Temperature-responsive underwater-adhesive carbon nanodot-based janus hydrogel, preparation method and application

Abstract

The application belongs to the field of hydrogel materials, and relates to a temperature-responsive underwater adhesion carbon nanodot-based Janus hydrogel, a preparation method and application, in particular to a preparation method of a conductive hydrogel capable of realizing temperature-regulated underwater adhesion based on carbon nanodots. The temperature-regulated underwater adhesion conductive hydrogel is prepared from N-isopropyl acrylamide as a temperature-responsive material and aldehyde cellulose grafted dopamine, the dopamine is grafted to dialdehyde cellulose and is sintered into carbon dots, excellent adhesion is given, and the temperature is changed so that the carbon dots also have adhesion in hot water, a unique temperature-responsive underwater adhesion hydrogel is constructed, the preparation process is simple, the performance is excellent, and the temperature-responsive underwater adhesion hydrogel is suitable for promotion and application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of hydrogel materials, and relates to a carbon nanodot-based hydrogel, a preparation method and application, in particular to a preparation method of a temperature-regulated underwater adhesion conductive hydrogel based on carbon nanodots. BACKGROUND

[0002] Hydrogels have become ideal materials in the field of electronic skin due to their excellent biocompatibility, electrical conductivity, flexibility and adhesion, and are widely used in various sensing technologies. However, most traditional hydrogels exhibit uniform and symmetrical adhesion, i.e., both sides have similar adhesion properties, which may actually limit their practical applications. Therefore, developing 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 applications in complex environments, such as in vivo tissue adhesion, wound healing, seawater desalination, etc., due to their different properties on both sides.

[0003] Intelligent responsive materials are a new type of functional material that can autonomously drive and change under the action of external stimuli (such as temperature, pH, light, etc.), thereby regulating their physical or chemical properties. Currently, hydrogels with response capabilities to temperature, light and pH changes have been widely used in human body sensing, drug delivery and release, etc., and have shown great application potential. Poly-N-isopropylacrylamide is a typical thermally responsive polymer widely used. Its molecular structure contains both hydrophilic amide groups and hydrophobic isopropyl groups, which exhibit unique response characteristics at different temperatures. When the temperature is higher than the lower critical solution temperature, the hydrophobic isopropyl group plays a dominant role, and the PNIPAM chain collapses, showing a globular conformation; while when the temperature is lower than the lower critical solution temperature, the hydrophilic amide group is stronger, and the chain conformation reverts from globular to chain-like. However, due to the weak intermolecular interaction of N-isopropylacrylamide, such hydrogels usually exhibit poor mechanical properties. Therefore, the introduction of a water / ionic liquid binary system can improve the mechanical strength of N-isopropylacrylamide hydrogels. Nevertheless, N-isopropylacrylamide 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 currently 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 easily absorb free radicals and are oxidized to quinones. This process hinders the polymerization of hydrogels and weakens the stability of catechol-based polymers. Therefore, the preparation of hydrogels containing catechol groups is quite challenging.

[0005] Therefore, how to provide a conductive hydrogel with excellent adhesion and conductivity, and the ability to achieve intelligent temperature control of adhesion properties in different environments and its preparation method 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 solutions:

[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, comprising the following steps:

[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,Nˋ-methylenebisacrylamide are used as reactants. After being stirred evenly, they are heated in an 80°C oven 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 of less than 10 nm, have attracted extensive attention due to their unique properties. Carbon nanodots not only have excellent electrical conductivity, low cytotoxicity and good water solubility, but also have excellent chemical modification. At present, carbon nanodots have been widely used in the fields of biological sensing 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 through hydrogen bonding, thereby crosslinking with the hydrogel network to promote the effective polymerization of the hydrogel. Therefore, carbon nanodots are often used as crosslinking agents in hydrogel systems. This design fully utilizes the multifunctional advantages of carbon nanodots in the field of hydrogels, providing a new idea for the research and development of functional hydrogels.

[0012] In addition, in order to improve the mechanical properties and adhesion properties of the hydrogel, a new method for adjusting the adhesion of the hydrogel in air and underwater by temperature is designed. Due to the special temperature responsiveness of N-isopropyl acrylamide, in hot water, it changes into a hydrophobic spherical conformation, and catechol is exposed, so that stable adhesion can be achieved underwater. The addition of ionic liquid makes the hydrogel more dense, significantly improving the mechanical properties of the hydrogel.

