Fibrous pressure sensor with ultralow detection limit, preparation method and application

Abstract

The invention provides a fibrous degradable flexible pressure sensor with ultralow detection limit and a preparation method and application thereof.The preparation method comprises the steps that lignin powder is dispersed in a sodium hydroxide aqueous solution, ultrasonically crushed and stirred to be uniform, then polyethylene oxide powder is uniformly dissolved in the solution in four times, stirring is conducted till the solution is uniform, and the pressure sensor is obtained; putting the solution into a vacuum cavity, and removing bubbles at room temperature to obtain an electrostatic spinning precursor solution; then preparing a lignin fiber thin film by adopting an electrostatic spinning process, and then drying the thin film; and finally, cutting the obtained lignin fiber film into a square film, placing an interdigital electrode mask on the square film, spraying a metal silver nanowire electrode by using a silver nanowire solution, and then embedding the fiber film in a polyimide film to prepare the flexible pressure sensor. According to the invention, the integrated design of the capacitive pressure sensor is realized, the cost is low, the process is simple, and the pressure sensor has excellent flexibility and sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensors, and particularly to a fibrous degradable flexible pressure sensor with an ultra-low detection limit, a preparation method thereof, and an application thereof. Background Art

[0002] Flexible pressure sensors have broad potential in the field of wearable electronics due to their good flexibility, sensitivity, and integration, and can meet the application requirements of various scenarios. However, traditional flexible pressure sensors are usually made of non-degradable silicon-based materials, which may face problems of environmental pollution and interfacial mismatch. Lignin, as the second most abundant renewable biopolymer on earth, has properties such as easy availability, biocompatibility, biodegradability, and easy processing, and is gradually being used in the field of wearable electronic devices, with great potential to contribute to the global green development economy. Obviously, these excellent properties cannot be achieved in traditional commercial silicon-based sensors, and traditional pressure sensors have problems such as complex preparation processes and inability to balance low detection limits, high sensitivity, and flexibility.

[0003] In recent years, electrospinning has been proposed as a simple and versatile technique to generate charged jets from polymer solutions using a high-voltage electric field and form fibrous films on a roller. Its unique loose fiber structure will undergo obvious deformation at the microscale when subjected to external pressure, and can be used to sense physiological signals in real time, having significant advantages in the field of health detection. Summary of the Invention

[0004] The purpose of the present invention is to provide a fibrous degradable flexible pressure sensor with an ultra-low detection limit, a preparation method thereof, and an application thereof, which solves the problems of complex preparation processes and inability to balance low detection limits, high sensitivity, and flexibility existing in traditional pressure sensors.

[0005] A preparation method of a fibrous degradable flexible pressure sensor with an ultra-low detection limit, the method comprising the following steps:

[0006] Step S1, preparing an electrospinning precursor solution, adding sodium hydroxide particles to deionized water, dispersing evenly to form a first mixture, adding lignin powder to the first mixture, and after ultrasonic fragmentation and stirring evenly, obtaining a second mixture; then adding polyethylene oxide powder to the second mixture in four portions, adjusting the solution viscosity, and after stirring evenly, obtaining a third mixture; placing the third mixture in a vacuum chamber and removing bubbles at room temperature to obtain a dark brown viscous electrospinning precursor solution;

[0007] Step S2, preparing a lignin fiber film by an electrospinning process, and then drying the film to obtain a base layer and a sensing functional layer of the flexible pressure sensor;

[0008] Step S3: Cut the obtained lignin fiber film into a square film. Place an interdigital electrode mask on the square film, spray the silver nanowire solution to form a silver nanowire electrode, connect the wire to the silver nanowire electrode with tape, and then embed the fiber film in a polyimide film to obtain a fibrous degradable flexible pressure sensor with an ultra-low detection limit.

[0009] Further, the electrospinning precursor solution in step S1 includes: sodium hydroxide particles, lignin powder, polyethylene oxide powder, and deionized water. Among them, polyethylene oxide serves as a dispersant, and the mass ratio of sodium hydroxide particles, lignin powder, polyethylene oxide powder, and deionized water is 3:5:5:150.

