A fiber-type flexible strain sensor with interlaced soft and hard segments and its preparation method

Abstract

The present invention discloses a fiber-type flexible strain sensor with interlaced soft and hard segments and a preparation method thereof. The invention adopts a coaxial wet spinning process to prepare thermoplastic polyurethane-coated polyvinylidene fluoride (TPU@PVDF) core-sheath structure fiber, and utilizes ultrasonic impregnation to load multi-walled carbon nanotubes (MWCNTs) on the fiber surface, or blends ionic liquids (ILs) in the TPU matrix to construct a conductive path. Subsequently, a core-sheath structure fiber with "soft-hard" segments is formed by pre-stretching. Finally, conductive silver paste is coated on both ends of the fiber as electrodes to obtain a flexible fiber-type strain sensor. Through the "soft-hard" structural design, the present invention makes the flexible fiber-type strain sensor have a greatly improved sensitivity while maintaining a wide strain response range, and its preparation method is simple and efficient.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer-based flexible strain sensors, and in particular relates to a fiber-type flexible strain sensor with interlaced soft and hard segments and a preparation method thereof. Background Art

[0002] Flexible strain sensors, as functional devices that can convert mechanical deformation into electrical signals, have broad application prospects in wearable devices, health monitoring, human-computer interaction, intelligent robots and other fields. In recent years, fiber-type flexible strain sensors have attracted widespread attention due to their unique structural and performance advantages. Compared with traditional thin-film or block-shaped flexible sensors, fiber-type sensors have excellent flexibility, weavability and breathability. They can be seamlessly integrated into clothing or wearable devices to achieve real-time monitoring of physiological signals such as human movement, breathing, and heartbeat. At the same time, their lightweight, breathable and comfortable properties make them suitable for long-term wear. In addition, fiber-type sensors can be easily produced continuously through mature spinning processes (such as wet spinning and melt spinning), with the significant advantages of simple process, low cost and suitability for mass production.

[0003] However, despite the aforementioned advantages, fiber-based flexible strain sensors still face significant performance challenges. First, existing fiber-based sensors are mostly made of uniform structures or simple composite materials, and their sensitivity is limited by the mechanical and electrical properties of the material itself. Second, improving sensitivity often comes at the expense of operating range. For example, the introduction of a crack structure can significantly improve sensor sensitivity, but its strain response range is typically narrow (e.g., <50%). Furthermore, complex preparation processes or expensive material costs also limit their large-scale application.

[0004] Therefore, the development of a fiber-type flexible strain sensor that significantly improves sensitivity through structural design, while taking into account a wide strain response range, and maintains a simple process, low cost, and is suitable for mass production has important scientific significance and application value. Summary of the Invention

[0005] The first object of the present invention is to address the deficiencies of the prior art and provide a fiber-type flexible strain sensor with interlaced soft and hard segments, which has high sensitivity and a wide strain response range.

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

[0007] A fiber-type flexible strain sensor with interlaced soft and hard segments comprises a polyvinylidene fluoride fiber as a core structure and a thermoplastic polyurethane layer as a sheath structure. The thermoplastic polyurethane layer is coated around the polyvinylidene fluoride fiber, and the surface of the thermoplastic polyurethane layer has a conductive path layer. The fiber-type flexible strain sensor is pre-stretched to form an interlaced soft-segment-hard segment structure, wherein the soft segment is the thermoplastic polyurethane layer and the hard segment is the polyvinylidene fluoride fiber.

[0008] Preferably, the conductive path layer is a multi-walled carbon nanotube conductive layer or an ionic liquid conductive layer.

[0009] A second objective of the present invention is to provide a method for preparing a highly sensitive, flexible fiber-based strain sensor based on an electronic conductive mechanism that is simple, low-cost, and suitable for mass production. This method utilizes structural design to prepare core-sheath fibers using a coaxial wet spinning process. This fiber-based flexible strain sensor, characterized by interlaced soft and hard segments, is then pre-stretched and tailored to produce the aforementioned flexible strain sensor.

