Single-layer Janus fiber membrane with pore and wettability double gradients and one-step electrospinning preparation method of single-layer Janus fiber membrane

Abstract

The invention discloses a single-layer Janus fiber membrane with pore and wettability double gradients and a one-step electrospinning preparation method of the single-layer Janus fiber membrane, and belongs to the technical field of electrostatic spinning functional fiber materials. According to the method disclosed by the invention, polyacrylonitrile (PAN) has weak hydrophilicity, and hydrophobic modification and hydrophilic modification of the PAN fiber membrane can be realized by respectively adding fluorinated titanium dioxide (F-TiO2) particles and tannic acid (TA); gradient regulation and control of pores are realized by regulating and controlling the concentration of the PAN spinning solution. The method comprises the following steps: S1, mixing F-TiO2 particles with PAN to obtain a spinning solution A; s2, mixing TA and PAN to obtain a spinning solution B; s3, the spinning solution A and the spinning solution B are sequentially sucked into the same injector, and a pre-spinning solution C is obtained; and S4, preparing the single-layer fiber membrane through electrostatic spinning. The fiber membrane has a pore / wettability double-gradient structure, shows excellent one-way moisture conduction performance, and has wide application prospects in the fields of personal protection masks, outdoor sportswear and the like.

Description

Technical Field

[0001] This invention relates to the field of electrospun functional fiber materials technology, specifically to a single-layer Janus fiber membrane with dual gradients in pore size and wettability and its one-step electrospinning preparation method. Background Technology

[0002] With the improvement of people's living standards and the growth in demand for functional textiles, fiber materials with one-way moisture-wicking function have shown great application potential in sportswear, medical dressings, hygiene products, personal protective masks, and other fields. One-way moisture-wicking materials can utilize the pores between material layers and the difference in wettability to create a difference in moisture absorption between the inner and outer layers, enabling sweat to be transferred from the skin side of the fabric to the outer side and effectively preventing the back penetration of liquid, thereby ensuring that the skin remains dry.

[0003] Most existing technical solutions employ multilayer composite structures to create materials with drastically different wetting properties on both sides. For example, a hydrophilic fiber membrane and a hydrophobic fiber membrane are bonded together through physical lamination, thermoforming, or adhesive lamination. Another common approach is to apply hydrophilic and hydrophobic finishing to different surfaces of a base fabric, forming a bilayer structure with asymmetric wetting properties. However, bilayer Janus wetting materials exhibit a stepped difference in wetting properties between layers, which limits liquid transport to some extent. Furthermore, the incompatibility between layers in multilayer materials affects their structural stability, thus limiting their service life. For instance, Chinese patent CN202110366242.2 involves depositing a hydrophilic membrane and spraying a hydrophobic polymer on both sides of a substrate layer. While this achieves unidirectional moisture conduction, it is essentially a physical superposition of different materials and cannot fundamentally solve the problem of interlayer bonding stability. Existing technologies have also attempted to mitigate the hindering effect of interlayer wettability changes on liquid transport and improve interlayer bonding by introducing a transition layer between the hydrophilic and hydrophobic layers to construct a wettability gradient. For example, Chinese patent CN201710435876.2 discloses a method that uses a complex three-step electrospinning process to prepare a flow-guiding layer composed of a mixture of hydrophilic and hydrophobic fibers through multi-nozzle co-spinning between the hydrophilic and hydrophobic layers. However, the gradient prepared by this method only represents the macroscopic change in the mixing ratio of the two different fibers. At the microscopic level, the change in wettability remains stepwise and discontinuous, which still hinders the smooth transport of water molecules to some extent. Furthermore, the method not only requires multiple spinning steps, but the preparation of the intermediate transition layer also requires complex multi-nozzle co-spinning equipment, resulting in high costs.

[0004] In summary, most current technologies for preparing unidirectional moisture-wicking fiber membranes employ multilayer composites, which are prone to delamination at the interlayer interfaces. Furthermore, the prepared gradient cannot form a truly continuous wetting gradient, failing to synergistically construct the pore gradient and wettability gradient, thus limiting the improvement of unidirectional moisture-wicking efficiency.

