Temperature-responsive underwater adhesion carbon nanodot-based Janus hydrogel as well as preparation method and application of temperature-responsive underwater adhesion carbon nanodot-based Janus hydrogel

Abstract

The invention belongs to the field of hydrogel materials, relates to a Janus hydrogel based on temperature-responsive underwater adhesion carbon nanodots as well as a preparation method and application of the Janus hydrogel, and particularly relates to a preparation method of a conductive hydrogel capable of realizing temperature-controlled underwater adhesion based on carbon nanodots. The temperature-controlled underwater adhesion conductive hydrogel is prepared by taking N-isopropylacrylamide as a temperature response material and grafting hydroformylated cellulose with dopamine, dopamine is grafted to dialdehyde cellulose and fired into carbon dots, excellent adhesion is given, the hydrogel also has adhesion in hot water by changing the temperature, and the temperature-controlled underwater adhesion conductive hydrogel can be applied to the field of temperature-controlled underwater adhesion conductive hydrogel, so that the temperature-controlled underwater adhesion conductive hydrogel can be applied to the field of temperature-controlled underwater adhesion conductive hydrogel, and the temperature-controlled underwater adhesion conductive hydrogel can be applied to the field of temperature-controlled underwater adhesion conductive hydrogel. The unique temperature response type underwater adhesive hydrogel is constructed, the preparation process is simple, the performance is excellent, and the temperature response type underwater adhesive hydrogel is suitable for popularization and application.

Description

Technical Field

[0001] The present invention belongs to the field of hydrogel materials, and relates to a carbon nanodot-based hydrogel, a preparation method and an application thereof, and specifically relates to a preparation method of a conductive hydrogel based on carbon nanodots that can achieve temperature-controlled underwater adhesion. Background Art

[0002] Hydrogels have become ideal materials in the field of electronic skin due to their excellent biocompatibility, conductivity, flexibility and adhesion, and are widely used in various sensing technologies. However, most traditional hydrogels exhibit uniform and symmetrical adhesion, that is, both sides have similar adhesion properties, which may bring limitations in practical applications. Therefore, the development of hydrogels with asymmetric adhesion properties can effectively overcome this problem and open up new possibilities for the functional expansion and multi-scenario application of hydrogel electronic skin. Janus structure hydrogels are suitable for use in complex environments, such as in vivo tissue adhesion, wound healing, and seawater desalination, because their two sides have different properties.

[0003] Smart responsive materials are a new type of functional materials that can autonomously drive and change under the action of external stimuli (such as temperature, pH, light, etc.), thereby regulating their own physical or chemical properties. At present, hydrogels that are responsive to external changes such as temperature, light and pH have been widely used in human sensing, drug delivery and release, and have shown great application potential. Poly (N-isopropylacrylamide) is a typical widely used thermoresponsive polymer. Its molecular structure contains both hydrophilic amide groups and hydrophobic isopropyl groups, and exhibits unique response characteristics at different temperatures. When the temperature is higher than the minimum critical solution temperature, the hydrophobic isopropyl effect is dominant, and the PNIPAM chain collapses and presents a globular conformation; when the temperature is lower than the minimum critical solution temperature, the hydrophilic amide effect is stronger, and the chain conformation changes from spherical to chain again. However, due to the weak intermolecular interaction of N-isopropylacrylamide, this type of hydrogel usually exhibits poor mechanical properties. To this end, the introduction of a water / ionic liquid binary system can improve the mechanical strength of N-isopropylacrylamide hydrogels. Nevertheless, N-isopropylacrylamide still has poor adhesion in both hydrophilic and hydrophobic states, and its uniform structure limits its application potential in fields with high adhesion requirements such as electronic skin.

[0004] Inspired by mussels, catechol groups can react chemically or physically with a variety of substances due to their active chemical properties, including hydrogen bonds, π-π interactions, and electrostatic interactions. These interactions are concentrated at the interface between the substance and the substrate, greatly enhancing its adhesion properties. The current commonly used adhesion strategy is to introduce catechol groups into polymer chains through copolymerization or modification. However, catechol groups have certain limitations in their applications. For example, they are easy to absorb free radicals and be oxidized to quinones. This process will hinder the polymerization of hydrogels and weaken the stability of catechol-based polymers. Therefore, the preparation of hydrogels containing catechol groups is very challenging.

