Self-healing double-network structure conductive hydrogel of temperature-sensitive sensor and preparation method of self-healing double-network structure conductive hydrogel

Abstract

The invention relates to the technical field of hydrogel, and discloses a self-healing double-network structure conductive hydrogel of a temperature-sensitive sensor and a preparation method of the self-healing double-network structure conductive hydrogel. Monovinyl-terminated polydimethylsiloxane and acrylamide are used as chemical cross-linking agents, octadecyl methacrylate micelle of dodecyl acrylate is used as a physical cross-linking agent, and the self-healing double-network structure conductive hydrogel of the temperature-sensitive sensor is prepared through a hydrothermal method. According to the physical-chemical bi-crosslinking conductive hydrogel produced by copolymerization of the silver nanowires serving as conductive substances, the stretchability, the strength and the rebound resilience of the hydrogel are greatly improved, meanwhile, interaction of physical-chemical interpenetrating network crosslinking structures is beneficial to ion migration, free moving ions with the maximum concentration can be released, and the tensile strength, the strength and the rebound resilience of the hydrogel are improved. The ion migration rate and the conductivity are improved, and sensitive transmission of signals is facilitated. The conductive hydrogel not only shows high stretchability, high strength and high rebound resilience, but also has unique self-healing performance.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, specifically relating to a self-healing thermosensitive hydrogel for use in temperature sensors and its preparation method. Background Technology

[0002] Hydrogels, as a type of soft material, play an irreplaceable role in the field of flexible electronic devices. Conductive hydrogels can be prepared by combining traditional hydrogels with conductive polymers or conductive nanoparticles. Conductive hydrogels, as the name suggests, are hydrogels that respond to electrical signals. The addition of conductive materials not only does not compromise the flexibility of the hydrogel but also endows it with excellent electrical properties. These hydrogels combine the flexibility of traditional hydrogels with the electrochemical properties of conductive materials and are commonly used in flexible wearable electronic devices, biosensors, capacitors, and other applications.

[0003] Dual-network hydrogels are typically composed of two polymer backbones with opposite properties. A highly cross-linked, rigid polyelectrolyte network is called the first network, while a less cross-linked, flexible, neutral polymer network is called the second network. These two networks interweave to form the dual-network structure. Although both individual networks have poor mechanical properties, the interwoven dual-network structure perfectly combines their advantages. The introduction of high cross-linking and energy dissipation mechanisms gives dual-network hydrogels both high strength and high toughness.

[0004] Despite the rapid development of stretchable electronic devices and flexible devices, significant challenges remain in fabricating stretchable devices with practical applications. The flexibility of these devices requires that the conductive materials also be flexible, and hydrogels offer significant advantages due to their excellent stretchability and resilience. Currently fabricated supercapacitors generally lack self-healing properties; once damaged during repeated stretching and bending, their lifespan will be severely reduced. Researchers have developed various methods for preparing conductive hydrogels, but reports on hydrogels with high elasticity, conductive stability, and self-healing properties are limited. Therefore, improving the conductivity of self-healing hydrogels to adapt to the development of flexible electronic sensors is a pressing issue that needs to be addressed. Summary of the Invention

[0005] To overcome the shortcomings of existing conductive hydrogels, such as poor tensile properties and inability to achieve self-healing, the present invention aims to provide a self-healing conductive hydrogel and its preparation method, which solves the problems of poor tensile properties, poor conductivity and mechanical properties of existing conductive hydrogels, so as to meet the actual needs of flexible temperature sensors for accurate monitoring of various moving objects.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a self-healing conductive hydrogel, comprising the following steps: Step (1), adding octadecyl methacrylate to a sodium dodecyl sulfate solution and stirring thoroughly to obtain a sodium dodecyl sulfate octadecyl methacrylate micelle solution;

[0008] Step (2): Dissolve monovinyl-terminated polydimethylsiloxane in deionized water and sonicate until completely dissolved to form a self-assembled nanoparticle solution. Mix the sodium dodecyl sulfate methacrylate micelle solution with the nanoparticle solution and stir thoroughly. Add silver nanowires while stirring and then sonicate until uniformly dispersed.

[0009] In step (3), acrylamide, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine are added sequentially to the dispersion obtained in step (2), and the mixture is stirred vigorously to form a reactant solution. Finally, the reactant solution is transferred to a mold and a polymerization reaction occurs to obtain a self-healing conductive hydrogel.

