A multifunctional composite flexible fabric and its preparation method

Abstract

This invention discloses a multifunctional composite flexible fabric with multiple functions including radiative cooling, energy harvesting, hydrophobicity, and antibacterial properties. The composite flexible fabric consists of several electrospun fiber layers, each formed sequentially by electrospinning in a top-to-bottom order. It includes at least two polymer electrospun fiber layers and at least one nanofunctional electrospun fiber layer, wherein the nanofunctional electrospun fiber layer serves as an intermediate sandwich layer, forming a sandwich structure with the polymer electrospun fiber layers located on the upper and lower surfaces. This invention also discloses a method for preparing this flexible fabric, using electrospinning to prepare it by electrospinning a PVDF or related polymer solution and a polymer solution modified with functional nanoparticles. This preparation method can effectively control the morphology of the nanofibers and the functions of the nanoparticles, enabling a synergistic effect between the functional nano-scattering particles and the nanofibers, resulting in an integrated functional fabric with thermal management, energy harvesting, and antibacterial properties.

Description

Technical Field

[0001] This invention relates to the field of flexible wearable device technology, and in particular to a multifunctional composite flexible fabric and its preparation method. Background Technology

[0002] With advancements in science and technology, the expectations for flexible wearable devices in production and the market are growing. These devices typically include functional components such as displays, sensors, and batteries, and can operate for extended periods on or inside the human body. Thanks to their lightweight, soft, and skin-friendly properties, flexible wearable electronic devices, especially those made of flexible fabrics, are demonstrating enormous potential and application value in fields such as human health monitoring, motion tracking, and medical diagnostics.

[0003] Ensuring optimal thermal comfort for users is a crucial functional indicator for flexible fabrics, especially when wearers are exposed to direct sunlight for extended periods outdoors, which can easily lead to heat stress disorders and overheating of electronic devices. Therefore, ensuring that flexible fabrics provide good thermal comfort is particularly critical. Consequently, finding a simple and effective cooling technology to integrate into flexible fabrics is a current technical challenge in the textile industry. Radiative cooling, a passive cooling technology, differs from traditional active cooling, which requires external energy input such as electricity or fuel. Radiative cooling utilizes the inherent properties of objects or environmental conditions to achieve cooling without external energy input. Compared to energy-intensive traditional air conditioning systems, passive radiative cooling systems can radiate heat into the cold external universe through atmospheric windows (8-13 μm) with almost no energy consumption. Therefore, passive radiative cooling technology has gained increasing attention in recent years, but currently, its applications are mainly in outdoor buildings, thermal power equipment, and dew collection.

[0004] Furthermore, achieving a continuous and stable long-term power supply is also a crucial issue for flexible smart fabrics. Traditional power sources (such as batteries and supercapacitors) have short lifespans, poor rigidity, and are difficult to integrate with fabrics. Therefore, harvesting energy from the environment is an important direction for simplifying processes and improving sustainability. Triboelectric nanogenerators (TENGs) can harvest waste mechanical energy from human movement and power electronic devices, offering advantages in smart fabric design. This is a promising solution that can reduce the thermal and energy loads in smart fabric design and significantly simplify thermal management and energy supply systems within smart fabrics.

[0005] To address the surface contamination problem of flexible smart fabrics, research focuses on enhancing surface hydrophobicity and antibacterial properties. The introduction of hydrophobicity facilitates the formation of a thin air layer on the fabric surface, effectively preventing rapid liquid absorption and improving resistance to bacterial solutions. When water rolls off the fabric, it carries away residual dust particles, achieving a significant self-cleaning effect. Furthermore, given the evolution and development of novel viruses and their potential catastrophic consequences for human well-being, preventative measures must be taken to address this significant safety risk. The potential for bacterial growth poses a major threat to the sustainable application of flexible fabrics and the health of wearers. Therefore, achieving a balance between hydrophobicity and antibacterial properties in flexible fabrics is crucial.

[0006] Currently, the various functional requirements of flexible fabrics are typically achieved through surface integration or stacking of different functional modules. On the one hand, this stacking integration method results in complex fabric structures and difficult integration processes. On the other hand, this complex stacking structure increases the thermal and electrical loads of the flexible fabric, affecting wearer comfort and placing higher demands on continuous power supply. Furthermore, using this stacked microstructure enhances surface irregularity, increasing the likelihood of surface contamination and bacterial growth, negatively impacting fabric durability and long-term stability. Therefore, how to rationally design and comprehensively optimize solutions to address issues such as thermal comfort, continuous energy supply, and surface cleanliness, providing a convenient overall solution for smart flexible fabrics, is a crucial issue in the field of smart fabrics. Summary of the Invention

[0007] Based on the aforementioned problems in the prior art, this invention aims to explore an overall solution for flexible fabrics, namely, to provide a simple and multifunctional composite flexible fabric that can simultaneously meet the needs of flexible fabrics for thermal comfort, continuous and stable energy supply, and hydrophobic and antibacterial functions. Furthermore, it provides a method for integrating the multifunctional flexible fabric, i.e., a method for preparing the multifunctional flexible fabric, in order to solve the technical problems of complex structure and difficult integration of the aforementioned intelligent flexible fabrics.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution.