[0010] When the conductive path layer is a multi-walled carbon nanotube conductive layer, the method includes the following steps:

[0011] Step (1): dissolving thermoplastic polyurethane (TPU) in N,N-dimethylformamide (DMF) to prepare a TPU solution, dissolving polyvinylidene fluoride (PVDF) in DMF to prepare a PVDF solution, and then preparing TPU@PVDF core-sheath structure fibers through a coaxial wet spinning device, and drying in an oven to obtain dry TPU@PVDF core-sheath structure fibers;

[0012] Step (2): soaking the dried TPU@PVDF core-sheath structure fiber in an organic solvent to cause the fiber to swell;

[0013] Step (3): Dispersing multi-walled carbon nanotubes (MWCNTs) in deionized water, adding a dispersant to the deionized water to improve the dispersibility of MWCNTs in deionized water, and adding an emulsifier to the deionized water to improve the loading capacity of MWCNTs on the fiber surface, and ultrasonicating the mixed liquid in a cell crusher to obtain a uniformly dispersed MWCNTs dispersion;

[0014] Step (4): placing the swollen TPU@PVDF fiber in step (2) in the MWCNTs dispersion prepared in step (3), and loading a layer of MWCNTs on the surface of the TPU@PVDF fiber by ultrasonic wave of a cell crusher to construct a conductive path of MWCNTs. The prepared fiber is named TPU / MWCNTs@PVDF fiber;

[0015] Step (5): Pre-stretch the TPU@PVDF core-sheath structure fiber loaded with MWCNTs by ultrasonication to construct a soft-segment-hard-segment interlaced structure; the introduction of this "soft-hard" segment structure will significantly improve the sensitivity of this fiber-type strain sensor. The TPU / MWCNTs@PVDF fiber is cut, and silver paste is applied to both ends of the cut fiber as electrodes, which are then connected to copper wire to produce a highly sensitive flexible fiber-type strain sensor.

[0016] Preferably, the mass concentration of the TPU solution in step (1) is 30-35 wt%, more preferably 30 wt%; the mass concentration of the PVDF solution is 10-15 wt%, more preferably 12 wt%.

[0017] Preferably, the organic solvent used in step (2) is ethanol (EtOH), acetone (Ace), ethyl acetate (EA), xylene, etc., and the soaking time is 24 h.

[0018] Preferably, in step (3), the dispersant is polyvinylpyrrolidone (PVP), the emulsifier is Triton-100, the mass concentration of MWCNTs is 1-2 wt %, more preferably 1 wt %. The ultrasonication time is 1-1.5 h, more preferably 1 h.

[0019] Preferably, the ultrasonication time in the cell crusher in step (4) is 2-2.5 h, more preferably 2 h.

[0020] Preferably, the TPU / MWCNTs@PVDF fiber used in step (5) is pre-stretched under 100% strain, the fiber length after cutting is 5-7 cm, and the electrode spacing is 2 cm.

[0021] When the conductive path layer is an ionic liquid conductive layer, the method comprises the following steps:

[0022] Step (1): Dissolve TPU in DMF to prepare a TPU solution, add ionic liquid (ILs) to the TPU solution, and stir evenly to obtain an ILs / TPU solution. Dissolve PVDF in DMF to prepare a PVDF solution.

[0023] Step (2): The ILs / TPU solution and PVDF solution prepared in step (1) are passed through a coaxial wet spinning device to prepare TPU / ILs@PVDF core-sheath structure fibers, which are then dried in an oven to obtain TPU / ILs@PVDF core-sheath structure fibers.

[0024] Step (3): After pre-stretching the TPU / ILs@PVDF core-sheath structure fiber prepared in step (2), it is cut and the two ends of the fiber are connected to copper wires to prepare a flexible strain sensor.

[0025] The mass concentration of the TPU solution in step (1) is 30-35 wt%, more preferably 30 wt%; the mass concentration of the added ILs is 30-35 wt%, more preferably 30 wt%; and the mass concentration of the PVDF solution is 10-15 wt%, more preferably 12 wt%.

[0026] Preferably, the ionic liquid in step (1) is one or more of 1-ethyl-3-methylimidazolium tetrafluoroborate, N-methyl, methoxyethyl pyrrolidine bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, N-methylpropylpiperidinium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0027] Preferably, the TPU / ILs@PVDF fiber used in step (3) is pre-stretched under 100% strain, the fiber length after cutting is 5-7 cm, and the electrode spacing is 2 cm.