[0010] Further, the mass ratio of the polyethylene oxide powder added in four times in step S1 is 1:1:1:1.

[0011] Further, the electrospinning process adopted in step S2 is to fill the electrospinning precursor solution into a syringe and apply high-voltage electrospinning at the syringe needle to form a fibrous film. Among them, the high-voltage power supply voltage is 10 KV, the electrospinning flow rate is 1 mL / h, the distance between the needle and the collection device is 15 cm, the roller speed is 20 rpm, the collection material is aluminum foil, and the experimental environment temperature is controlled at 26 °C.

[0012] Further, the drying temperature in the drying treatment in step S2 is 50 °C, and the heat treatment time is 1 h.

[0013] Further, the interdigital electrode mask in step S3 is made by 3D printing with a polylactic acid material. The number of pairs n of the interdigital electrodes is 4, the length x0 is 1 cm, the width w0 is 1.5 mm, and the spacing d0 is 1.25 mm.

[0014] Further, the concentration of the silver nanowire solution is 4 mg / ml, and the solvent is absolute ethanol.

[0015] Further, the size of the square film obtained by cutting the fiber film in step S3 is 3 * 2 cm 2 .

[0016] The fibrous degradable flexible pressure sensor with an ultra-low detection limit prepared by the above preparation method includes an electrospun lignin fibrous substrate and a silver nanowire fibrous interdigital electrode. The electrode extends through a wire to realize the acquisition and processing of the sensor capacitance signal.

[0017] Further, the flexible pressure sensor is prepared by an electrospinning process, and the electrospun lignin film serves as the basic support layer and the functional sensing layer.

[0018] Furthermore, the lignin fibrous film obtained by electrospinning is a composite fiber structure composed of micron-scale fiber backbones and nanoscale fiber villi.

[0019] The above-mentioned fibrous degradable flexible pressure sensor with an ultra-low detection limit can be applied in the field of physiological signal detection, such as for monitoring signals of human cough, swallowing, etc.

[0020] The present invention provides a fibrous degradable flexible pressure sensor with an ultra-low detection limit and a preparation method. By using the electrospinning method, a composite fiber structure film composed of micron-scale fiber backbones and nanoscale fiber villi is obtained. Then, a silver nanowire interdigitated electrode is sprayed on the surface of the lignin fibrous film by using a customized mask template, realizing the integrated design of the capacitive pressure sensor. In the interdigitated electrode design, two adjacent electrode fingers act as charging electrodes, and the electrospun lignin in between acts as the dielectric layer of the capacitor. Since there is a large amount of air in the lignin fiber substrate, the dielectric constant of the interdigitated capacitor is the average value of lignin and air. When the device is subjected to an external pressure, the air content in the lignin fiber substrate decreases, the overall dielectric constant increases, and the capacitance value changes, thus reflecting the change of the external pressure. Due to its unique loose fibrous structure, this pressure sensor has high sensitivity in monitoring human subtle physiological signals. Also, because of its excellent flexibility, it can achieve conformal adhesion with curved surfaces, laying a good foundation for the applications of human wearable sensing and physiological signal detection. The present invention has the following beneficial technical effects:

[0021] The raw materials used in the solution of the present invention are natural biomass materials, which have low cost, are easy to obtain and process, and have biocompatibility and biodegradability, which are of great significance for the sustainable green development of the global economy;

[0022] The present invention adopts the electrospinning process to complete the preparation of the pressure sensing functional layer. Its unique composite fiber structure composed of micron-scale fiber backbones and nanoscale fiber villi gives it an ultra-low pressure detection limit, is very sensitive to external dynamic loads, and has the characteristics of low cost, mature and simple process technology, and easy large-scale automated production, with broad application prospects;

[0023] The fibrous degradable flexible pressure sensor of the present invention has excellent flexibility and can be attached to the human skin for physiological signal monitoring. On the one hand, it can be applied to intelligent medicine to promote the quantification and precision of medical diagnosis. On the other hand, this sensing system can be reused, saving costs. Description of the Drawings

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a flowchart of a preparation method of a fibrous degradable flexible pressure sensor with an ultra-low detection limit provided by an embodiment of the present invention; wherein, i represents the electrospinning process, and ii represents the spraying process using a mask template.

