Preparation method and application of silver nanowire hydrogel electrode

Abstract

The application provides a preparation method of super-stretching and high-adhesion silver nanowire hydrogel and application thereof, and is a conductive hydrogel. The silver nanowire hydrogel takes acrylamide, silver nanowire, acrylic acid, polyvinylpyrrolidone and water as main raw materials, silver nanowire is added in the hydrogel system, the toughness and elasticity of the material are enhanced, and the conductivity of the hydrogel is improved. The finally prepared silver nanowire hydrogel has super strong tensile property, extremely high adhesion, excellent conductivity and low contact impedance. The hydrogel prepared by the application can be used for a pressure sensor, can be attached on the skin to collect various physiological signals of the human body, and can be used for electrocardiosignal monitoring. In the aspect of the pressure sensor, the hydrogel can accurately identify different numbers and letters, the accuracy reaches 93%, and can identify various small movements of the human body; in the aspect of physiological signal collection, the hydrogel has good stability, high precision, low impedance, and the material is easy to obtain and simple to operate.

Description

Technical Field

[0001] This invention relates to a silver nanowire hydrogel, its preparation method and application, belonging to the field of conductive hydrogel technology. Background Technology

[0002] Pressure sensing is a dynamic and promising emerging research topic in contemporary science and technology, integrating 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 metallic materials are often limited by their inherent metallic properties, specifically insufficient tensile strength, low adhesion, and low sensitivity. These limitations significantly restrict their application potential in high-precision and widely adaptable wearable devices.

[0003] Conductive hydrogels, composed of a hydrophilic polymer matrix and conductive fillers, possess a flexible cross-linked polymer network. In recent years, they have shone brightly in the vast field of flexible electronic devices, demonstrating immense application potential due to their excellent biocompatibility, tunable mechanical properties, and rich bioactivity. However, limited by the mechanical and electrical properties of existing materials, fabricating pressure sensing materials that simultaneously meet practical application and mechanical performance requirements, exhibiting high tensile strength, good recovery after compression, and high sensitivity, remains a challenge. Furthermore, the poor fatigue resistance of hydrogels leads to poor cyclic stability and short service life in pressure sensor applications. Therefore, the rational design and fabrication of conductive gels with resilience, high tensile strength, high adhesion, and stability are of great significance for the development of next-generation high-performance pressure sensors. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a method for preparing and applying a highly tensile and highly adhesive silver nanowire hydrogel. This hydrogel is conductive, using acrylamide as the hydrogel framework. The polymerization reaction between acrylic acid and acrylamide enhances the hydrogel's mechanical properties. This invention possesses advantages such as super-stretchability, high adhesion, high conductivity, high signal-to-noise ratio, simple structure, and good biocompatibility. It can be used in pressure sensors, exhibiting fast response speed and generating stable resistance change signals under external force. It can accurately identify different numbers and letters, and detect minute movements of various body parts. It can also be used to monitor human motion signals, such as the continuous acquisition of physiological signals like electrocardiograms. The innovative conductive hydrogel preparation method provided by this invention has advantages such as simple operation process, low cost, good biocompatibility, and multifunctionality, which is conducive to promoting the development of next-generation smart wearable electronics and energy storage devices. It plays a positive role in promoting the innovation and development of next-generation smart wearable electronic devices and sensors.

[0005] The technical solution of this invention is:

[0006] A silver nanowire hydrogel is a porous hydrogel whose main raw materials include acrylamide, acrylic acid, silver nanowires, polyvinylpyrrolidone and water, and also include an initiator and a crosslinking agent.

[0007] Acrylamide and acrylic acid are polymerized to form a hydrogel, providing a tough framework;

[0008] Silver nanowires are uniformly distributed in the hydrogel, providing electrical conductivity and improving the mechanical properties of the hydrogel, while reducing the material impedance.

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

[0010] The crosslinking 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 polyvinylpyrrolidone to silver nanowires is 1:1-4;

[0015] The mass ratio of the crosslinking agent to polyvinylpyrrolidone is 1:7-7.5.

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

[0017] Step 1: Prepare the Am-AA solution. The specific method is as follows: add acrylamide and acrylic acid to deionized water, add an initiator, and stir magnetically to dissolve them completely to obtain the Am-AA solution.

[0018] Step 2, prepare PVP-AgNWs solution. The specific method is as follows: add silver nanowires and polyvinylpyrrolidone to deionized water, add crosslinking agent, stir thoroughly and then sonicate to obtain PVP-AgNWs solution.

[0019] Step 3: Mix the Am-AA solution obtained in Step 1 and the PVP-AgNWs solution obtained in Step 2 evenly, pour the mixture into a mold, place it in an oven and heat it to react. After the reaction is complete, remove the mold and wait for the temperature to drop to room temperature before removing the product to obtain silver nanowire hydrogel (PA-AgNWs hydrogel).