[0013] Specifically, the temperature-regulated underwater adhesion conductive hydrogel is prepared from N-isopropyl acrylamide as a temperature-responsive material and aldehyde cellulose grafted dopamine. By grafting dopamine onto dialdehyde cellulose and sintering it into carbon dots, excellent adhesion is achieved. By changing the temperature, it also has adhesion in hot water, constructing a unique temperature-responsive underwater adhesion hydrogel. The preparation process is simple, the performance is excellent, and it is suitable for popularization and application.

[0014] Further, the amount ratio of 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] Further, the sintering temperature is 160℃, and the time is 0-5h, specifically 0h, 1h, 2h, 3h, 4h and 5h, preferably 3h.

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

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

[0018] The application discloses a temperature-responsive underwater-adhesive carbon nanodot-based Janus hydrogel, which is a conductive hydrogel capable of realizing temperature-regulated underwater adhesion based on carbon nanodots and is prepared from N-isopropyl acrylamide as a temperature-responsive material and aldehyde cellulose grafted dopamine. The dopamine is grafted onto dialdehyde cellulose and is sintered into carbon dots, so that excellent adhesion is achieved. The temperature is changed to enable the carbon nanodots to also have adhesion in hot water, a unique temperature-responsive underwater-adhesive hydrogel is constructed, and the adhesion is asymmetric. Specifically, when in room-temperature air, the A surface of the hydrogel has excellent adhesion, and the B surface has almost no adhesion. When the hydrogel is placed in 50 DEG C hot water, the B surface has underwater adhesion, and the A surface completely loses adhesion. The hydrogel has simple preparation process and excellent performance, and is suitable for promotion and application. BRIEF DESCRIPTION OF DRAWINGS

[0019] 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 other drawings can be obtained by those skilled in the art without any creative effort on the basis of the provided drawings.

[0020] Figure 1 The tensile strength and toughness strength strength columnar diagram of the hydrogel prepared for the examples and comparative examples are shown in the following table:

[0021] Figure 2 The adhesion peeling strength columnar diagram of the hydrogel prepared for the examples and comparative examples in air (T<50 DEG C) and water (T>50 DEG C) is shown in the following table:

[0022] Figure 3 The adhesion peeling strength columnar diagram of the hydrogel prepared for example 1 to polytetrafluoroethylene material is shown in the following table:

[0023] Figure 4 The adhesion peeling strength columnar diagram of the hydrogel prepared for example 1 after long-time storage in room-temperature air is shown in the following table:

[0024] Figure 5 Synthesis scheme for hydrogel preparation;

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

[0026] Figure 7 Adhesive peeling and AB face schematic of hydrogel. DETAILED DESCRIPTION

[0027] Various exemplary embodiments of the present application will now be described in detail, with reference to the figures. The detailed description is made with reference to the accompanying drawings, in which like elements are denoted by like reference numerals.

[0028] 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. Additionally, the use of the term "about" in the present application is intended to mean that the value is within a standard range of error for the particular measurement. In any statement of a value or range of values, the intermediate values of the range, and any other stated or intervening value of the range, are encompassed. The upper and lower limits of these smaller ranges can independently be included or excluded in the stated ranges.

[0029] 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 preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in full the methods and / or materials which are described herein. In the case of conflict between the present specification and any document incorporated herein by reference, the present specification will control.

[0030] Many modifications and variations of this application can be made in the light of the above teachings without departing from the spirit and scope thereof, and it is to be understood that all such modifications and variations warrant the patentable subject matter under the patent laws. 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. The specification and examples given are exemplary only.

[0031] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended terms that are intended to mean "including but not limited to".

[0032] Unless otherwise indicated, all temperatures are in degrees Celsius. All temperatures are room temperature, unless otherwise indicated.

[0033] The starting materials and reagents used in the embodiments of the present application are commercially available.

[0034] Example 1

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

[0036] S1, 0.5 g of dialdehyde cellulose and 0.5 g of dopamine were added to 100 mL of deionized water, and the mixture was heated to 160°C in a pressure-resistant reaction bottle for 3 h. The reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (CDs);

[0037] S2, 4 g of CDs, 2 g of 1-butyl-3-methylimidazolium chloride, 2.26 g of N-isopropyl acrylamide (NIPAM), 0.72 g of acrylic acid (AA) (the molar ratio of NIPAM to AA was 2:1), 0.06 g of ammonium persulfate, and 0.006 g of N,N'-methylenebisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0038] Example 2

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

[0040] S1, 1 g of dialdehyde cellulose and 1 g of dopamine were added to 100 mL of deionized water, and the mixture was heated to 160°C in a pressure-resistant reaction bottle for 3 h. The reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (2% CDs);

