A magnetic field-induced Janus viscoelastic hydrogel and its preparation method and application

Abstract

The present invention relates to the technical field of materials of functional polymer networks, and specifically to a magnetic field-induced Janus viscous hydrogel and a preparation method thereof, which are used in the fields of wearable strain sensors and effective waste heat collection and conversion. A preparation method of a magnetic field-induced Janus viscous hydrogel comprises the following steps: S1, obtaining polydopamine-modified ferroferric oxide magnetic nanoparticles; S2, obtaining a hydrogel precursor solution; S3, preparing a magnetic field-induced Janus viscous hydrogel. Based on the magnetic field induction effect and polydopamine-modified ferroferric oxide magnetic nanoparticles, the present invention constructs a Janus hydrogel with different adhesion properties on both sides of an acrylamide / calcium alginate hydrogel, wherein the polyacrylamide / calcium alginate double network structure has good mechanical stability and can give the hydrogel durability.

Description

Technical Field

[0001] The present invention relates to the technical field of materials of functional polymer networks, and in particular to a magnetic field-induced Janus viscoelastic hydrogel and a preparation method thereof, which are used for wearable strain sensors and effective waste heat collection and conversion. Background Art

[0002] Most biological tissues are rich in water, and synthetic hydrogels can perfectly mimic their structure. Therefore, hydrogels have become ideal materials for implantable devices, wound dressings, and flexible electronics. Clearly, adhesion is crucial for the harmonious integration of hydrogels with tissues and skin. However, asymmetric adhesion is necessary in practical applications to avoid the problems caused by the isotropy and self-adhesion of hydrogels. Janus hydrogels with two surfaces of different properties can achieve this goal. Although there are many existing methods for preparing Janus hydrogels, such as medium-guided diffusion, molecular one-sided diffusion, and temperature-induced modification, the adhesion surfaces obtained by these diffusion-based methods are uncontrolled on a time scale, and most of them only achieve a single functionality—asymmetric adhesion—which limits the new application window of Janus hydrogels. Therefore, the preparation of Janus hydrogels with dual functionality is of great practical significance.

[0003] Magnetic nanoparticles (MNPs) of ferroferric oxide are not only used as carriers for drug delivery systems or multifunctional nanomaterials, but also exhibit excellent responsiveness to magnetic fields and good thermal conductivity. Furthermore, polydopamine (PDA), an emerging bioinspired material, possesses multifunctional properties such as photothermal effects and strong adhesion. The ease of preparing PDA on nearly any material also makes it a versatile coating. The combination of PDA and magnetic nanoparticles of ferroferric oxide provides a new material that can be introduced as a functional filler into hydrogel precursor solutions.

[0004] By inducing external fields, such as electric, optical, and magnetic fields, and doping hydrogel precursor solutions with responsive fillers, it is possible to construct stable Janus structures within hydrogels and impart multifunctionality. However, strategies for simultaneously achieving strong adhesion and high thermal conductivity on one side of Janus-like hydrogels have yet to be reported. Summary of the Invention

[0005] To address the shortcomings of the aforementioned prior art, the present invention provides a magnetic field-induced Janus hydrogel and its preparation strategy. Based on the unilateral induction of a magnetic field on polydopamine-modified ferroferric oxide magnetic nanoparticles, Janus hydrogels with different adhesive properties are constructed on both sides of the hydrogel. The prepared Janus hydrogel exhibits excellent mechanical properties, universal adhesion, and effective ability to collect and convert waste heat from the human body.

