An electrochromic spiral-coated piezoelectric composite yarn and its preparation method

Abstract

This invention introduces an electrochromic spiral-coated piezoelectric composite yarn and its preparation method, belonging to the field of functional materials technology. It includes: a silver-plated nylon core yarn and, sequentially disposed outside the silver-plated nylon core yarn, a nanofiber layer, an encapsulation layer, a transparent conductive layer, an electrochromic active layer, an ion gel electrolyte layer, and an ion storage layer. The nanofiber layer is a PVDF / BaTiO3 nanofiber yarn spirally and cross-coated on the surface of the silver-plated nylon core yarn. The transparent conductive layer is formed by curing a PEDOT:PSS conductive polymer dispersion. The electrochromic active layer is tungsten trioxide nanowires uniformly deposited on the transparent conductive layer. The ion storage layer is a Prussian blue nanolayer. This invention solves the problems of poor environmental adaptability, insufficient mechanical durability, and unstable piezoelectric output in existing piezoelectric yarns.

Description

Technical Field

[0001] This invention relates to an electrochromic spiral-coated piezoelectric composite yarn and its preparation method, belonging to the field of functional materials technology. Background Technology

[0002] With the breakthrough development of flexible electronics technology, the demand for piezoelectric materials in fields such as smart textiles, wearable health monitoring, and environmental energy harvesting has increased dramatically. Traditional piezoelectric materials are mainly inorganic ceramics, which, while possessing high piezoelectric coefficients and stable output characteristics, suffer from inherent brittleness, high stiffness, and incompatibility with flexible substrates, severely limiting their direct application in deformable electronic devices. In recent years, polymeric piezoelectric materials have become a research hotspot due to their flexibility. Among them, polyvinylidene fluoride (PVDF) and its copolymers are widely used in flexible piezoelectric sensors and energy harvesting devices due to their excellent piezoelectric response, chemical stability, and ease of processing. To improve the overall performance of PVDF-based piezoelectric materials, researchers have conducted multi-dimensional composite modification: on the one hand, by introducing conductive fillers or piezoelectric reinforcing phases, a "conductive-piezoelectric" synergistic network is constructed, simultaneously improving the material's conductivity and piezoelectric output; on the other hand, structural design strategies are employed to optimize stress transfer efficiency and energy conversion efficiency. Furthermore, surface encapsulation technology is used to improve the material's environmental stability and mechanical durability. These technological approaches have, to some extent, promoted the transformation of flexible piezoelectric materials from the laboratory to practical applications.

[0003] Although existing technologies have improved the performance of PVDF-based piezoelectric materials through composite modification and structural design, they still face three major bottlenecks that restrict their practical application in complex scenarios. Pure PVDF and most modified materials are highly sensitive to humidity, easily experiencing decreased crystallinity and polarization degradation after moisture absorption, leading to a decline in piezoelectric performance. Simultaneously, their chemical corrosion resistance is limited, easily swelling or degrading in complex liquid environments such as sweat and seawater, limiting their application in underwater sensors, wearable medical devices, and other scenarios. The interfacial bonding between conductive / piezoelectric fillers and the polymer matrix in composite materials is weak. During long-term repeated deformation, the fillers are prone to detachment or aggregation, leading to conductive network breakage and unstable piezoelectric output. Furthermore, due to structural anisotropy, fibrous piezoelectric materials are prone to fiber breakage or interlayer delamination under dynamic loads, further reducing device lifespan. Existing piezoelectric materials mostly focus on single piezoelectric signal output and lack the ability to synchronously sense multimodal signals, making it difficult to meet the integrated "sensing-feedback-interaction" requirements of smart fabrics. At the same time, during long-term cyclic use, the output performance of the materials continuously degrades due to polarization fatigue and structural aging, limiting their application in high-frequency energy harvesting or long-term health monitoring.

[0004] Therefore, existing piezoelectric yarns suffer from poor environmental adaptability, insufficient mechanical durability, and unstable piezoelectric output. Summary of the Invention

[0005] The purpose of this invention is to provide an electrochromic spiral-coated piezoelectric composite yarn and its preparation method. By using nanofiber layers to multi-layer coat and encapsulate silver-plated nylon core yarn, the invention solves the problems of poor environmental adaptability, insufficient mechanical durability, and unstable piezoelectric output of existing piezoelectric yarns. It significantly improves the piezoelectric properties, mechanical flexibility, and long-term stability of the fiber, providing a new solution for the application of flexible electronic devices.

[0006] To solve the above-mentioned technical problems, the present invention is implemented using the following technical solution:

[0007] In a first aspect, the present invention provides an electrochromic spiral-coated piezoelectric composite yarn, comprising a silver-plated nylon core yarn and a nanofiber layer, an encapsulation layer, a transparent conductive layer, an electrochromic active layer, an ion gel electrolyte layer and an ion storage layer sequentially disposed outside the silver-plated nylon core yarn.

[0008] The nanofiber layer is a PVDF / BaTiO3 nanofiber yarn that is spirally and crosswise wrapped around the surface of a silver-plated nylon core yarn. The transparent conductive layer is formed by curing a PEDOT:PSS conductive polymer dispersion. The electrochromic active layer is a tungsten trioxide nanowire uniformly deposited on the transparent conductive layer. The ion storage layer is a Prussian blue nanolayer.

[0009] Furthermore, the nanofiber layer has 2-8 coating layers;

[0010] And / or, the thickness of the transparent conductive layer is 0.5-2 μm;

[0011] And / or, the thickness of the electrochromic active layer is 5-20 μm;

[0012] And / or, the thickness of the ion storage layer is 3-15 μm;

[0013] And / or, the thickness of the ionogel electrolyte layer is 10-30 μm.

[0014] Furthermore, the encapsulation layer is a PDMS (polydimethylsiloxane) encapsulation layer with a thickness of 20-30 μm.

[0015] In a first aspect, the present invention provides a method for preparing an electrochromic spiral-coated piezoelectric composite yarn as described in the first aspect, characterized in that it comprises:

[0016] A nanofiber layer is formed by spirally wrapping PVDF / BaTiO3 nanofiber yarn along the axial direction of silver-plated nylon core yarn.