[0010] Furthermore, the structural formula of monovinyl-terminated polydimethylsiloxane is as follows:

[0011]

[0012] Furthermore, in step (1), sodium dodecyl sulfate is insoluble in water; therefore, the sodium dodecyl sulfate solution is prepared using a sodium chloride solution of a certain concentration as a solvent.

[0013] Further, in step (1), the mixture is stirred thoroughly for 2-3 hours to obtain a sodium dodecyl sulfate methacrylate micelle solution.

[0014] Furthermore, the mass ratio of sodium dodecyl sulfate to octadecyl methacrylate is 1:0.672.

[0015] Furthermore, the mass ratio of monovinyl-terminated polydimethylsiloxane to silver nanowires is 1:0.12.

[0016] Furthermore, the mass ratio of monovinyl-terminated polydimethylsiloxane to acrylamide is 1:0.24-0.96.

[0017] Furthermore, in step (2), the sodium dodecyl sulfate methacrylate micelle solution and the nanoparticle solution are stirred thoroughly for 2-3 hours.

[0018] Furthermore, the mass ratio of sodium dodecyl sulfate, acrylamide, and ammonium persulfate is 1:0.70:0.04, and the ratio of N,N,N',N'-tetramethylethylenediamine to sodium dodecyl sulfate is 5-25 μL:1-5 g.

[0019] In a second aspect, the present invention provides a self-healing conductive hydrogel prepared by the method described in the first aspect.

[0020] Thirdly, the present invention provides the use of the self-healing conductive hydrogel prepared by the method described in the first aspect in the preparation of a flexible temperature sensor.

[0021] Furthermore, flexible temperature sensors are used in the fabrication of electronic skin, intelligent equipment, flexible intelligent robots, foldable displays, and tensile strain testing equipment.

[0022] Compared with existing technologies, the advantages of this invention are as follows: This invention provides a conductive hydrogel containing hydrophilic and hydrophobic micelles, its preparation method, and its applications. It offers advantages such as fast physicochemical crosslinking reaction speed, simple conditions, and ease of operation, allowing for rapid polymer curing and high production efficiency. The introduction of silver nanowires improves the tensile and electrical properties of the photocurable conductive hydrogel, enabling the development of stable hydrogels adaptable to flexible, temperature-sensitive environments. The prepared hydrophilic and hydrophobic silver nanowire conductive hydrogel exhibits good self-healing properties, excellent mechanical properties, superior electrical conductivity, high sensitivity, and rapid response, showing promising application prospects. Detailed Implementation

[0023] The present application will be further described below with reference to specific embodiments.

[0024] It should be noted that terms such as "upper", "lower", "left", "right", and "middle" used in this specification are only for clarity of description and are not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of this application.

[0025] Unless otherwise defined, 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 pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0026] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0027] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0028] Conductive hydrogels combine the excellent flexibility of hydrogels with the conductivity and electrochemical responsiveness of conductive materials, and are widely used in biomedical engineering, bioelectrodes, flexible energy storage devices, sensors, and conductive adhesives. Although conductive hydrogels offer many advantages, their high water content presents significant challenges in preparing high-strength, highly resilient, and rapidly responsive conductive hydrogels. Traditional conductive hydrogels often contain excessively high levels of rigid components, resulting in poor mechanical properties that severely limit their applications.

[0029] In view of this, the present invention incorporates silver nanowires as a conductive material into a physicochemically cross-linked hydrogel formed by a solution of monovinyl-terminated polydimethylsiloxane and sodium dodecyl sulfate octadecyl methacrylate micelles. Through multiple cross-linking mechanisms involving free radical copolymerization of hydrophilic acrylamide, physical cross-linking agent (sodium dodecyl sulfate octadecyl methacrylate micelles), chemical cross-linking agent (monovinyl-terminated polydimethylsiloxane), and silver nanowire nanoparticles, along with the conductive nanomaterial, the mechanical and electrical properties are enhanced. The resulting conductive hydrogel not only exhibits high stretchability, high strength, and high resilience, but also possesses unique self-healing properties. This conductive hydrogel is used to prepare flexible temperature-sensitive sensors.

