A fast-gelling conductive hydrogel and its preparation method and application

Abstract

The application discloses a kind of quick gelation conductive hydrogel and its preparation method and application, the preparation method, including the following steps: diatomite and tannic acid are dissolved in water, stirring preparation tannic acid coated diatomite solution;Zinc chloride is added to the tannic acid coated diatomite solution, stirring is uniform, then acrylic acid and 1-vinyl-3-carboxy imidazole ionic liquid are stirred uniformly;Then initiator and crosslinking agent are added, immediately pour into mould after stirring is uniform, carry out quick gelation reaction in 10~30s, namely obtain.The raw material of hydrogel provided by the application is low in toxicity, high in safety, and the preparation method is very simple, without heating, and the gelation time is very short, suitable for industrial production;The obtained hydrogel has good conductivity, repeated adhesion and low temperature resistance, can be applied as flexible sensor, and has wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of hydrogel preparation technology, and in particular to a rapidly gelling conductive hydrogel, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Flexible strain sensors have been widely used in various fields, including human health monitoring, intelligent robots, electronic skin, human-computer interaction, and wearable devices. Wearable sensors typically convert mechanical deformation into changes in electrical signals to monitor human activity. In recent years, cross-linked three-dimensional network polymer hydrogels containing a large amount of water have been well developed due to their potential applications in drug delivery, artificial tissues, and flexible electronic sensors. Among them, conductive polymer hydrogels have received widespread attention over the past decade due to their conductivity, softness, and broad prospects in wearable devices.

[0004] Patent CN 108110234B (authorization announcement date: March 6, 2020) discloses a conductive polymer hydrogel, its preparation method, and its application. It uses acrylic acid and aniline as copolymerizing monomers, and performs a copolymerization reaction under inert gas protection and 50°C water bath heating for 0.5-5 hours to obtain a one-step synthesized polyacrylic acid-doped polyaniline-stabilized polyaniline conductive polymer gel. This patent does not prepare a flexible hydrogel; rather, it dries the polymer gel and uses it as a positive electrode material for lithium-ion batteries. Furthermore, aniline has high toxicity and low safety; and the gelation time is relatively long.

[0005] Patent CN 110922611B (authorization announcement date: April 12, 2022) discloses a high-strength, conductive, and high / low temperature resistant MXene hydrogel. This hydrogel is prepared from water, a water-retaining agent, acrylamide, acrylic acid, chitosan, MXene, a silicon crosslinking agent SiHX, an initiator, and acetic acid. It exhibits excellent high / low temperature resistance and does not require photothermal initiation, gelling rapidly at room temperature (5–10 min). However, it uses acrylamide as one of the polymer monomers in its raw materials. Acrylamide is listed as a Group 2A carcinogen and has high toxicity.

[0006] Patent CN 114957806B (authorization announcement date: April 25, 2023) discloses a method for preparing and applying a modified starch-polyacrylic acid reusable conductive hydrogel. The method involves heating modified starch (obtained by esterification of starch with maleic anhydride) and acrylic acid monomers at 60–65°C for 1–3 hours, followed by free radical polymerization under the initiator of ammonium persulfate. It is evident that this patent involves a relatively long preparation time and a high temperature for the hydrogel.

[0007] As can be seen from the above patents, the existing technology for preparing conductive hydrogels has problems such as long polymerization time, high temperature, and low raw material safety. Therefore, how to provide a conductive hydrogel that can gel rapidly at room temperature and has good safety, repeatability, and low temperature resistance is an urgent problem to be solved. Summary of the Invention

[0008] In view of this, the present invention provides a rapidly gelling conductive hydrogel, its preparation method and application, which simultaneously possesses excellent conductivity, good safety, stable and repeatable adhesion, low temperature resistance and rapid gelation at room temperature.

[0009] In a first aspect, the present invention provides a method for preparing a rapidly gelled conductive hydrogel, comprising the following steps:

[0010] A tannic acid-coated diatomaceous earth solution was prepared by dissolving diatomaceous earth and tannic acid in water and stirring.