[0020] In 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 mixing temperature is 20-30℃; and the magnetic stirring time is 30 min.

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

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

[0023] One application of silver nanowire hydrogel involves attaching zinc sheets as electrodes to both ends of the prepared silver nanowire hydrogel and connecting it to a circuit to obtain a resistive pressure sensor that can accurately identify different numbers and letters and detect minute movements of various parts of the body. At the same time, the silver nanowire hydrogel can be attached to the skin and connected to an electrocardiogram (ECG) acquisition device to measure ECG signals.

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

[0025] This invention uses a polyacrylamide-acrylic acid copolymer obtained by the polymerization reaction of acrylamide and acrylic acid as the hydrogel framework. Acrylamide and acrylic acid contain a large number of hydrogen bonds, which reduces the polymerization of silver nanowires and makes the silver nanowires uniformly dispersed in the matrix. While ensuring the stability of the hydrogel electrode, the conductivity of the hydrogel is significantly improved.

[0026] This invention incorporates silver nanowires as conductive molecules into the raw materials, which improves the conductivity of the hydrogel and also makes the hydrogel exhibit better sensing characteristics. Various pressure signals can be accurately and quickly transmitted to the electrodes with an extremely short response time, enabling this invention to better identify various subtle human movements.

[0027] This invention uses acrylamide and acrylic acid as raw materials to prepare a hydrogel with extremely high tensile strength, excellent adhesion and compression resilience, good biocompatibility, and can closely adhere to the skin without causing skin irritation.

[0028] In the silver nanowire hydrogel electrode prepared by the method of this invention, the acrylamide, after cross-linking, forms non-toxic and harmless polyacrylamide, thus improving the biocompatibility of the electrode. Furthermore, all other constituent materials of this invention are free of hazardous chemicals, further ensuring the biocompatibility of the electrode. Moreover, the materials selected in this preparation method are relatively inexpensive, possessing broad development prospects and enormous market potential.

[0029] This invention provides a method for preparing a highly stretchable and highly adhesive silver nanowire hydrogel and its applications, belonging to the field of conductive hydrogels. The silver nanowire hydrogel of this invention uses acrylamide, silver nanowires, and acrylic acid as main raw materials. The addition of silver nanowires to the hydrogel system enhances the material's toughness and elasticity, and improves the hydrogel's conductivity. The final prepared silver nanowire hydrogel exhibits superior stretchability, extremely high adhesion, excellent conductivity, and low contact impedance. The hydrogel electrode prepared by this invention can be used as a pressure sensor or attached to the skin to collect various physiological signals from the human body. In pressure sensing, the electrode of this invention can accurately identify different numbers and letters with an accuracy rate of 93%, and can also identify various subtle human movements. In physiological signal acquisition, it offers better stability and higher accuracy compared to commercial electrodes, and the materials are readily available and the operation is simple, showing great application potential. Attached Figure Description

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

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

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

[0033] Figure 4 The XPS spectrum and Ag 3d high-resolution spectrum of the silver nanowire hydrogel of this invention are shown below.

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

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

[0036] Figure 7 This is a graph showing the relative change in resistance of the silver nanowire hydrogel of the present invention under different mass pressures of weights.

[0037] Figure 8 This is a graph showing the relative change in electrical resistance of the silver nanowire hydrogel of the present invention during swallowing and wrist flexion.

[0038] Figure 9This refers to the response time of the silver nanowire hydrogel of this invention;

[0039] Figure 10 This is a bar chart showing the adhesion properties of the silver nanowire hydrogel of this invention;

[0040] Figure 11 The waveforms of the silver nanowire hydrogel pressure sensor prepared using this invention are used to record the writing of the numbers 0-9 and the letters B, I, and T.

[0041] Figure 12 It is a confusion matrix for writing the ten digits 0-9 using the hydrogel pressure sensor of this invention.

[0042] Figure 13 This is a comparison chart of electrocardiogram signals measured by the silver nanowire hydrogel electrode prepared in this invention and a signal-to-noise ratio histogram. Detailed Implementation

[0043] The present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. However, these should not be construed as limiting the scope of protection of the present invention. It should be emphasized that the specific embodiments described below are merely examples to illustrate the present invention, and not as limitations on its scope of protection. The experimental methods involved in the present invention all follow conventional operating procedures, and the materials, reagents, and instruments used, unless otherwise specified, are all standard items widely used in the art, and can be easily obtained commercially by those skilled in the art. This design aims 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 includes the following steps:

[0045] Step 1: Prepare the Am-AA solution. The specific method is as follows: add acrylamide and acrylic acid to deionized water, add an initiator, and stir magnetically to dissolve them completely to obtain the Am-AA solution.

