Ultra-thin asymmetric double-structure triboelectric flexible sensor with wide linear range and low detection limit and preparation method of ultra-thin asymmetric double-structure triboelectric flexible sensor

Abstract

The invention relates to the technical field of triboelectric flexible sensors, in particular to an ultrathin asymmetric double-structure triboelectric flexible sensor with a wide linear range and a low detection limit and a preparation method of the ultrathin asymmetric double-structure triboelectric flexible sensor, MXene is introduced into PVDF-HFP, beta phase formation is promoted through dipole induction, out-phase nucleation and electric field polarization, and the polarizability and the charge storage capacity are enhanced. Aminated carbon nanotubes are attached to TPU fibers through ultrasound, so that a work function is reduced through an electron donor effect and surface energy level modulation, and TPU is more prone to electron loss. An ultra-thin, breathable and flexible PVDF-HFP / MXene (PM) and TPU / NH2-CNTs (TN) composite film with microstructures uniformly distributed on the surface is manufactured by using an electrostatic spinning and beaded fiber forming technology and an ultrasonic technology, and the PM and the TN are respectively used as a negative friction layer and a positive friction layer to construct the spacing-layer-free triboelectric flexible sensor (TFS). The ultra-linear range, the ultra-low pressure detection limit, the ultra-thin overall thickness and the good applicability in the field of human health are shown.

Description

Technical Field

[0001] The present invention relates to the technical field of triboelectric flexible sensors, and in particular to an ultra-thin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and a low detection limit and a preparation method thereof. Background Art

[0002] Flexible sensors have become an important development direction for intelligent electronic devices due to their widespread applications in fields such as tactile perception, medical monitoring, human motion detection, and human-computer interaction. However, most existing flexible sensors (such as capacitive and piezoresistive sensors) require external power supply, which limits their application in wearable devices. Therefore, self-powered flexible sensors play a key role in the development of flexible electronic technology. They can achieve stable operation without an external power supply, thereby expanding their application scenarios.

[0003] The output performance of TENG directly determines its applicability in different application scenarios, and improving the triboelectric properties of the friction layer material is the key to improving the overall performance of TENG. However, the charge storage capacity and output performance of a single friction material are usually low, which makes it difficult to meet the needs of high-performance sensors. Therefore, researchers generally use surface modification technology to increase the triboelectric charge density. For example, polar or charged groups (such as hydroxyl groups, carboxyl groups, etc.) are introduced through chemical modification, or highly electronegative or highly electropositive molecules are grafted onto the surface of the material to enhance its triboelectric effect. In addition, functional nanofillers can be introduced to increase the dielectric constant of the friction layer and further improve its output performance. Among them, two-dimensional materials such as MXene and graphene can be used to regulate the charge capture and transfer characteristics of the friction layer due to their high specific surface area and rich surface functional groups, thereby significantly enhancing the triboelectric performance of TENG.

[0004] Although the above strategies have improved the output performance of TENG to a certain extent, traditional TENG still faces many challenges. For example, its linear detection range is narrow and its sensitivity is limited, which makes it difficult to meet the precise detection requirements of flexible sensors. In addition, the output performance of TENG is greatly affected by the effective contact area, and the contact interface of traditional TENG is difficult to optimize, resulting in insufficient output stability. To address this problem, researchers introduced structural engineering technology to regulate the effective contact area by precisely designing the microstructure of the friction layer to improve the charge transfer efficiency of TENG. For example, Chinese patent document CN202411882036.7 discloses a preparation method and application of ALD modified nano-microstructured film, which includes: using magnetron sputtering to form an Ag atomic layer on the surface of a PTFE film as an etching mask; using ICP reactive ion etching to blow plasma across the mask surface to form a nanocolumn morphology; alternating between the first precursor Al2(CH3)3 and the second precursor H2O to chemically adsorb and react on the surface of the obtained PTFE to form AlO X Insulating layer, x ranges from 1 to 2, and finally an ALD modified nanostructured film is obtained. The film prepared by this method has a microstructure. The distribution of electrons at the tip of the microstructure reduces the effective area of charge on the same plane, reduces the relative polarization field strength, and enhances the performance of the triboelectric nanogenerator. However, the charge concentration effect at the tip of the nanopillar can increase the instantaneous voltage, but the total charge density may be limited due to the reduced contact area. The nanopillar structure may wear or collapse during repeated contact, especially for high-hardness AlO X The combination of the coating and the soft PTFE may cause interfacial delamination, which will limit the service life of the triboelectric nanogenerator. Therefore, the structural design of traditional TENG still has limitations, such as structural instability caused by the manufacturing process (template method, photolithography method and chemical etching method, etc.), dielectric properties limited by the material structure, and energy loss caused by assembly. Energy loss makes TENG unable to detect small pressure when used as a flexible sensor. Therefore, it is necessary to design triboelectric flexible sensors with better wearability, better stability, larger linear range, and lower detection limit. Summary of the Invention

