Preparation method and application of silver nanowire hydrogel electrode

Abstract

The invention provides a preparation method and application of a super-tensile and high-adhesiveness silver nanowire hydrogel, and the super-tensile and high-adhesiveness silver nanowire hydrogel is a conductive hydrogel. According to the silver nanowire hydrogel disclosed by the invention, acrylamide, silver nanowires, acrylic acid, polyvinylpyrrolidone and water are taken as main raw materials, and the silver nanowires are added into a hydrogel system, so that the toughness and the elasticity of the material are enhanced, and the conductivity of the hydrogel is improved. The finally prepared silver nanowire hydrogel has super-strong stretchability, extremely high adhesiveness, excellent conductivity and relatively low contact resistance. The hydrogel prepared by the invention can be used for a pressure sensor, and also can be attached to the skin to collect various physiological signals of a human body and monitor electrocardiosignals. In the aspect of pressure sensing, the hydrogel can accurately identify different numbers and letters, the accuracy rate reaches 93%, and various tiny motions of a human body can be identified; in the aspect of physiological signal acquisition, the stability is good, the precision is high, the impedance is low, materials are easy to obtain, and the operation is simple.

Description

Technical Field

[0001] The invention relates to a silver nanowire hydrogel and a preparation method and application thereof, belonging to the technical field of conductive hydrogels. Background Art

[0002] Pressure sensing is an emerging research topic with great vitality and potential in the field of contemporary science and technology. It integrates cutting-edge knowledge from multiple disciplines such as materials science, physics, micro-nano technology, and computer science, and has broad application prospects. However, traditional pressure sensors based on metal materials are often limited by their inherent metal properties, such as insufficient stretchability, low adhesion, and low sensitivity. These limitations significantly restrict their application potential in the field of high-precision and widely adaptable wearable devices.

[0003] Conductive hydrogels are composed of a hydrophilic polymer matrix and a conductive filler, and have a flexible cross-linked polymer network. In recent years, it has shined in the vast world of flexible electronic devices with its good biocompatibility, adjustable mechanical properties and rich biological activity, showing great application prospects. However, due to the limitations of the mechanical and electrical properties of existing materials, it is always a challenge to prepare pressure sensing materials that meet both practical application and mechanical performance requirements, high stretchability, good recovery ability after compression, and high sensitivity. In addition, the fatigue resistance of hydrogels is poor, resulting in poor cyclic stability and short service life in pressure sensor applications. Therefore, the rational design and manufacture of conductive gels with resilience, high stretchability, high adhesion and stability are of great significance for the new generation of high-performance pressure sensors. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art, and propose a preparation method and application of a high-stretch and high-adhesion silver nanowire hydrogel. The hydrogel is a conductive hydrogel, and acrylamide is used as the hydrogel skeleton. The polymerization reaction between acrylic acid and acrylamide makes the hydrogel have better mechanical properties. The present invention has the advantages of ultra-stretching, high adhesion, high conductivity, high signal-to-noise ratio, simple structure, and good biocompatibility. It can be used for pressure sensors, with fast response speed, can generate stable resistance change signals under the action of external forces, can accurately identify different numbers and letters, and identify small movements of various parts of the body; it can also be used to monitor human motion signals, such as continuous collection of physiological signals such as electrocardiograms. The innovative preparation method of the conductive hydrogel provided by the present invention has the advantages of simple operation process, low cost, good biocompatibility, and multifunctionality, which is conducive to promoting the development of the next generation of intelligent wearable electronics and energy storage devices. It has played a positive role in promoting the innovation and development of the next generation of intelligent wearable electronic devices and sensor devices.