[0006] A method for preparing a magnetic field-induced Janus viscoelastic hydrogel comprises the following steps:

[0007] S1. After preparing ferroferric oxide magnetic nanoparticles, the ferroferric oxide magnetic nanoparticles are mixed with a dopamine hydrochloride aqueous solution and subjected to ultrasonic treatment to obtain polydopamine-modified ferroferric oxide magnetic nanoparticles;

[0008] S2, dissolving the monomer, cross-linking agent, initiator and electrolyte salt in deionized water to obtain a hydrogel precursor solution;

[0009] S3. After pasting the NdFeB magnet in the mold, add the polydopamine-modified magnetic nanoparticle aqueous solution prepared in S1 into the mold. After removing excess water in the mold, slowly pour the hydrogel precursor solution prepared in S2 into the mold and seal it. After the polymerization reaction, let it stand to obtain the magnetic field-induced Janus viscoelastic hydrogel. The polymerization reaction temperature conditions are 50℃~70℃ and the time conditions are 3-6h.

[0010] Furthermore, in S1, the ferrosoferric oxide nanoparticles are prepared by a co-precipitation method.

[0011] Furthermore, in S1, the concentration of dopamine hydrochloride is 0.002-0.008 g / mL, the mass ratio of ferroferric oxide magnetic nanoparticles: dopamine hydrochloride is 1:1-5, and the ultrasonic treatment time is 4-6 h.

[0012] Furthermore, in S2, the molar ratio of monomer: cross-linking agent: initiator is 725-900:70:1-5 ， The content of electrolyte salt is 0.5-2.5 mol / L;

[0013] Further, in S2, the monomer is a mixture of acrylamide and alginate, and the mass ratio of acrylamide:alginate is 4 to 10:1, wherein the alginate can be one of sodium alginate, potassium alginate, magnesium alginate, ammonium alginate, calcium alginate, and propylene glycol alginate;

[0014] The crosslinking agent is a mixture of N,N′-methylenebisacrylamide and calcium sulfate dihydrate, and the mass ratio is N,N′-methylenebisacrylamide: calcium sulfate dihydrate = 11 to 20:1;

[0015] The initiator is ammonium persulfate;

[0016] The electrolyte salt is lithium chloride.

[0017] Furthermore, in S2, the specific steps of preparing the hydrogel precursor solution are:

[0018] S21, dissolving acrylamide, N,N′-methylenebisacrylamide, ammonium persulfate, calcium sulfate dihydrate, and lithium chloride in deionized water, and stirring in the dark to obtain solution A;

[0019] S22, dissolving alginate in deionized water, protecting from light and stirring to obtain solution B;

[0020] S23. Mix solution A and solution B to prepare a hydrogel precursor solution, wherein the volume ratio of solution A to solution B is 1:1-5.

[0021] Furthermore, in S2, the concentration of the initiator is 0.0006 to 0.0024 g / mL.

[0022] The magnetic field-induced Janus viscoelastic hydrogel prepared by the above-mentioned method for preparing the magnetic field-induced Janus viscoelastic hydrogel.

[0023] The above-mentioned magnetic field-induced Janus viscoelastic hydrogel is used in the preparation of wearable strain sensors.

[0024] The above-mentioned magnetic field-induced Janus viscoelastic hydrogel is used in the field of achieving effective waste heat collection and conversion.

[0025] The technical solution provided by the present invention has the following beneficial effects: Based on magnetic field induction and polydopamine-modified ferroferric oxide magnetic nanoparticles, the present invention constructs a Janus hydrogel with different adhesive properties on both sides of an acrylamide / calcium alginate hydrogel. The polyacrylamide / calcium alginate double network structure has excellent mechanical stability, which can impart durability to the hydrogel. The polydopamine on the magnetic field-induced side provides a large number of catechol groups, which can form numerous hydrogen bonds and ionic complexation interactions with various substrate surfaces, imparting excellent adhesion to the hydrogel and enabling wearable strain sensing. The excellent thermal conductivity of the ferroferric oxide magnetic nanoparticles enables the Janus hydrogel to quickly establish an effective temperature difference between the human skin surface and the air, exhibiting a large Seebeck coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 ab are pictures of the hydrogel products prepared in Comparative Example 1 and Example 1 of the present invention, respectively;

[0027] Figure 2is a cross-sectional SEM image of the magnetic field-induced Janus viscoelastic hydrogel prepared in Example 1 of the present invention;