[0005] The purpose of the present invention is to provide an ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and a low detection limit, and a method for preparing the same. The present invention introduces MXene into PVDF-HFP to promote the formation of the β phase through dipole induction, heterogeneous nucleation, and electric field polarization, thereby enhancing the polarizability and charge storage capacity. Aminated carbon nanotubes are attached to TPU fibers through ultrasound to reduce the work function through the electron donor effect and surface energy level modulation, making the TPU more electron-losable. Electrospinning, beaded fiber formation technology, and ultrasound technology are used to produce ultrathin, breathable, flexible, and surface-uniformly distributed microstructured PVDF-HFP / MXene (PM) and TPU / NH2-CNTs (TN) composite films. A spacer-free triboelectric flexible sensor (TFS) is constructed using PM and TN as the negative and positive friction layers, respectively. The sensor exhibits an ultra-wide linear range (linearity of 0.995 at 1.25Pa-100kPa), an ultra-low pressure detection limit (1.25Pa), an ultra-thin overall thickness (860μm-900μm), and good applicability in the field of human health.

[0006] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0007] An ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit, wherein the layered structure comprises:

[0008] The smooth side electrode of the positive friction layer is made of flexible copper strip;

[0009] A positive friction layer with a micro-cone structure distributed on the surface is composed of a TPU / NH2-CNTs (TN) composite film formed by a composite of thermoplastic polyurethane (TPU) and amino-modified carbon nanotubes (NH2-CNTs), and the micro-cone height is 76μm-192μm;

[0010] A negative friction layer with a micro-cone structure distributed on the surface is composed of a PVDF-HFP / MXene (PM) composite film formed by a composite of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and MXene. The micro-cone height is 17μm-66μm.

[0011] The smooth side electrode of the negative friction layer is made of flexible copper strip;

[0012] an encapsulation layer, composed of polyimide (PI) tape and wrapping the above layers;

[0013] The micro-conical surfaces of the positive friction layer and the negative friction layer are assembled face to face, the overall thickness of the sensor is 860 μm-900 μm, and the plane size is 2 cm×2 cm.

[0014] Furthermore, in the TPU / NH2-CNTs composite film:

[0015] The concentration of TPU is 10wt%-14wt%, and the solvent is a mixed solution of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF) in a volume ratio of 1:1;

[0016] The mass volume ratio of the amino-modified carbon nanotube dispersion is 1.5-3 mg / ml, and the dispersion is loaded on the surface of the TPU fiber through an ultrasound-assisted dispersion process, with an ultrasound power ratio of 13% and a treatment time of 45 minutes.

[0017] Furthermore, in the PVDF-HFP / MXene composite membrane:

[0018] The concentration of PVDF-HFP is 6wt%-10wt%, and the mass proportion of MXene is 0.1wt%-1wt%;

[0019] MXene was evenly distributed in the PVDF-HFP matrix through a room temperature stirring dispersion process. The dispersion conditions were stirring at 300 RPM for 10 hours, and the solvent was a mixed solution of DMF and THF with a volume ratio of 1:1.

[0020] Furthermore, the preparation parameters of the positive friction layer include:

[0021] The electrospinning voltage was 7.8-8.2 kV, and the distance between the spinning needle and the receiving plate was 14 cm;

[0022] The solution advancing rate is 1.45-1.55 ml / h, and the spinning time is 60-90 minutes;

[0023] A 21G spinning needle was used, and the spinning environment humidity was 35% and the temperature was 25°C.

[0024] Furthermore, the preparation parameters of the negative friction layer include:

[0025] The electrospinning voltage was 8.4-8.8 kV, and the distance between the spinning needle and the receiving plate was 14 cm;

[0026] The solution advancing rate is 1.25-1.4 ml / h, and the spinning time is 60-90 minutes;

[0027] A 21G spinning needle was used, and the spinning environment humidity was 35% and the temperature was 25°C.