[0041] S2, 4 g of CDs, 2 g of 1-butyl-3-methylimidazolium chloride, 2.26 g of N-isopropyl acrylamide (NIPAM), 0.72 g of acrylic acid (AA) (the molar ratio of NIPAM to AA was 2:1), 0.06 g of ammonium persulfate, and 0.006 g of N,N'-methylenebisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0042] Example 3

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

[0044] S1, 0.75 g of dialdehyde cellulose and 0.75 g of dopamine were added to 100 mL of deionized water, and the mixture was heated to 160°C in a pressure-resistant reaction bottle for 3 h. The reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (1.5% CDs);

[0045] S2, 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropyl acrylamide (NIPAM), 0.72 g acrylic acid (AA) (molar ratio of NIPAM to AA is 2:1), 0.06 g ammonium persulfate and 0.006 g N,N'-methylenebisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain the temperature-regulated underwater-adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0046] Example 4

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

[0048] S1, 0.25 g dialdehyde cellulose and 0.25 g dopamine were added to 100 mL deionized water, placed in a pressure-resistant reaction bottle, heated to 160°C for 3 h, and the reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (0.5% CDs);

[0049] S2, 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropyl acrylamide (NIPAM), 0.72 g acrylic acid (AA) (molar ratio of NIPAM to AA is 2:1), 0.06 g ammonium persulfate and 0.006 g N,N'-methylenebisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain the temperature-regulated underwater-adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0050] Example 5

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

[0052] S1, 0.5 g dialdehyde cellulose and 0.5 g dopamine were added to 100 mL deionized water, placed in a pressure-resistant reaction bottle, heated to 160°C for 3 h, and the reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-3h);

[0053] S2, 4 g CDs, 2 g 1-butyl-3-methylimidazolium chloride, 2.26 g N-isopropyl acrylamide (NIPAM), 0.72 g acrylic acid (AA) (molar ratio of NIPAM to AA is 2:1), 0.06 g ammonium persulfate and 0.006 g N,N'-methylenebisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain the temperature-regulated underwater-adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0054] Example 6

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

[0056] S1, 0.5 g of dialdehyde cellulose and 0.5 g of dopamine were added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle, heated to 160°C for 3 h, and the reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-3h);

[0057] S2, 4 g of CDs, 3 g of 1-butyl-3-methylimidazolium chloride, 2.26 g of N-isopropyl acrylamide (NIPAM), 0.72 g of acrylic acid (AA) (molar ratio of NIPAM to AA is 2:1), 0.06 g of ammonium persulfate, and 0.006 g of N,Nˋ- methylene bisacrylamide were stirred uniformly and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater-adhesion conductive hydrogel (PAA-co-PNIPAM / CDs).

[0058] Example 7

[0059] The steps for preparing the hydrogel using different N-isopropyl acrylamide to acrylic acid ratios are as follows:

[0060] S1, 0.5 g of dialdehyde cellulose and 0.5 g of dopamine were added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle, heated to 160°C for 3 h, and the reaction vessel was 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-isopropyl acrylamide (NIPAM) (1.13 g), acrylic acid (AA) (0.72 g) (molar ratio of NIPAM to AA is 1:1), ammonium persulfate (0.06 g), and N,Nˋ- methylene bisacrylamide (0.006 g) were stirred uniformly and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater-adhesion conductive hydrogel (PAA-co-PNIPAM / CDs).

[0062] Example 8

[0063] The steps for preparing the hydrogel using different N-isopropyl acrylamide to acrylic acid ratios are as follows:

[0064] S1, 0.5 g of dialdehyde cellulose and 0.5 g of dopamine were added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle, heated to 160°C for 3 h, and the reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-3h);

[0065] S2, 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,N'-methylenebisacrylamide were stirred uniformly and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater-adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0066] Example 9

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

[0068] S1, 0.5 g of dialdehyde cellulose and 0.5 g of dopamine were added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle, heated to 160°C for 0 h, and the reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-0h);

[0069] S2, 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,N'-methylenebisacrylamide were stirred uniformly and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater-adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0070] Example 10

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

[0072] S1, 0.5 g of dialdehyde cellulose and 0.5 g of dopamine were added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle, heated to 160°C for 0 h, and the reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-0h);

[0073] S2, 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,N'-methylenebisacrylamide were stirred uniformly and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater-adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0074] Example 11