[0028] Figure 3 is an infrared spectrum of the magnetic field-induced Janus viscoelastic hydrogel prepared in Example 1 of the present invention;

[0029] Figure 4 1 is the stress-strain curve of the hydrogel products prepared in Example 1, Comparative Example 2 and Comparative Example 3 of the present invention;

[0030] Figure 5 af are schematic diagrams of the magnetic field-induced Janus viscoelastic hydrogel prepared in Example 1 of the present invention adhering to six substrates: plastic, glass, iron sheet, PMMA, pigskin, and rubber;

[0031] Figure 6 is the GF value of the magnetic field-induced Janus viscoelastic hydrogel prepared in Example 1 of the present invention for wearable strain sensing;

[0032] Figure 7 This is a Seebeck coefficient test chart of the hydrogel products prepared in Example 1 of the present invention and Comparative Example 3. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0034] Sources of the raw materials used in the following examples are as follows: Acrylamide (99%), N,N′-methylenebisacrylamide, dopamine nitrate, and ammonium persulfate were purchased from Aladdin Co., Ltd. Sodium alginate (90%) and calcium sulfate dihydrate were purchased from Sinopharm Co., Ltd. Lithium chloride was purchased from Maclean Co., Ltd. All chemicals were used as received without further purification.

[0035] <Example 1>

[0036] A method for preparing a magnetic field-induced Janus viscoelastic hydrogel comprises the following steps:

[0037] (1) 1 g of ferroferric oxide magnetic nanoparticles prepared by coprecipitation was dissolved in 500 mL of a dopamine hydrochloride aqueous solution at pH 11 and ultrasonicated for 5 h, wherein the concentration of the dopamine hydrochloride aqueous solution was 0.002 g / mL;

[0038] (2) Weigh 2 g of acrylamide, 0.4125 g of N,N′-methylenebisacrylamide, 0.01 g of ammonium persulfate, 0.022 g of calcium sulfate dihydrate, and 1.39 g of lithium chloride and dissolve them in 6.5 mL of deionized water to form solution A. Stir the mixture at 200 rpm in the dark at 25°C for 60 min.

[0039] (3) Weigh 0.25 g of sodium alginate and dissolve it in 10 mL of deionized water to form solution B. Stir at 200 rpm in the dark at 25°C for 120 min.

[0040] (4) 1 mL of polydopamine-modified magnetic nanoparticle solution was added to a custom mold of 80 mm × 15 mm × 3 mm and the water was removed with a pipette. The custom mold was composed of NdFeB bonded to the bottom of a PMMA mold. The hydrogel precursor solution obtained by uniformly mixing solution A and solution B was slowly poured into the custom mold and sealed.

[0041] (5) The samples were thermally polymerized in a vacuum drying oven at 60 °C for 3 h, and then taken out and allowed to stand at 25 °C for 24 h to obtain a magnetic field-induced Janus viscoelastic hydrogel.

[0042] <Example 2>

[0043] A method for preparing a magnetic field-induced Janus viscoelastic hydrogel comprises the following steps:

[0044] (1) Weigh 1 g of ferroferric oxide magnetic nanoparticles prepared by coprecipitation and dissolve them in 500 mL of a dopamine hydrochloride aqueous solution with a pH of 11, and sonicate for 6 h. The concentration of the dopamine hydrochloride aqueous solution is 0.004 g / mL.

[0045] (2) Weigh 2.5 g acrylamide, 0.4125 g N,N′-methylenebisacrylamide, 0.02 g ammonium persulfate, 0.022 g calcium sulfate dihydrate, and 1.39 g lithium chloride and dissolve them in 6.5 mL deionized water to form solution A. Stir at 200 rpm in the dark at 25°C for 60 min.

[0046] (3) Weigh 0.25 g of sodium alginate and dissolve it in 10 mL of deionized water to form solution B. Stir at 200 rpm in the dark at 25°C for 120 min.

