to the upper or lower limit of the ranges is also specifically included. Each smaller range that falls within the broader ranges is also specifically included. The upper and lower limits of these smaller ranges can independently be included or excluded in the range, and each range is inclusive of its end points.

[0033] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All patents, patent applications, publications, and descriptions mentioned herein are incorporated by reference to the extent allowed by law. Nothing herein is to be construed as an admission that the application is not entitled to antedate such disclosure by virtue of prior application.

[0034] Various modifications and variations of the described embodiments of the application will be apparent to those skilled in the art from the foregoing detailed description of the application. Other embodiments of the application will be apparent from the foregoing detailed description of the application and from the examples described herein. The detailed description and examples are intended to be illustrative only and are not intended to limit the scope of the application. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope of the application being indicated by the following claims.

[0035] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean including, but not limited to.

[0036] Unless otherwise indicated, all room temperature means 25 ± 5 °C. Also, all starting materials and reagents used in the embodiments of the present application are commercially available.

[0037] Example 1:

[0038] 0.25% lignosulfonate sodium carbon dots based hydrogel preparation steps are as follows:

[0039] S1, 0.25 g of lignosulfonate sodium was added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle and heated to 160°C for 1 h, and the reaction vessel was naturally cooled to room temperature to obtain a lignosulfonate sodium carbon dot solution;

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

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

[0042] S4, mix the mixed solutions A and B obtained in steps S2 and S3, and pour into a mold to obtain a rapid gelation hydrogel;

[0043] S5, place the rapid gelation hydrogel obtained in step S4 in a 50°C environment for 30 min to obtain a rapid gelation tough hydrogel.

[0044] Example 2:

[0045] 0.5% lignosulfonate sodium carbon dots based hydrogel preparation steps are as follows:

[0046] S1, 0.5 g of lignosulfonate sodium was added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle and heated to 160°C for 1 h, and the reaction vessel was naturally cooled to room temperature to obtain a lignosulfonate sodium carbon dot solution;

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

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

[0049] S4, mix the mixed solutions A and B obtained in steps S2 and S3, and pour into a mold to obtain a rapid gelation hydrogel;

[0050] S5, place the rapid gelation hydrogel obtained in step S4 in a 50°C environment for 30 min to obtain a rapid gelation tough hydrogel.

[0051] Example 3:

[0052] 1% lignosulfonate sodium carbon dots based hydrogel preparation steps are:

[0053] S1, 1 g of lignosulfonate sodium was added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle and heated to 160°C for 1 h, and the reaction vessel was naturally cooled to room temperature to obtain a lignosulfonate sodium carbon dot solution;

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

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

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

[0057] S5, place the fast-gelling hydrogel obtained in step S4 in a 50°C environment for 30 min to obtain a fast-gelling strong and tough hydrogel.

[0058] Example 4:

[0059] 2% lignosulfonate sodium carbon dots based hydrogel preparation steps are:

[0060] S1, 2 g of lignosulfonate sodium was added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle and heated to 160°C for 1 h, and the reaction vessel was naturally cooled to room temperature to obtain a lignosulfonate sodium carbon dot solution;

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

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

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

[0064] S5, place the fast-gelling hydrogel obtained in step S4 in a 50°C environment for 30 min to obtain a fast-gelling strong and tough hydrogel.

[0065] Example 5:

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

[0067] S1, 3 g of sodium lignosulfonate was added to 100 mL of deionized water, and the mixture was heated to 160°C in a pressure-resistant reaction bottle for 1 h. The reaction vessel was naturally cooled to room temperature to obtain a sodium lignosulfonate carbon dot solution;

[0068] S2, the sodium lignosulfonate carbon dot solution (7.5 g) was mixed with ferric chloride (15 mg), and a uniform mixed solution A was obtained after ultrasonic treatment for 10 min at room temperature and stirring for 30 min;

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

[0070] S4, the mixed solutions A and B obtained in steps S2 and S3 were mixed and poured into a mold to obtain a rapid gelation hydrogel;

[0071] S5, the rapid gelation hydrogel obtained in step S4 was placed in a 50°C environment for 30 min to obtain a rapid gelation tough hydrogel.