[0028] The beneficial effects of the present invention are:

[0029] This invention provides a novel fiber-based flexible strain sensor. Based on a core-sheath structure, it incorporates a unique "soft-hard" segment structure. Under strain, this structure significantly increases the degree of damage to the conductive pathway, resulting in a more pronounced resistance change than with conventional fibers, ultimately achieving a significant improvement in sensitivity. This structural design has universal applicability in improving the sensitivity of flexible fiber-based strain sensors. Using flexible fiber-based strain sensors as a reference, it is possible to demonstrate that multilayer films and other materials with the same or similar structures can achieve similar performance improvements through this structural design.

[0030] In addition, the present invention uses a coaxial wet spinning process to prepare core-sheath structured fibers, and then constructs a conductive path on the fiber surface through ultrasonic impregnation technology, thereby achieving low-cost and mass production of flexible sensors. The process is simple and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The following is a brief introduction to the drawings related to the embodiments of the present invention. In the drawings, GF (Gauge Factor) represents the ratio of resistance change to strain, that is, the slope of a curve in a certain interval in the strain-resistance change graph, and is represented by a straight line in the drawings.

[0032] Figure 1 Schematic diagram of coaxial wet spinning to prepare TPU@PVDF core-sheath structure fibers.

[0033] Figure 2 These are digital photos of core-sheath structure fibers, where a is a digital image of the prepared TPU@PVDF core-sheath structure fiber, and b is a digital image of the "soft-hard" segment structure that appears after pre-stretching.

[0034] Figure 3 SEM images of the samples, a is the surface of TPU / MWCNTs@PVDF fiber, b is the enlarged surface of TPU / MWCNTs@PVDF fiber, c is the cross-section of TPU / MWCNTs@PVDF fiber, and d is the enlarged cross-section of TPU / MWCNTs@PVDF fiber.

[0035] Figure 4 This is the relative resistance change curve of the flexible strain sensor prepared by TPU / MWCNTs@PVDF fiber under uniaxial tension, where GF1 is the sensing sensitivity of TPU / MWCNTs@PVDF fiber at 0-100% strain, GF2 is the sensing sensitivity at 100-200% strain, and GF3 is the sensing sensitivity at 200-300% strain.

[0036] Figure 5 This is the relative resistance change curve of the flexible strain sensor prepared by TPU / MWCNTs fiber under uniaxial tension, where GF1 is the sensing sensitivity of TPU / MWCNTs fiber at 0-100% strain, GF2 is the sensing sensitivity at 100-200% strain, and GF3 is the sensing sensitivity at 200-300% strain.

[0037] Figure 6 SEM images of the samples, a is the surface of TPU / ILs@PVDF fiber, b is the enlarged surface of TPU / ILs@PVDF fiber, c is the cross-section of TPU / ILs@PVDF fiber, and d is the enlarged cross-section of TPU / ILs@PVDF fiber.

[0038] Figure 7 Figure 2 is the relative resistance change curve of the flexible strain sensor prepared by TPU / ILs@PVDF fiber under uniaxial tension, where GF1 is the sensing sensitivity of TPU / ILs@PVDF fiber under 0-250% strain, and GF2 is the sensing sensitivity under 250-600% strain.

[0039] Figure 8 is the relative resistance change curve of the flexible strain sensor prepared by TPU / ILs fiber under uniaxial tension, where GF1 is the sensing sensitivity of TPU / ILs fiber under 0-280% strain, and GF2 is the sensing sensitivity under 280-625% strain. DETAILED DESCRIPTION

[0040] As mentioned above, in view of the deficiencies of the prior art, the inventors of this case have proposed the technical solution of the present invention after long-term research and extensive practice, the main basis of which includes at least the following: (1) Based on the prior art, wet spinning is already a relatively mature fiber preparation process. By changing the needle, coaxial wet spinning can be achieved to prepare core-sheath structure fibers. With the assistance of a temperature-controlled circulating water bath, the accurate temperature of the coagulation bath in the coagulation bath pool can be achieved, so that the state of the fiber during molding can be more accurately controlled; (2) MWCNTs, as a widely used one-dimensional conductive filler, can construct a conductive path on the polymer surface through technologies such as ultrasonic loading. When the material is deformed, cracks will form. As the degree of deformation increases, the material resistance will change significantly; (3) ILs have strong mutual solubility with the polymer matrix, so they can be dispersed more evenly in the polymer matrix, and the performance of flexible sensors prepared using ILs is also more stable; (4) The fiber material can be obtained into cloth by simple weaving through a weaving mold, which is also more suitable for sensor applications.