[0047] (4) 1 mL of polydopamine-modified magnetic nanoparticle solution was added to a special mold of 80 mm × 15 mm × 3 mm and the water was removed with a pipette. The special mold was composed of NdFeB glued to the bottom of a PMMA mold. The hydrogel precursor solution obtained by uniformly mixing solution A and solution B was slowly poured into the special mold and sealed.

[0048] (5) The samples were thermally polymerized in a vacuum drying oven at 60 °C for 3 h, and then taken out and allowed to stand at 25 °C for 24 h to obtain a magnetic field-induced Janus viscoelastic hydrogel.

[0049] <Example 3>

[0050] A method for preparing a magnetic field-induced Janus viscoelastic hydrogel comprises the following steps:

[0051] (1) Weigh 1 g of ferroferric oxide magnetic nanoparticles prepared by coprecipitation and dissolve them in 500 mL of a dopamine hydrochloride aqueous solution with a pH of 11, and sonicate for 6 h. The concentration of the dopamine hydrochloride aqueous solution is 0.006 g / mL.

[0052] (2) Weigh 2.5 g acrylamide, 0.4125 g N,N′-methylenebisacrylamide, 0.02 g ammonium persulfate, 0.022 g calcium sulfate dihydrate, and 1.39 g lithium chloride and dissolve them in 6.5 mL deionized water to form solution A. Stir at 200 rpm in the dark at 25°C for 60 min.

[0053] (3) Weigh 0.25 g of sodium alginate and dissolve it in 10 mL of deionized water to form solution B. Stir at 200 rpm in the dark at 25°C for 120 min.

[0054] (4) 1 mL of polydopamine-modified magnetic nanoparticle solution was added to a special mold of 80 mm × 15 mm × 3 mm and the water was removed with a pipette. The special mold was composed of NdFeB glued to the bottom of a PMMA mold. The hydrogel precursor solution obtained by uniformly mixing solution A and solution B was slowly poured into the special mold and sealed.

[0055] (5) The samples were thermally polymerized in a vacuum drying oven at 60 °C for 3 h, and then taken out and allowed to stand at 25 °C for 24 h to obtain a magnetic field-induced Janus viscoelastic hydrogel.

[0056] <Example 4>

[0057] A method for preparing a magnetic field-induced Janus viscoelastic hydrogel comprises the following steps:

[0058] (1) 1 g of ferroferric oxide magnetic nanoparticles prepared by coprecipitation was dissolved in 500 mL of a dopamine hydrochloride aqueous solution at pH 11, and ultrasonicated for 6 h, wherein the concentration of the dopamine hydrochloride aqueous solution was 0.008 g / mL;

[0059] (2) Weigh 2.5 g acrylamide, 0.4125 g N,N′-methylenebisacrylamide, 0.04 g ammonium persulfate, 0.022 g calcium sulfate dihydrate, and 0.695 g lithium chloride and dissolve them in 6.5 mL deionized water to form solution A. Stir at 200 rpm in the dark at 25°C for 60 min.

[0060] (3) Weigh 0.25 g of sodium alginate and dissolve it in 10 mL of deionized water to form solution B. Stir at 200 rpm in the dark at 25°C for 120 min.

[0061] (4) 1 mL of polydopamine-modified magnetic nanoparticle solution was added to a special mold of 80 mm × 15 mm × 3 mm and the water was removed with a pipette. The special mold was composed of NdFeB glued to the bottom of a PMMA mold. The hydrogel precursor solution obtained by uniformly mixing solution A and solution B was slowly poured into the special mold and sealed.

[0062] (5) The samples were thermally polymerized in a vacuum drying oven at 60 °C for 3 h, and then taken out and allowed to stand at 25 °C for 24 h to obtain a magnetic field-induced Janus viscoelastic hydrogel.