[0009] This invention first provides a multifunctional composite flexible fabric, which possesses multiple functions including radiation cooling, energy harvesting, hydrophobicity, and antibacterial properties. The composite flexible fabric is composed of several layers of electrospun fiber, each layer being formed sequentially by electrospinning in a top-to-bottom order; it includes at least two polymer electrospun fiber layers and at least one nanofunctional electrospun fiber layer, wherein the nanofunctional electrospun fiber layer serves as an intermediate sandwich layer, forming a sandwich structure with the polymer electrospun fiber layers located on the upper and lower surfaces respectively.

[0010] The polymer electrospun fiber layer consists of a plurality of polymer fibers intersecting to form a three-dimensional network porous structure (for ease of distinction, the plurality of polymer fibers constituting the polymer electrospun fiber layer are referred to as the first polymer fibers); the nanofunctional electrospun fiber layer comprises a plurality of polymer fibers and a plurality of nanoparticles, wherein the polymer fibers intersecting to form a three-dimensional network porous structure, and the nanoparticles are uniformly distributed within or on the surface of the network porous structure formed by the polymer fibers (for ease of distinction, the plurality of polymer fibers contained in the nanofunctional electrospun fiber layer are referred to as the second polymer fibers). The polymer fiber material is one or more selected from polyvinylidene fluoride (PVDF) and its series copolymers, preferably one or more of PVDF, polyvinylidene fluoride-hexafluoropropylene PVDF-HFP, and polyvinylidene fluoride-trifluoroethylene PVDF-TRFE. The nanoparticles are at least one of SiO2 / ZnO core-shell particles, SiO2 / Zn2SiO4 core-shell particles, or SiO2 / ZnO / ZIF-8 core-shell particles.

[0011] Furthermore, the composite flexible fabric consists of three single-layer electrospun layers, which are, in order, a single-layer first polymer electrospun fiber layer, a nano-functional electrospun fiber layer, and a second polymer electrospun fiber layer.

[0012] Furthermore, the diameter of the polymer fibers in the polymer electrospun fiber layer, i.e., the first polymer fiber, is 100–700 nm; the diameter of the polymer fibers in the nanofunctional electrospun fiber layer, i.e., the second polymer fiber, is 200–1000 nm.

[0013] Furthermore, the nanoparticles have a particle size of 500–900 nm, and the nanoparticle content is 40–60% of the mass fraction of the polymer fiber (second polymer fiber) in the nanofunctional electrospun fiber layer.

[0014] Furthermore, the SiO2 / ZnO core-shell particles consist of a core-shell structure formed by tiny ZnO nanoparticles encapsulating the surface of SiO2 nanospheres. Further, the SiO2 / Zn2SiO4 core-shell particles are formed by a surface solid-phase reaction between SiO2 nanospheres and surface ZnO nanoparticles. Further, the SiO2 / ZnO / ZIF-8 core-shell particles are formed by in-situ chemical assembly of SiO2 nanospheres, ZnO nanoparticles, and bulk ZIF-8 nanoparticles. The ZnO nanoparticles are uniformly dispersed on the surface of the SiO2 nanospheres, and the bulk ZIF-8 particles are further encapsulated on the surface.

[0015] Furthermore, the SiO2 nanospheres have a diameter of 500–600 nm, the nano ZnO particles have a diameter of 10–30 nm, and the bulk nano ZIF-8 particles have a size of 90–110 nm.

[0016] In designing the composite flexible fabric of this invention to achieve optimal thermal comfort, the inventors employed a method of controlling thermal comfort through passive radiative cooling in the fabric structure and material selection. This approach is based on the fact that radiative heat loss accounts for 40-60% of total human body heat loss, and passive radiative cooling fabrics demonstrate significant advantages in personal thermal management. The composite flexible fabric provided by this invention consists of a structure formed by stacking polymer fiber layers and core-shell nanoparticle-modified polymer fiber layers. Its three-dimensional mesh-like porous structure strongly scatters incident sunlight to obtain a high solar reflectivity; for example, in Example 1 of this invention, the solar reflectivity of the composite flexible fabric reached 84.7%. Furthermore, the abundant chemical bonds (such as Si-O bonds, CF bonds, etc.) contained in the composite structure of the flexible fabric fiber layers and core-shell nanoparticles can strongly emit infrared radiation in the 8-13 μm range to obtain a high infrared emissivity; for example, in Example 1 of this invention, the infrared emissivity of the composite flexible fabric reached 94.9%. Combining these two aspects enables the flexible fabric to achieve passive daytime radiative cooling, providing continuous heat dissipation and cooling with zero energy consumption throughout the day.