[0005] Therefore, how to provide a conductive hydrogel and a preparation method thereof that have excellent adhesion and conductivity and can realize intelligent temperature control of adhesion properties in different environments is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a temperature-responsive underwater adhesive carbon nanodot-based Janus hydrogel, a preparation method and an application.

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

[0008] One of the technical solutions of the present invention is to provide a method for preparing a temperature-responsive underwater adhesive carbon nanodot-based Janus hydrogel, which is a method for preparing a conductive hydrogel with temperature-controlled underwater adhesiveness based on carbon nanodots, and the steps include:

[0009] Using dialdehyde cellulose and dopamine as raw materials and water as solvent, a carbon nanodot solution is prepared through firing and cooling;

[0010] The carbon nanodot solution, 1-butyl-3-methylimidazolium chloride (ionic liquid), N-isopropylacrylamide (NIPAM), acrylic acid (AA), ammonium persulfate and N,N'-methylenebisacrylamide are used as reactants. After being stirred evenly, they are heated in an oven at 80°C for 1-5 hours to obtain a conductive hydrogel with temperature-controlled underwater adhesion.

[0011] It should be noted that carbon dots, as a new type of carbon material with a size less than 10nm, have attracted widespread attention due to their unique properties. Carbon nanodots are not only easy to chemically modify, but also have excellent conductivity, low cytotoxicity and good water solubility. They have been widely used in the fields of biosensing and chemical sensing. In addition, studies have shown that the surface of carbon nanodots is rich in functional groups such as hydroxyl and carboxyl groups. These functional groups can interact with water molecules by forming hydrogen bonds, thereby cross-linking with the hydrogel network and promoting the effective polymerization of hydrogels. Therefore, carbon nanodots are often used as cross-linking agents in hydrogel systems. This design gives full play to the multifunctional advantages of carbon nanodots in the field of hydrogels and provides new ideas for the research and development of functional hydrogels.

[0012] In addition, in order to improve the mechanical properties and adhesion properties of the hydrogel, the present invention designs a new method for regulating the adhesion of the hydrogel in the air and underwater by temperature. Due to the special temperature responsiveness of N-isopropylacrylamide, it is transformed into a hydrophobic spherical conformation in high-temperature water, and catechol is exposed, so that stable adhesion can be achieved underwater; and the addition of ionic liquid makes the hydrogel denser, which significantly improves the mechanical properties of the hydrogel.

[0013] Specifically, the temperature-regulated underwater adhesive conductive hydrogel described in the present invention is prepared by using N-isopropylacrylamide as a temperature-responsive material and aldehyded cellulose grafted with dopamine. Dopamine is grafted onto dialdehyde cellulose and fired into carbon dots to impart excellent adhesion. The temperature is then changed to make it adhesive in hot water, thereby constructing a unique temperature-responsive underwater adhesive hydrogel. The hydrogel has a simple preparation process and excellent performance, and is suitable for promotion and application.

[0014] Furthermore, the dosage ratio of the dialdehyde cellulose, dopamine and water is 0.25-1g:0.25-1g:100mL, specifically 0.5g:0.5g:100mL, 0.25g:0.25g:100mL and 1g:1g:100mL, preferably 0.5g:0.5g:100mL.

[0015] Furthermore, the firing temperature is 160° C., and the firing time is 0-5 h, specifically 0 h, 1 h, 2 h, 3 h, 4 h and 5 h, preferably 3 h.

[0016] Furthermore, the amount ratio of the carbon nanodot solution, 1-butyl-3-methylimidazolium chloride, N-isopropylacrylamide (NIPAM), acrylic acid (AA), ammonium persulfate and N,N'-methylenebisacrylamide is 2-4g:2g:1.13-3.39g:0.72g:0.06g:0.006g, the molar ratio of NIPAM to AA is 1-3:1, specifically 1:1, 2:1 and 3:1; the stirring time is 30min.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The invention discloses a temperature-responsive underwater adhesive carbon nanodot-based Janus hydrogel, which is a conductive hydrogel based on carbon nanodots that can achieve temperature-controlled underwater adhesiveness. It is prepared by using N-isopropylacrylamide as a temperature-responsive material and aldehyde-modified cellulose grafted with dopamine. Dopamine is grafted onto dialdehyde cellulose and fired into carbon dots to impart excellent adhesiveness. Then, by changing the temperature, it also has adhesiveness in hot water, and a unique temperature-responsive underwater adhesive hydrogel is constructed. The adhesiveness is asymmetric. Specifically, when in room temperature air, the A side of the hydrogel has excellent adhesiveness, while the B side has almost no adhesiveness; and when it is placed in 50°C hot water, the B side has underwater adhesiveness, while the A side completely loses adhesiveness. This hydrogel has both simple preparation process and excellent performance, and is suitable for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] 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.