[0030] Sodium dodecyl sulfate octadecyl methacrylate micelles act as physical crosslinking agents, enhancing the toughness and self-healing properties of hydrogels. Monovinyl-terminated polydimethylsiloxanes can self-assemble into micelles in aqueous solution and act as multifunctional crosslinking agents. Physical-chemical dual crosslinking is achieved through free radical copolymerization of vinyl groups and the crosslinking agent. Due to the multiple crosslinking points present in monovinyl-terminated polydimethylsiloxanes, these micelles significantly improve the stretchability, strength, and resilience of the hydrogel. The reversibility of sodium dodecyl sulfate octadecyl methacrylate micelles allows them to reassemble under certain conditions after breakage. Therefore, the resulting conductive hydrogel not only exhibits high stretchability, high strength, and high resilience but also possesses unique self-healing properties.

[0031] Unless otherwise specified in the examples, the procedures were performed under standard conditions or conditions recommended by the manufacturer. Reagents and instruments used, unless otherwise specified, were all commercially available products. Specifically, monovinyl-terminated polydimethylsiloxane was commercially available with a molecular weight of 1000. Silver nanowires (Ag NWs) were commercially available with a length of 70 nm and a solubility of 20 μL / mL in aqueous solution.

[0032] Example 1

[0033] (1) Add 1.0 g of sodium dodecyl sulfate to 5 mL of 0.5 M NaCl solution and sonicate until transparent to obtain a sodium dodecyl sulfate solution. Then add 0.672 g of octadecyl methacrylate to the sodium dodecyl sulfate solution and stir at 35 °C for 2 h to obtain a sodium dodecyl sulfate octadecyl methacrylate micelle solution.

[0034] (2) Dissolve 2.90g of self-made monovinyl-terminated polydimethylsiloxane monomer in 5mL of deionized water and self-assemble it into an aqueous solution of nanoparticles by ultrasonic treatment.

[0035] (3) Mix the sodium dodecyl sulfate methacrylate micelle solution and the monovinyl-terminated polydimethylsiloxane monomer nanoparticle solution evenly, add 0.36 g of Ag NWs under stirring, and then sonicate until evenly dispersed.

[0036] (4) 0.7 g acrylamide, 0.04 g ammonium persulfate, and N,N,N',N'-tetramethylethylenediamine (5 μL) were dissolved in the dispersion from step (3) by vigorous stirring to form a reactant solution. Finally, the reactant solution was transferred to a mold and polymerized in an oven at 55 °C to obtain conductive hydrogel product 1.

[0037] Example 2

[0038] (1) Add 2.0 g of sodium dodecyl sulfate to 10 mL of 0.5 M NaCl solution and sonicate until transparent to obtain a sodium dodecyl sulfate solution. Then add 0.1344 g of octadecyl methacrylate to the sodium dodecyl sulfate solution and stir at 35 °C for 2 h to obtain a sodium dodecyl sulfate octadecyl methacrylate micelle solution. (2) The prepared 2.90g of monovinyl-terminated polydimethylsiloxane monomer was dissolved in 5mL of deionized water and self-assembled into an aqueous solution of nanoparticles by ultrasonic treatment.

[0039] (3) Mix the sodium dodecyl sulfate methacrylate micelle solution and the silicon monomer nanoparticle solution evenly, add 0.43 g of silver nanowires under stirring, and then sonicate until evenly dispersed.

[0040] (4) 1.4 g acrylamide, 0.08 g ammonium persulfate, and N,N,N',N'-tetramethylethylenediamine (10 μL) were dissolved in the dispersion from step (3) by vigorous stirring to form a reactant solution. Finally, the reactant solution was transferred to a mold and polymerized in an oven at 55 °C to obtain conductive hydrogel product 2.

[0041] Example 3

[0042] (1) Add 3.0 g of sodium dodecyl sulfate to 15 mL of 0.5 M NaCl solution and sonicate until transparent to obtain a sodium dodecyl sulfate solution. Then add 0.2016 g of octadecyl methacrylate to the sodium dodecyl sulfate solution and stir at 35 °C for 2 h to obtain a sodium dodecyl sulfate octadecyl methacrylate micelle solution. (2) The prepared 2.90g of monovinyl-terminated polydimethylsiloxane monomer was dissolved in 5mL of deionized water and self-assembled into an aqueous solution of nanoparticles by ultrasonic treatment.

[0043] (3) Mix the sodium dodecyl sulfate methacrylate micelle solution and the monovinyl-terminated polydimethylsiloxane monomer nanoparticle solution evenly, add 0.50 g of silver nanowires under stirring, and then sonicate until evenly dispersed.