[0028] On the other hand, the present invention provides a method for preparing the above-mentioned triboelectric flexible sensor, comprising the following steps:

[0029] S1: Preparation of positive friction layer:

[0030] S1.1: Dissolve TPU pellets in a 1:1 (volume ratio) DMF / THF mixture at 60°C and stir at 600 RPM for 2 hours to form a homogeneous solution.

[0031] S1.2: Prepare TPU spinning membrane using electrospinning process, controlling the spinning voltage to 7.8-8.2 kV and the solution propulsion rate to 1.45-1.55 ml / h;

[0032] S1.3: Immerse the TPU spinning membrane in a dispersion of amino-modified carbon nanotubes in ethanol at a mass volume ratio of 1.5-3 mg / ml and ultrasonicate for 45 minutes.

[0033] S1.4: After drying at 70°C for 2 hours, a TPU / NH2-CNTs composite film with a micro-pyramidal structure on the surface was obtained;

[0034] S2: Preparation of negative friction layer:

[0035] S2.1: Disperse the MXene in a 1:1 volume ratio DMF / THF mixture and stir at 300 RPM for 10 h at room temperature.

[0036] S2.2: Add PVDF-HFP powder and stir at 600 RPM for 2 h at 60°C to form a uniform suspension.

[0037] S2.3: Prepare PVDF-HFP / MXene spinning membrane by electrospinning process, controlling the spinning voltage to 8.4-8.8 kV and the solution propagation rate to 1.25-1.4 ml / h;

[0038] S2.4: After drying at 70°C for 2 h, a PVDF-HFP / MXene composite membrane with a micro-pyramidal structure on the surface was obtained;

[0039] S3: Sensor assembly:

[0040] S3.1: Composite the TPU / NH2-CNTs composite membrane and the PVDF-HFP / MXene composite membrane with the flexible copper electrode respectively;

[0041] S3.2: Assemble the micro-conical surfaces of the two composite films relative to each other and encapsulate them with polyimide tape to form a flexible sensor with a thickness of ≤900 μm.

[0042] Furthermore, the method for forming the micro-cone structure in steps S1.2 and S2.3 includes:

[0043] Adjusting the surface tension and charge density of the spinning solution to induce the formation of beaded fibers;

[0044] Through the coupling of electrostatic repulsion and solution surface tension, the beaded fibers self-assemble into a uniformly distributed micro-cone array.

[0045] Beneficial effects of the present invention:

[0046] The present invention discloses an ultra-thin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and a low detection limit and a preparation method thereof. The present invention utilizes electrospinning technology and ultrasonic processing technology to produce a positive friction layer (TN) and a negative friction layer (PM) with micro-cones on the surface, and then utilizes the friction layer, electrodes and PI to assemble a triboelectric flexible sensor without a spacer layer.

[0047] The introduction of MXene into a PVDF-HFP matrix synergistically modulates its crystallization behavior and dielectric properties through multiple mechanisms. The abundant functional groups (-OH, -F) on the MXene surface induce directional alignment of CF2 dipoles in the PVDF-HFP molecular chains through electrostatic interactions, thereby promoting the formation of a highly polar β phase (all-trans-TTTT conformation) rather than a non-polar α phase (TGTG' conformation). This process is due to the heterogeneous nucleation effect of the MXene two-dimensional sheets—their high surface area effectively restricts the freedom of movement of the PVDF-HFP molecular chains, favoring the crystallization process towards the thermodynamically stable β phase. Furthermore, under the high-voltage electric field environment of electrospinning, the high intrinsic conductivity of MXene may induce a local electric field enhancement effect, further polarizing the PVDF-HFP molecular chains and stabilizing the β phase structure. This crystal phase transition significantly enhances the dielectric constant and charge-trapping ability of PVDF-HFP, enabling more efficient surface charge accumulation through electron transfer and dipole polarization during contact-separation processes.