[0017] A nanofiber layer is encapsulated with PDMS as a curing agent to form an encapsulation layer, and then immersed in PEDOT:PSS conductive polymer dispersion to form a transparent conductive layer.

[0018] An electrochromic layer is formed on the surface of a transparent conductive layer by spraying a suspension of tungsten trioxide nanowires in ethanol.

[0019] An ion gel electrolyte was spin-coated onto the surface of an electrochromic layer, and after curing, it was covered with a Prussian blue nanolayer to form an ion storage layer.

[0020] Furthermore, the expression for calculating the twist between the silver-plated nylon core yarn and the nanofiber layer is as follows:

[0021] ;

[0022] In the formula, This indicates the twist between the silver-plated nylon core yarn and the nanofiber layer, expressed in r / m. The speed of the silver-plated nylon core yarn is expressed in m / min. This indicates the encapsulation speed of the nanofiber layer, expressed in m / min.

[0023] Furthermore, the thickness of the cured layer was adjusted to 20-30 μm by using COMSOL to simulate the interfacial stress distribution between the encapsulation layer and the nanofiber layer.

[0024] Furthermore, the method for preparing the PVDF / BaTiO3 nanofiber yarn includes:

[0025] Dissolve the PVDF masterbatch in dimethylformamide solvent to prepare a 10-20 wt% PVDF solution, and stir magnetically in a water bath at 60℃ for 1-3 h until completely dissolved;

[0026] Weigh 5-15 wt% of barium titanate nanopowder (equivalent to PVDF masterbatch) and add it to the above solution. After ultrasonic dispersion for 8-16 h, a uniformly dispersed spinning solution is obtained.

[0027] The spinning solution was injected into the electrostatic spinning nozzle to repeatedly and cross-wrap 4-8 layers of silver-plated nylon core yarn, and then dried at 60℃ for 1-3 h to remove residual solvent, thus obtaining PVDF / BaTiO3 nanofiber yarn.

[0028] Furthermore, the method for encapsulating the nanofiber layer with PDMS as a curing solution to form an encapsulation layer includes:

[0029] Mix the base adhesive and PDMS at a mass ratio of 8:1-12:1, stir for 20-40 min, and let stand for pre-curing for 10-14 h to obtain a PDMS solution.

[0030] The nanofiber layer is immersed in PDMS solution, brushed for 3-7 minutes to ensure uniform coverage, then straightened and fixed at 60℃ for 20-40 minutes for secondary curing to form an encapsulation layer with a thickness of about 20-30 μm.

[0031] Furthermore, the method for preparing the electrochromic active layer includes:

[0032] Tungsten trioxide nanowires were uniformly deposited on the surface of a transparent conductive layer by electrostatic spraying of a tungsten trioxide nanowire ethanol suspension with a concentration of 20-40 min. After drying, an electrochromic active layer with a thickness of 10±2 μm was formed.

[0033] Furthermore, the method for preparing the ion storage layer includes:

[0034] An ion gel electrolyte is spin-coated onto the surface of the electrochromic layer and cured to form an ion gel electrolyte layer.

[0035] An ion storage layer is formed by coating a Prussian blue nanolayer onto an ion gel electrolyte layer.

[0036] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0037] 1. The electrochromic spiral-coated piezoelectric composite yarn provided by this invention achieves a multimodal response from mechanical stimulation perception to electrical signal transmission, and from electrical signal transmission to visual feedback, through the synergistic design of the spirally cross-coated nanofiber layer and the encapsulation layer: When the electrochromic spiral-coated piezoelectric composite yarn is subjected to external force, the spirally coated nanofiber layer converts mechanical energy into an electrical signal. The electrical signal is transmitted to the electrochromic active layer through the transparent conductive layer on the surface of the encapsulation layer, driving ions to migrate between the active layer and the ion storage layer via the ion gel electrolyte layer, triggering real-time color change; at the same time, the spiral cross-coating structure enhances the interfacial bonding force between the piezoelectric layer and the silver-plated nylon core yarn, and combined with the moisture resistance and bending resistance of the encapsulation layer and the curing layer, it significantly improves the mechanical durability and functional stability of the material in complex environments.

[0038] 2. The method for preparing electrochromic spiral-coated piezoelectric composite yarn provided by the present invention optimizes stress transmission and charge accumulation by using silver-plated nylon core yarn as the conductive core yarn and forming a nanofiber layer. By encapsulating the nanofiber layer, the hydrophobicity, mechanical stability, and environmental adaptability of the electrochromic spiral-coated piezoelectric composite yarn are improved. At the same time, it also suppresses humidity penetration and friction loss, so that the output voltage fluctuation of the electrochromic spiral-coated piezoelectric composite yarn is less than the preset range within the preset temperature range. The present invention achieves self-powered color change driven by piezoelectric signals by sequentially providing a transparent conductive layer, an electrochromic active layer, and an ion storage layer on the upper surface of the encapsulation layer, while improving the external stress transmission efficiency and charge collection efficiency. Attached Figure Description

[0039] Figure 1 This is a schematic flowchart of a method for preparing an electrochromic spiral-coated piezoelectric composite yarn according to an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the structure of the yarn spiral coating device provided in an embodiment of the present invention;

[0041] Figure 3 This is a schematic diagram of the piezoelectric output performance test curve of the electrochromic spiral-coated piezoelectric composite yarn provided in an embodiment of the present invention;

[0042] Figure 4 This is a mechanical property test diagram of the electrochromic spiral-coated piezoelectric composite yarn provided in an embodiment of the present invention.

[0043] Reference numerals: 1-Double helix chuck device; 2-Silver-plated nylon core yarn; 3-Sliding device; 4-Nanofiber layer. Detailed Implementation

[0044] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations thereof. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0045] Example 1

[0046] This embodiment describes an electrochromic spiral-coated piezoelectric composite yarn, comprising:

[0047] The silver-plated nylon core yarn and the nanofiber layer, encapsulation layer, transparent conductive layer, electrochromic active layer, ion gel electrolyte layer and ion storage layer sequentially disposed outside the silver-plated nylon core yarn.

