CN114478923B

CN114478923B - High-toughness antifreezing conductive hydrogel and preparation method thereof

Info

Publication number: CN114478923B
Application number: CN202210283256.2A
Authority: CN
Inventors: 高传慧; 王彦庆; 王日璇; 陈丕成; 周新婕; 刘月涛; 武玉民
Original assignee: Qingdao University of Science and Technology
Current assignee: Qingdao University of Science and Technology
Priority date: 2022-03-22
Filing date: 2022-03-22
Publication date: 2023-09-15
Anticipated expiration: 2042-03-22
Also published as: CN114478923A

Abstract

The invention relates to a preparation method of hydrogel, in particular to high-toughness antifreezing conductive hydrogel and a preparation method thereof, and belongs to the field of polymer preparation. The hydrogel is prepared from polyvinyl alcohol, acrylamide, N-vinyl pyrrolidone, sodium alginate and glycerin monomers serving as raw materials, borax serving as a cross-linking agent of the polyvinyl alcohol, N-methylene bisacrylamide serving as a cross-linking agent of the acrylamide, potassium persulfate serving as an initiator through free radical reaction, and finally, a final product is obtained through post-treatment by a drying-swelling method. The hydrogel prepared by the invention has higher toughness and anti-freezing performance, and the cost of the selected raw materials is lower, so that the hydrogel has wide market prospect. Simple steps, convenient operation and strong practicability.

Description

High-toughness antifreezing conductive hydrogel and preparation method thereof

Technical Field

The invention relates to a preparation method of hydrogel, in particular to a preparation method of high-toughness antifreezing conductive hydrogel, and belongs to the field of polymer preparation.

Background

The disclosure of this background section is only intended to increase the understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art already known to those of ordinary skill in the art.

Hydrogels are a class of polymeric materials that have a three-dimensional cross-linked network structure and contain a large amount of water within. In the gel network, water molecules are tightly combined with hydrophilic groups of polymer chains, and the polymer chains are converted from a liquid state which is difficult to process at normal temperature and normal pressure into a quasi-solid state with limited fluidity. Therefore, the hydrogel material has both good solid mechanical property and fluid thermodynamic property of the traditional bulk phase material. The hydrogel is used as a soft material with water as a main component, has strong plasticity, good elasticity and biocompatibility, and has great application prospect in the fields of soft robots, intelligent brakes, tissue engineering, flexible electronic devices and the like.

Flexible electronics with significant electrical conductivity and similar sensing functions to human skin are of great importance in advancing human epidermis detection, implantable sensors and real-time monitoring sensors. In general, these devices should have suitable mechanical toughness, elastic modulus matching that of the human body, and high sensitivity to effectively convert physiological parameters into detectable electrical signals. Among the different types of sensing materials, hydrogels are used as a highly hydrophilic three-dimensional network structure gel, and deformed and tough conductive hydrogels are one of the most suitable sensor candidate materials. The sensor has adjustable biocompatibility elastic modulus, has mechanical properties designed according to requirements, and covers all moduli of human tissues so as to be suitable for sensing application.

However, conventional hydrogels typically use water as the electron ionic medium. Although electrical and mechanical properties are obtained, most composite hydrogels are not capable of withstanding extreme environments and are not environmentally stable. It will dry at high temperature and freeze below zero. Even at room temperature, hydrogels inevitably lose water, resulting in poor mechanical hardening and deformability, impeding the environmental stability and operational durability of the electrical devices that can be performed. Ion-conducting hydrogels are particularly attractive because of their simple manufacturing process, low cost, and high conductivity, however, while the abundance of water in ion-conducting hydrogels can provide desirable conductivity and efficient ion transport, they often result in insufficient mechanical strength, while the poor freezing resistance of ion-conducting hydrogels limits their use in extremely cold environments. This is because a large amount of water in the hydrogel is inevitably frozen at a sub-zero temperature, thereby affecting the mechanical elasticity and ion transport capacity of the hydrogel.

Disclosure of Invention

The invention aims to overcome the defects in the existing materials and provide high-toughness anti-freezing conductive hydrogel and a preparation method thereof.

In order to achieve the technical purpose, the invention adopts the following technical scheme:

in a first aspect of the invention, a method for preparing a high-toughness, anti-freezing conductive hydrogel is provided, comprising:

sequentially adding polyvinyl alcohol, acrylamide, N-vinyl pyrrolidone, a cross-linking agent of the acrylamide, a cross-linking agent of the polyvinyl alcohol and an initiator into the sodium alginate solution, uniformly mixing, and heating for copolymerization to obtain hydrogel;

and drying and swelling the hydrogel to obtain the hydrogel.