[0048] In the present invention, when amino-modified carbon nanotubes (NH2-CNTs) are loaded onto the surface of TPU fibers with the aid of ultrasound, the NH2 group acts as a strong electron donor, and its lone pair electrons can reduce the effective work function of TPU through physical adsorption, thereby reducing the electron escape barrier. This modification makes TPU more likely to lose electrons during friction. Moreover, the introduction of NH2-CNTs constructs a dual-functional structure: (1) its conductive network forms a distributed microcapacitor with the TPU insulating matrix, enhancing the charge storage capacity; (2) the NH2 group induces new surface states at the TPU / CNT interface, promoting the directional transfer of electrons from TPU to the friction partner material PVDF-HFP. It is worth noting that the charge redistribution at the interface further strengthens the contact electrification effect. When the NH2-CNTs-modified TPU contacts the β-phase-enriched PVDF-HFP / MXene composite, the difference in work function and dielectric properties of the two work synergistically to achieve more efficient triboelectric charge generation and maintenance.

[0049] By precisely controlling the surface tension and charge density of the PVDF-HFP / MXene and TPU solutions during the electrospinning process and strategically employing charge neutralization, the smooth fibers can be effectively transformed into beaded fibers. Subsequently, under the coupled effects of electrostatic repulsion and the surface tension of the solution, these beaded fibers spontaneously self-assemble into microcones on the collection plate. The resulting PVDF-HFP / MXene (PM) composite film and TPU film have microcones evenly distributed on their surfaces. The presence of these microcones not only increases the contact area of the friction layer during the contact-separation process, thereby improving the efficiency of charge transfer, but also causes the contact area to vary in a gradient, thereby enhancing the linearity of the sensor.

[0050] Since the assembled sensor does not require a spacer layer, it fully utilizes the energy required for the deformation of the spacer layer, giving the sensor a very small pressure detection limit, broadening the application range of the sensor in the fields of human health and human movement, and also making the overall thickness of the assembled sensor very small, increasing the convenience of wearing.

[0051] The present invention uses electrospinning technology to produce a micro-cone structure, which not only improves the sensing performance but also simplifies the production process and minimizes the production cost. In addition, the film produced by the spinning technology has a small thickness, good air permeability and excellent flexibility, which makes the sensor more wearable and comfortable.

[0052] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0054] Figure 1 Structural diagram of an ultra-thin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit.

[0055] Figure 2 The preparation flow chart of the structural diagram of an ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit.

[0056] Figure 3 The voltage output of an ultra-thin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit under different pressures and the linear relationship between pressure and voltage are presented.

[0057] Figure 4Cycle number of an ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit.

[0058] Figure 5 It is an ultra-thin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit, which is used to measure voltage signals during joint bending and wrist pulse.

[0059] Figure: 1. Encapsulation layer, 2. TPU / NH2-CNTs composite film, 3. TPU beaded fibers, 4. Aminated carbon nanotubes, 5. PVDF-HFP / MXene composite film, 6. PVDF-HFP / MXene beaded fibers, 7. Structural model of the interaction between PVDF-HFP and MXene, 8. Flexible copper electrode, 9. N,N-dimethylformamide (DMF), 10. TPU particles, 11. PVDF-HFP powder, 12. Tetrahydrofuran (THF), 13. Beaker, 14. TPU solution, 15. Magnetic rotor, 16. Stirrer, 17. Electrospinning machine, 18. Constant temperature and humidity tester, 19. Electrospinning receiving plate, 20. Electrospinning needle, 21. Ultrasonic crusher, 22. Syringe, 23. Beaker, 24. PVDF-HFP / MXene suspension, 25. Magnetic rotor, 26. Stirrer, 27. Suspension of amino-modified carbon nanotubes and ethanol, 28. Beaker, 29. MXene dispersion, 30. Stirrer, 31. Flake MXene. DETAILED DESCRIPTION

[0060] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0061] Example 1

[0062] The ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit described in this embodiment comprises, from top to bottom, an electrode, a friction layer, and an encapsulation layer. The electrode is located on the smooth side of the friction layer and is composed of a flexible copper strip. The friction layer includes a positive friction layer and a negative friction layer, whose micro-conical surfaces face each other. The positive friction layer is composed of thermoplastic polyurethane (TPU) and amino-modified carbon nanotubes (NH2-CNTs). The negative friction layer is composed of PVDF-HFP and MXene. The encapsulation layer is composed of polyimide (PI) tape.