[0063] Comparative Example 1

[0064] A method for preparing a hydrogel without magnetic field induction comprises the following steps:

[0065] (1) 1 g of ferroferric oxide magnetic nanoparticles prepared by coprecipitation was dissolved in 500 mL of a dopamine hydrochloride aqueous solution at pH 11, and ultrasonicated for 6 h, wherein the concentration of the dopamine hydrochloride aqueous solution was 0.008 g / mL;

[0066] (2) Weigh 2.5 g acrylamide, 0.4125 g N,N′-methylenebisacrylamide, 0.04 g ammonium persulfate, 0.022 g calcium sulfate dihydrate, and 0.695 g lithium chloride and dissolve them in 6.5 mL deionized water to form solution A. Stir at 200 rpm in the dark at 25°C for 60 min.

[0067] (3) Weigh 0.25 g of sodium alginate and dissolve it in 10 mL of deionized water to form solution B. Stir at 200 rpm in the dark at 25°C for 120 min.

[0068] (4) 1 mL of polydopamine-modified magnetic nanoparticle solution was added to a custom-made mold of 80 mm × 15 mm × 3 mm and the water was removed with a pipette. Using a conventional PMMA mold, the hydrogel precursor solution obtained by uniformly mixing solution A and solution B was slowly poured into the conventional PMMA mold and sealed.

[0069] (5) The samples were thermally polymerized in a vacuum drying oven at 60 °C for 3 h, and then taken out and allowed to stand at 25 °C for 24 h to obtain a hydrogel without magnetic field induction.

[0070] Comparative Example 2

[0071] A method for preparing a polyacrylamide hydrogel comprises the following steps:

[0072] (1) Weigh 2.5 g acrylamide, 0.4125 g N,N′-methylenebisacrylamide, and 0.04 g ammonium persulfate in 16.5 mL deionized water to form a precursor solution;

[0073] (2) Using a conventional PMMA mold, slowly pour the precursor solution into the conventional PMMA mold and seal it.

[0074] (3) The polyacrylamide hydrogel was obtained by thermal polymerization in a vacuum drying oven at 60°C for 3 h, and then the sample was taken out and allowed to stand at 25°C for 24 h.

[0075] Comparative Example 3

[0076] A method for preparing a polyacrylamide / calcium alginate hydrogel comprises the following steps:

[0077] (1) 2.5 g acrylamide, 0.4125 g N,N′-methylenebisacrylamide, 0.04 g ammonium persulfate, 0.022 g calcium sulfate dihydrate, and 0.695 g lithium chloride were dissolved in 6.5 mL deionized water to form solution A. The mixture was stirred at 200 rpm in the dark at 25°C for 60 min.

[0078] (3) Weigh 0.25 g of sodium alginate and dissolve it in 10 mL of deionized water to form solution B. Stir at 200 rpm in the dark at 25°C for 120 min.

[0079] (4) Using a conventional PMMA mold, the hydrogel precursor solution obtained by uniformly mixing solution A and solution B is slowly poured into the conventional PMMA mold and sealed.

[0080] (5) The polyacrylamide / calcium alginate hydrogel was obtained by thermal polymerization in a vacuum drying oven at 60°C for 3 h, and then the sample was taken out and allowed to stand at 25°C for 24 h.

[0081] Janus adhesive hydrogels were prepared in the presence and absence of a magnetic field. The presence of a magnetic field is crucial for the uniform formation of the hydrogel's adhesive surface. Figure 1 As shown, under the condition of no magnetic field induction (Comparative Example 1), the magnetic nanoparticles are irregularly distributed in the hydrogel matrix after thermal polymerization, forming an uneven adhesion surface; while under the condition of magnetic field induction (Example 1), the magnetic nanoparticles are evenly distributed at the bottom of the hydrogel matrix after thermal polymerization, forming a flat adhesion surface.

[0082] The cross section of the magnetic field-induced Janus viscoelastic hydrogel prepared in Example 1 was observed using a field emission scanning electron microscope (SU8010, Hitachi, Japan) at an accelerating voltage of 10 kV. Figure 2 As shown, it can be seen that the tough matrix region of the magnetic field-induced Janus viscous hydrogel prepared in Example 1 has a dense pore structure, while the viscous matrix region has a loose pore structure.