[0017] The composite flexible fabric of this invention is mainly composed of polymer electrospun fibers. The polymer PVDF and its series copolymers are ferroelectric polymers, and their β phase exhibits high electron affinity, large spontaneous polarization, and excellent polarization stability, making it an excellent material for triboelectric nanogenerators (TENGs). Simultaneously, this invention employs an electrospinning process to form the fiber layers of the composite flexible fabric. During electrospinning, the strong voltage applied to the polymer induces the polymer to transform from a nonpolar α phase to a polar β phase, thereby enhancing the piezoelectric properties of the fabric and improving the efficiency of mechanical energy harvesting. In effect, this is equivalent to assembling several triboelectric nanogenerators within the composite flexible fabric of this invention. This allows the composite flexible fabric to effectively convert small amounts of waste mechanical energy in the environment into electrical energy through the charge pump effect of the triboelectric potential, achieving the purpose of energy harvesting. For example, in the flexible fabric prepared in Example 1 of this invention, when an external load of 60 MΩ is applied, the maximum output power of the triboelectric nanogenerators formed can reach 10.97 mW·m. -2 .

[0018] Hydrophobicity and antibacterial properties are crucial for composite flexible fabrics, helping to reduce surface contamination and bacterial growth. The polymer PVDF and its series copolymers in the composite flexible fabric of this invention are fluoropolymers with low surface energy and excellent hydrophobicity. For example, the composite flexible fabric prepared in Example 1 has a water contact angle of 134.3°, demonstrating good hydrophobicity. This hydrophobicity prevents rapid water absorption, allowing it to effectively remove surface contaminants. On the other hand, the core-shell structured nanoparticles contained in the composite flexible fabric can generate a photocatalytic effect. By absorbing ultraviolet light from the environment, they produce reactive oxygen species, which then destroy the bacterial cell membrane, leading to bacterial death. For example, the composite flexible fabric prepared in Example 1 achieved an antibacterial rate of 99.9% against Staphylococcus aureus and Escherichia coli in co-culture experiments, exhibiting highly efficient broad-spectrum antibacterial activity.

[0019] In addition, the present invention also provides a method for preparing the above-mentioned multifunctional composite flexible fabric, comprising the steps of: (1) dissolving polymer material in a mixed solvent to form a precursor solution; (2) adding functional nanoparticle material to the precursor solution to obtain a composite solution; (3) sequentially electrospinning the precursor solution, the composite solution and the precursor solution, and drying to obtain the multifunctional composite flexible fabric.

[0020] Further, the polymer material in step (1) is selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyvinylidene fluoride-trifluoroethylene (PVDF-TRFE). The mixed solvent contains a high-boiling-point solvent and a low-boiling-point solvent; the high-boiling-point solvent is one of N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAC); the low-boiling-point solvent is acetone; the volume ratio of the high-boiling-point solvent to the low-boiling-point solvent is 6:4 to 4:6. The mass fraction of the polymer material in the precursor solution is 13 to 16 wt%.

[0021] Further, the functional nanoparticle material mentioned in step (2) is selected from SiO2 / ZnO core-shell particles, SiO2 / Zn2SiO4 core-shell particles, and SiO2 / ZnO / ZIF-8 core-shell particles. The functional nanoparticle material accounts for 40-60% of the mass fraction of the polymer material in the composite solution.

[0022] Furthermore, in the electrospinning process described in step (3), the spinning voltage is 8-12kV, the feed speed is 0.8-1.0mL / h, and the receiving distance is 14-18cm.

[0023] Furthermore, the specific preparation method of the functional nanoparticle material described in step (2) is as follows:

[0024] 1) Add SiO2 particles, an inorganic zinc source, and ascorbic acid to an aqueous solution, and then treat with ultrasound to obtain a SiO2 dispersion; the inorganic zinc source is either zinc acetate or zinc nitrate.

[0025] 2) Add hexamethylenetetramine (HMTA) to the SiO2 dispersion, stir and then sonicate to obtain the first pre-solution; the molar ratio of SiO2:inorganic zinc source:ascorbic acid:hexamethylenetetramine is 8:10:3:20.

[0026] 3) The first pre-solution is subjected to a solution reaction at a temperature of 90-100°C for 2-4 hours to obtain a precipitate.

[0027] 4) The precipitated product is centrifuged, washed, and dried to obtain a powder;

[0028] 5) Grind the powder and calcine it in air atmosphere at a heating rate of 5-10℃ / min and a holding time of 1-3h to obtain the SiO2 / ZnO core-shell particles at a temperature of 600-800℃, and obtain the SiO2 / Zn2SiO4 core-shell particles at a temperature of 900-1100℃.

[0029] 6) The SiO2 / ZnO core-shell particles, N,N-dimethylformamide (DMF), and 2-methylimidazole are mixed and dispersed by ultrasonic treatment to obtain the second pre-solution;

[0030] 7) The second pre-solution is subjected to a solution reaction, using solvothermal reaction to dissolve the 2-methylimidazole and ZnO in the solution, producing Zn. 2+ Ion assembly transforms ZnO into a metal-organic framework ZIF-8, yielding SiO2 / ZnO / ZIF-8 core-shell nanomaterials. The reaction temperature is 90–110 °C, and the time is 1–3 h. After the reaction, SiO2 / ZnO / ZIF-8 core-shell nanomaterials are precipitated.