[0026] Figure 2 It is a scanning electron microscope image (SEM) of a fibrous degradable flexible pressure sensor with an ultra-low detection limit obtained by an embodiment of the present invention.

[0027] Figure 3 It is a mechanical-electrical response diagram of the flexible pressure sensor obtained by an embodiment of the present invention.

[0028] Figure 4 It is a pressure response diagram of the ultra-low detection limit obtained by an embodiment of the present invention.

[0029] Figure 5 It is a stability diagram of the flexible pressure sensor obtained by an embodiment of the present invention.

[0030] Figure 6 It is an application diagram of physiological signal monitoring of the flexible pressure sensor obtained by an embodiment of the present invention. Detailed implementation manners

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0032] As Figure 1 shown, a preparation method of a fibrous degradable flexible pressure sensor with an ultra-low detection limit provided by the present invention specifically includes the following steps:

[0033] Step 1: Prepare an electrospinning precursor solution

[0034] The electrospinning precursor solution has four components, including sodium hydroxide particles, lignin powder, polyethylene oxide powder, and deionized water. Among them, the polyethylene oxide powder serves as a dispersant for deionized water, and the mass ratio of sodium hydroxide particles, lignin powder, polyethylene oxide powder, and deionized water is 3:5:5:150.

[0035] The preparation process of the electrospinning precursor solution in this example is as follows: First, disperse 1 g of lignin powder in 30 mL of 0.5 mol / L sodium hydroxide aqueous solution, ultrasonically fragment and stir evenly for 30 minutes. Then, dissolve 1 g of polyethylene oxide powder evenly in the above solution in four portions and stir for 30 minutes until uniform. Next, place the aforementioned solution in a vacuum chamber to remove air bubbles at room temperature, obtaining a dark brown viscous electrospinning precursor solution. The overall fluidity is similar to that of mucilage. Compared with traditional lignin spinning solutions, the solvent of the electrospinning precursor solution prepared in this example does not select a mixture of multiple high-molecular organic toxic solvents, but instead uses a water solvent formulation scheme, streamlining the preparation process.

[0036] Step 2: Electrospinning process

[0037] Fill the electrospinning precursor solution into a syringe and extrude it using an electrospinning device at a controllable feeding rate of 1 mL / h. The experimental environment temperature is controlled at 26 °C, the roller speed is 20 rpm, and the collection material is aluminum foil. Then, connect the applied positive high-voltage DC power supply to the syringe needle and set it to 10 kV, while grounding the collection end. Adjust the distance between the needle and the collector to 15 cm. Finally, peel off the lignin film collected on the aluminum foil paper and place it in an oven at 50 °C for heat treatment for 1 h to obtain a substrate used as a flexible pressure sensor.

[0038] Step 3: Spraying using a mask

[0039] Cut the lignin film into a square shape, place a mask above it for spraying, and use a 3D-printed polylactic acid material to make an interdigital electrode mask. The number of pairs (n), length (x0), width (w0), and spacing (d0) of the interdigital electrodes are 4, 1 cm, 1.5 mm, and 1.25 mm respectively. Add the prepared 4 mg / mL silver nanowire (AgNWs) solution to a high-pressure spray gun and spray 30 times. Connect the wire to the silver nanowire electrode through tape, and then embed the fiber film in polyimide to obtain a fibrous degradable flexible pressure sensor with an ultra-low detection limit composed of an electrospun lignin film and AgNWs interdigital electrodes.