[0063] A method for fabricating an ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and a low detection limit comprises the following fabrication steps:

[0064] Preparation of the positive friction layer: TPU is added to a mixed solvent, heated and stirred on a stirrer to dissolve, the TPU solution is placed in a 5ml syringe and electrospun to obtain a TPU spun composite membrane. After drying in a constant temperature and humidity tester, the spun film is then immersed in ethanol and a suspension of amino carbon nanotubes for ultrasonic treatment. The ultrasonically treated composite membrane is dried at room temperature for 2 hours. The positive friction layer is obtained by first electrospinning the TPU solution, and then immersing the TPU spun membrane in a suspension of amino carbon nanotubes and ethanol and ultrasonically treating it. The TPU is granular and commercially available, PVDF-HFP is powdery and commercially available, the amino carbon nanotubes are tubular and commercially available, and MXene is flake and commercially available.

[0065] Fabrication of the negative friction layer: First, MXene flakes were added to a mixed solvent and stirred at room temperature at 300 RPM for 10 hours to form a suspension. PVDF-HFP powder was then added to the suspension and heated and stirred on a blender until the PVDF-HFP was completely dissolved. The PVDF-HFP / MXene (PM) suspension was placed in a 5ml syringe and electrospun to produce a PM spun composite membrane. The membrane was then dried in a constant temperature and humidity tester to obtain a dry PM composite membrane.

[0066] Fabrication of triboelectric flexible sensor: Flexible copper strips are used as electrodes, TN as the positive friction layer, PM as the negative friction layer, and PI as the encapsulation layer to assemble an ultra-thin asymmetric dual-structure triboelectric flexible sensor.

[0067] In this embodiment, the TPU solution is obtained by dissolving TPU particles in a mixed solvent of DMF and THF, and then stirring to dissolve the TPU.

[0068] In this embodiment, the concentration of the TPU solution is 10-14 wt %.

[0069] In this embodiment, the TPU electrospinning voltage is 7.8-8.2 KV, the distance between the spinning needle and the receiving plate is 14 cm, the pushing speed is 1.45-1.55 ml / h, and the spinning time is 60-120 min.

[0070] In this embodiment, the mass-to-volume ratio of the suspension of amino-modified carbon nanotubes and ethanol is 2 mg / ml, and the ultrasonication time is 45 minutes.

[0071] In this embodiment, the height of the micro-cones on the surface of the TN composite film is 76-192 μm.

[0072] In this embodiment, the concentration of the PVDF-HFP solution is 10-14 wt %.

[0073] In this embodiment, the content of MXene is 0-1 wt%.

[0074] In this embodiment, the PM electrospinning voltage is 8.4-8.8 KV, the distance between the spinning needle and the receiving plate is 14 cm, the pushing speed is 1.25-1.4 ml / h, and the spinning time is 60-120 min.

[0075] In this embodiment, the height of the micro-cones on the surface of the PM composite film is 17-66 μm.

[0076] In this embodiment, the drying temperature is 70° C. and the drying time is 2 hours.

[0077] In this embodiment, the volume ratio of the mixed solvent is 1:1 (DMF:THF).

[0078] In this embodiment, the stirring speed is 600 RPM and the stirring time is 2 hours.

[0079] In this embodiment, the micro-cones on the surface of the friction layer are obtained by controlling the surface force and charge density of the spinning solution and utilizing charge neutralization technology.

[0080] Example 2

[0081] like Figure 2 As shown, an ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit consists of an electrode 8, a positive friction layer 2, a negative friction layer 5, and an encapsulation layer 1. The electrode is a flexible copper electrode, which is attached to the smooth side of the friction layer. The positive friction layer is composed of TPU / NH2-CNTs, the negative friction layer is composed of PVDF-HFP / MXene, and the friction layer has a surface face-to-face assembly of micro-cones. The encapsulation layer is composed of polyimide (PI) tape, which encapsulates the electrode and the friction layer inside. The preparation of an ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit includes the following steps:

[0082] (1) 1 g of TPU particles 10 was added to a beaker 13, 7.33 g of a solvent with a volume ratio of 1:1 (DMF9:THF12) was added to the beaker 13, a magnetic rotor was placed in the beaker 13, and the beaker 13 containing TPU and solvent was placed on a stirrer 16 for 2 hours until the TPU 10 was completely dissolved. The temperature of the stirrer was set to 60°C and the speed was set to 600 RPM.

[0083] (2) The dissolved TPU solution 14 was drawn with a 5 ml syringe 22 and placed on the push pump of the electrospinning machine 17. The distance between the spinning needle 20 and the collecting plate 19 was set to 14 cm. The specification of the spinning needle 20 was selected as 21G. The pushing speed was set to 1.5 ml / h. The humidity of the spinning machine was set to 35%, the temperature was set to 25°C, and the spinning high voltage was set to 8 kV. The spinning time was set to 90 min.