[0011] Zinc chloride was added to the tannic acid-coated diatomaceous earth solution and stirred until homogeneous. Then, acrylic acid and 1-vinyl-3-carboxyimidazole ionic liquid were added and stirred until homogeneous.

[0012] Then add the initiator and crosslinking agent, stir evenly, and immediately pour into the mold. A rapid gelation reaction will occur within 10 to 30 seconds to obtain the final product.

[0013] Preferably, the mass ratio of diatomaceous earth, tannic acid, zinc chloride, acrylic acid, and water is 1:1-3:60-80:40-50:80-120.

[0014] Preferably, diatomaceous earth and tannic acid are dissolved in water, the pH is adjusted to 7.5-9 with 0.5-2M Tris solution, and then stirred to prepare a tannic acid-coated diatomaceous earth solution.

[0015] Preferably, in the step of preparing the tannic acid-coated diatomaceous earth solution by stirring, the stirring time is 2-5 hours and the stirring speed is 300-500 rpm.

[0016] Preferably, in the step of adding zinc chloride and stirring evenly, the stirring time is 3 to 6 hours and the stirring speed is 300 to 500 rpm.

[0017] Preferably, the mass ratio of the acrylic acid to the 1-vinyl-3-carboxyimidazole ionic liquid is 3 to 5:1.

[0018] Preferably, in the step of adding acrylic acid and 1-vinyl-3-carboxyimidazole ionic liquid and stirring until homogeneous, the stirring time is 10-30 min and the stirring speed is 300-500 rpm.

[0019] Preferably, the initiator is selected from ammonium persulfate or potassium persulfate, and the crosslinking agent is selected from N,N'-methylenebisacrylamide.

[0020] Preferably, the amount of the initiator added is 3 to 6 wt% of the mass of acrylic acid; and the amount of the crosslinking agent added is 1 to 3 wt% of the mass of acrylic acid.

[0021] Secondly, the present invention provides a rapidly gelled conductive hydrogel prepared by the above preparation method.

[0022] Thirdly, the present invention provides the application of the above-mentioned rapidly gelled conductive hydrogel in the preparation of electronic skin, strain sensors, and wearable electronic devices.

[0023] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0024] (1) The hydrogel raw material provided by the present invention has low toxicity and high safety. The preparation method is very simple. No heating is required. The preparation process of conductive hydrogel can be completed at room temperature. It consumes little energy and the gelation time is very short. Conductive hydrogel can be formed in only 40 seconds, which is suitable for industrial production.

[0025] (2) The hydrogel prepared by the present invention has good conductivity, repeated adhesion and low temperature resistance, and can be used as a flexible sensor, with broad application prospects. Attached Figure Description

[0026] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0027] Figure 1 The infrared spectrum of tannic acid, diatomaceous earth, and tannic acid-coated diatomaceous earth solution in Example 1 of this invention is shown.

[0028] Figure 2 This is a scanning electron microscope image of the interior of the CT-ZnCl2-PZA gel in Embodiment 1 of the present invention;

[0029] Figure 3 This refers to the adhesion strength of CT-ZnCl2-PZA in Example 1 of the present invention adhered to pigskin for ten cycles of adhesion-peeling.

[0030] Figure 4 The CT-ZnCl2-PZA gel of Example 1 of this invention was used to monitor the relative resistance change after 5 strain cycles of 10%-100%;

[0031] Figure 5 These are macroscopic and thermal images of the CT-ZnCl2-PZA gel of Embodiment 1 of the present invention at -30°C.

[0032] Figure 6 This refers to the adhesion strength of the CT-ZnCl2-PZA gel to different substrates in Example 2 of the present invention;

[0033] Figure 7 These are the stress-strain curves of Embodiment 1 and Comparative Example 1 of the present invention;

[0034] Figure 8 These are the stress-strain curves of Embodiment 1, Embodiment 2 and Comparative Example 2 of the present invention;

[0035] Figure 9 It refers to the adhesion strength of Embodiment 1, Embodiment 2 and Comparative Example 2 on glass. Detailed Implementation

[0036] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, 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 invention pertains.