[0041] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0042] The present invention provides a fiber-type flexible strain sensor with interlaced soft and hard segments, which comprises, from the inside out, a polyvinylidene fluoride fiber as a core structure and a thermoplastic polyurethane layer as a sheath structure. The thermoplastic polyurethane layer is coated on the periphery of the polyvinylidene fluoride fiber, and the surface of the thermoplastic polyurethane layer has a conductive path layer.

[0043] When the conductive path layer is a multi-walled carbon nanotube conductive layer, the method includes the following steps:

[0044] Step (1): dissolving thermoplastic polyurethane (TPU) in N,N-dimethylformamide (DMF) to prepare a TPU solution with a mass concentration of 30-35 wt%, dissolving polyvinylidene fluoride (PVDF) in DMF to prepare a PVDF solution with a mass concentration of 10-15 wt%, and then preparing TPU@PVDF core-sheath structure fibers through a coaxial wet spinning device, and drying in an oven to obtain dry TPU@PVDF core-sheath structure fibers;

[0045] Step (2): Soak the dried TPU@PVDF core-sheath structure fiber in an organic solvent such as ethanol (EtOH), acetone (Ace), ethyl acetate (EA), and xylene for 24 h;

[0046] Step (3): Multi-walled carbon nanotubes (MWCNTs) with a mass concentration of 1-2 wt% are dispersed in deionized water. In order to improve the dispersibility of MWCNTs in deionized water, a dispersant polyvinylpyrrolidone (PVP) is added to the deionized water. In order to improve the loading capacity of MWCNTs on the fiber surface, an emulsifier Triton-100 is added to the deionized water. The mixed liquid is ultrasonicated in a cell crusher for 1-1.5 h to obtain a uniformly dispersed MWCNTs dispersion.

[0047] Step (4): placing the swollen TPU@PVDF fiber in step (2) in the MWCNTs dispersion prepared in step (3), and ultrasonicating the TPU@PVDF fiber for 2-2.5 h to load a layer of MWCNTs on the surface of the TPU@PVDF fiber to obtain TPU / MWCNTs@PVDF fiber;

[0048] Step (5): The TPU@PVDF core-sheath structure fiber loaded with ultrasonic MWCNTs was pre-stretched at 100% strain to construct a "soft-hard" segment structure. The introduction of the "soft-hard" segment structure will greatly improve the sensitivity of this fiber-type strain sensor. The TPU / MWCNTs@PVDF fiber was cut into fiber segments of 5-7 cm, and silver paste was applied to both ends of the fiber segment as electrodes. Then, the electrodes were connected to copper wire to obtain a highly sensitive flexible fiber-type strain sensor with an electrode spacing of 2 cm.

[0049] When the conductive path layer is an ionic liquid conductive layer, the method comprises the following steps:

[0050] Step (1): dissolving TPU in DMF to prepare a TPU solution with a mass concentration of 30-35 wt%, adding ILs with a mass concentration of 30-35 wt% to the TPU solution, and stirring evenly to obtain an ILs / TPU solution. Dissolving PVDF in DMF to prepare a PVDF solution with a mass concentration of 10-15 wt%; the ILs are one or more of 1-ethyl-3-methylimidazolium tetrafluoroborate, N-methyl, methoxyethyl pyrrolidine bistrifluoromethanesulfonyl imide, 1-ethyl-3-methylimidazolium bistrifluoromethanesulfonyl imide, N-methylpropylpiperidinium bistrifluoromethanesulfonyl imide, 1-ethyl-3-methylimidazolium bistrifluoromethanesulfonyl imide, 1-butyl-3-methylimidazolium bistrifluoromethanesulfonyl imide, and 1-hexyl-3-methylimidazolium bistrifluoromethanesulfonyl imide;

[0051] Step (2): The ILs / TPU solution and PVDF solution prepared in step (1) are passed through a coaxial wet spinning device to prepare TPU / ILs@PVDF core-sheath structure fibers, and the fibers are dried in an oven to obtain TPU / ILs@PVDF core-sheath structure fibers;

[0052] Step (3): The TPU / ILs@PVDF core-sheath structure fiber prepared in step (2) was pre-stretched under 100% strain, and then cut to obtain fiber segments with a length of 5-7 cm. The two ends of the fiber were connected with copper wire to obtain a flexible strain sensor with an electrode spacing of 2 cm.

