A triboelectric self-powered flexible force sensing sensor based on conductive ionic gel

Abstract

The present invention discloses a triboelectric self-powered flexible force sensing sensor based on a conductive ionic gel, belonging to the technical field of flexible sensors. The sensor prepared by using an ionic liquid, a monomer, a photoinitiator, a crosslinking agent and silicone rubber has a simple sandwich structure. Among them, the silicone rubber serving as the friction layer and the encapsulation layer is beneficial to protecting the flexible electrode and enhancing the output performance of the sensor, and the ionic liquid gel plays a conductive role. This flexible sensor has good stability, durability and hydrophobicity, and can be stretched, twisted and bent. This flexible sensor has a mapping relationship between the pressure value and the output voltage of the sensor, and can be used as a flexible force sensing sensor. The sensor can charge a capacitor to drive wearable electronic devices. This work provides a new method for constructing stretchable power sources and self-powered sensors, and has potential applications in different fields such as robotics, kinematics and biomechanics.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensors, and particularly to a friction self-powered flexible force sensing sensor based on a conductive ionic gel. Background Art

[0002] Force sensing sensors made of compliant and extensible materials can provide safer and more robust human-machine interactions, bridging the gap between machines and humans. High-precision flexible and stretchable force sensing sensors are crucial for realizing force feedback in electronic skin and wearable devices. Currently, flexible pressure sensors mainly include capacitive, resistive, piezoelectric, and triboelectric types. Capacitive sensors are suitable for measuring pressure changes within a small range. Resistive sensors have the characteristics of simplicity, durability, and low cost. Piezoelectric sensors are applicable to high-precision pressure measurement. However, sensors often undergo large deformations. Even thin film sensors with relatively simple structures and small volumes cannot withstand the large deformations generated during application, and the accuracy of data cannot be guaranteed under bending. In addition, existing sensors require continuous power supply. Triboelectric sensors, on the other hand, have simple structures, a wide range of material selections, can better meet the needs of flexible structures, and can achieve self-power supply of the sensors. These characteristics make triboelectric sensors an ideal choice for flexible sensors.

[0003] The flexible friction layer of triboelectric flexible sensors can be composed of flexible materials such as polydimethylsiloxane (PDMS), polyurethane (PU), and silicone rubber. However, the electrodes of triboelectric nanogenerators (TENGs) are usually made of metal materials lacking stretchability, such as silver, gold, or copper, which greatly limits the application and development of stretchable TENGs. Electrodes with high mechanical properties and conductivity are the core of flexible TENGs. Liquid metals, graphene, carbon nanotubes, conductive fibers, and hydrogels are considered suitable materials. However, the application of liquid metals in the field of fresh food is not yet safe enough; the high cost and irreversible damage of graphene and carbon nanotubes limit their development. However, there are still few examples of using hydrogels, especially ionic liquid gels, as TENG electrodes.

[0004] Good mechanical properties and high electrical conductivity are prerequisites for ionic gels as flexible electrodes. The patent "CN115466355B A Multifunctional Conductive Ionic Gel, Preparation Method and Application Thereof" introduces a method for preparing ionic gels by ionizing radiation technology, with an ionic conductivity reaching 4.9 ms / cm; when the maximum strain is 546%, the tensile strength level is relatively low, about 50 Kpa; when the tensile strength is increased to 225 Kpa, the tensile strain is reduced to less than 275%. The patent "CN115028769A A Super-Stretchable Conductive Ionic Gel and Its Preparation Method and Application" introduces a preparation method for a super-stretchable conductive ionic gel. Although the prepared ionic gel has certain stretchability and tensile strength, its conductivity is only 2.02 ms / cm. It can be seen that designing an ionic gel with excellent comprehensive properties as a flexible electrode to achieve a balance between high electrical conductivity and good mechanical strength remains a huge challenge. Summary of the Invention

[0005] In view of the above-mentioned prior art, the object of the present invention is to provide a triboelectric self-powered flexible force sensing sensor based on conductive ionic gels. This flexible force sensing self-powered sensor has good stretchability and sensitivity, overcomes the conflict between conductivity and mechanical properties, has a mapping relationship between the pressure value and the output voltage of the sensor, and can achieve force sensing through self-power supply.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In the first aspect of the present invention, a triboelectric nanogenerator is provided. The triboelectric nanogenerator includes an ionic liquid gel, silicone rubbers attached to opposite sides of the ionic liquid gel, and wires connecting the ionic liquid gel and the silicone rubbers. The silicone rubber is Ecoflex silicone rubber; the ionic liquid gel is made from the following raw materials: ionic liquid, monomer, photoinitiator, and crosslinking agent;