[0072] Example 6:

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

[0074] S1, 4 g of sodium lignosulfonate was added to 100 mL of deionized water, and the mixture was heated to 160°C in a pressure-resistant reaction bottle for 1 h. The reaction vessel was naturally cooled to room temperature to obtain a sodium lignosulfonate carbon dot solution;

[0075] S2, the sodium lignosulfonate carbon dot solution (7.5 g) was mixed with ferric chloride (15 mg), and a uniform mixed solution A was obtained after ultrasonic treatment for 10 min at room temperature and stirring for 30 min;

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

[0077] S4, the mixed solutions A and B obtained in steps S2 and S3 were mixed and poured into a mold to obtain a rapid gelation hydrogel;

[0078] S5, the rapid gelation hydrogel obtained in step S4 was placed in a 50°C environment for 30 min to obtain a 4% sodium lignosulfonate carbon dot-based hydrogel.

[0079] Example 7:

[0080] The preparation steps of the lignosulfonate sodium carbon dot-based hydrogel burned at 180°C are as follows:

[0081] S1, 4g of lignosulfonate sodium was added to 100mL of deionized water, placed in a pressure-resistant reaction bottle and heated to 180°C for 4h, and the reaction container was naturally cooled to room temperature to obtain a lignosulfonate sodium carbon dot solution;

[0082] S2, the lignosulfonate sodium carbon dot solution (7.5g) was mixed with ferric chloride (15mg), ultrasonic treatment was carried out at room temperature for 10min, and then stirring was carried out for 30min to obtain a uniform mixed solution A;

[0083] S3, ammonium persulfate (0.05g), N,N-methylene bisacrylamide (4mg), acrylic monomer (2.5g) and deionized water (2.5g) were stirred for 30min to obtain a uniform mixed solution B;

[0084] S4, the mixed solutions A and B obtained in steps S2 and S3 were mixed and poured into a mold to obtain a fast-gelated hydrogel;

[0085] S5, the fast-gelated hydrogel obtained in step S4 was placed in a 50°C environment for 30min to obtain a fast-gelated tough hydrogel.

[0086] Example 8:

[0087] The preparation steps of the lignosulfonate sodium carbon dot-based hydrogel burned for 2h are as follows:

[0088] S1, 4g of lignosulfonate sodium was added to 100mL of deionized water, placed in a pressure-resistant reaction bottle and heated to 160°C for 2h, and the reaction container was naturally cooled to room temperature to obtain a lignosulfonate sodium carbon dot solution;

[0089] S2, the lignosulfonate sodium carbon dot solution (7.5g) was mixed with ferric chloride (15mg), ultrasonic treatment was carried out at room temperature for 10min, and then stirring was carried out for 30min to obtain a uniform mixed solution A;

[0090] S3, ammonium persulfate (0.05g), N,N-methylene bisacrylamide (4mg), acrylic monomer (2.5g) and deionized water (2.5g) were stirred for 30min to obtain a uniform mixed solution B;

[0091] S4, the mixed solutions A and B obtained in steps S2 and S3 were mixed and poured into a mold to obtain a fast-gelated hydrogel;

[0092] S5, the fast-gelated hydrogel obtained in step S4 was placed in a 50°C environment for 30min to obtain a fast-gelated tough hydrogel.

[0093] In order to further prove the beneficial effects of the present application and better understand the present application, the technical features disclosed by the present application are further illustrated by the following comparative examples, but can not be understood as limiting the present application. Other improvements made by those skilled in the art without creative work according to the above invention content are also considered to fall within the protection scope of the present application.

[0094] Comparative Example 1:

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

[0096] S1, take ammonium persulfate (0.05 g), N, N-methylene bisacrylamide (4 mg), acrylic acid monomer (2.5 g), deionized water (7.5 g) and acrylic acid (2.5 g) and stir for 30 min, place in 60℃ environment for 1 h, polyacrylic acid hydrogel.