[0005] Therefore, the technical problem to be solved by this invention is to develop a method for preparing a unidirectional moisture-wicking fiber membrane with an integrated structure, simple process, and continuous pore / wetting dual gradient. Summary of the Invention

[0006] To overcome some shortcomings in existing technologies, this invention provides a single-layer Janus fiber membrane with dual gradients in pore size and wettability, and its one-step electrospinning preparation method. The membrane is composed of PAN as the substrate material for electrospinning. Hydrophilic and hydrophobic modifications are achieved by adding hydrophobic F-TiO2 particles and hydrophilic TA to the spinning solution. The pore size gradient of the fiber membrane is controlled by adjusting the concentration of PAN in the spinning solution. Utilizing the concentration difference and molecular diffusion between the spinning solutions, the two spinning solutions exist independently in the same syringe, and their interfaces are mutually integrated, achieving a gradient change in wettability and concentration based on the continuous distribution of PAN components. Through electrospinning technology, a single-layer fiber membrane material with dual gradients in pore size and wettability is obtained, enabling unidirectional liquid hygroscopicity.

[0007] Specifically, this invention provides a single-layer Janus fiber membrane with a gradient of pore size and wettability; the fiber membrane is a single-layer membrane with an integrated structure composed of PAN fibers; The monolayer membrane comprises continuously distributed hydrophobic regions, transition regions, and hydrophilic regions along its thickness direction; the fibers in the hydrophobic regions are loaded with hydrophobic particles, and the fibers in the hydrophilic regions are loaded with hydrophilic additives; the monolayer membrane exhibits a pore gradient and wettability gradient with the average pore size gradually decreasing from the hydrophobic regions to the hydrophilic regions.

[0008] A one-step electrospinning method for preparing a monolayer Janus fiber membrane with a pore size and wettability gradient includes the following steps: Step S1, preparing electrospinning solution A containing hydrophobic particles: F-TiO2 particles are ultrasonically dispersed in N,N-dimethylformamide, then PAN is added and stirred evenly to obtain electrospinning solution A; Step S2, preparing electrospinning solution B containing hydrophilic additives: TA and PAN are dissolved in N,N-dimethylformamide successively and stirred evenly to obtain electrospinning solution B; wherein the PAN concentration in step S1 is higher than the PAN concentration in step S2; Step S3, preparing pre-electrostatic spinning solution C: Spinning solutions A and B are sequentially drawn into the same syringe, and the two spinning solutions exist independently. They are allowed to stand so that the interfaces of the two solutions can be fused together to form a gradient pre-spinning solution C. Step S4, Preparation of monolayer fiber membrane: Electrospinning is performed on the assembled pre-electrospinning solution C, and the prepared fiber membrane is placed in an oven to dry, thereby obtaining a target pore / wetness dual-gradient monolayer fiber membrane.

[0009] In step S1, the F-TiO2 particles are obtained by reacting titanium dioxide with 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane using conventional methods.

[0010] In step S1, the concentration of PAN in N,N-dimethylformamide is 12-14 wt%. The mass ratio of F-TiO2 particles to PAN is 1:20 to 3:20; In step S2, the concentration of PAN in N,N-dimethylformamide is 9-11 wt%. The mass ratio of TA to PAN is 3:50 to 9:50.

[0011] In step S3, the volume ratio of electrospinning solutions A and B in the pre-electrospinning solution C is 1:50 to 3:50. The settling time for solutions A and B after assembly is 0.1 to 2 hours.

[0012] In step S4, the electrospinning voltage is 10~20 kV, the roller collection speed is 250~500 r / min, the receiving distance is 10~15 cm, the spinning solution injection speed is 1.0~1.5 mL / h, the ambient temperature is 23~30 ºC, and the ambient relative humidity is 45~60%.