[0008] The ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and the monomer is selected from at least one of N,N-dimethylacrylamide or acrylamide; the photoinitiator is initiator 1173, and the crosslinking agent is methylene bisacrylamide;

[0009] The mass ratio of the ionic liquid, monomer, photoinitiator, and crosslinking agent is (1 - 10):1:(0.0001 - 0.05):(0.0001 - 0.05).

[0010] In the second aspect of the present invention, a preparation method of the triboelectric nanogenerator is provided, including the following steps:

[0011] (1) Mix the ionic liquid, monomer, photoinitiator, and crosslinking agent, heat and stir evenly to obtain a precursor solution, and perform an ultraviolet light irradiation reaction on the precursor solution to obtain an ionic liquid gel;

[0012] (2) Prepare silicone rubber, connect a wire to the silicone rubber, and sandwich the ionic liquid gel between two pieces of silicone rubber to obtain a triboelectric nanogenerator.

[0013] Further, the mass ratio of the ionic liquid to the monomer is (5 - 8):1, and the sum of the masses of the photoinitiator and the crosslinking agent accounts for (0.1 - 5)% of the mass of the monomer.

[0014] Further, in step (1), in the monomer, the mass ratio of N,N-dimethylacrylamide to acrylamide is (1 - 10):1.

[0015] Further, in step (1), the heating and stirring temperature is 90 - 130 °C, the stirring speed is 400 - 1500 rpm, and the stirring time is 1 - 10 min.

[0016] Further, in step (1), the wavelength used for ultraviolet light irradiation is 365 nm, and the irradiation time is 5 - 30 min.

[0017] Further, in step (2), the ionic liquid gel and the two pieces of silicone rubber are clamped by van der Waals forces.

[0018] Further, in step (2), after sandwiching the ionic liquid gel between two pieces of silicone rubber, use Ecoflex-00-30 silicone rubber to connect the joint between the ionic liquid gel and the Ecoflex silicone rubber, and heat and cure at a temperature of 90 - 110 °C for 0.5 - 5 min.

[0019] In the third aspect of the present invention, there is provided a triboelectric self-powered flexible force sensing sensor based on a conductive ionic gel, and the triboelectric self-powered flexible force sensing sensor includes the triboelectric nanogenerator.

[0020] In the fourth aspect of the present invention, there is provided an application of the triboelectric self-powered flexible force sensing sensor based on the conductive ionic gel in manufacturing a flexible manipulator.

[0021] The beneficial effects of the present invention:

[0022] (1) The flexible conductive ionic gel provided by the present invention is prepared by a one-pot method, the preparation process is simple, the manufacturing cost is low, and it has good conductivity, stretchability, and electrochemical stability, and is an excellent flexible electrode.

[0023] (2) The self-powered flexible force sensing sensor provided by the present invention adopts a sandwich structure, which simplifies the internal structure of the sensor. By completely wrapping the hydrogel film, it effectively reduces its water loss and prevents the influence of the external environment on the internal gel of the sensor, and has good environmental adaptability. The sensor has excellent tensile performance, can achieve modular series connection, improve the output performance, and realizes the self-power supply of the sensor through the coupling effect of electrostatic induction and triboelectrification.

[0024] (3) The self-powered flexible force sensing sensor provided by the present invention has good stability, durability and hydrophobicity. Among them, the silicone rubber as the friction layer and the encapsulation layer is beneficial to protecting the flexible electrode and enhancing the output performance of the sensor, and the conductive ionic gel plays a conductive role. The self-powered flexible force sensing sensor provided by the present invention has good output performance, and it has a mapping relationship between the pressure value and the output voltage of the sensor, and can accurately measure the force received on the contact surface of the flexible hand. The prepared flexible sensor can be stretched, twisted and bent. The self-powered flexible force sensing sensor can be compliantly attached to the surface of the manipulator without damaging the fruit, and can realize the real-time and dynamic monitoring of the clamping force, which helps to realize the mechanization and intelligence of fruit and vegetable harvesting. Description of the Drawings

[0025] Figure 1 It is a flow chart for preparing the conductive ionic gel;