[0031] 8) The precipitated product is centrifuged, washed, and dried to obtain the SiO2 / ZnO / ZIF-8 core-shell particles.

[0032] The beneficial results of this invention are as follows:

[0033] (1) This invention selects appropriate processes for structural design based on the multifunctional integration requirements of flexible fabrics. Electrospinning can form nanofiber membranes by relying on electrostatic force and achieve rich fiber structures. By adding different nanoparticles to the fibers, flexible fabrics with specific functions can be dynamically designed for different applications. The method of this invention provides an optimized multifunctional fabric design strategy that integrates personal thermal management, energy harvesting, and hydrophobic and antibacterial properties using a simple process. It comprehensively considers the three functional requirements and designs the structure holistically to achieve synergistic effects, rather than simply stacking functional units. This has reference value for the design and fabrication of flexible wearable devices. This simple multifunctional composite approach can be extended to spinning processes at other scales, which is of great significance in the field of energy conservation and environmental protection.

[0034] (2) The composite flexible fabric prepared by the present invention, through bottom-up micro-nano structure design, relies on core-shell structure scattering particles and hierarchical porous fiber structure, and nano-scattering particles and nanofibers produce a synergistic effect. The reflectivity reaches 84.7% in the entire solar spectrum range, the infrared emissivity reaches 94.9% in the atmospheric window (8-13μm) range, and the temperature is 2.9℃ lower than that of commercial pure cotton fabric under sunny outdoor conditions.

[0035] (3) The composite flexible fabric prepared by the present invention integrates the energy harvesting function into the design of the radiation cooling fabric. The composite flexible fabric is formed by electrospinning process to obtain a fabric with piezoelectric properties. This allows the composite flexible fabric to effectively convert the small mechanical energy discarded in the environment into electrical energy by relying on the charging pump effect of the friction point potential, so as to realize the continuous collection of discarded mechanical energy and provide continuous power to the flexible wearable device.

[0036] (4) The composite flexible fabric prepared by this invention has good hydrophobicity and antibacterial properties. When water flows over the fiber surface, it can effectively clean the dust remaining on the surface, achieving the purpose of self-cleaning. Due to the photocatalytic antibacterial effect of the added functional nanomaterials, the fabric has a broad-spectrum and highly efficient antibacterial ability. Its antibacterial rate against Staphylococcus aureus and Escherichia coli is >99.9%. Attached Figure Description

[0037] Figure 1 The image shows a scanning electron microscope (SEM) image of the SiO2 / ZnO / ZIF-8 core-shell nanoparticles prepared in Example 1.

[0038] Figure 2 The image shows a scanning electron microscope (SEM) image of the SiO2 / Zn2SiO4 core-shell nanoparticles prepared in Example 2.

[0039] Figure 3The image shows a scanning electron microscope (SEM) image of the SiO2 / ZnO core-shell nanoparticles prepared in Example 3.

[0040] Figure 4 The diagram shows the structure of the composite flexible fabric prepared in Example 1, along with scanning electron microscope (SEM) images of each layer.

[0041] Figure 5 The ultraviolet-visible-near-infrared reflectance curves and infrared emissivity curves of the composite flexible fabric prepared in Example 1.

[0042] Figure 6 This is a comparison of the cooling effect of the composite flexible fabric prepared in Example 1 with different materials in a sunny outdoor environment.

[0043] Figure 7 The open-circuit voltage characteristics of the triboelectric nanogenerator assembled using the composite flexible fabric prepared in Example 1 as the friction material.

[0044] Figure 8 The external load and power characteristics of the triboelectric nanogenerator assembled using the composite flexible fabric prepared in Example 1 as the friction material.

[0045] Figure 9 Cyclic stability characteristics of the triboelectric nanogenerator assembled using the composite flexible fabric prepared in Example 1 as the friction material.

[0046] Figure 10 The surface water contact angle diagram of the composite flexible fabric prepared in Example 1 is shown.

[0047] Figure 11 Colony diagrams of the composite flexible fabric prepared in Example 1 after co-culturing with Escherichia coli and Staphylococcus aureus. Detailed Implementation

[0048] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand the present invention.

[0049] Example 1

[0050] 1.4142 g of P(VDF-HFP) was weighed and dissolved in a mixed solvent of 5 mL acetone and 5 mL DMF. The mixture was stirred at 40 °C for 2 h to obtain a polymer solution with a mass concentration of 14 wt%. Three portions of this polymer solution were prepared. 0.7071 g of SiO2 / ZnO / ZIF-8 core-shell nanoparticles (50% of the polymer mass) were added to one portion of the polymer solution and stirred for 4 h to obtain a composite solution. The electrospinning machine parameters were set as follows: spinning voltage of 10.5 kV, feed rate of 0.8 mL / h, and receiving distance of 15 cm. The polymer solution, composite solution, and polymer solution were successively transferred to the electrospinning machine for continuous electrospinning for 3 h, 6 h, and 3 h, respectively. After spinning, the composite fiber membrane was transferred to an oven and dried at 60 °C for 8 h to obtain a flexible composite fabric functionalized with SiO2 / ZnO / ZIF-8 core-shell nanoparticles.