[0097] Comparative Example 2:

[0098] The preparation steps of the sodium lignosulfonate-based hydrogel are as follows:

[0099] S1, mix sodium lignosulfonate (75 mg) with ferric chloride (15 mg), ultrasonic for 10 min at room temperature, then stir for 30 min to get a uniform mixed solution A;

[0100] S2, take ammonium persulfate (0.05 g), N, N-methylene bisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) and stir for 30 min to get a uniform mixed solution B;

[0101] S3, mix the mixed solutions A and B obtained in steps S1 and S2, then pour into a mold to get a fast-gelling hydrogel;

[0102] S4, place the fast-gelling hydrogel obtained in step S3 in a 50℃ environment for 30 min to get a sodium lignosulfonate-based hydrogel.

[0103] Comparative Example 3:

[0104] The preparation steps of the sodium lignosulfonate carbon dot-based hydrogel burned for 3 hours are as follows:

[0105] S1, add 4 g of sodium lignosulfonate to 100 mL of deionized water, place in a pressure-resistant reaction bottle and heat to 160℃ for 3 h, then naturally cool the reaction container to room temperature to get a sodium lignosulfonate carbon dot solution;

[0106] S2, mix the sodium lignosulfonate carbon dot solution (7.5 g) with ferric chloride (15 mg), ultrasonic for 10 min at room temperature, then stir for 30 min to get a uniform mixed solution A;

[0107] S3, take over the ammonium sulfate (0.05g), NN methylene double acrylamide (4mg), acrylic monomer (2.5g) and deionized water (2.5g) stirring 30min, get uniform mixed solution B;

[0108] S4, the mixed solution A and B obtained in steps S2 and S3 are mixed and poured into a mold to obtain a rapid gelation hydrogel;

[0109] S5, the rapid gelation hydrogel obtained in step S4 is placed in a 50℃ environment for 30min to obtain a rapid gelation tough hydrogel.

[0110] Comparative example 4:

[0111] The preparation steps of the sodium lignosulfonate carbon dot-based hydrogel fired for 4h are:

[0112] S1, 4g of sodium lignosulfonate is added to 100mL of deionized water, placed in a pressure-resistant reaction bottle, heated to 160℃ and reacted for 4h, and the reaction vessel is naturally cooled to room temperature to obtain a sodium lignosulfonate carbon dot solution;

[0113] S2, the sodium lignosulfonate carbon dot solution (7.5g) is mixed with ferric chloride (15mg), ultrasonic for 10min at room temperature, and then stirred for 30min to obtain a uniform mixed solution A;

[0114] S3, take over the ammonium sulfate (0.05g), NN methylene double acrylamide (4mg), acrylic monomer (2.5g) and deionized water (2.5g) stirring 30min, get uniform mixed solution B;

[0115] S4, the mixed solution A and B obtained in steps S2 and S3 are mixed and poured into a mold to obtain a rapid gelation hydrogel;

[0116] S5, the rapid gelation hydrogel obtained in step S4 is placed in a 50℃ environment for 30min to obtain a rapid gelation tough hydrogel.

[0117] Comparative example 5:

[0118] The preparation steps of the sodium lignosulfonate carbon dot-based hydrogel fired at 140℃ are:

[0119] S1, 4g of sodium lignosulfonate is added to 100mL of deionized water, placed in a pressure-resistant reaction bottle, heated to 140℃ and reacted for 4h, and the reaction vessel is naturally cooled to room temperature to obtain a sodium lignosulfonate carbon dot solution;

[0120] S2, the sodium lignosulfonate carbon dot solution (7.5g) is mixed with ferric chloride (15mg), ultrasonic for 10min at room temperature, and then stirred for 30min to obtain a uniform mixed solution A;

[0121] S3, stirring ammonium sulfate (0.05 g), N-methylene bisacrylamide (4 mg), acrylic acid monomer (2.5 g) and deionized water (2.5 g) 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 into a mold to obtain a rapid gelation hydrogel;

[0123] S5, placing the rapid gelation hydrogel obtained in step S4 in a 50℃ environment for 30 min to obtain a rapid gelation tough hydrogel.

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

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

[0126] Toughness was calculated according to the area under the stress-strain curve by the following formula:

[0127] ΔU = ∫σdε

[0128] Wherein, 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 x 2 cm) and placed between two wooden boards, and tested after waiting for 30 min.