[0083] The magnetic field-induced Janus viscoelastic hydrogel prepared in Example 1 was characterized by using a Thermo Fisher Nicolet 6700 infrared spectrometer (FT IR) at a wave number of 400 to 4000 cm 1 The infrared spectra of the tough side and the adhesive side of the Janus viscoelastic hydrogel induced by the magnetic field are obtained respectively. The results are as follows Figure 3 As shown in the figure, it can be seen that the Janus hydrogel with different properties on both sides was successfully prepared in Example 1, wherein the adhesion surface curve is 1065.96 cm -1 The peak at is attributed to the stretching vibration of the benzene ring in polydopamine.

[0084] The magnetic field-induced Janus viscoelastic hydrogel prepared in Example 1 was subjected to tensile tests at 25°C and 56% relative humidity. The strip-shaped magnetic field-induced Janus viscoelastic hydrogel (width 15 mm, thickness 3 mm) was loaded into an electronic universal testing machine (E43.104, MTS, USA) with an initial gauge length of 10 mm and stretched at 50 mm min. -1 After stretching at a speed of , the tensile strength and elongation at break of the hydrogel were tested, and the average value was obtained by multiple measurements. Comparative Example 2 and Comparative Example 3 were used as controls, and the results were as follows Figure 4 As shown in the figure, it can be seen from the results that compared with polyacrylamide hydrogel and double-network polyacrylamide / calcium alginate hydrogel, the magnetic field induced Janus viscoelastic hydrogel of the present invention can show better tensile strength and also has a larger elongation at break.

[0085] The adhesive surface of the magnetic field-induced Janus adhesive hydrogel prepared in Example 1 was placed in contact with the surfaces of different substrates, and slight pressure was applied to allow the gel to adhere fully to the substrate. The results were as follows: Figure 5 As shown, the magnetic field-induced Janus viscoelastic hydrogel prepared in Example 1 can directly adhere to different substrate surfaces, including plastic, glass, iron sheet, PMMA, pigskin and rubber, indicating that the Janus viscoelastic hydrogel has a wide range of adhesion and can be applied to different substrate surfaces.

[0086] The magnetic field-induced Janus viscoelastic hydrogel prepared in Example 1 was assembled with a platinum wire into a wearable strain sensor. When a voltage of 0.5 V was applied, the current change was recorded by a CHI760D electrochemical workstation. The sensor can fit closely to the human body and effectively detect subtle human movements. The GF value reaches 0.842 in the 0-100% strain range and 0.646 in the 100-600% strain range. Figure 6 shown.

[0087] The magnetic field-induced Janus viscoelastic hydrogel and polyacrylamide / calcium alginate hydrogel prepared in Example 1 were prepared into cylindrical samples of 15 mm × φ10 mm. The samples were placed under temperature differences of 5 K, 7 K, 10 K, and 13 K. The open circuit voltages of the two hydrogels at different temperature differences were measured using a CHI760D electrochemical workstation to obtain the Seebeck coefficients of the two hydrogels. The results are shown in FIG. Figure 7 As shown, it can be seen that the Seebeck coefficient of the magnetic field-induced Janus viscoelastic polyacrylamide calcium alginate hydrogel is 3.01m / K; the Seebeck coefficient of the polyacrylamide calcium alginate hydrogel is 8.09mV / K, indicating that the polydopamine-modified ferroferric oxide magnetic nanoparticles present in the adhesive surface of the magnetic field-induced Janus viscoelastic hydrogel prepared in Example 1 have good thermal conductivity and adhesion, and have a significant positive effect on the rapid construction of the temperature difference between the two ends of the hydrogel.