[0005] The technical solution of the present invention is:

[0006] A silver nanowire hydrogel is a porous hydrogel, the main raw materials of which include acrylamide, acrylic acid, silver nanowires, polyvinyl pyrrolidone and water, and also include an initiator and a cross-linking agent;

[0007] Acrylamide and acrylic acid polymerize into hydrogel, providing a tough skeleton;

[0008] Silver nanowires are evenly distributed in the hydrogel, providing conductivity and improving the mechanical properties of the hydrogel, reducing material impedance;

[0009] The initiator is any one of ammonium persulfate, benzoyl peroxide and potassium persulfate;

[0010] The cross-linking agent is N,N'-methylenebisacrylamide;

[0011] The mass ratio of acrylic acid to acrylamide is 1:10-11;

[0012] The mass ratio of the initiator to acrylic acid is 1:8-10;

[0013] The concentration of the silver nanowires is 10 mg / ml;

[0014] The mass ratio of polyvinyl pyrrolidone to silver nanowires is 1:1-4;

[0015] The mass ratio of the cross-linking agent to polyvinyl pyrrolidone is 1:7-7.5.

[0016] A method for preparing a silver nanowire hydrogel comprises the following steps:

[0017] Step 1, preparing an Am-AA solution, specifically, adding acrylamide and acrylic acid into deionized water, and adding an initiator, and fully dissolving them by magnetic stirring to obtain an Am-AA solution;

[0018] Step 2, preparing a PVP-AgNWs solution, specifically, adding silver nanowires and polyvinyl pyrrolidone into deionized water, adding a crosslinking agent, stirring thoroughly, and then ultrasonically crushing to obtain a PVP-AgNWs solution;

[0019] Step 3, the Am-AA solution obtained in step 1 and the PVP-AgNWs solution obtained in step 2 are uniformly mixed and poured into a mold, placed in an oven for heating to react, and the mold is taken out after the reaction is completed. After the temperature drops to room temperature, the product is taken out to obtain a silver nanowire hydrogel (PA-AgNWs hydrogel).

[0020] In the step 1, the mass ratio of acrylic acid to acrylamide is 1:10-11; the mass ratio of acrylic acid to deionized water is 1:10; the mass ratio of initiator to acrylic acid is 1:8-10; the temperature during mixing is 20-30° C., and the magnetic stirring time is 30 min.

[0021] In the step 2, the concentration of silver nanowires is 10 mg / ml, the mass ratio of polyvinyl pyrrolidone to silver nanowires is 1:1-4, the mass ratio of polyvinyl pyrrolidone to deionized water is 1:25; the mass ratio of the crosslinking agent to polyvinyl pyrrolidone is 1:7-7.5; the stirring time is 0.5-1h, and the ultrasonic crushing time is 5min.

[0022] In the step 3, the mass ratio of the PVP-AgNWs solution to the Am-AA solution is 1:1.75-2, the oven heating temperature is 70-90°C, and the heating time is 0.5-1h.

[0023] An application of silver nanowire hydrogel, wherein zinc sheets are attached to both ends of the prepared silver nanowire hydrogel as electrodes, and a circuit is connected to obtain a resistive pressure sensor, which can accurately identify different numbers and letters and identify tiny movements of various parts of the body; at the same time, the silver nanowire hydrogel is attached to the skin and connected to an electrocardiogram acquisition device, so that it can be used to measure electrocardiogram signals.

[0024] Compared with the prior art, the present invention exhibits a series of significant and beneficial effects:

[0025] The present invention adopts polyacrylamide-acrylic acid copolymer obtained by polymerization reaction of acrylamide and acrylic acid as the hydrogel skeleton. Acrylamide and acrylic acid contain a large number of hydrogen bonds, which reduces the phenomenon of silver nanowire polymerization and makes the silver nanowires evenly dispersed in the matrix. On the basis of ensuring the stability of the hydrogel electrode, the conductive performance of the hydrogel is significantly improved.

[0026] The present invention adds silver nanowires as conductive molecules to the raw materials, which improves the conductivity of the hydrogel and also makes the hydrogel show better sensing characteristics. Various pressure signals can be accurately and quickly transmitted to the electrodes with an extremely short response time, so that the present invention can better identify various tiny movements of the human body.

[0027] The present invention uses acrylamide and acrylic acid as raw materials, and the prepared hydrogel has extremely high stretchability, excellent adhesion and compression resilience, good biocompatibility, and can fit the skin tightly without causing skin irritation.