[0037] As described in the background section, existing processes for preparing conductive hydrogels suffer from problems such as long processing time, high energy consumption, and high toxicity of raw materials. Therefore, this invention provides a method for preparing a rapidly gelled conductive hydrogel, comprising the following steps:

[0038] A tannic acid-coated diatomaceous earth solution was prepared by dissolving diatomaceous earth and tannic acid in water and stirring.

[0039] Zinc chloride was added to the tannic acid-coated diatomaceous earth solution and stirred until homogeneous. Then, acrylic acid and 1-vinyl-3-carboxyimidazole ionic liquid were added and stirred until homogeneous.

[0040] Then add the initiator and crosslinking agent, stir evenly, and immediately pour into the mold. A rapid gelation reaction will occur within 10 to 30 seconds to obtain the final product.

[0041] The introduction of tannic acid and zinc chloride can significantly improve the gelation rate. The catechol groups of tannic acid undergo a redox reaction with zinc ions to generate elemental zinc. Elemental zinc can promote the decomposition of the initiator into free radicals, thereby initiating the polymerization reaction. Therefore, the hydrogel system of this invention can gel rapidly at room temperature. In addition, the surface of tannic acid contains a large number of phenolic hydroxyl groups, which can effectively improve the adhesion properties of the hydrogel.

[0042] The addition of diatomaceous earth can improve the mechanical properties of hydrogels. The main component of diatomaceous earth is SiO2. When added to hydrogels as a filler, it can enhance the mechanical properties of the hydrogels. Under the coating effect of tannic acid, diatomaceous earth is uniformly dispersed in aqueous solution, forming a good inorganic-organic bond. The system has good compatibility, thus maximizing the reinforcing effect of diatomaceous earth.

[0043] Acrylic acid is a commonly used hydrogel comonomer. It is inexpensive and has a suitable polymerization ratio with 1-vinyl-3-carboxyimidazole ionic liquid, which ensures that zwitterions are evenly distributed in the polymerization network to maximize their effect.

[0044] 1-Vinyl-3-carboxyimidazole ionic liquid, as an amphoteric monomer, exhibits lower toxicity, simpler preparation process, milder reaction, and lower cost compared to existing amphoteric monomers. After copolymerization with acrylic acid, amphoteric ions are introduced onto the macromolecular chain of 1-vinyl-3-carboxyimidazole ionic liquid. Through electrostatically induced hydration, water molecules are firmly bound, forming a dense hydrated layer on the gel surface. This results in excellent hydrophilicity and consequently, superior antibacterial and antiprotein properties in the amphoteric hydrogel. The dipole-dipole interaction between anions and cations induces a synergistic effect, facilitating ion separation during ion migration and increasing the conductivity of the ion transport system, thus providing electrical conductivity. Furthermore, the electrostatic interaction of the zwitterions also contributes to the excellent self-healing properties of the amphoteric hydrogel.

[0045] In this invention, the mass ratio of diatomaceous earth, tannic acid, zinc chloride, acrylic acid, and water is 1:1–3:60–80:40–50:80–120. This suitable mass ratio ensures that the prepared hydrogel exhibits good overall performance.

[0046] This invention involves dissolving diatomaceous earth and tannic acid in water, adjusting the pH to 7.5-9 with 0.5-2M Tris solution, and then stirring to prepare a tannic acid-coated diatomaceous earth solution. An alkaline environment is beneficial for coating.

[0047] In the step of preparing the tannic acid-coated diatomaceous earth solution by stirring, the stirring time is 2-5 hours and the stirring speed is 300-500 rpm. Sufficient stirring time ensures that the tannic acid is uniformly coated on the surface of the diatomaceous earth.

[0048] In this invention, after adding zinc chloride, the mixture is stirred for 3 to 6 hours at a stirring speed of 300 to 500 rpm.