[0020] Figure 1 The tensile strength and toughness strength bar graphs of the hydrogels prepared in the examples and comparative examples are shown;

[0021] Figure 2 The following are histograms of the adhesion peel strength of the hydrogels prepared in the examples and comparative examples in air (T<50°C) and water (T>50°C);

[0022] Figure 3 This is a bar graph of the adhesion peel strength of the hydrogel prepared in Example 1 to the polytetrafluoroethylene material;

[0023] Figure 4 This is a bar graph of the adhesion peel strength of the hydrogel prepared in Example 1 after long-term storage in air at room temperature;

[0024] Figure 5 Synthesis mechanism diagram for hydrogel preparation;

[0025] Figure 6 FT-IR infrared spectra of raw materials and carbon nanodots.

[0026] Figure 7 Schematic diagram of the adhesion and peeling of the hydrogel and the AB surface. DETAILED DESCRIPTION

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0032] Unless otherwise specified, the room temperature in the specific embodiments of the present invention refers to 25±5°C.

[0033] The raw materials and reagents used in the specific embodiments of the present invention are all commercially available products.

[0034] Example 1

[0035] The preparation steps of the carbon nanodot temperature-controlled underwater adhesive conductive hydrogel are as follows:

[0036] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 3 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs);

[0037] S2. Take 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropylacrylamide (NIPAM), 0.72 g acrylic acid (AA) (the molar ratio of NIPAM to AA is 2:1), 0.06 g ammonium persulfate and 0.006 g N,Nˋ-methylenebisacrylamide, stir evenly, and place in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0038] Example 2

[0039] The steps for preparing hydrogel using carbon nanodot solutions of different concentrations are as follows:

[0040] S1. Add 1 g of dialdehyde cellulose and 1 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 3 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (2% CDs);

[0041] S2. Take 4g CDs, 2g 1-butyl-3-methylimidazolium chloride, 2.26g N-isopropylacrylamide (NIPAM), 0.72g acrylic acid (AA) (the molar ratio of NIPAM to AA is 2:1), 0.06g ammonium persulfate and 0.006g N,Nˋ-methylenebisacrylamide, stir evenly, and place in an oven at 80°C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0042] Example 3

[0043] The steps for preparing hydrogel using carbon nanodot solutions of different concentrations are as follows:

[0044] S1. Add 0.75 g of dialdehyde cellulose and 0.75 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 3 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (1.5% CDs);

[0045] S2. Take 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropylacrylamide (NIPAM), 0.72 g acrylic acid (AA) (the molar ratio of NIPAM to AA is 2:1), 0.06 g ammonium persulfate and 0.006 g N,Nˋ-methylenebisacrylamide, stir evenly, and place in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0046] Example 4

[0047] The steps for preparing hydrogel using carbon nanodot solutions of different concentrations are as follows:

[0048] S1. Add 0.25 g of dialdehyde cellulose and 0.25 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 3 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (0.5% CDs);

[0049] S2. Take 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropylacrylamide (NIPAM), 0.72 g acrylic acid (AA) (the molar ratio of NIPAM to AA is 2:1), 0.06 g ammonium persulfate and 0.006 g N,Nˋ-methylenebisacrylamide, stir evenly, and place in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0050] Example 5

[0051] The steps for preparing hydrogels using different 1-butyl-3-methylimidazolium chloride (ionic liquid) contents are as follows:

[0052] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 3 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-3h);

[0053] S2. Take 4g CDs, 1g 1-butyl-3-methylimidazolium chloride, 2.26g N-isopropylacrylamide (NIPAM), 0.72g acrylic acid (AA) (the molar ratio of NIPAM to AA is 2:1), 0.06g ammonium persulfate and 0.006g N,Nˋ-methylenebisacrylamide, stir evenly, and place in an oven at 80°C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0054] Example 6