[0048] The nanofiber layer is a PVDF / BaTiO3 nanofiber yarn that is spirally and crosswise wrapped around the surface of a silver-plated nylon core yarn. The transparent conductive layer is formed by curing a PEDOT:PSS conductive polymer dispersion. The electrochromic active layer is a tungsten trioxide nanowire uniformly deposited on the transparent conductive layer. The ion storage layer is a Prussian blue nanolayer.

[0049] In this embodiment, the number of coating layers of the nanofiber layer is 2-8;

[0050] And / or, the thickness of the transparent conductive layer is 0.5-2 μm;

[0051] And / or, the thickness of the electrochromic active layer is 5-20 μm;

[0052] And / or, the thickness of the ion storage layer is 3-15 μm;

[0053] And / or, the thickness of the ionogel electrolyte layer is 10-30 μm;

[0054] And / or, the encapsulation layer is a PDMS encapsulation layer with a thickness of 20-30 μm.

[0055] In this embodiment, the silver-plated nylon core yarn serves as the conductive core of the electrochromic spiral-coated piezoelectric composite yarn. Its silver plating treatment imparts high conductivity to the core yarn, enabling efficient transmission of electrical signals generated by the piezoelectric layer. The nylon substrate retains flexibility and mechanical strength, serving as both a supporting framework for the nanofiber layer and ensuring that the electrochromic spiral-coated piezoelectric composite yarn maintains structural stability during dynamic deformation, thus avoiding functional failure due to core yarn breakage.

[0056] In this embodiment, the helical cross-coated nanofiber layer significantly improves piezoelectric performance through a multi-layer structure design: the helical cross-coating increases the contact area between the nanofibers and the core yarn, strengthening the interfacial bonding force; the introduction of barium titanate nanoparticles in this embodiment enhances the piezoelectric coefficient of PVDF through the piezoelectric enhancement effect; the multi-layer structure further optimizes the stress distribution, enabling the piezoelectric layer to respond uniformly and output a stable electrical signal when the electrochromic helical-coated piezoelectric composite yarn is subjected to external force, avoiding the stress concentration or signal attenuation problems that are prone to occur in single-layer coating.

[0057] In this embodiment, the PDMS encapsulation layer balances environmental adaptability and flexibility with a thickness of 20-30 μm. The hydrophobicity and chemical stability of PDMS can effectively block water vapor, sweat or seawater erosion, and avoid the decrease in β phase crystallinity caused by moisture absorption of the nanofiber layer. At the same time, the 20-30 μm thickness retains the flexibility of the electrochromic spiral-coated piezoelectric composite yarn, ensuring that it does not crack or fall off during dynamic deformation, and significantly improving the durability of the nanofiber layer in complex environments.

[0058] In this embodiment, the transparent conductive layer achieves a synergy of high transmittance and low resistivity. The thickness of 0.5-2μm optimizes the film formation quality of PEDOT:PSS, avoiding the decrease in transmittance caused by excessive thickness while ensuring conductivity. As an electrode of the electrochromic active layer, the transparent conductive layer can efficiently transmit the electrical signals generated by the piezoelectric layer, while retaining the transparent characteristics of the electrochromic spiral-wrapped piezoelectric composite yarn.

[0059] In this embodiment, the electrochromic active layer accelerates the reaction of lithium ions (Li) through its high specific surface area. + and hydrogen ions H + Plasma insertion / extraction and a thickness of 5-20 μm optimize the color change rate and cycling stability; when the electrical signal output from the piezoelectric layer is applied to the electrochromic active layer, the tungsten trioxide nanowires can quickly undergo a redox reaction to trigger a significant color change, realizing a visual feedback of mechanical stimulation.

[0060] In this embodiment, the Prussian blue ion storage layer covering the electrochromic active layer balances the charge during the electrochromic process through its high ion storage capacity, and the 3-15 μm thickness adjusts the ion buffering capacity. When the active layer undergoes an oxidation reaction, Prussian blue can simultaneously receive and store ions with opposite charges, maintain the charge balance of the system, avoid color shift or failure due to charge accumulation, and significantly improve the cycle stability of the electrochromic function.

[0061] In this embodiment, the ion gel electrolyte layer disposed between the transparent conductive layer and the ion storage layer promotes lithium-ion Li-ion storage through its high ionic conductivity and flexibility. + and hydrogen ions H + Rapid migration of plasma between the active layer and the storage layer, with a thickness of 10-30 μm balancing ion transport efficiency and yarn flexibility; the ion gel electrolyte layer, as an ion transport channel, can respond to the electrical signal output by the piezoelectric layer, driving ions to migrate directionally between the tungsten trioxide active layer and the ion storage layer formed by Prussian blue, realizing rapid response and low-voltage drive of electrochromic function, adapting to the low power consumption requirements of wearable devices.

[0062] In this embodiment, the 6 V voltage generated by the composite electrochromic layer under 10 N pressure can directly trigger the blue / white state switching, and its performance is as follows: Figure 4 As shown in Table 1.

[0063] Table 1 Test data on the synergistic performance of piezoelectric electrochromism

[0064] Test conditions Performance parameters 10 N pressure drive Output voltage: 6.0 ± 0.2 V Transmittance change (ΔT): 42% Color switching time: 4.3 s 90° underwater bend Output voltage: 0.31 V → Triggers light blue color change

[0065] Example 2

[0066] like Figure 1 As shown in the figure, this embodiment introduces a method for preparing an electrochromic spiral-coated piezoelectric composite yarn, including:

[0067] Step 1: The PVDF / BaTiO3 nanofiber yarn is spirally wrapped around the silver-plated nylon core yarn to form a nanofiber layer.