[0028] In the silver nanowire hydrogel electrode prepared by the preparation method of the present invention, the polyacrylamide formed by cross-linking acrylamide is non-toxic and harmless, which improves the biocompatibility of the electrode. In addition, the other constituent materials of the present invention are all non-hazardous chemicals, which further ensures the biocompatibility of the electrode. And the cost price of the materials selected by the preparation method is relatively low, and it has broad development prospects and huge market potential.

[0029] The present invention provides a method for preparing a super-stretchable and highly adhesive silver nanowire hydrogel and its application, which belongs to the scope of conductive hydrogel. The silver nanowire hydrogel of the present invention uses acrylamide, silver nanowires, and acrylic acid as main raw materials. Silver nanowires are added to the hydrogel system to enhance the toughness and elasticity of the material and improve the conductivity of the hydrogel. The silver nanowire hydrogel finally prepared has super-stretchability, extremely high adhesion, excellent conductivity and low contact impedance. The hydrogel electrode prepared by the present invention can be used for pressure sensors, and can also be attached to the skin to collect various physiological signals of the human body. In terms of pressure sensing, the electrode of the present invention can accurately identify different numbers and letters with an accuracy rate of 93%, and can identify various small movements of the human body; in terms of physiological signal collection, compared with commercial electrodes, it has better stability and higher precision, and the material is easy to obtain, the operation is simple, and it has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the preparation process of the silver nanowire hydrogel of the present invention;

[0031] Figure 2 is a physical picture of the silver nanowire hydrogel of the present invention;

[0032] Figure 3 is a microscopic structure diagram of the silver nanowire hydrogel of the present invention;

[0033] Figure 4 It is the XPS spectrum of the silver nanowire hydrogel of the present invention and its Ag 3d high-resolution spectrum;

[0034] Figure 5 is the compression cycle curve of the silver nanowire hydrogel of the present invention;

[0035] Figure 6 is the tensile stress-strain curves of different embodiments of the silver nanowire hydrogel of the present invention;

[0036] Figure 7 is a graph showing the relative change in resistance of the silver nanowire hydrogel of the present invention when subjected to pressures of different weight masses;

[0037] Figure 8 is a graph showing the relative change in resistance of the silver nanowire hydrogel of the present invention when swallowing and bending the wrist;

[0038] Fig. 9is the response time of the silver nanowire hydrogel of the present invention;

[0039] Fig.10 is a bar graph of the adhesion performance of the silver nanowire hydrogel of the present invention;

[0040] Fig.11 The present invention is a waveform diagram of recording the written numbers 0-9 and letters B, I, T using the silver nanowire hydrogel pressure sensor prepared by the present invention.

[0041] Fig.12 This is a confusion matrix for writing the ten digits 0-9 using the hydrogel pressure sensor of the present invention.

[0042] Fig.13 It is a comparison diagram of electrocardiographic signals measured by the silver nanowire hydrogel electrode prepared by the present invention and a commercial electrode, as well as a signal-to-noise ratio bar graph. DETAILED DESCRIPTION

[0043] The present invention will be described in more detail below in conjunction with the accompanying drawings and specific embodiments. However, they should not be understood as limiting the scope of protection of the present invention. It should be emphasized that the specific implementation cases described below are only examples for explaining the present invention, rather than limiting the scope of protection thereof. The experimental methods involved in the present invention all follow conventional operating procedures, and the materials, reagents and instruments and equipment used, unless otherwise specified, are all standard items widely used in the art, and professionals in the art can easily obtain them through commercial channels. Such a design is intended to ensure the repeatability and wide applicability of the present invention.