[0026] Figure 2 It is a structure diagram of the flexible force sensing self-powered sensor;

[0027] Figure 3 It is a working principle diagram of the sensor based on a single-electrode triboelectric nanogenerator;

[0028] Figure 4 It is a physical diagram of the flexible force sensing self-powered sensor of the present invention;

[0029] Figure 5 It is a tensile-stress curve of Examples 1-4 of the present invention;

[0030] Figure 6 It is a broken line graph of resistivity and conductivity of Examples 1-4 of the present invention;

[0031] Figure 7 It is a comparison graph of the output voltage of the triboelectric nanogenerators prepared in Examples 1-4 of the present invention;

[0032] Figure 8 It is a fitting graph of the output voltage under different pressures of Example 3 of the present invention;

[0033] Figure 9 It is an anti-fatigue test graph of Example 3 of the present invention. Detailed Embodiments

[0034] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application pertains.

[0035] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

[0036] The test materials not specifically described used in the embodiments of the present invention are all conventional test materials in the art and can be obtained through commercial channels.

[0037] It is often difficult to simultaneously meet the mechanical properties and electrical conductivity of ionic liquid gels. In the formulation of ionic gels, the ratio of ionic liquid to monomer often faces a contradiction between conductivity and stretchability. When a large amount of ionic liquid is added to improve the electrical conductivity, the excessive ionic liquid content will cause a significant decrease in the mechanical strength and stretchability of the gel. The gel becomes too soft and easily broken, making it difficult to meet the mechanical requirements in practical applications; while if the proportion of the monomer is increased to enhance the mechanical properties and stretchability, the insufficient ionic liquid content in the gel will affect the formation of ionic conduction channels and reduce the electrical conductivity of the material. Therefore, it is of great significance to obtain an ionic liquid gel that ensures excellent mechanical properties while having high electrical conductivity, and thus the present invention is produced.

[0038] Example 1

[0039] The preparation method of the ionic gel TENG is shown in Figure 1 、 Figure 2 , and specifically includes the following steps:

[0040] (1) Take 2.40 g of the ionic liquid BMIMTF2N (1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and add it to a glass container. Then, sequentially add 0.384 g of the monomer DMAA (N,N-Dimethylacrylamide), 0.096 g of the monomer AM (Acrylamide), the photoinitiator 1173, and the crosslinking agent MBAA (N,N'-methylenediacrylamide) to obtain a precursor solution. Among them, the masses of the photoinitiator 1173 and the crosslinking agent MBAA are both 1 wt% of the total monomer mass. After being stirred at 110 °C and 800 rpm for 5 min in a thermostatic magnetic stirrer until completely dissolved, they are added. The mass ratio of the ionic liquid to the total monomers (monomer DMAA and monomer AM) is 5:1.

[0041] (2) Immediately transfer the homogeneous and transparent precursor solution to a mold and cool it to room temperature. Then, irradiate it with 365 nm ultraviolet light for 15 min to finally obtain an ionic liquid gel.

[0042] (3) Mix the silicone rubber solutions A and B (Ecoflex-00-30) in a mass ratio of 1:1 and pour them into a polytetrafluoroethylene mold with a hollow structure. Evacuate the air bubbles in an electrothermal constant temperature blast drying oven and cure at 65 °C for 2 hours. Then, demold the silicone rubber (20 mm × 4 mm) from the polytetrafluoroethylene mold. Repeat the above process to obtain two Ecoflex silicone rubbers of the same size.

[0043] (4) Cut the previously prepared ionic gel into a size of 15 mm × 20 mm × 2 mm and place it in the groove of the Ecoflex layer. Connect the copper wire to the surface of the ionic gel. Take another silicone rubber of the same kind. The two silicone rubbers sandwich the gel in the middle, encapsulate the hydrogel, and squeeze out the air to achieve tight adhesion between the materials through van der Waals forces. To ensure the airtightness of the device, use a small amount of Ecoflex-00-30 silicone rubber to bond the seams of the two opposite silicone rubbers, and then cure by heating with a hot air gun at a temperature of 100 °C for 1 min to obtain a TENG based on ionic gel with a thickness range of 4 mm.