[0013] In step S3, electrospinning solutions A and B in the pre-electrospinning solution C initially exist independently. After standing, the interface between spinning solutions A and B mixes to form a transition layer, and the surface of the roller receiver sequentially receives hydrophilic fibers, mixed fibers, and hydrophobic fibers.

[0014] In step S4, the obtained pore / wetting dual-gradient monolayer fiber membrane has a large pore size on the hydrophobic side, with an average pore size of 2.0 ~ 3.0 μm; and a small pore size on the hydrophilic side, with an average pore size of 1.0 ~ 1.6 μm; the overall average pore size of the fiber membrane is 1.5 ~ 2.2 μm.

[0015] The present invention also provides a single-layer Janus fiber membrane with dual gradients in porosity and wettability and a one-step electrospinning preparation method thereof. The membrane prepared by the method can be used in masks, outdoor sportswear or protective clothing.

[0016] The beneficial effects of this invention are as follows: (1) The present invention prepares a single-layer integrated fiber membrane, which is composed of a continuous PAN fiber skeleton and does not have any physical interface. PAN is selected as the same polymer material as the substrate, and the wettability difference between the two sides of the fiber membrane is achieved by directly adding hydrophobic F-TiO2 particles and hydrophilic TA. By controlling the concentration of the spinning solution, a certain concentration difference is achieved between the two, thereby realizing the difference in pore size of the fiber membrane after electrospinning. Based on the continuous distribution of PAN components, the principle of similar compatibility of the same system and molecular diffusion can be used to naturally form a transition layer between the two spinning solutions at the interface where there is a clear stratification due to the concentration difference, forming a gradient distribution. Thus, a dual gradient of pore size / wetting property can be constructed on the single-layer fiber membrane.

[0017] (2) The introduction of F-TiO2 particles and TA in this invention enables the fiber membrane to have a certain UV resistance and also gives the fiber membrane a huge difference in wettability on both sides, which can unidirectionally transport water from the hydrophobic side to the hydrophilic layer; the single-layer continuous fiber membrane with a pore / wetting property dual gradient structure can avoid the interference of the step-like wettability difference between multiple Janus wettability materials. The gradient transition region formed by molecular diffusion in this invention is microscopic and continuous, which effectively improves the unidirectional water transport rate of the membrane, enabling water to be transferred spontaneously, continuously and rapidly, with a faster water permeation rate and higher unidirectional moisture conduction efficiency.

[0018] (3) The pore and wettability dual gradients have a synergistic enhancement effect on performance. This invention not only constructs a wettability gradient, but also constructs a pore gradient (hydrophobic macropores and hydrophilic micropores) using concentration difference. The two gradient driving forces have a synergistic effect, effectively preventing reverse osmosis and making the unidirectional moisture conduction performance better than that of materials with only a single gradient. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, wherein: Figure 1 This is a flowchart of the preparation process in Example 1 of the present invention.

[0020] Figure 2 For the PAN nanofibers prepared in Comparative Example 1, the electron microscopy scan images and diameter distribution histograms of F-TiO2 / PAN and TA / PAN nanofibers on both sides of the fiber membrane prepared in Example 1 are shown.

[0021] Figure 3 The diagram shows the variation of the hydrophilic side water contact angle of the PAN nanofiber membrane prepared in Comparative Example 1 and the pore / wetness dual-gradient monolayer fiber membranes prepared in Examples 1, 4-7, respectively.

[0022] Figure 4For comparative examples 2-3, the pore size distribution and air flux diagrams of the F-TiO2 / PAN, TA / PAN and pore / wetting dual-gradient monolayer Janus PAN fiber membranes prepared in Example 1 are shown.

[0023] Figure 5 This is a diagram showing the state of spinning solutions A and B after vertical assembly of spinning solution C during the preparation process of Example 1.

[0024] Figure 6 The image is a laser confocal microscope image along the thickness direction of the pore / wetting dual-gradient monolayer fiber membrane prepared in Example 1.

[0025] Figure 7 Dynamic water contact angle images of pore / wetting dual-gradient monolayer fiber membranes with different ratios of hydrophilic and hydrophobic layers prepared in Comparative Example 4, Examples 1-3, respectively.