[0044] like Figure 1 As shown, a method for preparing a silver nanowire hydrogel comprises the following steps:

[0045] Step 1, preparing an Am-AA solution, specifically, adding acrylamide and acrylic acid into deionized water, and adding an initiator, and fully dissolving them by magnetic stirring to obtain an Am-AA solution;

[0046] Step 2, preparing a PVP-AgNWs solution, specifically, adding silver nanowires and polyvinyl pyrrolidone into deionized water, adding a crosslinking agent, stirring thoroughly, and then ultrasonically crushing to obtain a PVP-AgNWs solution;

[0047] Step 3, the Am-AA solution obtained in step 1 and the PVP-AgNWs solution obtained in step 2 are uniformly mixed and poured into a mold, placed in an oven for heating to react, and the mold is taken out after the reaction is completed. After the temperature drops to room temperature, the product is taken out to obtain PA-AgNWs hydrogel.

[0048] Example 1

[0049] A method for preparing a silver nanowire hydrogel comprises the following steps:

[0050] Step 1, add 5 g acrylamide and 0.5 g acrylic acid into 5 ml deionized water, add 30 mg initiator KPS, and stir magnetically for 30 min to fully dissolve the mixture to obtain an Am-AA solution;

[0051] Step 2, 0.2 g of silver nanowires and 0.2 g of polyvinyl pyrrolidone were added to 5 ml of deionized water, and 30 mg of cross-linking agent N, N'-methylenebisacrylamide was added, and the mixture was stirred for 30 min, and ultrasonically crushed for 5 min to obtain a PVP-AgNWs solution;

[0052] Step 3, the Am-AA solution obtained in step 1 and the PVP-AgNWs solution obtained in step 2 are uniformly mixed and poured into a mold, placed in an oven, and heated at 80°C for 1 hour. After the reaction is completed, the mold is taken out, and after the temperature drops to room temperature, the product is taken out to obtain PA-0.2AgNWs hydrogel.

[0053] Example 2

[0054] The difference from Example 1 is that the mass of the silver nanowires added in step 2 is 0.4 g, and the obtained product is PA-0.4AgNWs hydrogel.

[0055] Example 3

[0056] The difference from Example 1 is that the mass of the silver nanowires added in step 2 is 0.6 g, and the obtained product is PA-0.6AgNWs hydrogel.

[0057] Example 4

[0058] The difference from Example 1 is that the mass of the silver nanowires added in step 2 is 0.8 g, and the obtained product is PA-0.8AgNWs hydrogel.

[0059] Figure 2 This is a real photo of the PA-0.2AgNWs hydrogel in Example 1. Figure 2 a shows the hydrogel of the present invention, which has extremely remarkable light transmittance. The background image can be clearly observed through the silver nanowire hydrogel, which fully proves its high light transmittance property. Figure 2 b shows the hydrogel of the present invention attached to the arm. After being pressed by fingers, the hydrogel firmly adheres to the fingers, demonstrating the excellent adhesion of the hydrogel of the present invention.

[0060] Figure 3 a and Figure 3b shows a scanning electron microscope (SEM) image of the hydrogel of Example 4 of the present invention. By carefully observing these two images, the uniform porous structure of the hydrogel can be clearly identified, and its internal cross-linked network is extremely well constructed. In addition, the silver nanowires are well distributed in the hydrogel matrix, showing excellent dispersibility, which further verifies that the silver nanowires are successfully embedded and distributed in the hydrogel matrix.

[0061] Figure 4 a is the full XPS spectrum of the hydrogel in Example 4. Figure 4 b is the high-resolution XPS spectrum of Ag 3d, in which the two main signal peaks of the Ag element correspond to Ag 3d 5 / 2 and Ag 3d 3 / 2, respectively, which further illustrates the existence of the Ag element and indicates that the silver nanowires are dispersed in the silver nanowire hydrogel matrix.

[0062] The compression performance of the silver nanowire hydrogel was tested using an American Mark-10 dynamometer. The silver nanowire hydrogel was made into a cylinder (r=7.5 mm, h=100 mm) and placed on a test platform for a compression test. Figure 5 The rebound curve of the hydrogel under 80% compression strain conditions and 100 compression load-unloading tests was recorded. It can be seen that the hydrogel has only slight plastic deformation during this compression process, fully demonstrating its stable mechanical properties. Further, in the test data, the strain curve of the hydrogel of the present invention shows very little hysteresis, and the almost consistent curve in 100 cycles shows that the hydrogel of the present invention has excellent mechanical stability and good fatigue resistance.