[0044] Example 2

[0045] The preparation method of the TENG with ionic gel specifically includes the following steps:

[0046] (1) 2.88 g of the ionic liquid BMIMTF2N was added to a glass container, and 0.384 g of monomer DMAA, 0.096 g of monomer AM, photoinitiator 1173, and crosslinking agent MBAA were successively added to obtain a precursor solution. Among them, the mass of both the photoinitiator 1173 and the crosslinking agent MBAA was 1 wt% of the total monomer mass. After being stirred at 110 °C and 800 rpm for 5 min until completely dissolved in a constant-temperature magnetic stirrer, they were added. The mass ratio of the ionic liquid to the total monomers (monomer DMAA and monomer AM) was 6:1.

[0047] (2) The uniform and transparent precursor solution was immediately transferred to a mold and cooled to room temperature, and then irradiated with ultraviolet light at 365 nm for 15 min to finally obtain an ionic liquid gel.

[0048] (3) Silicone rubber solutions A and B (Ecoflex-00-30) were mixed at a mass ratio of 1:1 and poured into a polytetrafluoroethylene mold with a hollow structure. After evacuating bubbles in an electrothermal constant-temperature forced-air drying oven and curing at 65 °C for 2 h, the silicone rubber (2 mm × 4 mm) was demolded from the polytetrafluoroethylene mold. The above process was repeated to obtain two Ecoflex silicone rubbers of the same size.

[0049] (4) The previously prepared ionic gel was cut into a size of 15 mm × 20 mm × 2 mm and placed in the groove of the Ecoflex layer. Copper wires were connected to the surface of the ionic gel. Another piece of the same silicone rubber was taken, and the two silicone rubbers clamped the gel in the middle to encapsulate the hydrogel and squeeze out the air, achieving tight adhesion between the materials through van der Waals forces. To ensure the airtightness of the device, a small amount of Ecoflex-00-30 silicone rubber was used to bond the seams of the two opposite silicone rubbers, and then it was cured by heating with a hot air gun at a temperature of 100 °C for 1 min to obtain a TENG based on ionic gel with a thickness range of 4 mm.

[0050] Example 3

[0051] The preparation method of the TENG with ionic gel specifically includes the following steps:

[0052] (1) 3.36 g of the ionic liquid BMIMTF2N was added to a glass container, and 0.384 g of monomer DMAA, 0.096 g of monomer AM, photoinitiator 1173, and crosslinking agent MBAA were successively added to obtain a precursor solution. Among them, the mass of both the photoinitiator 1173 and the crosslinking agent MBAA was 1 wt% of the total monomer mass. After being stirred at 110 °C and 800 rpm for 5 min until completely dissolved in a constant-temperature magnetic stirrer, they were added. The mass ratio of the ionic liquid to the total monomers (monomer DMAA and monomer AM) was 7:1.

[0053] (2) Immediately transfer the uniform and transparent precursor solution into a mold and cool it to room temperature. Subsequently, initiate it under 365 nm ultraviolet light for 15 minutes to finally obtain an ionic liquid gel.

[0054] (3) Mix silicone rubber solutions A and B (Ecoflex-00-30) in a mass ratio of 1:1 and pour them into a polytetrafluoroethylene mold with a hollow structure. Remove air bubbles by vacuumizing in an electrothermal constant temperature forced air drying oven, and after curing at 65 °C for 2 hours, demold the silicone rubber (2 mm × 4 mm) from the polytetrafluoroethylene mold. Repeat the above process to obtain two Ecoflex silicone rubbers of the same size.

[0055] (4) Cut the previously prepared ionic gel into dimensions of 15 mm × 20 mm × 2 mm and place it in the groove of the Ecoflex layer. Connect copper wires to the surface of the ionic gel. Take another silicone rubber of the same kind, sandwich the gel between the two silicone rubbers, encapsulate the hydrogel, and squeeze out the air to achieve tight adhesion between the materials through van der Waals forces. To ensure the airtightness of the device, use a small amount of Ecoflex-00-30 silicone rubber to bond the seams of the two opposite silicone rubbers, and then cure it by heating with a hot air gun at a temperature of 100 °C for 1 minute to obtain an ionic gel-based TENG with a thickness range of 4 mm.

[0056] Example 4

[0057] The preparation method of the ionic gel-based TENG specifically includes the following steps:

[0058] (1) Take 3.84 g of ionic liquid BMIMTF2N and add it to a glass container. Sequentially add 0.384 g of monomer DMAA, 0.096 g of monomer AM, photoinitiator 1173, and crosslinking agent MBAA to obtain a precursor solution. Among them, the masses of photoinitiator 1173 and crosslinking agent MBAA are both 1 wt% of the total monomer mass, and they are added after being completely dissolved by stirring at 110 °C and 800 rpm for 5 minutes in a constant temperature magnetic stirrer. The mass ratio of the ionic liquid to the total monomers (monomer DMAA and monomer AM) is 8:1.