[0044] (4) 2.1 g acrylamide, 0.12 g ammonium persulfate, and N,N,N',N'-tetramethylethylenediamine (15 μL) were dissolved in the dispersion of step (3) by vigorous stirring to form a reactant solution. Finally, the reactant solution was transferred to a mold and polymerized in an oven at 55 °C to obtain conductive hydrogel product 3.

[0045] Example 4

[0046] (1) Add 4.0 g of sodium dodecyl sulfate to 20 mL of 0.5 M NaCl solution and sonicate until transparent to obtain a sodium dodecyl sulfate solution. Then add 0.2688 g of octadecyl methacrylate to the sodium dodecyl sulfate solution and stir at 35 °C for 2 h to obtain a sodium dodecyl sulfate octadecyl methacrylate micelle solution. (2) The prepared 2.90g of monovinyl-terminated polydimethylsiloxane monomer was dissolved in 5mL of deionized water and self-assembled into an aqueous solution of nanoparticles by ultrasonic treatment.

[0047] (3) Mix the sodium dodecyl sulfate methacrylate micelle solution and the monovinyl-terminated polydimethylsiloxane monomer nanoparticle solution evenly, add 0.57 g of silver nanowires under stirring, and then sonicate until evenly dispersed.

[0048] (4) 2.8 g acrylamide, 0.16 g ammonium persulfate, and N,N,N',N'-tetramethylethylenediamine (20 μL) were dissolved in the dispersion from step (3) by vigorous stirring to form a reactant solution. Finally, the reactant solution was transferred to a mold and polymerized in an oven at 55 °C to obtain conductive hydrogel product 4.

[0049] Example 5

[0050] (1) Add 5.0 g of sodium dodecyl sulfate to 25 mL of 0.5 M NaCl solution and sonicate until transparent to obtain a sodium dodecyl sulfate solution. Then add 0.3360 g of octadecyl methacrylate to the sodium dodecyl sulfate solution and stir at 35 °C for 2 h to obtain a sodium dodecyl sulfate octadecyl methacrylate micelle solution. (2) The prepared 2.90g of monovinyl-terminated polydimethylsiloxane monomer was dissolved in 5mL of deionized water and self-assembled into an aqueous solution of nanoparticles by ultrasonic treatment.

[0051] (3) Mix the sodium dodecyl sulfate methacrylate micelle solution and the monovinyl-terminated polydimethylsiloxane monomer nanoparticle solution evenly, add 0.64 g of silver nanowires under stirring, and then sonicate until evenly dispersed.

[0052] (4) 3.5 g acrylamide, 0.20 g ammonium persulfate, and N,N,N',N'-tetramethylethylenediamine (25 μL) were dissolved in the dispersion from step (3) by vigorous stirring to form a reactant solution. Finally, the reactant solution was transferred to a mold and polymerized in an oven at 55 °C to obtain the conductive hydrogel product 5.

[0053] Comparative Example 1

[0054] (1) Dissolve 2.90g of self-made monovinyl-terminated polydimethylsiloxane monomer in 5mL of deionized water and self-assemble it into an aqueous solution of nanoparticles by ultrasonic treatment.

[0055] (2) Mix the monovinyl-terminated polydimethylsiloxane monomer nanoparticle solution evenly, add 0.36g of AgNWs under stirring, and then sonicate until evenly dispersed.

[0056] (3) 0.7 g acrylamide, 0.04 g ammonium persulfate, and N,N,N',N'-tetramethylethylenediamine (5 μL) were dissolved in the mixed solution of step (2) by vigorous stirring to form a reactant solution. Finally, the reactant solution was transferred to a mold and polymerized in an oven at 55 °C to obtain conductive hydrogel comparative product 1.

[0057] Performance testing:

[0058] (1) Mechanical properties and self-healing test: The tensile properties and self-healing properties of the conductive hydrogel matrix were tested using a universal testing machine. The samples were cut into dumbbell shapes with dimensions of 35mm × 2mm × 1.5mm, and the tensile test speed was fixed at 60mm / min. -1The gauge length between the fixtures was 10.0 mm. Mechanical properties of the rectangular hydrogel samples repaired for 20 minutes were tested under the same conditions, and the results are shown in Table 1, accurately quantifying the self-healing effect of the hydrogel.