[0068] Step 1.1: Fix the silver-plated nylon core yarn 2 onto the double-helix chuck device 1 of the yarn spiral coating equipment and control the twisting speed of the silver-plated nylon core yarn 2 to 500 r / min. The yarn spiral coating equipment used in this embodiment is as follows: Figure 2 As shown.

[0069] Step 1.2: Using the sliding device 3, the PVDF / BaTiO3 nanofiber yarn is spirally wrapped along the axial direction of the silver-plated nylon core yarn 2 at a first linear speed, while the speed of the sliding device 3 is adjusted to form the nanofiber layer 4.

[0070] Step 1.2.1: Prepare the PVDF / BaTiO3 nanofiber yarn by electrospinning.

[0071] The PVDF masterbatch was dissolved in dimethylformamide solvent to prepare a 15 wt% PVDF solution, and then magnetically stirred in a water bath at 60°C for 2 h until completely dissolved.

[0072] 10 wt% of barium titanate nanopowder with a mass ratio of PVDF was weighed and added to the above solution. After ultrasonic dispersion for 12 h, a uniformly dispersed spinning solution was obtained.

[0073] The spinning solution was injected with an electrostatic spinning nozzle at a voltage of 15 kV and a receiving distance of 15 cm. The nozzle was then used to repeatedly and crosswise wrap six layers of silver-plated nylon core yarn and dried at 60°C for 2 h to remove residual solvent, thus obtaining PVDF / BaTiO3 nanofiber yarn.

[0074] In this embodiment, the expression for calculating the twist between the silver-plated nylon core yarn and the nanofiber layer is as follows:

[0075] ;

[0076] In the formula, This indicates the twist between the silver-plated nylon core yarn and the nanofiber layer, expressed in r / m. The speed of the silver-plated nylon core yarn is expressed in m / min. This indicates the encapsulation speed of the nanofiber layer, expressed in m / min.

[0077] In this embodiment, the speed of the sliding device 3 is adjustable from 300 to 700 r / min. When the speed of the sliding device is adjusted to 300 r / min, 500 r / min, and 700 r / min, the corresponding twist of the PVDF / BaTiO3 nanofiber yarn is 2400 TPM, 1600 TPM, and 1000 TPM, respectively.

[0078] Step 2: Encapsulate the nanofiber layer with PDMS as curing liquid to form an encapsulation layer, and immerse it in PEDOT:PSS conductive polymer dispersion to form a transparent conductive layer.

[0079] Step 2.1: Mix the base adhesive and PDMS at a mass ratio of 10:1, stir for 30 min, and let stand for 12 h to pre-cure to obtain the PDMS solution.

[0080] In this embodiment, the base adhesive is a liquid siloxane prepolymer.

[0081] Step 2.2: Immerse the nanofiber layer in PDMS solution, brush it for 5 min to ensure uniform coverage, then straighten and fix it at 60℃ for 30 min for secondary curing to form an encapsulation layer with a thickness of about 20-30 μm.

[0082] In this embodiment, the encapsulated nanofiber layer has a hydrophobicity of 124°.

[0083] In this embodiment, COMSOL was used to simulate the interfacial stress distribution between the encapsulation layer and the nanofiber layer 4, and the thickness of the encapsulation layer was optimized to 20-30 μm. This maximized the surface potential difference between the silver-plated nylon core yarn 2 and the nanofiber layer 4 to 6V, while keeping the separation distance between the two stably controlled at 15 mm. This significantly improved the charge separation efficiency and power output performance of the piezoelectric nanofiber layer.

[0084] In this embodiment, the encapsulation layer retains ≥95% of its fracture strength after 50 cycles of 20% strain tensile testing, and the output voltage stability deviation is ≤3% after 7500 cycles of testing.

[0085] Step 3: Immerse the encapsulated nanofiber layer in PEDOT:PSS conductive polymer dispersion (solid content 1.5wt%), and dry at 60℃ for a preset time to form a transparent conductive layer.

[0086] Step 4: An electrochromic layer is formed on the surface of the transparent conductive layer by spraying a suspension of tungsten trioxide nanowires in ethanol.

[0087] In this embodiment, the electrostatic spraying voltage is set to 12 kV. Tungsten trioxide nanowires are uniformly deposited on the surface of the transparent conductive layer by electrostatic spraying of a 20 mg / mL ethanol suspension of tungsten trioxide nanowires. After drying, an electrochromic active layer with a thickness of 10 ± 2 μm is formed.

[0088] Step 5: Spin-coat the ionogel electrolyte onto the surface of the electrochromic layer, and cure it to form an ionogel electrolyte layer;

[0089] An ion storage layer is formed by coating a Prussian blue nanolayer onto an ion gel electrolyte layer.

[0090] Example 3

[0091] This embodiment provides a comparative verification method for electrochromic spiral-coated piezoelectric composite yarn. To verify and explain the technical effects of this method, this embodiment uses a traditional technical solution to conduct a comparative test with the method of this invention, and compares the test results with scientific demonstration methods to verify the real effect of this method.

[0092] I. Comparative Experiment:

[0093] Experiment 1: Comparison of Barium Titanate Doping Concentration

[0094] Experimental objective: To verify whether barium titanate affects the charge transfer efficiency of electrochromic spiral-coated piezoelectric composite yarns.

[0095] Experimental variables: Barium titanate doping concentration: 5 wt%, 10 wt%, 15 wt%.

[0096] Experimental steps:

[0097] (1) Prepare three spinning solution systems, including:

[0098] System A: 15 wt% PVDF + 5 wt% barium titanate;

[0099] System B: 15 wt% PVDF + 10 wt% barium titanate;

[0100] System C: 15 wt% PVDF + 15 wt% barium titanate;

[0101] (2) The three spinning solutions of system A, system B and system C were ultrasonically dispersed for 12 h to obtain uniformly dispersed spinning solutions. The spinning solutions were injected into an electrostatic spinning nozzle with a voltage of 15 kV and a receiving distance of 15 cm to cross-wrap three identical silver-plated nylon core yarns in 6 layers and dried at 60℃ for 2 h to remove residual solvent, thus obtaining three types of PVDF / BaTiO3 nanofiber yarns.