[0059] (2) Immediately transfer the uniform and transparent precursor solution into a mold and cool it to room temperature. Subsequently, initiate it under 365 nm ultraviolet light for 15 minutes to finally obtain an ionic liquid gel.

[0060] (3) Mix silicone rubber solutions A and B (Ecoflex-00-30) in a mass ratio of 1:1 and pour them into a polytetrafluoroethylene mold with a hollow structure. Remove air bubbles by vacuumizing in an electrothermal constant temperature forced air drying oven, and after curing at 65 °C for 2 hours, demold the silicone rubber (2 mm × 4 mm) from the polytetrafluoroethylene mold. Repeat the above process to obtain two Ecoflex silicone rubbers of the same size.

[0061] (4) Cut the previously prepared ion gel into a size of 15 mm × 20 mm × 2 mm and place it in the groove of the Ecoflex layer. Connect the copper wire to the surface of the ion gel. Take another piece of the same silicone rubber, sandwich the gel in the middle with the two silicone rubbers, encapsulate the hydrogel, and squeeze out the air to achieve tight adhesion between the materials through van der Waals forces. To ensure the airtightness of the device, use a small amount of Ecoflex-00-30 silicone rubber to bond the seams of the two opposite silicone rubbers, and then cure it by heating with a hot air gun at a temperature of 100 °C for 1 min to obtain an ion gel-based TENG with a thickness range of 4 mm.

[0062] The TENG of the present invention is based on the coupling effect of triboelectrification and electrostatic induction. The working principles of the TENGs prepared in Examples 1-4 are as Figure 3 shown: When another material with different electronegativity contacts the silicone rubber film, the silicone rubber has a strong tendency to lose electrons. Due to the principle of triboelectrification, charges are transferred from the surface of the red square object to the silicone rubber film, resulting in a positively charged surface of the red square object, while an equal amount of negative charges are generated on the surface of the silicone rubber film to reach electrostatic equilibrium ( Figure 3 -i). When the red square object separates from the silicone rubber film, the electrostatic equilibrium is broken, and the electrostatic induction causes corresponding positive charges to be generated on the ion gel electrode, and at the same time drives the transient charges to transfer from the external circuit to the ground, generating an electrical signal ( Figure 3 -ii). When the red square object is separated from the silicone rubber far enough, an electrostatic equilibrium is formed and no electrical signal is generated ( Figure 3 -iii). When the red square object approaches the silicone rubber again, the whole process will reverse, and the positive charges induced in the ion gel electrode are neutralized by the electrons from the ground, generating an opposite electrical signal ( Figure 3 -iv). When the contact-separation motion is repeatedly performed between the surface of the red square object and the silicone rubber, an alternating current can be generated.

[0063] In this process, the conductive ions in the ion gel electrode play an important role in improving the output of the TENG. The conductive ions further promote charge transfer by forming another triboelectrification layer at the interface between the ion gel electrode and the silicone rubber, making the ion gel electrode have good conductivity.

[0064] Test Example 1: Gel tensile test

[0065] Use a texture analyzer to perform a tensile test on the gel samples prepared in Examples 1-4. The size of the gel samples used for the tensile test is 20 mm × 2 mm × 3 mm (length × width × thickness), and the tensile rate is 50 mm / min -1 .

[0066] The results are as follows Figure 5 As shown, when constructing the ionic liquid gel with a higher ionic liquid content (Example 4, the mass ratio of ionic liquid to total monomer is 8:1), its formability and operability are lower, and both the tensile fracture stress and strain are the lowest. When using the ionic liquid gels of Examples 1 - 3 (the mass ratio of ionic liquid to total monomer is 5:1, 6:1, and 7:1), the gel forming rate and operability are higher. From the tensile stress-strain curves of the gel samples, as the mass ratio increases from 5:1 to 7:1, the tensile fracture strain of the ion gel increases from 614% to 711%, and the fracture stress decreases from 196 Kpa to 101 Kpa. However, due to the too high ionic liquid concentration in Example 4, the network structure of the gel becomes loose, reducing the mechanical strength and durability of the material. At the same time, the high concentration of ionic liquid will increase the viscosity of the gel, making processing and handling more difficult. Operational difficulties may occur during the preparation, coating, and forming processes, affecting production efficiency and the quality of the TENG as a sensor.