[0084] (3) The TPU spinning membrane on the collecting plate 19 is removed and placed in a constant temperature and humidity tester 18 for drying. The drying temperature is set to 70° C. and the drying time is set to 2 h.

[0085] (4) The dried TPU spinning membrane was taken out and then immersed in an amino carbon nanotube / ethanol dispersion 27 with a mass to volume ratio of 2 mg / ml. Ultrasonic treatment was performed using an ultrasonic crusher 21 with an ultrasonic power ratio of 13% and an ultrasonic time of 45 min.

[0086] (5) The ultrasonically treated TPU film was removed from the amino-treated carbon nanotube / ethanol dispersion and placed on a nonwoven fabric for natural airing for 2 h. Thus, the preparation of TPU / NH2-CNTs(TN) composite film 2 was completed. Microcones with a height of 117 μm were present on its surface.

[0087] (6) 5 mg of flake MXene31 was added to beaker 28, 11.5 g of a solvent with a volume ratio of 1:1 (DMF9:THF12) was added to beaker 28, a magnetic rotor was added to beaker 28, and the beaker 28 containing MXene, solvent and rotor was placed on a stirrer 30 for stirring. The stirring temperature was room temperature, the stirrer speed was set to 300 RPM, and the stirring time was set to 10 h so that MXene31 was fully dispersed in the solvent.

[0088] (7) 1 g of PVDF-HFP powder 11 was added to the dispersion 29, and the beaker 28 containing the dispersion, PVDF-HFP, and rotor was placed on the stirrer 26 for heating and stirring. The temperature of the stirrer was set to 60°C and the speed was set to 600 RPM.

[0089] (8) A 5 ml syringe 22 was used to extract the PVDF-HFP / MXene suspension 24 and placed it on the push pump of the electrospinning machine 17. The distance between the spinning needle 20 and the collecting plate 19 was set to 14 cm. The specification of the spinning needle 20 was selected as 21G. The pushing speed was set to 1.36 ml / h. The humidity of the spinning machine was set to 35%, the temperature was set to 25°C, and the spinning high voltage was set to 8.7 kV. The spinning time was set to 90 min.

[0090] (9) The PVDF-HFP / MXene (PM) spinning membrane was removed from the collecting plate 19 and placed in a constant temperature and humidity tester 18 for drying. The drying temperature was set to 70°C and the drying time was set to 2 hours. The preparation of the PVDF-HFP / MXene spinning membrane was completed, and micro-cones with a height of 45 μm were present on its surface.

[0091] (10) The TN composite film, PM composite film, PI flexible tape, and flexible copper tape were cut into 2 cm x 2 cm shapes, and the flexible copper tape was attached to the smooth side of the TN and PM. The TN micro-cone surface and the PM micro-cone surface were assembled face to face, and the PI was used as the encapsulation layer to encapsulate the electrodes, TN, and PM inside. In this way, an ultra-thin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit was assembled.

[0092] In order to verify the sensing performance of the ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit, the output performance of the sensor was measured. Figure 3 As shown in the figure, the sensor can detect a very small pressure of 1.25Pa, and within the pressure range of 1.25Pa-100kPa, the voltage output rises from 0.06V to 16V, and the linearity is 0.995. Figure 4 As shown, the proposed ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit exhibits significant output voltage attenuation after over 5000 cycles under a fixed pressure, demonstrating its excellent stability. Furthermore, the proposed ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit clearly captured key signals when used to detect joint flexion and wrist pulse, demonstrating its high application value in human health monitoring.

[0093] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. An ultrathin asymmetric dual-structure triboelectric flexible sensor with a wide linear range and low detection limit, characterized in that: Its layered structure includes from top to bottom: The smooth side electrode of the positive friction layer is made of flexible copper strip; A positive friction layer with a micro-cone structure distributed on the surface is composed of a TPU / NH2-CNTs composite film formed by a composite of thermoplastic polyurethane and amino-modified carbon nanotubes. The micro-cone height is 76μm-192μm. The negative friction layer has a micro-cone structure distributed on the surface, which is composed of a PVDF-HFP / MXene composite film formed by a composite of polyvinylidene fluoride-hexafluoropropylene and MXene. The height of the micro-cone is 17μm-66μm; The smooth side electrode of the negative friction layer is made of flexible copper strip; an encapsulation layer, consisting of a polyimide tape and wrapping the above layers; The micro-conical surfaces of the positive friction layer and the negative friction layer are assembled face to face, the overall thickness of the sensor is 860 μm-900 μm, and the plane size is 2 cm×2 cm.