[0063] The two ends of the silver nanowire hydrogel (10 mm × 5 mm × 2 mm) were clamped with clamps and tensile tested using a Mark-10 dynamometer. Figure 6 The tensile stress-strain curves of Examples 1-4 show that Example 1 achieves the highest elongation, which is as high as 1393%, demonstrating the excellent super-tensile properties of the present invention; while in Example 4, the highest tensile strength is recorded, with a specific value of 310 kPa, showing good tensile strength.

[0064] The pressure sensing properties of silver nanowire hydrogels were tested using Tonghui TH2830 precision LCR digital bridge. Zinc sheets were attached to the upper and lower ends of the silver nanowire hydrogels (r = 9mm, h = 2mm) and further bonded with insulating tape to obtain a resistive pressure sensor. Weights of different masses were placed on the pressure sensor, and the sensing performance of the sensor was tested by the LCR digital bridge. The pressure sensor was also attached to the joints of the body to detect body movements.

[0065] Figure 7The relative resistance change curve of the hydrogel under pressure applied by weights of different masses in Example 4 is shown in FIG. As the weight mass increases, the relative resistance change of the hydrogel sensor also increases accordingly, which indicates that the sensor can accurately distinguish different pressure levels and has a fast recovery capability. By comparing the intensity and shape of the curve, different levels of pressure can be clearly identified, thereby achieving continuous and accurate detection of pressure.

[0066] Figure 8 a is the throat swallowing signal detected by the hydrogel in Example 4. The hydrogel sensor of the present invention has high sensitivity and can accurately capture the subtle vibration signal generated by the movement of the Adam's apple. Figure 8 b is the wrist bending signal detected in Example 4, which shows that the hydrogel pressure sensor of the present invention is capable of detecting tiny human body movements and physiological signals, thereby not only proving its potential value in wearable applications, but also highlighting its excellent sensing performance.

[0067] Fig. 9 The response time of the hydrogel pressure sensor of Example 4 is 40 ms, which shows a very high response / recovery speed, which is of great significance for continuously detecting various movements of the human body and reflecting its health status.

[0068] Silver nanowire hydrogel (15 mm × 10 mm × 2 mm) was attached to different adhesive material substrates, and the two ends of the adhesive material were clamped by a clamp, and the adhesion test was carried out on an American Mark-10 dynamometer. Fig.10 This is a bar graph of the adhesion performance of the hydrogel obtained in Example 1. The hydrogel of the present invention has adhesion to various materials. Since the hydrogel will deform and move when it adheres to a rough surface, mechanical interlocking is automatically introduced into the adhesion surface, accompanied by hydrogen bonding and electrostatic interaction, the hydrogel of the present invention exhibits excellent adhesion performance. The adhesion force of Example 1 on pig skin in the figure is as high as 39 kPa.

[0069] Fig.11 The waveform diagram is obtained when the numbers 0 to 9 are written on the hydrogel pressure sensor prepared in Example 4. Among them, the waveforms of the numbers 2, 7, and 9, and the waveforms of the numbers 3 and 6 show certain similarities, and the waveforms of the remaining numbers are significantly different, enough to be distinguished by the naked eye.

[0070] Furthermore, machine learning processing was performed on the waveform data of these digits 0 to 9. Fig.12 The confusion matrix results of the hydrogel pressure sensor in Example 4 for recognizing the digital waveforms from 0 to 9 are presented. The results show that the accuracy of the sensor in recognizing different numbers is as high as 93%, which fully verifies the excellent sensing performance exhibited by the hydrogel of the present invention.

[0071] Fig.13 a is a comparison diagram of the electrocardiogram obtained by using the hydrogel electrode prepared in Example 4 and a commercial electrode (AMBU N-00-S / 25 gel electrode) through an electrocardiogram acquisition device (AD8232 chip). Fig.13 b is a histogram of the electrocardiogram noise ratio of Example 4 and a commercial electrode. Compared with commercial electrodes, the signal graph of the silver nanowire hydrogel electrode of the present invention has less noise, higher accuracy and better signal-to-noise ratio.