[0067] Test Example 2: Gel Conductivity Test

[0068] The resistance of the samples prepared in Examples 1 - 4 was measured by an electrochemical workstation at a test temperature of 26 degrees Celsius. The method used was the alternating current impedance method. The sample sizes of Examples 1 - 4 were all cylinders with a height of 5 mm and a diameter of 10 mm. After clamping the samples with two ITO conductive glasses (20 mm × 40 mm), the alternating current impedance test was carried out using the four-probe method to obtain resistivity and conductivity data. Both resistivity and conductivity are parameters describing the electrical conductivity of materials. The lower the resistivity and the higher the conductivity, the better the electrical conductivity of the material. Conductivity is represented by σ:

[0069] σ = L / R·A

[0070] In the formula, L is the height of the sample, with the unit of meter (m);

[0071] R is the resistance of the sample, with the unit of ohm (Ω);

[0072] A is the cross-sectional area of the sample, with the unit of square meter (m 2 ²).

[0073] The test results are as follows Figure 6 As shown, the resistivity of the ion gel gradually decreases as the ionic liquid concentration increases, and the conductivity gradually increases as the ionic liquid concentration increases.

[0074] Test Example 3: TENG Output Performance Test

[0075] To evaluate the output performance differences of the TENGs (20 mm × 40 mm) of Examples 1 - 4, a constant force test system was built as follows:

[0076] A copper foil (20×40mm 2 ) was used as the triboelectric layer for standard testing. The conducting copper wire of the TENG serving as the sensor was connected to an electrometer (Keithley 6517B). The glass slide with the copper foil attached exerted a force on the sensor to generate an output voltage, and real-time data was collected and recorded through LabVIEW interface programming. The output voltage response of the sensor under the same periodic pressure (1 kPa, 0.25 Hz) was recorded.

[0077] The experimental results are as Figure 7 shown. The sensor response was consistent with the conductivity performance, and Example 4 exhibited the highest output voltage. The high conductivity of the ion gel contributed to the rapid conduction of charges, and at the same time, it could effectively reduce the internal resistance loss, enabling the charges to move faster between the electrodes, thereby enhancing the output voltage.

[0078] Test Example 4

[0079] Combined with the data analysis of Test Examples 1 - 3, the mechanical properties and output performance of Examples 1 - 4 were considered. Considering the balance of the elongation rate and conductivity as well as the TENG output performance, Example 3 was selected as the final example.

[0080] To evaluate the output performance of the TENG (20 mm×40 mm) fabricated in Example 3, a constant force test system was set up as follows:

[0081] A copper foil (20×40mm 2 ) was used as the triboelectric layer for standard testing. The conducting copper wire of the TENG serving as the sensor was connected to an electrometer (Keithley 6517B). The glass slide with the copper foil attached exerted a force on the sensor to generate an output voltage, and real-time data was collected through LabVIEW interface programming.

[0082] Different contact pressures generated different output voltages. The generated output voltage increased with the increase of the contact pressure and returned to the baseline after the pressure was released. Sensitivity is an important index of the sensor, which refers to the ratio of the change in the output to the change in the input under the stable working state of the sensor, denoted by k:

[0083] k = Δy / Δx

[0084] In the formula, Δy is the increment of the output quantity; Δx is the increment of the input quantity.

[0085] The output voltage response and sensitivity of the sensor under periodic pressure (0 - 40 kPa, 0.25 Hz) were recorded.

[0086] The results are as Figure 8As shown, the sensitivity of the sensor is approximately 49.83 V / kPa in the range of 0–1.16 kPa, and it rapidly drops to 4.02 V / kPa in the range of 1.16–15.75 kPa. As the pressure further increases, the output voltage reaches saturation in the range of 15.75–33.13 kPa, and the sensitivity drops to 0.31 V / kPa. When the applied force exceeds 33.13 kPa, the output voltage shows a downward trend. This is due to the large dielectric constant of the silicone rubber film and the air gap between the two layers. Under the pressure of 0 to 15.75 kPa, the change in the output voltage during the contact-separation process is greatly enhanced. When the contact area reaches the maximum, the sensitivity begins to decline. As the pressure continues to increase, due to the small Young's modulus of the film, the friction layer and the electrode layer will deform, and the thickness of these films will decrease. The elastic deformation of the film causes the output voltage to increase slowly. When the elastic deformation reaches saturation, continuing to apply pressure will cause damage to the structure of the friction layer and the electrode layer. At this time, the pressure value exceeds the maximum range of the sensor, and the output voltage shows a downward trend.