[0053] The following further illustrates the technical solution of the present invention in conjunction with several preferred embodiments, but the experimental conditions and setting parameters therein should not be considered as limiting the basic technical solution of the present invention. Moreover, the scope of protection of the present invention is not limited to the following embodiments.

[0054] Example 1

[0055] 9 g of thermoplastic polyurethane (TPU) was added to the solvent DMF, and the mixture was heated and stirred at 50 °C on a heating stirrer. After sufficient stirring, a 30 wt% uniform TPU solution was obtained. 3.6 g of polyvinylidene fluoride (PVDF) was added to DMF, and after sufficient stirring on a stirrer, a 12 wt% uniform PVDF solution was obtained.

[0056] Preparation of TPU@PVDF core-sheath structure fibers Figure 1 As shown, the TPU solution and PVDF solution were allowed to stand for 1 h to degas, and then divided into 10 mL syringes respectively, and connected to the coaxial needle (needle model is 18G / 14G) through a polytetrafluoroethylene hose, wherein the polytetrafluoroethylene hose connected to the syringe containing the PVDF solution was connected to the inner channel of the coaxial needle, and the polytetrafluoroethylene hose connected to the syringe containing the TPU solution was connected to the outer channel of the coaxial needle. The propulsion pump injected the TPU solution and PVDF solution into the deionized water coagulation bath at a propulsion rate of 10 mL / h at the same time. After the fibers were collected, the TPU@PVDF core-sheath structure fibers were dried in an oven at 50 °C for 12 h to remove excess deionized water and residual DMF inside the fibers to obtain dry TPU@PVDF core-sheath structure fibers.

[0057] The TPU@PVDF core-sheath structure fibers prepared are as follows Figure 2As shown in a, the TPU@PVDF core-sheath structure fiber is then placed in a xylene solution and soaked for 24 hours. 0.1 g of polyvinyl pyrrolidone (PVP) and 0.1 g of Triton-100 are added to 98.8 g of deionized water, and then 1.0 g of multi-walled carbon nanotubes (MWCNTs) are added. The mixture is stirred on a stirrer for 30 minutes, and then the mixed solution is ultrasonicated in a cell crusher for 1 hour to obtain a uniformly dispersed MWCNTs dispersion. The swollen TPU@PVDF core-sheath structure fiber is wrapped around a homemade iron wire ring, placed in a MWCNTs dispersion, and ultrasonicated in a cell crusher for 2 hours. A layer of MWCNTs film is loaded on the surface of the TPU@PVDF core-sheath structure fiber to construct a conductive path to obtain TPU / MWCNTs@PVDF fiber. The structure of TPU / MWCNTs@PVDF fiber is shown in FIG. Figure 3 As shown in the SEM image, a MWCNTs layer can be seen attached to the surface of the TPU / MWCNTs@PVDF fiber. After pre-stretching at 100% strain, microcracks appeared on the MWCNTs layer on the surface of the TPU / MWCNTs@PVDF fiber. The macroscopic "soft-hard" structure is shown in Figure 2 As shown in b.

[0058] Finally, the TPU / MWCNTs@PVDF fiber was cut into 5 cm strips, silver paste was applied to both ends of the fiber as electrodes, and copper wire was wrapped around the silver paste. This simple method can produce a flexible strain sensor that can be mass-produced. Finally, the uniaxial tensile sensing performance of the sensor was tested. Figure 4 As shown, the sensing sensitivity of TPU / MWCNTs@PVDF fiber at 0-100% strain is GF1=16.9, the sensing sensitivity at 100-200% strain is GF2=102.27, and the sensing sensitivity at 200-300% strain is GF3=323.38.

[0059] Comparative Example 1

[0060] 9 g of thermoplastic polyurethane (TPU) was added to the solvent DMF, and the mixture was heated and stirred at 50 °C on a heating stirrer. After sufficient stirring, a 30 wt% uniform TPU solution was obtained.