[0072] In summary, the present invention has developed an ultra-stretchable, highly adhesive silver nanowire hydrogel. The hydrogel can accurately identify different numbers and letters with an accuracy rate of 93%, and can identify tiny movements of various parts of the body. In addition, the hydrogel of the present invention can also stably and accurately measure human physiological signals, and has the advantages of high conductivity, good biocompatibility, simple preparation method, etc. It is suitable for large-scale promotion and application in most physiological signal acquisition devices currently on the market.

[0073] The above is a preferred embodiment of the present invention, but the present invention is far more than this. Under the premise of following the basic principles and core spirit of the present invention, any solution obtained by equivalent substitution, reasonable adjustment or obvious change based on the content of the present invention specification shall be included in the protection scope of the present invention.

Claims

1. A silver nanowire hydrogel, characterized in that: The main raw materials include acrylamide, acrylic acid, silver nanowires, polyvinyl pyrrolidone and deionized water, as well as initiators and cross-linking agents; The mass ratio of acrylic acid to acrylamide is 1:10-11; The mass ratio of the initiator to acrylic acid is 1:8-10; The mass ratio of polyvinyl pyrrolidone to silver nanowires is 1:1-4; The mass ratio of the cross-linking agent to polyvinyl pyrrolidone is 1:7-7.

5.

2. The silver nanowire hydrogel according to claim 1, characterized in that: The initiator is any one of ammonium persulfate, benzoyl peroxide and potassium persulfate.

3. The silver nanowire hydrogel according to claim 1, characterized in that: The cross-linking agent is N,N'-methylenebisacrylamide.

4. The silver nanowire hydrogel according to claim 1, characterized in that: The concentration of the silver nanowires is 10 mg / ml.

5. A method for preparing a silver nanowire hydrogel, characterized in that The following steps are involved: Step 1, mixing acrylamide, acrylic acid, an initiator and deionized water, and stirring to obtain an Am-AA solution; Step 2, mixing silver nanowires, polyvinyl pyrrolidone, a crosslinking agent and deionized water, stirring, and ultrasonically grinding to obtain a PVP-AgNWs solution; Step 3, mixing the Am-AA solution obtained in step 1 with the PVP-AgNWs solution obtained in step 2 to obtain a silver nanowire hydrogel.

6. The method for preparing a silver nanowire hydrogel according to claim 5, characterized in that: In the step 1, the mass ratio of acrylic acid to acrylamide is 1:10-11; the mass ratio of acrylic acid to deionized water is 1:10; the mass ratio of initiator to acrylic acid is 1:8-10; the temperature during mixing is 20-30° C., and the stirring time is 30 min.

7. The method for preparing a silver nanowire hydrogel according to claim 5, characterized in that: In the step 2, the concentration of silver nanowires is 10 mg / ml, the mass ratio of polyvinyl pyrrolidone to silver nanowires is 1:1-4, the mass ratio of polyvinyl pyrrolidone to deionized water is 1:25; the mass ratio of the crosslinking agent to polyvinyl pyrrolidone is 1:7-7.5; the stirring time is 0.5-1h, and the ultrasonic crushing time is 3-5min.

8. The method for preparing a silver nanowire hydrogel according to claim 5, characterized in that: In step 3, the mass ratio of the PVP-AgNWs solution to the Am-AA solution is 1:1.75-2; The mixing temperature is 70-90°C and the mixing time is 0.5-1h.

9. An application of a silver nanowire hydrogel, characterized in that: Zinc sheets are attached to both ends of the silver nanowire hydrogel to obtain a resistive pressure sensor, which is then connected to a digital bridge to identify different numbers and letters as well as human limb movements.

10. An application of silver nanowire hydrogel, characterized in that: The silver nanowire hydrogel is attached to the skin and connected to the ECG acquisition device to measure ECG signals.

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