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

[0076] S1, 0.5 g of dialdehyde cellulose and 0.5 g of dopamine were added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle, heated to 160°C for 2 h, and the reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-2h);

[0077] S2, 4 g of CDs, 2 g of 1-butyl-3-methyl imidazolium chloride, 2.26 g of N-isopropyl acrylamide (NIPAM), 0.72 g of acrylic acid (AA), 0.06 g of ammonium persulfate, and 0.006 g of N,N'-methylene bisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0078] Example 12

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

[0080] S1, 0.5 g of dialdehyde cellulose and 0.5 g of dopamine were added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle, heated to 160°C for 2 h, and the reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-2h);

[0081] S2, 4 g of CDs, 2 g of 1-butyl-3-methyl imidazolium chloride, 2.26 g of N-isopropyl acrylamide (NIPAM), 0.72 g of acrylic acid (AA), 0.06 g of ammonium persulfate, and 0.006 g of N,N'-methylene bisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0082] Example 13

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

[0084] S1, 0.5 g of dialdehyde cellulose and 0.5 g of dopamine were added to 100 mL of deionized water, placed in a pressure-resistant reaction bottle, heated to 160°C for 2 h, and the reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-2h);

[0085] S2, 4 g of CDs, 2 g of 1-butyl-3-methyl imidazolium chloride, 2.26 g of N-isopropyl acrylamide (NIPAM), 0.72 g of acrylic acid (AA), 0.06 g of ammonium persulfate, and 0.006 g of N,N'-methylene bisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater adhesive conductive hydrogel (PAA-co-PNIPAM / CDs).

[0086] Comparative Example 1

[0087] The procedure for preparing the hydrogel without using 1-butyl-3-methylimidazolium chloride (ionic liquid) is as follows:

[0088] S1, 0.5 g of dialdehyde cellulose and 0.5 g of dopamine were added to 100 mL of deionized water, and placed in a pressure-resistant reaction bottle and heated to 160°C for 3 h. The reaction vessel was naturally cooled to room temperature to obtain a carbon nanodot solution (CDs-3h);

[0089] S2, 4 g of CDs, 2 g of water, 2.26 g of N-isopropyl acrylamide (NIPAM), 0.72 g of acrylic acid (AA), 0.06 g of ammonium persulfate, and 0.006 g of N,N'-methylenebisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater-adhesion conductive hydrogel (PAA-co-PNIPAM / CDs).

[0090] Comparative Example 2

[0091] The procedure for preparing the hydrogel without using a carbon nanodot solution is as follows:

[0092] S1, 4 g of water, 2 g of 1-butyl-3-methylimidazolium chloride, 2.26 g of N-isopropyl acrylamide (NIPAM), 0.72 g of acrylic acid (AA), 0.06 g of ammonium persulfate, and 0.006 g of N,N'-methylenebisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater-adhesion conductive hydrogel (PAA-co-PNIPAM).

[0093] Comparative Example 3

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

[0095] S1, 6 g of water, 2.26 g of N-isopropyl acrylamide (NIPAM), 0.72 g of acrylic acid (AA), 0.06 g of ammonium persulfate, and 0.006 g of N,N'-methylenebisacrylamide were stirred uniformly, and then placed in an oven at 80°C for one hour to obtain a temperature-regulated underwater-adhesion 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 testing and mechanical performance testing, the methods being as follows, and the results being shown in Table 1.

[0098] The hydrogels prepared in Example 1 and Comparative Examples 1-9 were cut into rectangular shapes (4 cm x 6 mm x 2 mm) for mechanical property testing. The instrument used was an electronic universal testing machine (Sunshine Technology Co., Ltd., Shenzhen, China) with an extension speed of 80 mm / min.

[0099] Toughness was calculated according to the area under the stress-strain curve, by the following formula:

[0100] ΔU = ∫σdε

[0101] In the formula, 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 samples (3.2 cm x 2 cm x 3 mm) for adhesive peeling tests in room temperature air and 50°C hot water. Since the hydrogels were prepared by molding with a polytetrafluoroethylene mold, the side that adhered to the polytetrafluoroethylene was called the A side, and the side that was exposed to the air was called the B side.