[0055] The steps for preparing hydrogels using different 1-butyl-3-methylimidazolium chloride (ionic liquid) contents are as follows:

[0056] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 3 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-3h);

[0057] S2. Take 4 g CDs, 3 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropylacrylamide (NIPAM), 0.72 g acrylic acid (AA) (the molar ratio of NIPAM to AA is 2:1), 0.06 g ammonium persulfate and 0.006 g N,Nˋ-methylenebisacrylamide, stir evenly, and place in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0058] Example 7

[0059] The steps for preparing hydrogels using different ratios of N-isopropylacrylamide to acrylic acid are as follows:

[0060] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 3 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-3h);

[0061] S2, CDs (4 g), 1-butyl-3-methylimidazolium chloride (2 g), N-isopropylacrylamide (NIPAM) (1.13 g), acrylic acid (AA) (0.72 g) (the molar ratio of NIPAM to AA is 1:1), ammonium persulfate (0.06 g) and NNˋ-methylenebisacrylamide (0.006 g) were stirred evenly and placed in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0062] Example 8

[0063] The steps for preparing hydrogels using different ratios of N-isopropylacrylamide to acrylic acid are as follows:

[0064] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 3 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-3h);

[0065] S2, CDs (4 g), 1-butyl-3-methylimidazolium chloride (2 g), N-isopropylacrylamide (NIPAM) (3.39 g), acrylic acid (AA) (0.72 g) (the molar ratio of NIPAM to AA is 3:1), ammonium persulfate (0.06 g) and NNˋ-methylenebisacrylamide (0.006 g) were stirred evenly and placed in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0066] Example 9

[0067] The steps for preparing hydrogel using carbon nanodots at different times are as follows:

[0068] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 0 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-0h);

[0069] S2. Take 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropylacrylamide (NIPAM), 0.72 g acrylic acid (AA), 0.06 g ammonium persulfate and 0.006 g N,Nˋ-methylenebisacrylamide, stir them evenly, and place them in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0070] Example 10

[0071] The steps for preparing hydrogel using carbon nanodots at different times are as follows:

[0072] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 1 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-1h).

[0073] S2. Take 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropylacrylamide (NIPAM), 0.72 g acrylic acid (AA), 0.06 g ammonium persulfate and 0.006 g N,Nˋ-methylenebisacrylamide, stir them evenly, and place them in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0074] Embodiment 11

[0075] The steps for preparing hydrogel using carbon nanodots at different times are as follows:

[0076] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 2 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-2h);

[0077] S2. Take 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropylacrylamide (NIPAM), 0.72 g acrylic acid (AA), 0.06 g ammonium persulfate and 0.006 g N,Nˋ-methylenebisacrylamide, stir them evenly, and place them in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0078] Example 12

[0079] The steps for preparing hydrogel using carbon nanodots at different times are as follows:

[0080] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 4 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-4h);

[0081] S2. Take 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropylacrylamide (NIPAM), 0.72 g acrylic acid (AA), 0.06 g ammonium persulfate and 0.006 g N,Nˋ-methylenebisacrylamide, stir them evenly, and place them in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0082] Example 13

[0083] The steps for preparing hydrogel using carbon nanodots at different times are as follows:

[0084] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 5 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-5h);

[0085] S2. Take 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropylacrylamide (NIPAM), 0.72 g acrylic acid (AA), 0.06 g ammonium persulfate and 0.006 g N,Nˋ-methylenebisacrylamide, stir them evenly, and place them in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0086] Comparative Example 1

[0087] The steps for preparing the hydrogel without using 1-butyl-3-methylimidazolium chloride (ionic liquid) are:

[0088] S1. Add 0.5 g of dialdehyde cellulose and 0.5 g of dopamine into 100 mL of deionized water, place in a pressure-resistant reaction bottle, heat to 160° C. and react for 3 h. The reaction container is naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-3h);

[0089] S2. Take 4g CDs, 2g water, 2.26g N-isopropylacrylamide (NIPAM), 0.72g acrylic acid (AA), 0.06g ammonium persulfate and 0.006g N,Nˋ-methylenebisacrylamide, stir evenly, and place in an oven at 80°C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0090] Comparative Example 2

[0091] The steps for preparing hydrogel without using carbon nanodot solution are:

[0092] S1. Take 4 g of water, 2 g of 1-butyl-3-methylimidazolium chloride, 2.26 g of N-isopropylacrylamide (NIPAM), 0.72 g of acrylic acid (AA), 0.06 g of ammonium persulfate and 0.006 g of N,N-methylenebisacrylamide, stir them evenly, and place them in an oven at 80 °C for one hour to obtain temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM).