[0051] The SiO2 / ZnO / ZIF-8 core-shell nanoparticles used can be obtained through the following specific preparation process: Weigh 20 mmol of zinc acetate dihydrate and 6 mmol of ascorbic acid, dissolve them in 100 mL of deionized water, and after complete dissolution, add 0.9613 g of SiO2 nanospheres, stir for 10 min, and sonicate for 15 min to obtain a dispersion solution; weigh 40 mmol of hexamethylenetetramine and add it to the dispersion solution, stir for 3 min, and sonicate for 5 min; then transfer it to a water bath and react at 90℃-100℃ for 2-4 h; after the reaction, obtain the reaction product by centrifugation, wash repeatedly with deionized water and ethanol 3-5 times, and dry at 60℃ for 12 h to obtain a yellow powder; grind the yellow powder and transfer it to a muffle furnace for calcination in air atmosphere at a heating rate of 5℃-10℃ / min, calcining at 600℃-800℃ for 1-3 h to obtain a white powder, which is then ground to obtain SiO2 / ZnO core-shell nanoparticles; take 0.2 g SiO2 / ZnO core-shell nanoparticles were dissolved in 25 mL of DMF and sonicated for 15 min. Then, 0.2932 g of 2-methylimidazole was added, and sonication was continued for another 5 min. After sonication, the dispersion was transferred to an oil bath and reacted at 90℃-110℃ for 1-3 h. After the reaction was completed, the reaction product was obtained by centrifugation, washed repeatedly with ethanol 3-5 times, and dried at 60℃ for 12 h to obtain the desired product, which is SiO2 / ZnO / ZIF-8 core-shell nanoparticles.

[0052] Example 2

[0053] 1.6848 g of P(VDF-HFP) was weighed and dissolved in a mixed solvent of 4 mL acetone and 6 mL DMF. The mixture was stirred at 40 °C for 2 h to obtain a polymer solution with a mass concentration of 16 wt%. Three portions of this polymer solution were prepared. 0.8420 g of SiO2 / Zn2SiO4 core-shell nanoparticles were added to one of the polymer solutions and stirred for 4 h to obtain a composite solution. The electrospinning machine parameters were set as follows: spinning voltage of 12 kV, feed rate of 0.9 mL / h, and receiving distance of 16 cm. The polymer solution, composite solution, and polymer solution were successively transferred to the electrospinning machine for continuous electrospinning for 3 h, 6 h, and 3 h, respectively. After spinning, the composite fiber membrane was transferred to an oven and dried at 60 °C for 8 h to obtain a flexible composite fabric functionalized with SiO2 / Zn2SiO4 core-shell nanoparticles.

[0054] The SiO2 / Zn2SiO4 core-shell nanoparticles used were prepared using the following specific process: 20 mmol of zinc nitrate hexahydrate and 6 mmol of ascorbic acid were weighed and dissolved in 100 mL of deionized water. After complete dissolution, 0.9613 g of SiO2 nanospheres were added, stirred for 10 min, and sonicated for 15 min to obtain a dispersion solution. 40 mmol of hexamethylenetetramine was weighed and added to the dispersion solution, stirred for 3 min, and sonicated for 5 min. The mixture was then transferred to a water bath and reacted at 90℃-100℃ for 2-4 h. After the reaction, the reaction product was obtained by centrifugation, washed repeatedly with deionized water and ethanol 3-5 times, and dried at 60℃ for 12 h to obtain a yellow powder. The yellow powder was ground and transferred to a muffle furnace for calcination in air atmosphere at a heating rate of 5-10℃ / min for 2-4 h to obtain a white powder. After grinding, the desired product, SiO2 / Zn2SiO4 core-shell nanoparticles, was obtained.

[0055] Example 3

[0056] 1.6548 g of P(VDF-HFP) was weighed and dissolved in a mixed solvent of 5 mL acetone and 5 mL DMF. The solution was stirred at 40 °C for 2 h to obtain a polymer solution with a mass concentration of 16 wt%. 0.8270 g of SiO2 / ZnO core-shell nanoparticles were added to the polymer solution and stirred for 4 h to obtain a composite solution. The electrospinning machine parameters were set as follows: spinning voltage of 9.5 kV, feed rate of 0.8 mL / h, and receiving distance of 14.5 cm. The polymer solution, composite solution, and polymer solution were successively transferred to the electrospinning machine for continuous electrospinning for 3 h, 6 h, and 3 h, respectively. After spinning, the composite fiber membrane was transferred to an oven and dried at 60 °C for 8 h to obtain a flexible composite fabric functionalized with SiO2 / ZnO core-shell nanoparticles.