[0049] In this invention, the mass ratio of acrylic acid to 1-vinyl-3-carboxyimidazole ionic liquid is 3 to 5:1. A suitable mass ratio ensures that the zwitterionic ions have appropriate density and guarantees that the hydrogel matrix has good overall properties. If the amount of 1-vinyl-3-carboxyimidazole ionic liquid added is too high, it will lead to a decrease in mechanical properties.

[0050] In this invention, in the step of adding acrylic acid and 1-vinyl-3-carboxyimidazole ionic liquid and stirring evenly, the stirring time is 10-30 min and the stirring speed is 300-500 rpm.

[0051] This invention does not impose any special limitations on the types of initiators and crosslinking agents. Commonly used initiators and crosslinking agents in the art for preparing acrylic hydrogels can be used. The preferred initiator is ammonium persulfate or potassium persulfate, and the preferred crosslinking agent is N,N'-methylenebisacrylamide. This invention also does not impose any special limitations on the amount of initiator and crosslinking agent added. Commonly used initiators and crosslinking agents in the art can be used. The amount of initiator added is 3–6 wt% of the mass of acrylic acid; the amount of crosslinking agent added is 1–3 wt% of the mass of acrylic acid, ensuring that the hydrogel crosslinking network has a suitable degree of crosslinking, thereby providing appropriate strength and strain.

[0052] This invention also provides a rapidly gelling conductive hydrogel prepared by the above-described method. Due to the presence of zwitterions, the gel exhibits excellent antifreeze and antifouling properties. Furthermore, the reversible interaction between the hydrogel and the substrate allows for repeated adhesion and peeling of the gel and substrate. In addition, the hydrogel also possesses excellent conductivity and sensitivity.

[0053] Based on the above-mentioned excellent properties, the present invention also provides the application of the above-mentioned rapid gelation conductive hydrogel in the preparation of electronic skin, strain sensors, and wearable electronic devices.

[0054] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0055] Unless otherwise specified, the following examples do not have special restrictions on the source of reagents, and commercially available products well known to those skilled in the art can be used; the molds used are molds made of glass and silicone rubber.

[0056] In the following examples, the preparation process of 1-vinyl-3-carboxyimidazole ionic liquid (ZIL) is as follows (the reaction equation is shown below):

[0057]

[0058] ① Using vinylimidazole (14.10 g, 0.15 mol) and methyl chloroacetate (17.90 g, 0.165 mol) as raw materials, the mixture was stirred at room temperature for 2 days. The product was washed three times with anhydrous diethyl ether and then dried under vacuum at 30 °C for 6 h to obtain a white powder 1-vinyl-3-methoxycarbonyl-imidazole.

[0059] ② Add 1-vinyl-3-methoxycarbonyl-imidazolium (3.50 g, 0.017 mol) and potassium hydroxide (1.07 g, 0.02 mol) to 20 mL of ethanol, react for 2 h, centrifuge at 8000 r / min for 5 min;

[0060] ③ The transparent solution was dried, washed three times with ethanol, and dried at room temperature to obtain a white powder, 1-vinyl-3-carboxyimidazole ionic liquid ZIL, the structural formula of which is shown below.

[0061]

[0062] Example 1

[0063] (1) Dissolve 0.1g of diatomaceous earth Clay and 0.1g of tannic acid TA in 10mL of deionized water, stir to dissolve, adjust the pH to about 8 with 1MTris solution, stir for 3h to obtain a uniform solution A of tannic acid coated diatomaceous earth.

[0064] (2) Add 6.82g of zinc chloride (ZnCl2) to solution A and stir for 4h to obtain a homogeneous mixed solution B.

[0065] (3) Add 4.5g of acrylic acid AA and 0.9g of ZIL to solution B, stir until homogeneous, and obtain a homogeneous mixed solution C.

[0066] (4) Add 0.05g of initiator ammonium persulfate (APS) and 0.03g of crosslinking agent N,N'-methylenebisacrylamide (MBA) to solution C, stir evenly, pour the mixed solution into a mold made of glass and silicone rubber, and form a conductive hydrogel within 30s. The resulting conductive hydrogel is called CT-ZnCl2-PZA gel.