[0093] Comparative Example 3

[0094] The steps for preparing the hydrogel without using 1-butyl-3-methylimidazolium chloride (ionic liquid) and carbon nanodot solution are as follows:

[0095] S1. Take 6 g of water, 2.26 g of N-isopropylacrylamide (NIPAM), 0.72 g of acrylic acid (AA), 0.06 g of ammonium persulfate and 0.006 g of N,N`-methylenebisacrylamide, stir them evenly, and place them in an oven at 80 °C for one hour to obtain the temperature-controlled underwater adhesive conductive hydrogel (PAA-co-PNIPAM).

[0096] Test example

[0097] The hydrogels prepared in Example 1 and Comparative Examples 1-9 were subjected to adhesion performance tests and mechanical performance tests. The methods are as follows. The results are shown in Table 1.

[0098] The hydrogels prepared in Example 1 and Comparative Examples 1-9 were cut into rectangles of 4 cm×6 mm×2 mm and subjected to mechanical property tests using an electronic universal testing machine (Shenzhen Sun Technology Co., Ltd., China) with an extension speed of 80 mm / min.

[0099] Toughness is calculated based on the area under the stress-strain curve using the following formula:

[0100] △U=∫σdε

[0101] Where σ and ε are the stress and strain of the hydrogel, respectively.

[0102] The hydrogels prepared in Example 1 and Comparative Examples 1-9 were cut into rectangular specimens (3.2 cm×2 cm×3 mm) and subjected to adhesion and peeling tests in room temperature air and 50° C. hot water. Since the hydrogels were prepared by shaping with a polytetrafluoroethylene mold, the surface close to the polytetrafluoroethylene was called the A surface, and the surface exposed to the air was called the B surface.

[0103] Table 1

[0104]

[0105]

[0106] It can be seen from the data in Table 1 that the toughness of the hydrogel prepared in Example 1 is the highest, reaching 571.35 kJ / m 3 . And in terms of adhesion, whether in room temperature air or underwater at 50°C, Example 1 has the best performance, reaching 237.8N / m and 47.75N / m respectively. The 1-butyl-3-methylimidazolium chloride used in Example 5 is only 1g. In this case, N-isopropylacrylamide cannot be dissolved, so the hydrogel cannot be successfully prepared. Examples 9 and 10 cannot successfully polymerize to form hydrogels due to the lack of carbonization and insufficient preparation time of carbon nanodots, and their performance cannot be tested. Comparative Examples 1 and 3 did not add 1-butyl-3-methylimidazolium chloride, N-isopropylacrylamide cannot be dissolved, and cannot be polymerized to form a hydrogel. Since no carbon nanodots were added to Comparative Example 2, not only is the adhesion very low, but it also does not have underwater adhesion properties.

[0107] Figure 1 The tensile strength and toughness strength bar graphs of the hydrogels prepared in the examples and comparative examples are shown in FIG. Figure 1 It can be seen that the hydrogel prepared by carbon nanodots fired for 3 hours has a tensile strength of 172.34 kPa and a toughness of 571.35 kJ / m. Although the tensile strength is higher than that of Example 1, it is still the best in terms of comprehensive mechanical properties.

[0108] The above experimental results fully prove that by regulating the concentration of carbon nanodots, the concentration of ionic liquids, the ratio of NIPAM and AA, and the firing time of carbon nanodots, the mechanical properties of the hydrogel can be optimized. The concentration and preparation time of carbon nanodots are because the carbon dots after firing have optimized surface properties and graphitization, which makes them more firmly bonded to the hydrogel, thereby improving the mechanical properties. The increase in concentration and preparation time may cause the surface or core structure of the carbon nanodots to aggregate or crack, resulting in poor dispersion of the carbon nanodots, thereby affecting the mechanical properties. In Examples 9 and 10, due to insufficient or too long preparation time of the carbon nanodots, it is impossible to polymerize to form a hydrogel and its performance cannot be tested. Ionic liquids increase the cations or anions in the ionic liquid that can interact physically or chemically with the functional groups (such as carboxyl, hydroxyl or amine groups) on the polymer chains of the hydrogel. These interactions can increase the crosslinking density between the polymer chains at the molecular level, thereby improving the mechanical strength of the hydrogel. Increasing the amount of ionic liquid and changing the ratio of NIPAM and AA will affect the adhesion properties of the hydrogel.