[0057] The SiO2 / ZnO core-shell nanoparticles used were prepared using the following specific process: 20 mmol of zinc acetate dihydrate and 6 mmol of ascorbic acid were weighed and dissolved in 100 mL of deionized water. After complete dissolution, 0.9613 g of SiO2 nanospheres were added, stirred for 10 min, and sonicated for 15 min to obtain a dispersion solution. 40 mmol of hexamethylenetetramine was weighed and added to the dispersion solution, stirred for 3 min, and sonicated for 5 min. The mixture was then transferred to a water bath and reacted at 90℃-100℃ for 2-4 h. After the reaction, the reaction product was obtained by centrifugation, washed repeatedly with deionized water and ethanol 3-5 times, and dried at 60℃ for 12 h to obtain a yellow powder. The yellow powder was ground and transferred to a muffle furnace for calcination in air at a heating rate of 5℃-10℃ / min for 2-4 h to obtain a white powder. After grinding, the desired product, SiO2 / ZnO core-shell nanoparticles, was obtained.

[0058] Example 4

[0059] In this embodiment, the polymer solution had a mass concentration of 13%, and the acetone and DMF in the polymer solution were mixed solvents in a volume ratio of 6:4. During electrospinning, the spinning voltage was 8 kV, the feed rate was 1.0 mL / h, and the receiving distance was 14 cm. Everything else was the same as in Example 1.

[0060] Example 5

[0061] In this embodiment, the nanoparticles in the prepared composite solution constitute 40 wt% of the polymer mass. The electrospinning process uses a spinning voltage of 12 kV, a feed rate of 1.0 mL / h, and a receiving distance of 18 cm. Other parameters are the same as in Example 1.

[0062] Example 6

[0063] In this embodiment, the nanoparticles in the prepared composite solution are 60 wt% of the polymer mass, and the rest is the same as in Example 3.

[0064] Performance testing:

[0065] 1) SEM testing: The samples prepared in the above embodiments were observed under a scanning electron microscope. (See attached image.) Figure 1The image shows the microstructure of the SiO2 / ZnO / ZIF-8 core-shell nanoparticle sample prepared in Example 1. It was assembled in situ by chemical bonding of SiO2 nanospheres, nano-ZnO particles, and bulk ZIF-8 nanoparticles. The nano-ZnO particles are uniformly dispersed on the surface of the SiO2 nanospheres, and the bulk ZIF-8 particles are further coated on the surface, resulting in a polyhedral spherical morphology. The overall particle size is 600–900 nm, with the ZIF-8 particles on the surface measuring 90–110 nm. The fine ZnO nanoparticles coating the surface of the SiO2 nanospheres have a particle size of 10–30 nm. (See attached image.) Figure 2 The image shows the microstructure of the SiO2 / Zn2SiO4 core-shell nanoparticle sample prepared in Example 2. The sample is formed by a surface solid-phase reaction between SiO2 nanospheres and surface-dwelling ZnO nanoparticles, resulting in a smooth spherical morphology with distinct grooves on the surface. The overall particle size is 540–600 nm. Figure 3 The image shows the microstructure of the SiO2 / ZnO core-shell nanoparticle sample prepared in Example 3. The sample exhibits a dense, fine particle-coated spherical morphology, consisting of a core-shell structure formed by fine ZnO nanoparticles encapsulating the surface of SiO2 nanospheres. The overall particle size is 500–700 nm; the fine ZnO nanoparticles distributed on the surface have a particle size of approximately 10–30 nm. Figure 4 This diagram shows the structure of the composite flexible fabric prepared in Example 1, along with the morphology and cross-sectional views of each layer. The upper and lower layers are polymer electrospun fiber layers, and the middle layer is a functional electrospun fiber layer modified with nanoparticles. The diagram shows that the polymer fibers in each layer are uniform in size and interwoven into a three-dimensional porous network structure. In the functional electrospun fiber layer, nanoparticles are observed to be uniformly dispersed within the interwoven network structure of polymer fibers and embedded on the fiber surface. The overall particle size of the nanoparticles is 500-900 nm. The diameter of the polymer fibers in the upper and lower polymer electrospun fiber layers is between 100 and 700 nm, while the diameter of the polymer fibers in the middle functional electrospun fiber layer is between 200 and 1000 nm. The diagram also shows that the total thickness of the three layers of the composite flexible fabric prepared in Example 1 is approximately 250 μm. The thickness of each layer and the total thickness can be adjusted by regulating the electrospinning time according to the needs of the fabric's use, and can meet the multifunctional requirements of the composite flexible fabric of this invention within the range of a few micrometers to millimeters.