[0067] Figure 1 These are the infrared spectra of clay (Clay), tannic acid (TA), and a homogeneous solution (CT). The images show that, compared to the original clay, phenolic groups appear in CT at 1202 cm⁻¹. -1 The characteristic vibrational bands of (CO), and the aromatic groups at 1531 cm⁻¹ -1 (CC) and 1613cm -1 The characteristic vibration band of (C=C) indicates that tannic acid was successfully coated on the clay.

[0068] Figure 2 This is an internal scanning electron microscope (SEM) image of the gel obtained in this embodiment. As can be seen from the image, the CT-ZnCl2-PZA gel exhibits a dense porous structure, which is mainly attributed to a highly cross-linked physical network. Furthermore, the dense porous structure increases the gel's porosity, which may provide more conductive network pathways to facilitate ion migration.

[0069] Figure 3 The adhesion strength of the CT-ZnCl2-PZA gel obtained in this embodiment to pigskin was measured after ten cycles of adhesion-peeling. During the ten cycles of adhesion, the adhesion strength of the CT-ZnCl2-PZA gel to pigskin remained stable without significant changes, indicating that it has the ability to be reused.

[0070] Figure 4 The CT-ZnCl2-PZA gel obtained in this embodiment monitors the relative resistance change of strain from 10% to 100%. The relative resistance increases with the increase of gel strain. At the same time, the CT-ZnCl2-PZA gel can sensitively monitor minute strains of 10% and can be applied to human body sensing.

[0071] Figure 5 These are macroscopic and thermal images of the CT-ZnCl2-PZA gel obtained in this embodiment at -30°C. It can be seen that even at -30°C, the CT-ZnCl2-PZA gel still has good torsion and bending properties, which shows that it has good low-temperature resistance.

[0072] Example 2

[0073] (1) Dissolve 0.1g of diatomaceous earth Clay and 0.3g of tannic acid TA in 10mL of deionized water, stir to dissolve, adjust the pH to about 8 with 1MTris solution, stir for 3h to obtain a uniform solution A of tannic acid coated diatomaceous earth.

[0074] (2) Add 6.82g of zinc chloride (ZnCl2) to solution A and stir for 4h to obtain a homogeneous mixed solution B.

[0075] (3) Add 4.5g of acrylic acid AA and 0.9g of ZIL to solution B, stir until homogeneous, and obtain a homogeneous mixed solution C.

[0076] (4) Add 0.05g of initiator APS and 0.03g of crosslinking agent MBA to solution C, stir evenly, pour the mixed solution into a mold made of glass and silicone rubber, and form a gel within 30s.

[0077] Figure 6The figure shows the adhesion strength of the CT-ZnCl2-PZA gel obtained in this embodiment to different substrates. As can be seen from the figure, the CT-ZnCl2-PZA gel can adhere to different substrates such as glass, pigskin, PET, PMMA, Ti, paper, Fe, Al, Cu, and Zn, and all of them have good adhesion strength.

[0078] Example 3

[0079] (1) Dissolve 0.1g of diatomaceous earth Clay and 0.1g of tannic acid TA in 10mL of deionized water, stir to dissolve, adjust the pH to about 8 with 1MTris solution, stir for 3h to obtain a uniform solution A of tannic acid coated diatomaceous earth.

[0080] (2) Add 6.82g of zinc chloride (ZnCl2) to solution A and stir for 4h to obtain a homogeneous mixed solution B.

[0081] (3) Add 4.5g of acrylic acid AA and 0.45g of ZIL to solution B, stir well to obtain a homogeneous mixed solution C.

[0082] (4) Add 0.05g of initiator APS and 0.03g of crosslinking agent MBA to solution C, stir evenly, pour the mixed solution into a mold made of glass and silicone rubber, and form a gel within 30s.

[0083] Example 4

[0084] (1) Dissolve 0.1g of diatomaceous earth Clay and 0.1g of tannic acid TA in 10mL of deionized water, stir to dissolve, adjust the pH to about 8 with 1MTris solution, stir for 3h to obtain a uniform solution A of tannic acid coated diatomaceous earth.