[0103] Table 1

[0104]

[0105]

[0106] As can be seen from the data in Table 1, the hydrogel prepared in Example 1 had the largest toughness, which could reach 571.35 kJ / m 3 . And in terms of adhesion, whether in room temperature air or under water at 50°C, the performance of Example 1 was also the best, reaching 237.8 N / m and 47.75 N / m, respectively. Example 5 used only 1 g of 1-butyl-3-methylimidazolium chloride, and in this case, the N-isopropyl acrylamide could not be dissolved, so the hydrogel could not be successfully prepared. Examples 9 and 10 could not be successfully polymerized to form hydrogels because carbonization was not performed and the preparation time of the carbon nanodots was not sufficient. Comparative Example 1 and Comparative Example 3 did not add 1-butyl-3-methylimidazolium chloride, so the N-isopropyl acrylamide could not be dissolved and could not be polymerized to form a hydrogel. Comparative Example 2 did not add carbon nanodots, so not only was the adhesion very low, but it also did not have the underwater adhesion property.

[0107] Figure 1 A bar graph of the tensile strength and toughness of the hydrogels prepared in the examples and comparative examples is shown in Figure 1 As can be seen, the tensile strength of the hydrogel prepared using carbon nanodots calcined for 3 hours could reach 172.34 kPa, and the toughness could reach 571.35 kJ / m, which was higher than that of Example 1 in terms of tensile strength, but in terms of comprehensive mechanical properties, Example 1 was still the best.

[0108] The above experimental results fully demonstrate that by adjusting the concentration of carbon nanodots, the concentration of ionic liquid, the ratio of NIPAM and AA, and the carbon nanodot baking time, the mechanical properties of the hydrogel can be optimized. The concentration and preparation time of carbon nanodots are because the carbon dots after baking have optimized surface properties and graphitization, which makes them more firmly combined with the hydrogel, thereby improving the mechanical properties. While increasing the concentration and preparation time may cause the carbon nanodot surface or core structure to aggregate or crack, resulting in poor dispersion of the carbon nanodots, thereby affecting the mechanical properties. Examples 9 and 10 failed to form a hydrogel due to insufficient or excessive carbon nanodot preparation time, and thus their performance could not be tested. Increasing the cations or anions in the ionic liquid can interact with the functional groups on the polymer chains of the hydrogel (such as carboxyl, hydroxyl, or amine groups, etc.) through physical or chemical interactions, which can increase the crosslinking density between the polymer chains at the molecular level, thereby improving the mechanical strength of the hydrogel. While 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 The adhesion peel strength column chart of the hydrogel prepared for the examples and comparative examples is shown in FIG. 3. Figure 2 It can be seen that the hydrogel prepared by the carbon nanodots baked for 3h has stable adhesion in both room temperature air and 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 the carbon nanodots baked for 3h is far superior to them, reaching 237.8N / m in room temperature air and 47.75N / m under 50℃ water.

[0110] Figure 3 The adhesion peel column chart of the hydrogel prepared for Example 1 to the polytetrafluoroethylene plate. The hydrogel was prepared using a polytetrafluoroethylene mold, and the hydrogel was divided into A and B sides, the A side was the side close to the mold, and the B side was the side exposed to the air. It can be seen that the A side has an adhesion strength of 52.8N / m in room temperature air, but has no adhesion under 50℃ water; while the B side is just the opposite, it has an adhesion of 8.4N / m under 50℃ water, but the adhesion in room temperature air is very low. This is due to the temperature responsiveness of N-isopropyl acrylamide, which changes from a chain conformation to a hydrophobic spherical conformation at 50℃, allowing the catechol structure of the hydrogel to be exposed to perform adhesion. At the same time, the adhesion difference between the two sides also provides convenience for use.

[0111] Figure 4For the test column chart of the long-time exposure in air, adhesion durability of Example 1, it can be seen from the chart that the hydrogel still showed excellent adhesion stability after being placed in air for 1 day, 3 days, 7 days, 15 days and 30 days respectively, and proved that it has certain self-recovery ability and long-term adhesion performance, which ensures the convenience in actual use.

[0112] The above-described embodiments are only used to describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

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 firing temperature is 160°C and the firing time is 2-4 hours; The carbon nanodot solution, N-isopropylacrylamide (NIPAM), acrylic acid (AA), 1-butyl-3-methylimidazolium chloride, 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; The usage 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.

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.

3. The preparation method according to claim 1, characterized in that The molar ratio of N-isopropylacrylamide NIPAM to acrylic acid AA is 1-3:1, and the stirring time is 30 minutes.

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 adhesive carbon nanodot-based Janus hydrogel.

6. Use of 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, or a conductive hydrogel with temperature-controlled underwater adhesion based on carbon nanodots according to claim 5 in flexible electronics, biosensing, environmental monitoring and smart materials.

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