[0087] The sensor shows good linearity (R 2 = 0.97) in the output voltage under the applied force of 0–1.16 kPa, and has extremely high sensitivity and response time. As the applied force increases in the range of 1.16–15.75 kPa, the sensitivity of the sensor decreases, and it reaches saturation in the range of 15.75–33.13 kPa, with the sensitivity dropping to 0.31 V / kPa. The output voltage shows better linearity (R 2 = 0.99) in these two stages.

[0088] To evaluate the electrical output performance of the TENG at different tapping frequencies under a constant pressure, a constant force test system was used to conduct output characteristic tests at different frequencies. First, the constant pressure was set to 1 Kpa. As the operating frequency increased from 0.25 Hz to 2 Hz, Voc showed a stable output. The short-circuit current (Isc) at different tapping frequencies gradually increased as the frequency increased. This is because the high-frequency reciprocating motion makes the contact time with the sensor shorter, resulting in an increase in the output current. However, the number of frictional charges under a constant pressure remains unchanged, so the output voltage remains constant.

[0089] The results are as Figure 9 shown. Voc remained basically constant during 4000 consecutive contact-separation movements. The sensor exhibited good anti-fatigue performance and stable electrical output performance. At the same time, the pressure detection range of 0–33.13 kPa and good linearity can accurately reflect the linear relationship between the applied force and the output voltage, with high reliability.

[0090] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A triboelectric nanogenerator, characterized in that, The triboelectric nanogenerator includes an ionic liquid gel, silicone rubbers attached to opposite sides of the ionic liquid gel, and wires connecting the ionic liquid gel and the silicone rubbers. The silicone rubber is Ecoflex silicone rubber. The ionic liquid gel is made from the following raw materials: an ionic liquid, a monomer, a photoinitiator, and a crosslinking agent. The ionic liquid is 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The monomer is selected from at least one of N,N-dimethylacrylamide or acrylamide. The photoinitiator is initiator 1173, and the crosslinking agent is methylenebisacrylamide. The mass ratio of the ionic liquid, the monomer, the photoinitiator, and the crosslinking agent is (1 - 10):1:(0.0001 - 0.05):(0.0001 - 0.05). The preparation method of the triboelectric nanogenerator includes the following steps: (1) Mix the ionic liquid, the monomer, the photoinitiator, and the crosslinking agent, heat and stir evenly to obtain a precursor solution, and carry out an ultraviolet light irradiation reaction on the precursor solution to obtain an ionic liquid gel. (2) Prepare the silicone rubber, connect wires to the silicone rubber, and sandwich the ionic liquid gel between two pieces of silicone rubber to obtain the triboelectric nanogenerator. The mass ratio of the ionic liquid to the monomer is (5 - 8):1, and the sum of the masses of the photoinitiator and the crosslinking agent accounts for (0.1 - 5)% of the mass of the monomer. In step (1), in the monomer, the mass ratio of N,N-dimethylacrylamide to acrylamide is (1 - 10):

1. The heating and stirring temperature is 90 - 130°C, the stirring speed is 400 - 1500 rpm, and the stirring time is 1 - 10 min. The wavelength used for ultraviolet light irradiation is 365 nm, and the irradiation time is 5 - 30 min. In step (2), the ionic liquid gel and the two pieces of silicone rubber are clamped by van der Waals forces. After sandwiching the ionic liquid gel between two pieces of silicone rubber, use Ecoflex-00-30 silicone rubber to connect the joint between the ionic liquid gel and the Ecoflex silicone rubber, and heat and cure at a temperature of 90 - 110°C for 0.5 - 5 min.

2. A friction self-powered flexible force sensing sensor based on a conductive ionic gel, characterized in that, The triboelectric self-powered flexible force sensing sensor includes the triboelectric nanogenerator described in claim 1.

3. Application of the triboelectric self-powered flexible force sensing sensor based on a conductive ionic gel described in claim 2 in manufacturing a flexible manipulator.

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