[0040] The scanning electron microscope image (SEM) of a fibrous degradable flexible pressure sensor with an ultra-low detection limit prepared by the above method is as Figure 2 shown, from Figure 2It can be seen that a composite fiber structure with a fiber main body in the order of hundreds of micrometers and fiber villi in the order of hundreds of nanometers is prepared by electrospinning. The diameter of the lignin fiber main body is relatively uniform, and its diameter range is mainly between 0.5 μm and 2 μm. Connecting the wire and the LCR bridge for signal transmission processing, the change in capacitance can be directly read out, which reflects the change in pressure in real time.

[0041] The performance test of a fibrous degradable flexible pressure sensor with an ultra-low detection limit prepared in the above embodiment is as follows:

[0042] The sensitivity of the prepared fibrous degradable flexible pressure sensor was tested using an LCR bridge. Figure 3 It shows the dependence of the capacitance change rate of the pressure sensor on different pressures. The abscissa of this figure shows the gradually increasing pressure values, and the ordinate shows the change rate of the capacitance value of this pressure sensor compared with the initial value. It can be seen from the figure that in the range of 0 Pa - 500 Pa, the sensitivity of the sensor is 4.2 kPa -1 , which can be regarded as a linear region. The composite fiber structure of the fiber main body in the order of hundreds of micrometers and fiber villi in the order of hundreds of nanometers endows the pressure sensor with high sensitivity. Due to the limited amount of air in the electrospun fiber membrane, the sensitivity of the sensor decreases as the pressure increases, and the curve gradually flattens. The enlarged view shows the capacitance response in a small pressure range, and it can be seen that the sensor has good sensitivity and linearity.

[0043] The ultra-low pressure detection limit test of the prepared fibrous degradable flexible pressure sensor was carried out specifically as follows:

[0044] When a 1 cm × 1 cm thin paper with a mass of 0.5 mg is placed on the pressure sensor, due to the deformation of the base fiber, the capacitance increases, as Figure 4 shown. The abscissa of this figure represents time, and the ordinate represents the change rate of the capacitance value of this pressure sensor compared with the initial value, which overall shows the change of capacitance with time when sensing low pressure values. It can be seen that the pressure sensor shows a minimum detection limit of about 0.05 Pa, highlighting the key role of the unique composite fiber structure of the fiber main body in the order of hundreds of micrometers and fiber villi in the order of hundreds of nanometers in achieving a low detection limit.

[0045] The stability and repeatability tests of the prepared fibrous degradable flexible pressure sensor were carried out specifically as follows:

[0046] Build a vibration platform, connect the modal exciter to a power amplifier and a waveform generator to form a pressure output system with controllable vibration amplitude and frequency. Then place the flexible pressure sensor under the oscillator of the modal exciter, and use an LCR bridge to test the capacitance change of the flexible pressure sensor. Adjust the frequency of the modal exciter to 1 Hz and apply 2000 loading / unloading cycles. The capacitance change is as Figure 5 shown. The abscissa of this figure represents time, and the ordinate represents the capacitance value of this pressure sensor. It is observed that the amplitude of the capacitance change is almost the same in multiple cycles, showing good robustness, which confirms the high mechanical stability and reliability of the flexible pressure sensor during long-term use.

[0047] An experimental test on the application of physiological signal monitoring was carried out on the prepared fibrous degradable flexible pressure sensor. Specifically:

[0048] Fix the four sides of the flexible pressure sensor on the skin of the human neck through tape, and extend the wires to connect to an LCR bridge to monitor muscle movement during coughing. Due to the high flexibility of the device, the flexible sensor can conformally adhere to the skin, and the sensor can detect clear coughing signals. In addition, this sensor can also detect swallowing signals, as Figure 6 shown. The abscissa of this figure represents time, and the ordinate represents the change rate of the capacitance value of this pressure sensor compared to the initial value. Since the flexible pressure sensor has the ability to conformally adhere to curved surfaces, it lays a good foundation for human wearable sensing and physiological signal monitoring, and has good performance and broad application prospects in the field of wearable electronics and other fields.