[0046] Step 2, prepare PVP-AgNWs solution. The specific method is as follows: add silver nanowires and polyvinylpyrrolidone to deionized water, add crosslinking agent, stir thoroughly and then sonicate to obtain PVP-AgNWs solution.

[0047] Step 3: Mix the Am-AA solution obtained in Step 1 and the PVP-AgNWs solution obtained in Step 2 evenly, pour the mixture into a mold, place it in an oven and heat it to react. After the reaction is complete, remove the mold and wait for the temperature to drop to room temperature before removing the product to obtain PA-AgNWs hydrogel.

[0048] Example 1

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

[0050] Step 1: Add 5g of acrylamide and 0.5g of acrylic acid to 5ml of deionized water, and add 30mg of initiator KPS. Stir magnetically for 30min to dissolve completely to obtain Am-AA solution.

[0051] Step 2: Add 0.2g of silver nanowires and 0.2g of polyvinylpyrrolidone to 5ml of deionized water, add 30mg of crosslinking agent N,N'-methylenebisacrylamide, stir thoroughly for 30min, and sonicate for 5min to obtain PVP-AgNWs solution.

[0052] Step 3: Mix the Am-AA solution obtained in Step 1 and the PVP-AgNWs solution obtained in Step 2 evenly, pour the mixture into a mold, place it in an oven, heat at 80°C for 1 hour, remove the mold after the reaction is complete, and remove the product after the temperature drops to room temperature to obtain PA-0.2AgNWs hydrogel.

[0053] Example 2

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

[0055] Example 3

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

[0057] Example 4

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

[0059] Figure 2 This is a photograph of the PA-0.2AgNWs hydrogel used in Example 1. Figure 2 The image shown is the hydrogel of the present invention, which has extremely high light transmittance. The background image can be clearly observed through the silver nanowire hydrogel, which fully demonstrates its high light transmittance. Figure 2 b shows the excellent adhesion of the hydrogel of the present invention when applied to the arm and pressed by the fingers.

[0060] Figure 3 a and Figure 3Image b shows a scanning electron microscope (SEM) image of the hydrogel from Embodiment 4 of this invention. Careful observation of these two images clearly reveals the uniform porous structure of the hydrogel, with its internal cross-linked network being extremely well-constructed. Furthermore, the silver nanowires are well-distributed within the hydrogel matrix, exhibiting excellent dispersibility, which further verifies that the silver nanowires are successfully embedded and distributed within the hydrogel matrix.

[0061] Figure 4 a is the XPS full spectrum of the hydrogel in Example 4. Figure 4 b shows the high-resolution XPS spectrum of Ag 3d, where the two main signal peaks of Ag correspond to Ag 3d 5 / 2 and Ag 3d 3 / 2, respectively. This further confirms the presence of Ag, indicating that the silver nanowires are dispersed within the silver nanowire hydrogel matrix.

[0062] The compressibility of silver nanowire hydrogels was tested using a Mark-10 force gauge from the United States. The silver nanowire hydrogels were made into cylinders (r = 7.5 mm, h = 100 mm) and placed on the testing platform for compression experiments. Figure 5 The rebound curves of the hydrogel under 80% compressive strain conditions and 100 compression load-unloading tests were recorded. It can be seen that the hydrogel exhibits only slight plastic deformation during this compression process, fully demonstrating its stable mechanical properties. Furthermore, in the test data, the strain curve of the hydrogel of this invention shows very small hysteresis, and the almost uniform curves throughout the 100 cycles indicate that the hydrogel of this invention possesses excellent mechanical stability and good fatigue resistance.

[0063] The silver nanowire hydrogel (10mm×5mm×2mm) was clamped at both ends with a clamp and a tensile test was performed using a Mark-10 force gauge. Figure 6 The figures show the tensile stress-strain curves for Examples 1-4. The figures indicate that Example 1 achieved the highest elongation, with a value as high as 1393%, demonstrating the excellent super-tensile properties of the present invention. In Example 4, the highest tensile strength was recorded, with a specific value of 310 kPa, demonstrating good tensile strength.

[0064] The pressure sensing characteristics of the silver nanowire hydrogel were tested using a Tonghui TH2830 precision LCR digital bridge. Zinc sheets were attached to both ends of the silver nanowire hydrogel (r=9mm, h=2mm), and then further bonded with insulating tape to obtain a resistive pressure sensor. Weights of different masses were placed on the pressure sensor, and its sensing performance was tested using the LCR digital bridge. The pressure sensor was also attached to a body joint to detect body movement.