[0130] Table 1

[0131]

[0132]

[0133] As can be seen from the data in Table 1, the tensile strength and toughness of the hydrogel prepared in Example 6 are the largest, which can reach 0.75 MPa and 2.74 MJ / m 3 . And from the data changes of Comparative Examples 1-5, it can be seen that the mechanical properties of the hydrogel gradually increase, indicating that the sodium lignosulfonate carbon dots used in the present application play the role of nanofiller and physical crosslinking in the hydrogel, thereby enhancing the mechanical properties of the hydrogel.

[0134] Figure 1 The stress-strain curves of the hydrogels prepared in Examples 1-6 are shown in Figure 1It can be seen that with the increase of the concentration of sodium lignosulfonate carbon dots, the breaking strength and toughness of the hydrogel also increase, because:

[0135] 1. Increased crosslinking density. Sodium lignosulfonate carbon dots not only provide redox activity during polymerization, but also physically or chemically crosslink with polyacrylic acid through their own chemical groups such as hydroxyl, carboxyl, etc. With the increase of carbon dot concentration, the crosslinking density is improved, thereby enhancing the rigidity and mechanical properties of the hydrogel network.

[0136] 2. Uniform radical generation. Sodium lignosulfonate carbon dots, as the core of the redox reaction, can improve the efficiency of free radical generation in the reaction system. 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 breaking toughness of the hydrogel.

[0137] 3. Enhancement of energy dissipation mechanism

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

[0139] 4. Filling effect of carbon dots

[0140] Sodium lignosulfonate carbon dots themselves act as a nanofiller, having a reinforcing effect. The addition of carbon dots not only improves the hardness and modulus of the hydrogel, but also improves the uniformity and crack resistance of the entire network. This physical reinforcement effect is more pronounced with increasing carbon dot concentration.

[0141] 5. Multiple network effect In the system with high concentration of sodium lignosulfonate carbon dots, a structure similar to a multiple network is formed. One network is a chemical crosslinking 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 For the stress-strain curve of Comparative Example 1, by comparing Figures 1-2 It can be seen that the mechanical properties of pure polyacrylic acid hydrogel are much lower than those of hydrogels based on sodium lignosulfonate carbon dots, because pure polyacrylic acid hydrogel, although forming a uniform whole, does not have any other crosslinking method, so it is much lower than any of the hydrogels based on sodium lignosulfonate carbon dots.

[0143] Figure 3The stress-strain curves of the hydrogels prepared for Comparative Example 2 can be compared by Figure 1 and Figure 3 It can be seen that the hydrogel prepared based on sodium lignosulfonate carbon dots is much higher than the sodium lignosulfonate hydrogel, because:

[0144] 1. The reinforcing effect of sodium lignosulfonate carbon dots

[0145] Sodium lignosulfonate carbon dots (LS-CDs) not only have the chemical functionality of sodium lignosulfonate, but also introduce the physical reinforcing properties of nanocarbon dots. Carbon dots can form a stronger physical and chemical crosslinking network with polyacrylic acid and ferric chloride, such as enhancing the network structure of the gel through hydrogen bonding, π-π interaction or electrostatic attraction. The nanosize and high specific surface area of carbon dots help to disperse the load, improve the tensile properties and toughness of the hydrogel.

[0146] 2. Optimization of the crosslinking network

[0147] Sodium lignosulfonate carbon dots increase the crosslinking point density, forming a more uniform crosslinking network, enabling the hydrogel to more effectively disperse and absorb external forces, improving the mechanical properties and toughness.

[0148] 3. Promotion of ionic crosslinking by nanocarbon dots

[0149] Carbon dots affect the ionic crosslinking behavior of ferric chloride (Fe 3+ ). For example, the surface functional groups of carbon dots (such as hydroxyl or carboxyl) form more stable coordination bonds with Fe 3+ , enhancing the stability of ionic crosslinking and further improving the strength and toughness of the hydrogel.

[0150] 4. Improvement of energy dissipation mechanisms

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

[0152] The lack of such additional dissipation paths in sodium lignosulfonate hydrogels leads to their easy breaking 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 more dense network structure.