[0102] (3) Three types of PVDF / BaTiO3 nanofiber yarns are spirally cross-wrapped along the axis of the silver-plated nylon core yarn to form nanofiber layers with the same number of coating layers;

[0103] (4) The nanofiber layer is encapsulated with PDMS as curing liquid to form an encapsulation layer, and then immersed in PEDOT:PSS conductive polymer dispersion to form a transparent conductive layer.

[0104] (5) An electrochromic layer is formed on the surface of the transparent conductive layer by spraying a suspension of tungsten trioxide nanowires in ethanol;

[0105] (6) The ion gel electrolyte was spin-coated onto the surface of the electrochromic layer, and after curing, it was covered with a Prussian blue nanolayer to form an ion storage layer, thus obtaining three kinds of electrochromic spiral-coated piezoelectric composite yarns.

[0106] Based on the barium titanate doping concentration comparison experiment and Figure 3 And from Table 5, we can see that:

[0107] The electrochromic spiral-coated piezoelectric composite yarn made of 5 wt% barium titanate has an output voltage of 4.8 V, a relatively low piezoelectric response sensitivity of 0.75 V / N, and a dielectric constant of 45; the electrochromic spiral-coated piezoelectric composite yarn made of 10 wt% barium titanate has an output voltage of 6.0 V, a significantly improved piezoelectric response sensitivity of 1.00 V / N, and an increased dielectric constant of 60; the electrochromic spiral-coated piezoelectric composite yarn made of 15 wt% barium titanate has a slightly lower output voltage of 5.2 V, a piezoelectric response sensitivity of 0.85 V / N, and a dielectric constant of 55.

[0108] Experiments show that 10 wt% barium titanate is the optimal doping concentration, achieving the best balance between piezoelectric and dielectric properties. A doping concentration that is too high, i.e., 15 wt%, may lead to nanoparticle aggregation, affecting charge transfer efficiency.

[0109] Experiment 2: Comparison of the number of nanofiber coating layers:

[0110] Experimental objective: To verify whether the number of nanofiber coating layers affects the piezoelectric response sensitivity and output voltage of electrochromic spiral-coated piezoelectric composite yarn.

[0111] Experimental variables: number of nanofiber coating layers: 2 layers, 4 layers, 6 layers, 8 layers.

[0112] Experimental steps:

[0113] (1) Prepare a spinning solution of 15 wt% PVDF + 10 wt% barium titanate;

[0114] (2) After ultrasonically dispersing the spinning solution for 12 h, a uniformly dispersed spinning solution was obtained. The spinning solution was injected into an electrostatic spinning nozzle with a voltage of 15 kV and a receiving distance of 15 cm to repeatedly and cross-wrap four identical silver-plated nylon core yarns in 6 layers and dried at 60°C for 2 h to remove residual solvent, thus obtaining four types of PVDF / BaTiO3 nanofiber yarns.

[0115] (3) Using the sliding device of the yarn spiral wrapping equipment, four kinds of PVDF / BaTiO3 nanofiber yarns are spirally wrapped along the axis of the silver-plated nylon core yarn at the first linear speed. At the same time, the speed of the sliding device is adjusted to wrap 2, 4, 6 and 8 nanofiber layers respectively.

[0116] (4) The nanofiber layer is encapsulated with PDMS as curing liquid to form an encapsulation layer, and then immersed in PEDOT:PSS conductive polymer dispersion to form a transparent conductive layer.

[0117] (5) An electrochromic layer is formed on the surface of the transparent conductive layer by spraying a suspension of tungsten trioxide nanowires in ethanol;

[0118] (6) The ion gel electrolyte was spin-coated onto the surface of the electrochromic layer, and after curing, it was covered with a Prussian blue nanolayer to form an ion storage layer, resulting in four types of electrochromic spiral-coated piezoelectric composite yarns with different numbers of coating layers.

[0119] Based on experiments comparing the number of nanofiber coating layers and Figure 4 And Table 5, in which, Figure 4 In the diagram, (a) represents the voltage of the 10wt% barium titanate modified electrochromic spiral-coated piezoelectric composite yarn at different frequencies with a fixed force of 10 N; (b) represents the current of the 10wt% barium titanate modified electrochromic spiral-coated piezoelectric composite yarn at different frequencies with a fixed force of 10 N; (c) represents the charge of the 10wt% barium titanate modified electrochromic spiral-coated piezoelectric composite yarn at different frequencies with a fixed force of 10 N; (d) represents the charge of the electrochromic spiral-coated piezoelectric composite yarn at different forces with a fixed frequency of 3 Hz; (e) represents the current of the electrochromic spiral-coated piezoelectric composite yarn at different forces with a fixed frequency of 3 Hz; and (f) represents the charge of the electrochromic spiral-coated piezoelectric composite yarn at different forces with a fixed frequency of 3 Hz. Therefore, it can be concluded that:

[0120] The 2-layer electrochromic spiral-coated piezoelectric composite yarn has an output voltage of 3.2 V, relatively weak mechanical properties (0.8 MPa), and a stress transfer efficiency of only 20%. The 4-layer electrochromic spiral-coated piezoelectric composite yarn has an output voltage of 4.1 V, a tensile strength of 1.4 MPa, and an external stress transfer efficiency of 25%. The 6-layer electrochromic spiral-coated piezoelectric composite yarn increases the output voltage to 6.0 V, significantly enhances mechanical properties to 1.8 MPa, and achieves a stress transfer efficiency of 30%. The 8-layer electrochromic spiral-coated piezoelectric composite yarn slightly decreases the output voltage to 5.5 V, but further improves mechanical properties to 2.1 MPa.

[0121] Experiments show that 6 layers of coating is the optimal solution, which balances high voltage output and mechanical properties. Too many coating layers may reduce the flexibility of the yarn and affect practical applications.

[0122] Experiment 3: Comparison of Encapsulation Materials

[0123] Experimental objective: To verify whether the encapsulation material of the encapsulation layer affects the performance of electrochromic spiral-coated piezoelectric composite yarn.