[0066] 2) UV-Vis-NIR Reflectance and Infrared Emissivity Tests: The composite flexible fabrics prepared in the above embodiments were subjected to radiation cooling performance tests, and their UV-Vis-NIR reflectance and infrared emissivity were measured. The test results showed that the average reflectance of the composite flexible fabrics prepared in each embodiment in the UV-Vis-NIR band was above 84%, and their emissivity in the infrared atmospheric window band within the 8-13 μm range was close to 95%. (See attached image) Figure 5The results are the spectral test results of the composite flexible fabric prepared in Example 1, which were measured in the ultraviolet-visible-near-infrared bands for reflectance and the infrared band for emissivity. Figure 5 As can be seen, the flexible composite fabric prepared in Example 1 has high reflectivity in the ultraviolet-visible-near-infrared band, with an average reflectivity of 84.7%, which can reflect most of the incident solar radiation. The flexible composite fabric prepared in Example 1 also has extremely strong emissivity in the infrared atmospheric window band (8-13 μm), with an average emissivity of 94.9%, which can facilitate intense heat exchange between the atmospheric window and the low-temperature universe.

[0067] 3) Outdoor cooling effect test: The composite flexible fabrics prepared in each embodiment were tested for their outdoor cooling effect. The test results of Example 1 are as follows: Figure 6 As shown in the figure (the curve corresponding to "the fabric" is the test curve of the composite flexible fabric obtained in Example 1), compared with the purchased pure cotton fabric, it can achieve a stable cooling effect, with a maximum cooling range of 2.9℃. The test results of other examples are comparable to those of Example 1.

[0068] 4) Energy Harvesting Performance: The energy harvesting performance of the composite flexible fabrics prepared in the above embodiments was evaluated through triboelectric nanogenerator performance testing. Using the composite flexible fabrics prepared in each embodiment as negative electrode materials, and combined with a nylon film, the energy harvesting performance of the flexible fabric triboelectric nanogenerator was tested. The test results of each embodiment showed excellent energy harvesting performance. (See attached...) Figure 7-9 These are the test results from Example 1. Figure 7 As shown, the open-circuit voltage of this device can reach ~48.99V at different operating frequencies (2Hz-6Hz). (See attached image.) Figure 8 As shown, when the applied load is 60MΩ, the maximum output power of this device can reach 9.87μW (10.97mW·m). -2 ). As attached Figure 9 As shown, the device maintains good stability after 9600 consecutive operating cycles.

[0069] 5) Hydrophobicity test: The composite flexible fabric prepared in Example 1 was subjected to a hydrophobicity test, and the water contact angle test diagram is shown in the attached figure. Figure 10 As shown, its contact angle is 134.3°, exhibiting good hydrophobicity. Fabrics prepared in other embodiments also possess comparable hydrophobicity.

[0070] 6) Co-culture antibacterial test: The composite flexible fabrics prepared in each example were co-cultured with *Escherichia coli* and *Staphylococcus aureus*, respectively. Colony diagrams were observed to test their antibacterial activity. (See attached...) Figure 11The results of the test on the flexible fabric of Example 1 are shown. Compared with the blank control group, the composite flexible fabric of Example 1 showed an inhibition rate of >99.9% against Escherichia coli and Staphylococcus aureus, demonstrating highly efficient and broad-spectrum antibacterial activity.

Claims

1. A multifunctional composite flexible fabric, characterized in that: The composite flexible fabric has multiple functions including radiation cooling, energy harvesting, hydrophobicity and antibacterial properties. The composite flexible fabric is composed of several electrospun fiber layers, each layer being formed sequentially by electrospinning in an upper and lower order; it includes at least two polymer electrospun fiber layers and at least one nanofunctional electrospun fiber layer, wherein the nanofunctional electrospun fiber layer is an intermediate layer, forming a sandwich structure with the polymer electrospun fiber layers located on the upper and lower surfaces respectively. The polymer electrospun fiber layer is formed by several polymer fibers, namely the first polymer fiber, intersecting to form a three-dimensional network porous structure; The nanofunctional electrospun fiber layer comprises several polymer fibers, namely second polymer fibers, and several nanoparticles, wherein the second polymer fibers cross to form a three-dimensional network porous structure, and the nanoparticles are uniformly distributed within or on the surface of the network porous structure formed by the second polymer fibers, and embedded on the second polymer fibers. The polymer fiber is selected from one or more of polyvinylidene fluoride and its series copolymers; the nanoparticles are at least one of SiO2 / ZnO core-shell particles, SiO2 / Zn2SiO4 core-shell particles or SiO2 / ZnO / ZIF-8 core-shell particles. The radiation cooling function refers to the following: the solar reflectivity of the composite flexible fabric reaches 84.7% or higher; the infrared emissivity of the composite flexible fabric in the infrared atmospheric window band of 8-13 μm reaches 94.9% or higher. The energy harvesting function refers to the energy harvesting performance of the composite flexible fabric triboelectric nanogenerator, which achieves an open-circuit voltage of 48.99 V at an operating frequency of 2Hz-6Hz and a maximum output power of 10.97 mW·m with an applied load of 60MΩ. -2 The composite flexible fabric exhibits hydrophobic properties, with a water contact angle of 134.3°. The composite flexible fabric also demonstrates antibacterial properties, with inhibition rates of over 99.9% against both Escherichia coli and Staphylococcus aureus.