2. The triboelectric flexible sensor according to claim 1, wherein: In the TPU / NH2-CNTs composite film: The concentration of TPU is 10wt%-14wt%, and the solvent is a mixed solution of N,N-dimethylformamide and tetrahydrofuran in a volume ratio of 1:1; The mass volume ratio of the amino-modified carbon nanotube dispersion is 1.5-3 mg / ml, and the dispersion is loaded on the surface of the TPU fiber through an ultrasound-assisted dispersion process, with an ultrasound power ratio of 13% and a treatment time of 45 minutes.

3. The triboelectric flexible sensor according to claim 1, wherein: In the PVDF-HFP / MXene composite membrane: The concentration of PVDF-HFP is 6wt%-10wt%, and the mass proportion of MXene is 0.1wt%-1wt%; MXene was evenly distributed in the PVDF-HFP matrix through a room temperature stirring dispersion process. The dispersion conditions were stirring at 300 RPM for 10 hours, and the solvent was a mixed solution of DMF and THF with a volume ratio of 1:

1.

4. The triboelectric flexible sensor according to claim 1, wherein: The preparation parameters of the positive friction layer include: The electrospinning voltage was 7.8-8.2 kV, and the distance between the spinning needle and the receiving plate was 14 cm; Solution advancing rate 1.45-1.55 ml / h, spinning time 60-90 minutes; A 21G spinning needle was used, and the spinning environment humidity was 35% and the temperature was 25°C.

5. The triboelectric flexible sensor according to claim 1, wherein: The preparation parameters of the negative friction layer include: The electrospinning voltage was 8.4-8.8 kV, and the distance between the spinning needle and the receiving plate was 14 cm; The solution advancing rate is 1.25-1.4 ml / h, and the spinning time is 60-90 minutes; A 21G spinning needle was used, and the spinning environment humidity was 35% and the temperature was 25°C.

6. A method for preparing a triboelectric flexible sensor according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: Preparation of positive friction layer: S1.1: Dissolve TPU pellets in a 1:1 (volume ratio) DMF / THF mixture at 60°C and stir at 600 RPM for 2 hours to form a homogeneous solution. S1.2: Prepare TPU spinning membrane using electrospinning process, controlling the spinning voltage to 7.8-8.2 kV and the solution propulsion rate to 1.45-1.55 ml / h; S1.3: Immerse the TPU spinning membrane in a dispersion of amino-modified carbon nanotubes in ethanol at a mass volume ratio of 1.5-3 mg / ml and ultrasonicate for 45 minutes. S1.4: After drying at 70°C for 2 hours, a TPU / NH2-CNTs composite film with a micro-pyramidal structure on the surface was obtained; S2: Preparation of negative friction layer: S2.1: Disperse the MXene in a 1:1 volume ratio DMF / THF mixture and stir at 300 RPM for 10 h at room temperature. S2.2: Add PVDF-HFP powder and stir at 600 RPM for 2 h at 60°C to form a uniform suspension. S2.3: Prepare PVDF-HFP / MXene spinning membrane by electrospinning process, controlling the spinning voltage to 8.4-8.8 kV and the solution propagation rate to 1.25-1.4 ml / h; S2.4: After drying at 70°C for 2 h, a PVDF-HFP / MXene composite membrane with a micro-pyramidal structure on the surface was obtained; S3: Sensor assembly: S3.1: Composite the TPU / NH2-CNTs composite membrane and the PVDF-HFP / MXene composite membrane with the flexible copper electrode respectively; S3.2: Assemble the micro-conical surfaces of the two composite films relative to each other and encapsulate them with polyimide tape to form a flexible sensor with a thickness of ≤900 μm.

7. The preparation method according to claim 6, wherein The method for forming the micro-cone structure in steps S1.2 and S2.3 includes: Adjusting the surface tension and charge density of the spinning solution to induce the formation of beaded fibers; Through the coupling of electrostatic repulsion and solution surface tension, the beaded fibers self-assemble into a uniformly distributed micro-cone array.

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