[0124] Experimental variables: Encapsulation material type: PDMS, thermoplastic polyurethane elastomer (TPU).

[0125] Experimental steps:

[0126] Step 1: Preparation of electrochromic spiral-coated piezoelectric composite yarn encapsulated with PDMS as curing solution:

[0127] (1) Prepare a spinning solution of 15 wt% PVDF + 10 wt% barium titanate, and after ultrasonic dispersion for 12 h, obtain a uniformly dispersed spinning solution. Inject the spinning solution into an electrostatic spinning nozzle with a voltage of 15 kV and a receiving distance of 15 cm to cross-wrap four identical silver-plated nylon core yarns in 6 layers and dry them at 60℃ for 2 h to remove residual solvent, thus obtaining PVDF / BaTiO3 nanofiber yarn.

[0128] (2) The PVDF / BaTiO3 nanofiber yarn is spirally wrapped along the axis of the silver-plated nylon core yarn to form a nanofiber layer;

[0129] (3) The nanofiber layer is encapsulated with PDMS as curing liquid to form an encapsulation layer, and then immersed in PEDOT:PSS conductive polymer dispersion to form a transparent conductive layer;

[0130] (4) An electrochromic layer is formed on the surface of the transparent conductive layer by spraying a suspension of tungsten trioxide nanowires in ethanol;

[0131] (5) The ion gel electrolyte is spin-coated onto the surface of the electrochromic layer, and after curing, it is covered with a Prussian blue nanolayer to form an ion storage layer, thus obtaining a PDMS-encapsulated electrochromic spiral-coated piezoelectric composite yarn.

[0132] Step 2: Preparation of electrochromic spiral-coated piezoelectric composite yarn encapsulated with thermoplastic polyurethane elastomer (TPU) as curing liquid:

[0133] (1) Prepare a spinning solution of 15 wt% PVDF + 10 wt% barium titanate, and after ultrasonic dispersion for 12 h, obtain a uniformly dispersed spinning solution. Inject the spinning solution into an electrostatic spinning nozzle with a voltage of 15 kV and a receiving distance of 15 cm to cross-wrap four identical silver-plated nylon core yarns in 6 layers and dry them at 60℃ for 2 h to remove residual solvent, thus obtaining PVDF / BaTiO3 nanofiber yarn.

[0134] (2) The PVDF / BaTiO3 nanofiber yarn is spirally wrapped along the axis of the silver-plated nylon core yarn to form a nanofiber layer;

[0135] (3) Encapsulating the nanofiber layer with a thermoplastic polyurethane elastomer (TPU) solution as a curing liquid to form an encapsulation layer, and then immersing it in a PEDOT:PSS conductive polymer dispersion to form a transparent conductive layer, including the following steps:

[0136] The base adhesive was mixed with thermoplastic polyurethane elastomer (TPU), stirred at 80°C for 4 h until completely dissolved, and then allowed to stand for pre-curing for 12 h to obtain a 15 wt% thermoplastic polyurethane elastomer (TPU) solution.

[0137] The nanofiber layer, after being wrapped with a nanofiber layer, is immersed in a 15 wt% thermoplastic polyurethane elastomer (TPU) solution. After brushing for 5 minutes to ensure uniform coverage and straightening and fixing, it is dried at 60℃ for 30 minutes for secondary curing to form a thermoplastic polyurethane elastomer (TPU) encapsulation layer with uniform thickness. It is then dried at 60℃ for 30 minutes for secondary curing to form an encapsulation layer with a thickness of approximately 20-30 μm.

[0138] (4) An electrochromic layer is formed on the surface of the transparent conductive layer by spraying a suspension of tungsten trioxide nanowires in ethanol;

[0139] (5) The ion gel electrolyte is spin-coated onto the surface of the electrochromic layer, and after curing, it is covered with a Prussian blue nanolayer to form an ion storage layer, thus obtaining an electrochromic spiral-encapsulated piezoelectric composite yarn encapsulated by thermoplastic polyurethane elastomer (TPU).

[0140] Based on comparative experiments of packaging materials and Figure 4 As shown in Tables 4-6:

[0141] PDMS-encapsulated electrochromic spiral-coated piezoelectric composite yarn: output voltage of 6.0 V, hydrophobic angle of 124°, and excellent water washability, i.e., 98% retention rate;

[0142] Thermoplastic polyurethane elastomer (TPU) encapsulated electrochromic spiral-coated piezoelectric composite yarn: output voltage is 5.0 V, hydrophobic angle is low (92°), and water washability is poor (85% retention rate).

[0143] Experiments show that PDMS significantly improves the environmental adaptability of electrochromic spiral-coated piezoelectric composite yarns due to its excellent hydrophobicity and interfacial stress optimization capabilities.

[0144] II. Performance Testing:

[0145] The electrochromic spiral-coated piezoelectric composite yarns prepared in the above experiments were subjected to system performance tests. The specific test methods are as follows:

[0146] Piezoelectric performance testing: According to GB / T 3389-2008 "Test Methods for Piezoelectric Ceramic Materials", the piezoelectric constant was measured using a quasi-static d33 meter, and the dielectric constant and electromechanical coupling coefficient were determined using an impedance analyzer. The test environment was controlled at 25±1℃ and relative humidity 50±5%.

[0147] Dynamic energy harvesting test: Build a custom dynamic load simulation test platform, apply a periodic load of 0.5-10N with a frequency of 1-5Hz, and record the changes in open-circuit voltage and short-circuit current in real time.

[0148] Hydrophobicity test: The contact angle of the material surface was tested using a contact angle meter according to the HY / T 266-2018 standard. The test was conducted using a 3μL droplet of deionized water in an indoor environment at 24°C.

[0149] Washability test: The test was conducted according to GB / T 3921-2008 standard using a standard washing machine (Type A). The test conditions were: detergent concentration 2 g / L, water temperature 40℃, and 30 minutes per wash.