[0059] Table 1 Mechanical property testing

[0060] Tensile strength (MPa) Elongation at break / % Self-healing rate / % Example 1 195 500 90 Example 2 162 900 92 Example 3 135 1230 93 Example 4 121 1560 96 Example 5 105 1800 96 Comparative Example 1 76 1200 0

[0061] The mechanical performance data (Table 1) show that acrylamide polymers can effectively enhance the tensile strength of conductive hydrogels. The physicochemically cross-linked network conductive hydrogel with low monovinyl-terminated polydimethylsiloxane content exhibits good stretchability, but low tensile strength. As the acrylamide content increases from 0.7 g to 3.5 g, the elongation at break of the conductive hydrogel increases from 500% to 1800%, but the tensile strength at break nearly doubles. The results of Comparative Example 1 indicate that the hydrogel matrix without sodium dodecyl sulfate micelles does not exhibit self-healing properties; therefore, the hydrophilic and hydrophobic sodium dodecyl sulfate micelles enhance the self-healing properties of the hydrogel matrix. The results demonstrate that the physicochemically double-crosslinked interpenetrating network structure conductive hydrogel possesses excellent mechanical properties.

[0062] (2) Conductivity test: The conductive hydrogel matrix was cut into circular pieces with a thickness of 2.0 mm and a diameter of 10.0 mm. The conductivity of the sheet samples was measured using a dual-electrode four-probe instrument to investigate the conductivity of the conductive hydrogel. The results are shown in Table 2.

[0063] Table 2 Conductivity Test

[0064] Electrical conductivity (S / m) Example 1 0.030 Example 2 0.030 Example 3 0.030 Example 4 0.030 Example 5 0.030

[0065] The conductivity of five sheet-like samples was measured using a dual-electrode four-probe instrument to investigate the conductivity of the conductive hydrogel. The results are shown in Table 2. The conductivity data indicate that the content of the crosslinking agent has no significant effect on the conductivity. Sodium dodecyl sulfate not only self-assembles with octadecyl methacrylate to form micelles but also promotes the dispersion of silver nanowires in the matrix, resulting in a conductive hydrogel with good conductivity (approximately 0.030 S / m) and stable conductivity.

[0066] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a self-healing conductive hydrogel, characterized in that, Includes the following steps: Step (1): Add octadecyl methacrylate to sodium dodecyl sulfate solution and stir thoroughly to obtain sodium dodecyl sulfate octadecyl methacrylate micelle solution; Step (2): Dissolve monovinyl-terminated polydimethylsiloxane in deionized water and sonicate until completely dissolved to form a self-assembled nanoparticle solution. Mix the sodium dodecyl sulfate methacrylate micelle solution with the nanoparticle solution and stir thoroughly. Add silver nanowires while stirring and then sonicate until uniformly dispersed. In step (3), acrylamide, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine are added sequentially to the dispersion obtained in step (2), and the mixture is stirred vigorously to form a reactant solution. Finally, the reactant solution is transferred to a mold and a polymerization reaction occurs to obtain a self-healing conductive hydrogel.

2. The method as described in claim 1, characterized in that, The structural formula of monovinyl-terminated polydimethylsiloxane is as follows:

3. The method as described in claim 1, characterized in that, In step (1), the mixture is stirred thoroughly for 2-3 hours to obtain a sodium dodecyl sulfate methacrylate micelle solution.

4. The method as described in claim 1, characterized in that, The mass ratio of sodium dodecyl sulfate to octadecyl methacrylate is 1:0.

672.

5. The method as described in claim 1, characterized in that, The mass ratio of monovinyl-terminated polydimethylsiloxane to silver nanowires is 1:0.

12.

6. The method as described in claim 1, characterized in that, The mass ratio of monovinyl-terminated polydimethylsiloxane to acrylamide is 1:0.24 to 0.

96.

7. The method as described in claim 1, characterized in that, Stir the sodium dodecyl sulfate octadecyl methacrylate micelle solution and the nanoparticle solution thoroughly for 2-3 hours.

8. The method as described in claim 1, characterized in that, The mass ratio of sodium dodecyl sulfate, acrylamide, and ammonium persulfate is 1:0.70:0.04, and the ratio of N,N,N',N'-tetramethylethylenediamine to sodium dodecyl sulfate is 5-25 μL:1-5 g.

9. A self-healing conductive hydrogel prepared by the method according to any one of claims 1-8.

10. The use of a self-healing conductive hydrogel prepared by the method of any one of claims 1-8 in the preparation of a flexible temperature sensor.

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