[0026] Figure 8 For comparative examples 5-6, breakthrough pressure maps of the bilayer Janus membrane, the wetted single-gradient monolayer fiber membrane, and the pore / wetting dual-gradient monolayer fiber membrane prepared in Example 1 are presented.

[0027] Figure 9 The image shows the water vapor transmission rate (WVTR) of the pore / wetting-gradient monolayer fiber membrane prepared in Example 1 under different humidity conditions.

[0028] Figure 10 Images of the water vapor permeation and surface wettability of the pore / wettability dual-gradient monolayer fiber membrane prepared in Example 1, placed on a beaker containing hot water (95ºC), are shown. Detailed Implementation

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0030] Unless otherwise specified, all raw materials used in the embodiments of this invention are commercially available, as detailed in Table 1.

[0031] Table 1

[0032] The preparation method of F-TiO2 particles is as follows: titanium dioxide is reacted in a mixed solution of 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane and cyclohexane for 12 h to produce the product; the mass concentration of titanium dioxide is 0.15% wt%; the volume ratio of 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane and cyclohexane is 1:100. Example 1:

[0033] (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 10% and the mass concentration of TA was 12% of PAN; (3) Preparation of pre-electrospinning solution C: Inject spinning solution A into a syringe, let it stand to stabilize the solution level, then slowly inject spinning solution B, let it stand for 0.5 h to obtain pre-electrospinning solution C; the volume ratio of electrospinning solution A to B in pre-electrospinning solution C is 2:50; the hydrophobic layer spinning solution is at the bottom and the hydrophilic layer spinning solution is at the top, and the upper layer solution is spun out first; (4) Preparation of monolayer fiber membrane: The assembled pre-electrospinning solution C was electrospinned. The electrospinning voltage was 12-16 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. The spinning solutions B and A were successively converted into fibers and deposited on the surface of the receiving device. The fiber membrane was placed in a 60 ºC oven and dried for 6 h to obtain a target pore / wetness dual gradient monolayer fiber membrane. Example 2:

[0034] (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 10% and the mass concentration of TA was 12% of PAN; (3) Preparation of pre-electrospinning solution C: Inject spinning solution A into a syringe, let it stand to stabilize the surface of the spinning solution, and then slowly inject spinning solution B. Let it stand for 0.5 h to obtain pre-electrospinning solution C; the volume ratio of electrospinning solution A to B in pre-electrospinning solution C is 1:50. (4) Preparation of monolayer fiber membrane: The assembled pre-electrospinning solution C was electrospinned. The electrospinning voltage was 12-16 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. The spinning solutions B and A were successively converted into fibers and deposited on the surface of the receiving device. The fiber membrane was placed in a 60 ºC oven and dried for 6 h to obtain a target pore / wetness dual gradient monolayer fiber membrane. Example 3:

[0035] (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 10% and the mass concentration of TA was 12% of PAN; (3) Preparation of pre-electrospinning solution C: Inject spinning solution A into a syringe, let it stand to stabilize the surface of the spinning solution, and then slowly inject spinning solution B. Let it stand for 0.5 h to obtain pre-electrospinning solution C; the volume ratio of electrospinning solution A to B in pre-electrospinning solution C is 3:50. (4) Preparation of monolayer fiber membrane: The assembled pre-electrospinning solution C was electrospinned. The electrospinning voltage was 12-16 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. The spinning solutions B and A were successively converted into fibers and deposited on the surface of the receiving device. The fiber membrane was placed in a 60 ºC oven and dried for 6 h to obtain a target pore / wetness dual gradient monolayer fiber membrane. Example 4:

[0036] (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 10% and the mass concentration of TA was 6% of PAN; (3) Preparation of pre-electrospinning solution C: Inject spinning solution A into a syringe, let it stand to stabilize the surface of the spinning solution, and then slowly inject spinning solution B. Let it stand for 0.5 h to obtain pre-electrospinning solution C; the volume ratio of electrospinning solution A to B in pre-electrospinning solution C is 2:50. (4) Preparation of monolayer fiber membrane: The assembled pre-electrospinning solution C was electrospinned. The electrospinning voltage was 12-16 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. The spinning solutions B and A were successively converted into fibers and deposited on the surface of the receiving device. The fiber membrane was placed in a 60 ºC oven and dried for 6 h to obtain a target pore / wetness dual gradient monolayer fiber membrane. Example 5:

[0037] (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 10% and the mass concentration of TA was 9% of PAN; (3) Preparation of pre-electrospinning solution C: Inject spinning solution A into a syringe, let it stand to stabilize the surface of the spinning solution, and then slowly inject spinning solution B. Let it stand for 0.5 h to obtain pre-electrospinning solution C; the volume ratio of electrospinning solution A to B in pre-electrospinning solution C is 2:50. (4) Preparation of monolayer fiber membrane: The assembled pre-electrospinning solution C was electrospinned. The electrospinning voltage was 12-16 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. The spinning solutions B and A were successively converted into fibers and deposited on the surface of the receiving device. The fiber membrane was placed in a 60 ºC oven and dried for 6 h to obtain a target pore / wetness dual gradient monolayer fiber membrane. Example 6:

[0038] (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 10% and the mass concentration of TA was 15% of that of PAN; (3) Preparation of pre-electrospinning solution C: Inject spinning solution A into a syringe, let it stand to stabilize the surface of the spinning solution, and then slowly inject spinning solution B. Let it stand for 0.5 h to obtain pre-electrospinning solution C; the volume ratio of electrospinning solution A to B in pre-electrospinning solution C is 2:50. (4) Preparation of monolayer fiber membrane: The assembled pre-electrospinning solution C was electrospinned. The electrospinning voltage was 12-16 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. The spinning solutions B and A were successively converted into fibers and deposited on the surface of the receiving device. The fiber membrane was placed in a 60 ºC oven and dried for 6 h to obtain a target pore / wetness dual gradient monolayer fiber membrane. Example 7:

[0039] (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 10% and the mass concentration of TA was 18% of that of PAN; (3) Preparation of pre-electrospinning solution C: Inject spinning solution A into a syringe, let it stand to stabilize the surface of the spinning solution, and then slowly inject spinning solution B. Let it stand for 0.5 h to obtain pre-electrospinning solution C; the volume ratio of electrospinning solution A to B in pre-electrospinning solution C is 2:50. (4) Preparation of monolayer fiber membrane: The assembled pre-electrospinning solution C was electrospinned. The electrospinning voltage was 12-16 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. The spinning solutions B and A were successively converted into fibers and deposited on the surface of the receiving device. The fiber membrane was placed in a 60 ºC oven and dried for 6 h to obtain a target pore / wetness dual gradient monolayer fiber membrane.

[0040] Comparative Example 1: Unlike Example 1, the PAN spinning solution was not modified to be hydrophilic or hydrophobic. (1) Preparation of electrospinning solution: PAN was added to N,N-dimethylformamide and stirred until homogeneous to obtain an electrospinning solution; the mass concentration of PAN in N,N-dimethylformamide was 10%; (2) Preparation of PAN fiber membrane: Electrospinning was performed on the electrospinning solution. The electrospinning voltage was 13 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. After spinning, the fiber membrane was placed in a 60 ºC oven for 6 h to dry, and PAN fiber membrane was obtained.

[0041] Comparative Example 2: The difference from Example 1 is that only spinning solution A is electrospinned. (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of hydrophobic fiber membrane: Electrospinning solution A was performed. The electrospinning voltage was 14 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. After spinning, the fiber membrane was placed in a 60 ºC oven for 6 h to dry, and a hydrophobic F-TiO2 / PAN fiber membrane was obtained. The difference from Example 1 is that only the spinning solution B is electrospinned.

[0042] (1) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 10% and the mass concentration of TA was 12% of PAN; (2) Preparation of hydrophilic fiber membrane: Electrospinning solution B was performed. The electrospinning voltage was 12 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. After spinning, the fiber membrane was placed in a 60 ºC oven for 6 h to dry, and a hydrophilic TA / PAN fiber membrane was obtained.