[0109] Figure 2 is a bar graph of the adhesion peel strength of the hydrogels prepared in the examples and comparative examples, Figure 2 It can be seen that the hydrogel prepared by carbon nanodots fired for 3 hours has stable adhesion both in room temperature air and in 50℃ water. Although the mechanical properties of the hydrogel are improved by changing the content of other components, especially increasing the content of ionic liquid, the adhesion of the hydrogel prepared by carbon nanodots fired for 3 hours far exceeds them, reaching 237.8N / m in room temperature air and 47.75N / m in 50℃ water.

[0110] Figure 3 This is a bar graph of the adhesion and peeling of the hydrogel prepared in Example 1 to the polytetrafluoroethylene plate. The hydrogel was prepared using a polytetrafluoroethylene mold, and the hydrogel was divided into side A and side B. Side A is the side close to the mold, and side B is the side exposed to the air. It can be seen that side A has an adhesion strength of 52.8N / m in room temperature air, but has no adhesion under 50°C water; while side B is just the opposite, with an adhesion of 8.4N / m under 50°C water, but very low adhesion in room temperature air. This is due to the temperature responsiveness of N-isopropylacrylamide. At 50°C, the chain conformation of N-isopropylacrylamide is transformed into a hydrophobic spherical conformation, so that the catechol structure of the hydrogel can be exposed for adhesion. At the same time, the difference in adhesion between the two sides also provides convenience for use.

[0111] Figure 4This is a bar graph showing the test of the adhesion persistence of Example 1 after long-term exposure to the air. It can be seen from the graph that the hydrogel still exhibits stable and excellent adhesion when placed in the air for a long time, for 1 day, 3 days, 7 days, 15 days and 30 days, respectively. It also proves that it has certain self-recovery ability and lasting adhesion performance, ensuring convenience in actual use.

[0112] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a conductive hydrogel with temperature-controlled underwater adhesion based on carbon nanodots, characterized in that the steps include: Using dialdehyde cellulose and dopamine as raw materials and water as solvent, a carbon nanodot solution is prepared through firing and cooling; The carbon nanodot solution, N-isopropylacrylamide NIPAM, acrylic acid AA, 1-butyl-3-methylimidazolium chloride (ionic liquid), ammonium persulfate and N,N'-methylenebisacrylamide are used as reactants, stirred evenly, and a conductive hydrogel with temperature-controlled underwater adhesion is obtained through reaction.

2. The preparation method according to claim 1, characterized in that: The dosage ratio of the dialdehyde cellulose, dopamine and water is 0.25-1g:0.25-1g:100mL; the firing temperature is 160°C and the firing time is 0-5h.

3. The preparation method according to claim 1, characterized in that: The amount ratio of the carbon nanodot solution, 1-butyl-3-methylimidazolium chloride, N-isopropylacrylamide NIPAM, acrylic acid AA, ammonium persulfate and N,N'-methylenebisacrylamide is 2-4g:2g:1.13-3.39g:0.72g:0.06g:0.006g, the molar ratio of N-isopropylacrylamide NIPAM and acrylic acid AA is 1-3:1, and the stirring time is 30min.

4. The preparation method according to claim 1, characterized in that: The reaction temperature is 80° C. and the reaction time is 1-5 h.

5. A conductive hydrogel with temperature-controlled underwater adhesion based on carbon nanodots prepared by the method according to any one of claims 1 to 4, characterized in that: The conductive hydrogel is a temperature-responsive underwater adherent carbon nanodot-based Janus hydrogel.

6. Use of a conductive hydrogel with temperature-regulated underwater adhesion based on carbon nanodots prepared by the method as described in any one of claims 1 to 4 or a conductive hydrogel with temperature-regulated underwater adhesion based on carbon nanodots as described in claim 5 in flexible electronics, biosensors, environmental monitoring and smart materials.

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