[0061] Preparation of TPU fiber Figure 1As shown, the TPU solution was allowed to stand for 1 hour to degas and then divided into 10 mL syringes. The syringes were connected to coaxial needles (needle model: 18G / 14G) through polytetrafluoroethylene hoses. The propulsion pump injected the TPU solution into the deionized water coagulation bath at a propulsion rate of 10 mL / h. After the TPU fibers were collected, they were dried in an oven at 50 °C for 12 hours to remove excess deionized water and residual DMF inside the fibers to obtain dry TPU fibers.

[0062] TPU fibers were immersed in a xylene solution for 24 hours. Weighed polyvinyl pyrrolidone (PVP) and Triton-100 were added to deionized water, followed by multi-walled carbon nanotubes (MWCNTs). The mixture was stirred on a blender for 30 minutes, and then sonicated in a cell grinder for 1 hour to obtain a uniformly dispersed MWCNTs solution. The swollen TPU fibers were then wrapped around a homemade wire loop, placed in the MWCNTs solution, and sonicated in a cell grinder for 2 hours. A layer of MWCNTs was then deposited on the TPU fiber surface, creating a conductive pathway and producing TPU / MWCNTs fibers.

[0063] Finally, the TPU / MWCNTs fibers were cut into 5 cm strips, silver paste was applied to both ends of the fibers as electrodes, and copper wire was wrapped around the silver paste. This simple method can produce a flexible strain sensor that can be mass-produced. Finally, the uniaxial tensile sensing performance of the sensor was tested. Figure 5 As shown, the sensing sensitivity of TPU / MWCNTs fiber at 0-100% strain is GF1=2.55, the sensing sensitivity at 100-200% strain is GF2=29.8, and the sensing sensitivity at 200-300% strain is GF3=31.95.

[0064] Example 2

[0065] 9 g of thermoplastic polyurethane (TPU) and 2.7 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt were added to the solvent DMF, placed on a heating stirrer and heated and stirred at 50 °C. After thorough stirring, a 30 wt% uniform TPU / ILs solution doped with 30 wt% ILs was obtained. 3.6 g of polyvinylidene fluoride (PVDF) was added to DMF and thoroughly stirred on a stirrer to obtain a 12 wt% uniform PVDF solution.

[0066] Preparation of TPU / ILs@PVDF core-sheath structure fibers Figure 1As shown, the TPU / ILs solution and the PVDF solution were allowed to stand for 1 hour to degas, and then ultrasonicated in an ultrasonic machine for 30 minutes to obtain a uniformly dispersed TPU / ILs solution, which was then divided into 10 mL syringes and connected to a coaxial needle (needle model 18G / 14G) through a polytetrafluoroethylene hose. The polytetrafluoroethylene hose connected to the PVDF solution syringe was connected to the inner channel of the coaxial needle, and the polytetrafluoroethylene hose connected to the TPU / ILs solution syringe was connected to the outer channel of the coaxial needle. The propulsion pump injected the TPU / ILs solution and the PVDF solution into the deionized water coagulation bath at a propulsion rate of 10 mL / h. After the fibers were collected, the TPU / ILs@PVDF core-sheath structure fibers were dried in an oven at 50 ° C for 12 hours to remove excess deionized water and residual DMF inside the fibers to obtain dry TPU / ILs@PVDF core-sheath structure fibers. The structure of the TPU / ILs@PVDF fiber is shown in FIG. Figure 6 As shown in the SEM image, the surface of TPU / ILs@PVDF fibers is relatively smooth. TPU / ILs and PVDF have a clear and tightly bonded interface.

[0067] Finally, the TPU / ILs@PVDF core-sheath structure fiber was pre-stretched under 100% strain and cut into 5-7 cm short strips. Copper wires were wrapped around both ends of the fiber. This simple method can produce a flexible strain sensor that can be mass-produced. Finally, the uniaxial tensile sensing performance of the sensor was tested. Figure 7 As shown in the figure, the sensing sensitivity of TPU / ILs@PVDF fiber under 0-250% strain is GF1=10.6, and the sensing sensitivity under 250-600% strain is GF2=37.47.

[0068] Comparative Example 2

[0069] 9 g of thermoplastic polyurethane (TPU) and 2.7 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt were added to the solvent DMF, placed on a heating stirrer and heated at 50 °C with stirring. After thorough stirring, a 30 wt% uniform TPU / ILs solution doped with 30 wt% ILs was obtained.