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

[0066] Figure 8 a represents 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 signals generated by the movement of the Adam's apple. Figure 8 b represents the wrist flexion signal detected in Example 4, indicating that the hydrogel pressure sensor of the present invention can detect minute human movements and physiological signals, thus demonstrating not only its potential value in wearable applications but also highlighting its superior sensing performance.

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

[0068] Silver nanowire hydrogel (15mm×10mm×2mm) was attached to different adhesive material substrates, and the two ends of the adhesive material were clamped by a fixture. Adhesion tests were conducted on a Mark-10 force gauge. Figure 10 The bar chart shows the adhesion properties of the hydrogel obtained in Example 1. The hydrogel of the present invention exhibits adhesion to various materials. Due to the deformation and movement of the hydrogel when it adheres to a rough surface, mechanical interlocking is automatically introduced into the adhesion surface. Accompanied by hydrogen bonding and electrostatic interactions, the hydrogel of the present invention exhibits excellent adhesion properties. In the figure, the adhesion force of Example 1 on pigskin is as high as 39 kPa.

[0069] Figure 11 The waveforms are 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 and 7, 9, and 3 and 6 show certain similarities, while the waveforms of the remaining numbers are significantly different and can be distinguished by the naked eye.

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

[0071] Figure 13 a) is a comparison image of the electrocardiograms obtained by the electrocardiogram acquisition device (AD8232 chip) using the electrocardiogram of the hydrogel electrode prepared in Example 4 and a commercial electrode (AMBU N-00-S / 25 gel electrode from Denmark). Figure 13 b is a bar chart showing the signal-to-noise ratio of Example 4 and the commercial electrode. Compared to the commercial electrode, the silver nanowire hydrogel electrode of this invention exhibits less noise, higher accuracy, and a better signal-to-noise ratio.

[0072] In summary, this invention has developed a highly stretchable and highly adhesive silver nanowire hydrogel. This hydrogel can accurately identify different numbers and letters with an accuracy rate of 93%, and can also detect minute movements of various parts of the body. Furthermore, the hydrogel of this invention can stably and accurately measure human physiological signals, and also possesses advantages such as high conductivity, good biocompatibility, and a simple preparation method. It is compatible with most physiological signal acquisition devices currently on the market and is suitable for large-scale promotion and application.

[0073] The above description represents a preferred embodiment of the present invention, but the invention is not limited thereto. Any equivalent substitutions, reasonable adjustments, or obvious changes made based on the content of this specification, provided that the basic principles and core spirit of the invention are followed, should be included within the scope of protection of the present invention.

Claims

1. A silver nanowire hydrogel, characterized in that: The main raw materials include acrylamide, acrylic acid, silver nanowires, polyvinylpyrrolidone and deionized water, as well as initiators and crosslinking 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 polyvinylpyrrolidone to silver nanowires is 1:1-4; The mass ratio of the crosslinking agent to polyvinylpyrrolidone is 1:7-7.5; The initiator is any one of ammonium persulfate, benzoyl peroxide, and potassium persulfate; The crosslinking agent is N,N'-methylenebisacrylamide; The concentration of the silver nanowires is 10 mg / ml; The preparation method of this silver nanowire hydrogel is as follows: Step 1: Mix acrylamide, acrylic acid, initiator and deionized water, stir to obtain Am-AA solution; Step 2: Mix silver nanowires, polyvinylpyrrolidone, crosslinking agent and deionized water, stir, and ultrasonically pulverize to obtain PVP-AgNWs solution; Step 3: Mix the Am-AA solution obtained in Step 1 with the PVP-AgNWs solution obtained in Step 2 to obtain silver nanowire hydrogel. In 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 mixing temperature is 20-30℃, and the stirring time is 30 min. In step 2, the concentration of silver nanowires is 10 mg / ml, the mass ratio of polyvinylpyrrolidone to silver nanowires is 1:1-4, the mass ratio of polyvinylpyrrolidone to deionized water is 1:25, the mass ratio of crosslinking agent to polyvinylpyrrolidone is 1:7-7.5, the stirring time is 0.5-1 h, and the ultrasonic crushing time is 3-5 min. In step 3, the mass ratio of PVP-AgNWs solution to Am-AA solution is 1:1.75-2; The mixing temperature is 70-90℃, and the mixing time is 0.5-1h.

2. An application of the silver nanowire hydrogel according to claim 1, characterized in that: A resistive pressure sensor is obtained by attaching zinc sheets to both ends of a silver nanowire hydrogel. The pressure sensor is then connected to a digital bridge to identify different numbers and letters, as well as human limb movements.

3. An application of the silver nanowire hydrogel according to claim 1, characterized in that: Silver nanowire hydrogel is applied to the skin and connected to an electrocardiogram (ECG) acquisition device for measuring ECG signals.

Images