2. The multifunctional composite flexible fabric according to claim 1, characterized in that: The polymer fiber is made of one or more of PVDF, PVDF-HFP, and PVDF-TRFE.

3. The multifunctional composite flexible fabric according to claim 1, characterized in that: The composite flexible fabric consists of three layers: two single-layer polymer electrospun fiber layers and one single-layer nanofunctional electrospun fiber layer. In order from top to bottom, they are the first polymer electrospun fiber layer, the nanofunctional electrospun fiber layer, and the second polymer electrospun fiber layer.

4. The multifunctional composite flexible fabric according to claim 3, characterized in that: The diameter of the first polymer fiber is 100~700 nm; the diameter of the second polymer fiber is 200~1000 nm.

5. The multifunctional composite flexible fabric according to claim 3, characterized in that: The nanoparticle content is 40-60% of the mass fraction of the second polymer fiber.

6. The multifunctional composite flexible fabric according to claim 1, characterized in that: Furthermore, the SiO2 / ZnO core-shell particles are composed of SiO2 nanospheres coated with fine nano-ZnO particles to form a core-shell structure; the SiO2 / ZnO / ZIF-8 core-shell particles are formed by in-situ chemical assembly of SiO2 nanospheres, nano-ZnO particles and bulk nano-ZIF-8 particles, wherein the nano-ZnO particles are uniformly dispersed on the surface of the SiO2 nanospheres, and the bulk ZIF-8 particles are further coated on the surface; the SiO2 / Zn2SiO4 core-shell particles are formed by a surface solid-phase reaction between SiO2 nanospheres and the nano-ZnO particles on the surface to form a core-shell structure; wherein the diameter of the SiO2 nanospheres is 500~600 nm, the diameter of the nano-ZnO particles is 10~30 nm, and the size of the bulk nano-ZIF-8 particles is 90~110 nm.

7. A method for preparing the multifunctional composite flexible fabric according to any one of claims 1-6, characterized in that, Including the following steps: 1) Dissolve the polymer material in a mixed solvent to form a precursor solution; 2) Add functional nanoparticle materials to the precursor solution to obtain a composite solution; 3) The precursor solution, composite solution and precursor solution are continuously electrospun in sequence, and dried to obtain the multifunctional composite flexible fabric; Wherein, the polymer material mentioned in step 1) is selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, or polyvinylidene fluoride-trifluoroethylene; the mixed solvent contains a high-boiling-point solvent and a low-boiling-point solvent, wherein the high-boiling-point solvent is one of N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAC); and the low-boiling-point solvent is acetone. The functional nanoparticle material mentioned in step 2) is selected from SiO2 / ZnO core-shell particles, SiO2 / Zn2SiO4 core-shell particles, or SiO2 / ZnO / ZIF-8 core-shell particles.

8. The method for preparing the multifunctional composite flexible fabric according to claim 7, characterized in that: The volume ratio of the high-boiling-point solvent to the low-boiling-point solvent is 6:4 to 4:6; the mass fraction of the polymer material in the precursor solution is 13 to 16 wt%; and the functional nanoparticle material in step 2) accounts for 40 to 60% of the mass fraction of the polymer material in the composite solution.

9. The method for preparing the multifunctional composite flexible fabric according to claim 7, characterized in that: In the electrospinning process described in step 3), the spinning voltage is 8~12 kV, the feed speed is 0.8~1.0 mL / h, and the receiving distance is 14~18 cm.

10. The method for preparing the multifunctional composite flexible fabric according to claim 7, characterized in that, Step 2) The specific preparation method of the functional nanoparticle material is as follows: a) Add SiO2 particles, an inorganic zinc source, and ascorbic acid to an aqueous solution, and then treat with ultrasound to obtain a SiO2 dispersion; the inorganic zinc source is either zinc acetate or zinc nitrate. b) Add hexamethylenetetramine (HMTA) to the SiO2 dispersion, stir and then sonicate to obtain the first pre-solution; the molar ratio of SiO2:inorganic zinc source:ascorbic acid:hexamethylenetetramine is 8:10:3:

20. c) The first pre-solution is subjected to a solution reaction at a temperature of 90-100°C for 2-4 hours to obtain a precipitate. d) The precipitated product is centrifuged, washed, and dried to obtain powder; the powder is ground and calcined in air at a heating rate of 5-10℃ / min and a holding time of 1-3 h to obtain the SiO2 / ZnO core-shell particles at a temperature of 600-800℃, or the SiO2 / Zn2SiO4 core-shell particles at a temperature of 900-1100℃. e) Mix the SiO2 / ZnO core-shell particles, N,N-dimethylformamide (DMF), and 2-methylimidazole, and sonicate to obtain the second pre-solution; f) The second pre-solution is subjected to a solution reaction at a temperature of 90-110℃ for 1-3 h to obtain a precipitate. The precipitated product was centrifuged, washed, and dried to obtain the SiO2 / ZnO / ZIF-8 core-shell particles.

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