[0070] Preparation of TPU / ILs fibers Figure 1As shown, the TPU solution was allowed to stand for 1 h to degas and then divided into 10 mL syringes. The syringes were connected to coaxial needles (needle model was 18G / 14G) through polytetrafluoroethylene hoses. The propulsion pump injected the TPU / ILs solution into the deionized water coagulation bath at a propulsion rate of 10 mL / h. After the fibers were collected, the TPU / ILs fibers were dried in an oven at 50°C for 12 h to remove excess deionized water and residual DMF inside the fibers to obtain dry TPU / ILs fibers.

[0071] Finally, the TPU / ILs fiber was pre-stretched under 100% strain and cut into 5-7 cm short strips. Copper wire was wrapped around both ends of the fiber. This simple method can produce a flexible strain sensor that can be mass-produced. Finally, the uniaxial tensile sensing performance of the sensor was tested. Figure 8 As shown, the sensing sensitivity of TPU / ILs fiber under 0-280% strain is GF1=3.82, and the sensing sensitivity under 280-625% strain is GF2=5.06.

[0072] The results of the Examples and Comparative Examples demonstrate that the present invention significantly improves sensor sensitivity through its "soft-hard" structural design. Compared to undesigned TPU / MWCNTs and TPU / ILs fiber-based strain sensors, under the same tensile conditions, the soft segments of the TPU / MWCNTs@PVDF and TPU / ILs@PVDF fibers undergo greater deformation, resulting in higher strain sensitivity. Tensile testing demonstrates that the flexible fiber-based strain sensor with this "soft-hard" structural design significantly improves sensitivity while maintaining a wide strain response range.

[0073] The above description is only a preferred embodiment of the present invention. The present invention is not limited to the scope of the specific implementation mode. For ordinary technicians in this technical field, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A fiber-type flexible strain sensor with a soft-hard segment interlaced structure, characterized in that: The invention comprises a polyvinylidene fluoride fiber as a core structure and a thermoplastic polyurethane layer as a sheath structure, wherein the thermoplastic polyurethane layer is coated on the outer periphery of the polyvinylidene fluoride fiber, and a conductive path layer is provided on the surface of the thermoplastic polyurethane layer, wherein the conductive path layer is a multi-walled carbon nanotube conductive layer; The fiber-type flexible strain sensor is pre-stretched to form a soft segment-hard segment interlaced structure, wherein the soft segment is a thermoplastic polyurethane layer and the hard segment is a polyvinylidene fluoride fiber; the pre-stretching is performed under 100% strain.

2. A method for preparing the fiber-type flexible strain sensor according to claim 1, characterized in that: The method comprises the following steps: Step (1): dissolving thermoplastic polyurethane (TPU) and polyvinylidene fluoride (PVDF) in N,N-dimethylformamide, mixing them, and wet spinning them to obtain TPU@PVDF core-sheath structure fibers, which are then dried; Step (2): soaking the dried TPU@PVDF core-sheath structure fiber in an organic solvent to obtain a swollen TPU@PVDF core-sheath structure fiber; Step (3): adding multi-walled carbon nanotubes (MWCNTs), a dispersant, and an emulsifier into deionized water and performing ultrasonication to obtain a uniformly dispersed multi-walled carbon nanotube dispersion; Step (4): placing the swollen TPU@PVDF core-sheath structure fiber obtained in step (2) in the multi-walled carbon nanotube dispersion obtained in step (3) and performing ultrasonication to obtain TPU / MWCNTs@PVDF core-sheath structure fiber; Step (5): Pre-stretch the TPU / MWCNTs@PVDF core-sheath structure fiber to construct a soft segment-hard segment interlaced structure. After cutting, silver paste is coated on both ends as electrodes, and then connected with copper wire to obtain a high-sensitivity flexible fiber-type strain sensor; the pre-stretching is performed under 100% strain.

3. The preparation method according to claim 2, characterized in that The organic solvent is selected from one or more of ethanol, acetone, ethyl acetate and xylene.

4. The preparation method according to claim 2, characterized in that The dispersant is polyvinyl pyrrolidone (PVP), the emulsifier is Triton-100, and the mass concentration of multi-walled carbon nanotubes MWCNTs is 1.0 wt%.

5. The preparation method according to claim 2, characterized in that The mass concentration of thermoplastic polyurethane TPU is 30-35wt%, and the mass concentration of polyvinylidene fluoride PVDF is 10-15wt%.

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