[0085] (2) Add 6.82g of zinc chloride (ZnCl2) to solution A and stir for 4h to obtain a homogeneous mixed solution B.

[0086] (3) Add 4.5g of acrylic acid AA and 1.35g of ZIL to solution B, stir until homogeneous, and obtain a homogeneous mixed solution C.

[0087] (4) Add 0.05g of initiator APS and 0.03g of crosslinking agent MBA to solution C, stir evenly, pour the mixed solution into a mold made of glass and silicone rubber, and form a gel within 30s.

[0088] Comparative Example 1

[0089] The difference compared to Example 1 is that no diatomaceous earth is added.

[0090] The stress-strain curves of Example 1 and Comparative Example 1 are as follows: Figure 7As shown in the figure, the hydrogel without diatomaceous earth has poor mechanical properties, while the mechanical properties are significantly improved after adding diatomaceous earth.

[0091] Comparative Example 2

[0092] The difference compared to Example 1 is that the amount of tannic acid (TA) added is 0.03g.

[0093] Figure 8 The stress-strain curves for Examples 1, 2, and 2 are shown below. Figure 9 The figure shows the adhesion strength of Examples 1, 2, and 2 on glass. As can be seen from the figure, although Comparative Example 2 has the best mechanical properties due to its higher diatomite content, its adhesion strength on glass is the lowest, only about 600 Pa. In contrast, the hydrogel adhesion strength of Examples 1 and 2 is above 3 kPa, which has a wider range of applications. Moreover, the strain can reach about 600%, and the tensile strength exceeds 70 kPa, indicating superior mechanical properties.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a rapidly gelled conductive hydrogel, characterized in that, Includes the following steps: A tannic acid-coated diatomaceous earth solution was prepared by dissolving diatomaceous earth and tannic acid in water and stirring. Zinc chloride was added to the tannic acid-coated diatomaceous earth solution and stirred until homogeneous. Then, acrylic acid and 1-vinyl-3-carboxyimidazole ionic liquid were added and stirred until homogeneous. Then add the initiator and crosslinking agent, stir evenly and immediately pour into the mold, and carry out a rapid gelation reaction within 10~30s to obtain the product; The mass ratio of diatomaceous earth, tannic acid, zinc chloride, acrylic acid, and water is 1:1~3:60~80:40~50:80~120; the mass ratio of acrylic acid and 1-vinyl-3-carboxyimidazole ionic liquid is 3~5:

1.

2. The preparation method according to claim 1, characterized in that, Diatomaceous earth and tannic acid were dissolved in water, and the pH was adjusted to 7.5-9 with 0.5-2M Tris solution. Then, the mixture was stirred to prepare a tannic acid-coated diatomaceous earth solution.

3. The preparation method according to claim 1, characterized in that, In the step of preparing the tannic acid-coated diatomaceous earth solution by stirring, the stirring time is 2-5 hours and the stirring speed is 300-500 rpm.

4. The preparation method according to claim 1, characterized in that, In the step of adding zinc chloride and stirring evenly, the stirring time is 3~6 hours and the stirring speed is 300~500 rpm.

5. The preparation method according to claim 1, characterized in that, In the step of adding acrylic acid and 1-vinyl-3-carboxyimidazole ionic liquid and stirring evenly, the stirring time is 10~30min and the stirring speed is 300~500rpm.

6. The preparation method according to claim 1, characterized in that, The initiator is selected from ammonium persulfate or potassium persulfate, and the crosslinking agent is selected from N,N'-methylenebisacrylamide.

7. The preparation method according to claim 6, characterized in that, The amount of the initiator added is 3-6 wt% of the mass of acrylic acid; the amount of the crosslinking agent added is 1-3 wt% of the mass of acrylic acid.

8. The rapidly gelling conductive hydrogel prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the rapidly gelling conductive hydrogel as described in claim 8 in the preparation of strain sensors and wearable electronic devices.

10. The application of the rapidly gelling conductive hydrogel as described in claim 8 in the preparation of electronic skin.

Images