Sodium Alginate (SA) is a natural and cheap polysaccharide, consists of two substitution units of alpha-Lgulonic acid and P-D-mannonic acid, is paid attention to because of good biocompatibility and biodegradability, and has wide application in the fields of chemistry, biology, medicine and food. Besides good biocompatibility, sodium alginate can also be used as polyelectrolyte, so that the hydrogel has good conductivity. In addition, the sodium alginate can also improve the mechanical strength in the hydrogel system. Conventional acrylamide hydrogels tend to be very low in strength, so we introduce N-vinylpyrrolidone into the system to form a co-polymer system with acrylamide to enhance the strength of the hydrogel. Meanwhile, the PVA microcrystal in the composite hydrogel is induced to form by a drying-swelling method, and the method can effectively improve the mechanical property of the hydrogel.

The research finds that: the glycerol can form a strong hydrogen bond with water molecules as an organic solvent, so that the ice crystal lattice is destroyed below zero to achieve the anti-freezing effect, and meanwhile, the water is prevented from evaporating. Furthermore, one glycerol molecule may provide three hydroxyl groups; therefore, glycerol can also act as a cross-linking agent for the polyvinyl alcohol chains, thereby improving the strength and toughness of the polyvinyl alcohol hydrogel. The polyvinyl alcohol can form boric acid ester bonds with borax solution to endow the system with good self-repairing effect. Meanwhile, rich hydroxyl groups on the polyvinyl alcohol chain can form compact hydrogen bonds with polyacrylamide and sodium alginate, so that the hydrogel is endowed with excellent toughness.

In a second aspect of the invention, a high-toughness, anti-freeze conductive hydrogel prepared by the method is provided.

In a third aspect of the invention, there is provided the use of the hydrogels in the manufacture of soft robots, smart brakes, tissue engineering and flexible electronics.

The invention has the beneficial effects that:

(1) The preparation process of the invention fully utilizes the viscosity characteristic of sodium alginate, and the conductive hydrogel mixed with sodium alginate has good mechanical strength and good conductivity.

(2) The introduction of the glycerol can form stronger hydrogen bonds with water molecules, damage ice lattices at the temperature below zero to achieve the anti-freezing effect, and can also be used as a cross-linking agent of a polyvinyl alcohol chain to improve the mechanical strength of the hydrogel.

(3) The drying-swelling method is further adopted to treat the hydrogel, so that PVA can be induced to crystallize, and the mechanical property and stability of the hydrogel are improved.

(4) The preparation method of the invention has the advantages of simplicity, low price, strong practicability and easy popularization

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.

FIG. 1 is a stress-strain diagram of hydrogels prepared in examples, wherein 5% -9% represents the sodium alginate content of the system.

FIG. 2 is a stress-strain diagram of hydrogels with different glycerol contents, wherein 0% -30% represents the glycerol content in the system.

FIG. 3 is a graph showing the toughness of hydrogels with different glycerol contents.

FIG. 4 is a plot of DSC for hydrogels with different glycerol contents.

Fig. 5 is an electrical signal of a conductive hydrogel as a strain sensor.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. 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 invention belongs.

A high-toughness antifreezing conductive hydrogel is prepared by adding sodium alginate and glycerin in different proportions into a polyvinyl alcohol, acrylamide and N-vinyl pyrrolidone hydrogel system. And then drying-swelling treatment is carried out to obtain the final product. In the system, the adding amount of sodium alginate is 5% -9% and the adding amount of glycerol is 0% -30%.

In some embodiments, sodium alginate is dissolved in water with heating and stirring, and then cooled to room temperature. Adding polyvinyl alcohol, acrylamide, N-vinyl pyrrolidone, potassium persulfate, N-methylene bisacrylamide and borax into the solution, heating in a water bath at 50-80 ℃, and copolymerizing the acrylamide and the N-vinyl pyrrolidone in the system to obtain the hydrogel. The resulting hydrogel is then completely dried and soaked in water to re-swell to give the final product.

In some embodiments, the optimal amount of sodium alginate added to the hydrogel is selected and then glycerol is added to the hydrogel system.

The invention will now be described in further detail with reference to the following specific examples, which should be construed as illustrative rather than limiting.

Example 1:

sodium alginate with the mass content of 5% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate and 5g of a borax solution of 0.6% by weight were added to the above solution. Stirring for one hour, and heating in water bath at 60 deg.c for 4-6 hr to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Example 2:

sodium alginate with the mass content of 6% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate and 5g of a borax solution of 0.6% by weight were added to the above solution. Stirring for one hour, and heating in water bath at 60 deg.c for 4-6 hr to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Example 3: sodium alginate with the mass content of 7% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate and 5g of a borax solution of 0.6% by weight were added to the above solution. Stirring for one hour, and heating in water bath at 60 deg.c for 4-6 hr to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Example 4: sodium alginate with the mass content of 8% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate and 5g of a borax solution of 0.6% by weight were added to the above solution. Stirring for one hour, and heating in water bath at 60 deg.c for 4-6 hr to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Example 5: sodium alginate with the mass content of 9% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate and 5g of a borax solution of 0.6% by weight were added to the above solution. Stirring for one hour, and heating in water bath at 60 deg.c for 4-6 hr to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Example 6: as shown in fig. 1, it can be seen from the stress strain diagram that the hydrogel has a good mechanical property at a sodium alginate content of 5%. The ratio was thus selected for the following experiments. Sodium alginate with the mass content of 7% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate, 5g of a 0.6% strength by weight borax solution and 5% glycerol were added to the above solution. Stirring for one hour, and heating in water area of 60 deg.c for 4-6 hr to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Example 7: sodium alginate with the mass content of 7% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate, 5g of a 0.6% strength by weight borax solution and 5% by mass of glycerol were added to the above solution. Stirring for one hour, and heating in water bath at 60 deg.c for 4-6 hr to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Example 8: sodium alginate with the mass content of 7% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate, 5g of a 0.6% strength by weight borax solution and 10% by mass of glycerol were added to the above solution. Stirring for one hour, and heating in water bath at 60 deg.c for 4-6 hr to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Example 9: sodium alginate with the mass content of 7% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate, 5g of a 0.6% strength by weight borax solution and 20% by mass of glycerol were added to the above solution. Stirring for one hour, and heating in water bath at 60 deg.c for 4-6 hr to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Example 10: sodium alginate with the mass content of 7% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate, 5g of a 0.6% strength by weight borax solution and 30% by mass of glycerol were added to the above solution. Stirring for one hour, and heating in water bath at 60 deg.c for 4-6 hr to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Comparative example 1:

16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate and 5g of borax solution with the concentration of 0.6wt% are mixed, stirred for one hour, and then placed in a water bath with the temperature of 60 ℃ for heating for 4-5 hours to obtain hydrogel. The resulting hydrogel was dried completely in an oven at 50-60 c, and then the dried gel was soaked in water for 2 hours to re-swell to obtain the final product.

Comparative example 2:

sodium alginate with the mass content of 7% is dissolved in a certain amount of water and heated at 90 ℃ until the sodium alginate is fully dissolved. After cooling to room temperature, 16g of polyvinyl alcohol, 4g of acrylamide, 2g N-vinylpyrrolidone, 0.01g of N, N-methylenebisacrylamide, 0.04g of potassium persulfate, 5g of a borax solution of 0.6wt% concentration were added to the above solution. Stirring for one hour, and heating in water bath at 60 deg.c for 4-6 hr to obtain hydrogel. The prepared hydrogel is placed in an oven at 50-60 ℃ to be completely dried, and then the dried gel is soaked in water for 2-4 hours to be swelled again, so that the final product is obtained.

As shown in fig. 2 and 3, the stress-strain curve and the toughness of the corresponding ratio of the hydrogels obtained in the examples are shown. From this, it is found that as the glycerol content increases, the stress and strain tend to increase and then decrease. It can also be seen that the toughness of the hydrogel reached a maximum at a glycerol content of 10%.

As shown in FIG. 4, with the increase of the glycerol content, the freezing point of the hydrogel is gradually reduced, and the hydrogel has good anti-freezing effect, and glycerol with different proportions can be selected according to the requirements of different applications.

As shown in fig. 5, the hydrogel as a strain sensor can deliver good electrical signals.

Finally, it should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and the present invention is not limited to the above-mentioned embodiments, but may be modified or substituted for some of them by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The preparation method of the high-toughness antifreezing conductive hydrogel is characterized by comprising the following steps of:

drying and swelling the hydrogel to obtain the hydrogel;

the content of the sodium alginate is 5% -9%;

the cross-linking agent of the polyvinyl alcohol is borax and glycerol;

the content of glycerol is 5-30%;

the mass ratio of the polyvinyl alcohol, the acrylamide and the N-vinyl pyrrolidone is 16:4:2.

2. the method for preparing the high-toughness antifreezing conductive hydrogel according to claim 1, wherein the copolymerization reaction is carried out at 50-80 ℃ for 4-6 hours.

3. The method for preparing the high-toughness antifreezing conductive hydrogel according to claim 1, wherein the cross-linking agent of the acrylamide is N, N-methylene bisacrylamide.

4. The method for preparing the high-toughness antifreezing conductive hydrogel according to claim 1, wherein the initiator is potassium persulfate.

5. The method for producing a high-toughness, antifreeze, electrically conductive hydrogel according to claim 1, wherein the drying temperature in the drying-swelling treatment is 50 to 60 ℃.

6. The method for preparing the high-toughness antifreezing conductive hydrogel according to claim 1, wherein the swelling time is 2-4h.

7. The high toughness, freeze-protected electrically conductive hydrogel made by the method of any one of claims 1-6.

8. Use of the hydrogel of claim 7 in the manufacture of soft robots, smart stoppers, tissue engineering and flexible electronic devices.