[0150] Mechanical property testing: Tensile strength testing was conducted according to GB / T 14337-2008 standard using a universal testing machine; fatigue performance testing was conducted in accordance with ISO 12106:2017 "Metallic materials - Fatigue testing - Axial force control method".

[0151] Electrochromic performance test: According to GB / T 25284-2010 "Methods for testing the optical performance of electrochromic devices", the transmittance change ΔT under a voltage of 0-6V is tested in the wavelength range of 380-780nm, and no less than 500 cycles of testing are performed.

[0152] The above comparative experiments and performance tests were all conducted by professionals in the field in strict accordance with relevant standard operating procedures. Detailed information on the experimental conditions and results are shown in Tables 2-6.

[0153] Table 2 Reagent Specifications

[0154] name Specification factory Silver-plated nylon yarn 210 D 3-strand Suzhou Tech Silver Fiber Technology Barium titanate 99.5% 3 μm McLean Biotech Co., Ltd. <![CDATA[PVDF / BaTiO3 nanofiber yarn]]> JDF05 Changsha Nayi Instrument Technology Co., Ltd. dimethylformamide Analytical Pure Shanghai Aladdin Biochemical Reagent Co., Ltd. Tetrahydrofuran (THF) Analytical Pure Shanghai Titan Technology Co., Ltd. PDMS Dow Corning DC184 Dow Chemical Company, Inc. Thermoplastic polyurethane elastomer (TPU) Elastollan® 1185A10 BASF PI tape 0.05 mm Suzhou Zhihe Adhesive Products Conductive copper foil tape 0.1 mm Shenzhen Benyida Technology Co., Ltd. Prussian blue nanoparticles Particle size 100 nm McLean Biotech PEDOT:PSS Dispersion Solid content 1.5 wt% Suzhou Nanotechnology Tungsten trioxide nanowires 99.9% purity, Ø50 nm Aladdin Reagents

[0155] Table 3. Experimental data comparing barium titanate doping concentrations

[0156] Barium titanate doping concentration (wt%) Output voltage (V) Piezoelectric response sensitivity (V / N) Dielectric constant (ε) 5 4.8 0.75 45 10 6.0 1.00 60 15 5.2 0.85 55

[0157] Table 4. Experimental data comparing the number of nanofiber coating layers.

[0158] Number of coating layers Output voltage (V) Mechanical properties (MPa) External stress transfer efficiency (%) 2 3.2 0.8 20 4 4.1 1.4 25 6 6.0 1.8 30 8 5.5 2.1 28

[0159] Table 5 Comparison of packaging materials experimental data

[0160] Encapsulation material type Output voltage (V) Contact angle (°) Water wash cycle resistance (%) PDMS 6.0 124 98 Thermoplastic polyurethane elastomer (TPU) 5.0 92 85

[0161] Table 6 Mechanical Performance Test Data

[0162] Test conditions Performance parameters After 50 cycles of 20% strain stretching Strength retention rate: ≥95% After 10,000 folds Deformation recovery rate: ≥98% 7500 cycles of testing Output voltage stability deviation: ≤3%

[0163] In summary, the electrochromic spiral-coated piezoelectric composite yarn provided by this invention encapsulates the nanofiber layer using PDMS as a curing agent. A PDMS encapsulation layer is formed through multiple brushing and drying processes. Based on the hydrophobic properties and interface stress optimization of the PDMS encapsulation layer, a hydrophobic angle of 124° is achieved when the thickness is adjusted to 20-30 μm. Furthermore, by placing an ion gel electrolyte layer between the transparent conductive layer and the ion storage layer, and employing a spiral cross-coating structure (i.e., alternating spiral directions of adjacent nanofiber layers), this invention ensures that the voltage decay rate of the electrochromic spiral-coated piezoelectric composite yarn does not exceed 5% after 10 standard water washes, and it can still stably output 0.3V when bent at 90° underwater. The synergistic effect of these technical features enables the nanofiber layer to maintain stable performance in complex environments such as humidity and washing, broadening its application scenarios, especially suitable for wearable devices and other fields that may come into contact with water or humid environments.

[0164] The electrochromic spiral-wrapped piezoelectric composite yarn provided by this invention, through the adoption of a spiral cross-wrapping structure and based on the piezoelectric response characteristics of the nanofiber layer, can stably output a 6V voltage under a 3Hz dynamic load and charge a 1μF capacitor to 0.4V within 20 seconds. At the same time, the twist of the nanofiber layer is optimized by jointly controlling the spiral speed of the double spiral clamp device and the first linear speed of the PVDF / BaTiO3 nanofiber yarn, ensuring that the output voltage is not lower than 6V under 10N pressure. These technical features enable the electrochromic spiral-wrapped piezoelectric composite yarn to provide reliable power support for small electronic devices, meeting the needs for continuous and stable power supply in scenarios such as wearable power supply and motion monitoring.

[0165] The electrochromic spiral-wrapped piezoelectric composite yarn provided by this invention, by adopting a spiral cross-wrapping structure and adjusting the PDMS encapsulation layer thickness to 20-30 μm, can withstand letter deformations such as A / D / U / S and multiple folds and curls, with a deformation recovery rate of ≥98%, thus optimizing the flexibility and interfacial stress of the PDMS encapsulation layer. Simultaneously, through the flexible conductive support of the silver-plated nylon core yarn and the spiral wrapping reinforcement effect of the nanofiber layer, the electrochromic spiral-wrapped piezoelectric composite yarn retains ≥95% strength after 50 cycles of 20% strain stretching and can withstand tens of thousands of folds. The synergistic effect of these technical features endows the electrochromic spiral-wrapped piezoelectric composite yarn with excellent mechanical properties, making it less prone to damage in environments with frequent deformation, extending its service life, and reducing usage costs.