[0155] Figure 4 The stress-strain curves of the hydrogels prepared for Examples 6, 8 and Comparative Examples 3-4 can be compared by Figure 4It can be seen that the hydrogel prepared based on the carbon dots calcined for 1-2 h has the highest mechanical strength and toughness, because the excessive removal or chemical rearrangement of surface functional groups of the carbon dots caused by the calcination time being too long (>2 hours) weakens the number or quality of active sites, reduces the initiation efficiency and interaction with the polymer, and the carbon dots calcined for a short time have suitable size distribution, electron transfer ability and rigidity-flexibility balance, which synergistically make them most efficient in initiating polymerization and enhancing the performance of the hydrogel. Therefore, the hydrogel initiated by the carbon dots calcined for 1-2 h exhibits the best mechanical properties and toughness.

[0156] Figure 5 The stress-strain curves of the hydrogels prepared for Examples 6, 7 and Comparative Example 5 are shown in FIG. 2. Figure 5 It can be seen that the hydrogel prepared based on the carbon dots calcined at 160°C has the highest mechanical properties and toughness, and the carbonization reaction of sodium lignosulfonate is not complete at a lower temperature of 140°C, and the generated carbon dots have fewer surface active groups, resulting in low radical generation efficiency, poor crosslinking density and mechanical properties of the hydrogel. The pyrolysis and functional group modification of sodium lignosulfonate at 160°C achieve the best balance, and the generated carbon dots have abundant and suitable distribution of active groups (such as carboxyl and hydroxyl groups), which promote the formation of radicals and uniform crosslinking network. While 180°C leads to excessive decomposition of surface functional groups or excessive graphitization of carbon dots, the surface active sites are reduced, and the interaction ability of the carbon dots with polyacrylic acid is reduced.

[0157] Figure 6 The adhesion of the hydrogel prepared for Example 6 on different substrates is shown in FIG. 3. Figure 6 It can be seen that the hydrogel has excellent adhesion to different substrates, even to hydrophobic PTFE, which still has an adhesion of more than 10 kPa. Importantly, the hydrogel still exhibits an adhesion of more than 20 kPa on pig skin, which indicates that the hydrogel also has good adhesion to human skin.

[0158] Figure 7 The resistance signal change of the hydrogel prepared for Example 6 as a flexible sensor during finger movement is shown in FIG. 4. It can be seen from the figure that when the finger is bent, the relative resistance increases, and when it is straightened, the relative resistance returns to the initial state, and in the process of cyclic bending, the peak value of the resistance hardly changes, which indicates that the hydrogel flexible sensor has high stability and repeatability.

[0159] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and that the appended claims are intended to cover all such modifications that do not depart from the true spirit and scope of the application. Therefore, the application is not limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a rapidly gelling, strong, and conductive hydrogel, characterized in that the steps include... include: 1) Sodium lignosulfonate (LS) was used as raw material and water was used as solvent. The solution was prepared by calcination and cooling. The ratio of sodium lignosulfonate (LS) to water is 0.25-4:100; the firing temperature is 160℃-180℃, and the firing time is 1-2 hours. 2) Using the sodium lignosulfonate carbon dots (LS-CDs) solution and ferric chloride as reactants, the mixture is sonicated and stirred until homogeneous to obtain precursor A; 3) Mix ammonium persulfate, N,N-methylenebisacrylamide, acrylic acid monomer and deionized water evenly to obtain precursor B; 4) After mixing the precursors A and B evenly, let them stand at room temperature to obtain the rapidly gelling hydrogel; 5) After placing the rapidly gelled hydrogel at a certain temperature for a certain time to remove unreacted acrylic monomers, a rapidly gelled, tough, and conductive hydrogel is obtained.

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

15.

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

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

5. A rapidly gelling, strong, and conductive hydrogel prepared by the method described in any one of claims 1 to 4.

6. The application of a rapidly gelling strong and tough conductive hydrogel prepared by the method of any one of claims 1 to 4, or the rapidly gelling strong and tough conductive hydrogel as described in claim 5, in flexible sensing.

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