[0088] In summary, the prepared magnetic field-induced Janus viscoelastic hydrogel has good adhesion and is an excellent material for preparing wearable strain sensors; and the polydopamine-modified ferroferric oxide nanoparticles in the adhesion layer have good thermal conductivity, which has a significant effect on constructing the temperature difference between the two ends of the hydrogel. Therefore, combined with the Soret effect, when the hot end temperature is less than 70°C, the hydrogel material of the present invention can also be used to realize waste heat collection and conversion, using the Seebeck effect to collect low-quality thermal energy and convert it into electrical energy.

[0089] In the absence of conflict, the above embodiments and features in the embodiments may be combined with each other.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a magnetic field-induced Janus viscoelastic hydrogel, characterized in that: The following steps are involved: S1. After preparing ferroferric oxide magnetic nanoparticles, the ferroferric oxide magnetic nanoparticles are mixed with a dopamine hydrochloride aqueous solution and subjected to ultrasonic treatment to obtain polydopamine-modified ferroferric oxide magnetic nanoparticles; S2. Prepare a hydrogel precursor solution. The specific steps are as follows: S21, dissolving acrylamide, N,N′-methylenebisacrylamide, ammonium persulfate, calcium sulfate dihydrate, and lithium chloride in deionized water, and stirring in the dark to obtain solution A; S22, dissolving alginate in deionized water, protecting from light and stirring to obtain solution B; S23, mixing solution A and solution B to prepare a hydrogel precursor solution, wherein the volume ratio of solution A to solution B is 1:1-5; S3. After pasting the NdFeB magnet in the mold, add the polydopamine-modified magnetic nanoparticle aqueous solution prepared in S1 into the mold. After removing excess water in the mold, slowly pour the hydrogel precursor solution prepared in S2 into the mold and seal it. After the polymerization reaction, the temperature conditions of the polymerization reaction are 50℃~70℃ and the time conditions are 3-6h. Let it stand to obtain the magnetic field-induced Janus viscoelastic hydrogel.

2. The method for preparing the magnetic field-induced Janus viscoelastic hydrogel according to claim 1, characterized in that: In S1, the ferrosoferric oxide nanoparticles are prepared by a co-precipitation method.

3. The method for preparing the magnetic field-induced Janus viscoelastic hydrogel according to claim 1, characterized in that: In S1, the concentration of dopamine hydrochloride is 0.002-0.008 g / mL, the mass ratio of ferroferric oxide magnetic nanoparticles to dopamine hydrochloride is 1:1-5, and the ultrasonic treatment time is 4-6 h.

4. The method for preparing the magnetic field-induced Janus viscoelastic hydrogel according to claim 1, characterized in that: In S2, the molar ratio of acrylamide and alginate: cross-linking agent: initiator is 725-900:70:1-5, and the content of the electrolyte salt is 0.5-2.5 mol / L.

5. The method for preparing the magnetic field-induced Janus viscoelastic hydrogel according to claim 4, characterized in that: In S2, the mass ratio of acrylamide to alginate is 4 to 10:1, wherein the alginate is one of sodium alginate, potassium alginate, magnesium alginate, ammonium alginate, calcium alginate, and propylene glycol alginate; The cross-linking agent is a mixture of N,N'-methylenebisacrylamide and calcium sulfate dihydrate, and the mass ratio of N,N'-methylenebisacrylamide:calcium sulfate dihydrate is 11-20:

1.

6. The method for preparing the magnetic field-induced Janus viscoelastic hydrogel according to claim 5, characterized in that: In S2, the concentration of the initiator is 0.0006 to 0.0024 g / mL.

7. The magnetic field-induced Janus viscoelastic hydrogel prepared according to the method for preparing the magnetic field-induced Janus viscoelastic hydrogel according to any one of claims 1 to 6.

8. The magnetic field-induced Janus viscoelastic hydrogel according to claim 7 is used in the preparation of wearable strain sensors.

9. The use of the magnetic field-induced Janus viscoelastic hydrogel according to claim 7, characterized in that: Combined with the soret effect, when the hot end temperature is less than 70°C, the magnetic field-induced Janus viscoelastic hydrogel can also be used to achieve waste heat collection and conversion.

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