[0166] The electrochromic spiral-coated piezoelectric composite yarn provided by this invention improves the external stress transmission efficiency by adopting a spiral cross-coating structure and a multi-layer spiral coating design based on nanofiber layers. When the number of coating layers is 2-8, the external stress transmission efficiency is improved by ≥30%. At the same time, this invention also optimizes the interface stress through the high conductivity of the silver-plated nylon core yarn and the PDMS encapsulation layer. When the thickness of the PDMS encapsulation layer is adjusted to 20-30 μm, the charge collection efficiency is improved by ≥25%. The synergistic effect of these technical features significantly improves the stress-to-electricity conversion efficiency, enabling more electrical energy to be generated under the same external force, thereby improving energy utilization efficiency and enhancing power generation capacity.

[0167] The electrochromic spiral-coated piezoelectric composite yarn provided by this invention can directly trigger the blue / white state switching by generating a 6V voltage under 10N pressure through the electrochromic active layer. The transmittance change ΔT triggered by the 6V voltage under 10N pressure is ≥40%, and the switching time is ≤5s. Its self-powered electrochromic characteristics enable it to achieve color change without an external power source. It is suitable for fields such as smart color-changing fabrics, adding unique visual effects and intelligent interactive functions to the product.

[0168] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. An electrochromic spiral-coated piezoelectric composite yarn, characterized in that, It includes a silver-plated nylon core yarn and a nanofiber layer, an encapsulation layer, a transparent conductive layer, an electrochromic active layer, an ion gel electrolyte layer, and an ion storage layer sequentially disposed outside the silver-plated nylon core yarn. The nanofiber layer is multi-layered, consisting of PVDF / BaTiO3 nanofiber yarns wrapped in a spiral cross-shaped manner on the surface of silver-plated nylon core yarn; the transparent conductive layer is formed by curing PEDOT:PSS conductive polymer dispersion; the electrochromic active layer is tungsten trioxide nanowires uniformly deposited on the transparent conductive layer; and the ion storage layer is a Prussian blue nanolayer. The thickness of the ion storage layer is 3-15 μm; The thickness of the encapsulation layer is 20-30 μm, and the separation distance between the silver-plated nylon core yarn and the nanofiber layer is controlled at 15 mm. The method for preparing the electrochromic spiral-coated piezoelectric composite yarn includes: A nanofiber layer is formed by spirally wrapping PVDF / BaTiO3 nanofiber yarn along the axial direction of silver-plated nylon core yarn. A nanofiber layer is encapsulated with PDMS as a curing agent to form an encapsulation layer, and then immersed in PEDOT:PSS conductive polymer dispersion to form a transparent conductive layer. An electrochromic layer is formed on the surface of a transparent conductive layer by spraying a suspension of tungsten trioxide nanowires in ethanol. An ion gel electrolyte was spin-coated onto the surface of an electrochromic layer, and after curing, it was covered with a Prussian blue nanolayer to form an ion storage layer.

2. The electrochromic spiral-coated piezoelectric composite yarn according to claim 1, characterized in that, The number of coating layers of the nanofiber layer is 2-8; And / or, the thickness of the transparent conductive layer is 0.5-2 μm; And / or, the thickness of the electrochromic active layer is 5-20 μm; And / or, the thickness of the ionogel electrolyte layer is 10-30 μm.

3. The electrochromic spiral-coated piezoelectric composite yarn according to claim 1, characterized in that, The encapsulation layer is a PDMS encapsulation layer.

4. The electrochromic spiral-coated piezoelectric composite yarn according to claim 1, characterized in that, The expression for calculating the twist between the silver-plated nylon core yarn and the nanofiber layer is as follows: ； In the formula, This indicates the twist between the silver-plated nylon core yarn and the nanofiber layer, expressed in r / m. The speed of the silver-plated nylon core yarn is expressed in m / min. This indicates the coating speed of the nanofiber layer, expressed in m / min.

5. The electrochromic spiral-coated piezoelectric composite yarn according to claim 4, characterized in that, The thickness of the cured layer was adjusted to 20-30 μm by using COMSOL to simulate the interfacial stress distribution between the encapsulation layer and the nanofiber layer.

6. The electrochromic spiral-coated piezoelectric composite yarn according to claim 4, characterized in that, The method for preparing the PVDF / BaTiO3 nanofiber yarn includes: Dissolve the PVDF masterbatch in DMF solvent to prepare a 10-20 wt% PVDF solution, and stir magnetically in a 60℃ water bath for 1-3 h until completely dissolved; Weigh 5-15 wt% BaTiO3 nanopowder (PVDF) and add it to the above solution. After ultrasonic dispersion for 8-16 h, a uniformly dispersed spinning solution is obtained. The spinning solution was injected into the electrostatic spinning nozzle to repeatedly and cross-wrap 4-8 layers of silver-plated nylon core yarn, and then dried at 60℃ for 1-3 h to remove residual solvent, thus obtaining PVDF / BaTiO3 nanofiber yarn.

7. The electrochromic spiral-coated piezoelectric composite yarn according to claim 4, characterized in that, The method for encapsulating a nanofiber layer with PDMS as a curing agent to form an encapsulation layer includes: Mix the base adhesive and PDMS at a mass ratio of 8:1-12:1, stir for 20-40 min, and let stand for pre-curing for 10-14 h to obtain a PDMS solution. The nanofiber layer is immersed in PDMS solution, brushed for 3-7 min to ensure uniform coverage, then straightened and fixed at 60℃ for 20-40 min for secondary curing to form an encapsulation layer with a thickness of 20-30 μm.

8. The electrochromic spiral-coated piezoelectric composite yarn according to claim 4, characterized in that, The method for preparing the electrochromic active layer includes: Tungsten trioxide nanowires were uniformly deposited on the surface of a transparent conductive layer by electrostatic spraying of an ethanol suspension with a concentration of 15-25 mg / mL. After drying, an electrochromic active layer with a thickness of 10±2 μm was formed.

9. The electrochromic spiral-coated piezoelectric composite yarn according to claim 4, characterized in that, The method for preparing the ion storage layer includes: An ion gel electrolyte is spin-coated onto the surface of the electrochromic layer and cured to form an ion gel electrolyte layer. An ion storage layer is formed by coating a Prussian blue nanolayer onto an ion gel electrolyte layer.

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