[0049] The present invention provides a fibrous degradable flexible pressure sensor with an ultra-low detection limit, a preparation method and an application. The lignin solution is processed into a fibrous film by electrospinning, serving as the basic support layer and the functional sensing layer. This device has excellent pressure sensing performance, with a sensitivity as high as 4.2 kPa -1 , an ultra-light detection limit of 0.05 Pa. In addition, its unique fibrous structure can keep the initial capacitance value stable on different curvature surfaces, which is of great significance for human health monitoring and applications in the human-machine interface. The fibrous degradable flexible pressure sensor proposed by the present invention opens up a new way for the next generation of wearable electronic products.

[0050] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a fibrous degradable flexible pressure sensor with an ultra-low detection limit, characterized in that: The method comprises the following steps: Step S1, preparing an electrospinning precursor solution, adding sodium hydroxide particles into deionized water, dispersing evenly to form a first mixture, adding lignin powder into the first mixture, ultrasonically crushing, and stirring evenly to obtain a second mixture; adding polyethylene oxide powder into the second mixture four times, adjusting the viscosity of the solution, and stirring evenly to obtain a third mixture; placing the third mixture into a vacuum chamber, removing bubbles at room temperature to obtain a dark brown viscous electrospinning precursor solution; Step S2, preparing a lignin fiber film by an electrospinning process, and then drying the film to obtain a base layer and a sensing function layer of the flexible pressure sensor; Step S3, cutting the obtained lignin fiber film into square films, placing an interdigitated electrode mask on the square film, spraying metal silver nanowire electrodes with a silver nanowire solution, connecting the wires to the silver nanowire electrodes with tape, and then embedding the fiber film in a polyimide film to obtain a fibrous degradable flexible pressure sensor with an ultra-low detection limit.

2. The preparation method according to claim 1, characterized in that: The electrospinning precursor solution in step S1 includes: sodium hydroxide particles, lignin powder, polyethylene oxide powder and deionized water, wherein polyethylene oxide is used as a dispersant, and the mass ratio of sodium hydroxide particles, lignin powder, polyethylene oxide powder and deionized water is 3:5:5:150, and the mass ratio of polyethylene oxide powder added in four times is 1:1:1:

1.

3. The preparation method according to claim 1, characterized in that: The electrospinning process used in step S2 is to fill the electrospinning precursor solution into a syringe, and apply high voltage electrospinning to the syringe needle to form a fibrous film, wherein the high voltage power supply voltage is 10KV, the electrospinning flow rate is 1mL / h, the distance between the needle and the collecting device is 15cm, the roller speed is 20rpm, the collecting material is aluminum foil, and the experimental environment temperature is controlled at 26°C.

4. The preparation method according to claim 1, characterized in that: The drying temperature of the drying treatment in step S2 is 50° C. and the heat treatment time is 1 hour.

5. The preparation method according to claim 1, characterized in that: The number n of the pairs of interdigital electrodes is 4, the length x0 is 1 cm, the width w0 is 1.5 mm, and the spacing d0 is 1.25 mm.

6. The preparation method according to claim 1, characterized in that: The concentration of the silver nanowire solution is 4 mg / ml, and the solvent is anhydrous ethanol.

7. A fibrous degradable flexible pressure sensor with an ultra-low detection limit prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The pressure sensor comprises an electrospun lignin fiber substrate and silver nanowire fiber interdigital electrodes, and the electrodes are extended through wires to realize the collection and processing of sensor capacitance signals.

8. The pressure sensor according to claim 7, characterized in that: The flexible pressure sensor is prepared by an electrostatic spinning process, and the lignin film obtained by spinning is used as a basic supporting layer and a functional sensing layer.

9. The pressure sensor according to claim 8, characterized in that: The lignin fiber film obtained by spinning is a composite fiber structure with a fiber trunk of hundreds of micrometers and hairs of hundreds of nanometers.

10. An application of the fibrous degradable flexible pressure sensor with ultra-low detection limit as claimed in any one of claims 7 to 9 in physiological signal monitoring, for monitoring signals of coughing and swallowing of the human body.

Images