[0043] Comparative Example 4: The difference from Example 1 is that the volume ratio of electrospinning solutions A and B in the pre-electrospinning solution C is 4:50; (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 10% and the mass concentration of TA was 12% of PAN; (3) Preparation of pre-electrospinning solution C: Inject spinning solution A into a syringe, let it stand to stabilize the solution level, then slowly inject spinning solution B, let it stand for 0.5 h to obtain pre-electrospinning solution C; the volume ratio of electrospinning solution A to B in pre-electrospinning solution C is 4:50. (4) Preparation of monolayer fiber membrane: The assembled pre-electrospinning solution C was electrospinned. The electrospinning voltage was 12-16 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, and the ambient relative humidity was 45%. The spinning solutions B and A were successively converted into fibers and deposited on the surface of the receiving device. The fiber membrane was placed in a 60 ºC oven and dried for 6 h to obtain a target pore / wetness dual gradient monolayer fiber membrane.

[0044] Comparative Example 5: Unlike Example 1, the spinning solution assembly in step (3) is not performed, and the spinning solutions A and B are electrospun sequentially.

[0045] (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 10% and the mass concentration of TA was 12% of PAN; (3) Preparation of hydrophilic fiber membrane: Electrospinning solution B was electrospinned at a voltage of 14 kV, a roller collection speed of 280 r / min, a receiving distance of 13 cm, a spinning solution injection speed of 1.2 mL / h, an ambient temperature of 25 ºC, and an ambient relative humidity of 45%. The fiber membrane was dried in a 60 ºC oven for 6 h to obtain a hydrophilic TA / PAN fiber membrane.

[0046] (4) Preparation of bilayer Janus fiber membrane: Electrospinning solution A was continued on the hydrophilic TA / PAN fiber membrane. The electrospinning voltage was 14 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, the ambient relative humidity was 45%, and the fiber membrane was dried in a 60 ºC oven for 6 h to obtain a Janus fiber membrane with a bilayer structure.

[0047] Comparative Example 6 (Single-gradient pure wetting gradient membrane): Prepare solutions A and B. The additives and proportions in both solutions are exactly the same as in Example 1. The only difference is that the PAN concentration in solutions A and B is adjusted to be the same.

[0048] (1) Preparation of electrospinning solution A: F-TiO2 particles were added to N,N-dimethylformamide and sonicated for 0.5 h until uniformly dispersed. Then PAN was added and stirred until uniform to obtain electrospinning solution A. The mass concentration of PAN in N,N-dimethylformamide was 13%, and the mass concentration of F-TiO2 particles was 15% of PAN. (2) Preparation of electrospinning solution B: TA and PAN were dissolved in N,N-dimethylformamide one after the other and stirred until homogeneous to obtain electrospinning solution B; the mass concentration of PAN in N,N-dimethylformamide was 13% and the mass concentration of TA was 12% of PAN; (3) Preparation of pre-electrospinning solution C: Inject spinning solution A into a syringe, let it stand to stabilize the solution level, then slowly inject spinning solution B, let it stand for 0.5 h to obtain pre-electrospinning solution C; the volume ratio of electrospinning solution A to B in pre-electrospinning solution C is 2:50. (4) Preparation of monolayer fiber membrane: Electrospinning was performed on the assembled pre-electrospinning solution C. The electrospinning voltage was 12-16 kV, the roller collection speed was 280 r / min, the receiving distance was 13 cm, the spinning solution injection speed was 1.2 mL / h, the ambient temperature was 25 ºC, the ambient relative humidity was 45%, and the fiber membrane was dried in a 60 ºC oven for 6 h to obtain a monolayer fiber membrane.

[0049] Experimental Examples: The surface morphology and fiber diameter distribution histograms of the PAN fiber membrane prepared in Comparative Example 1 and the F-TiO2 / PAN and TA / PAN nanofiber membranes prepared in Comparative Examples 2 and 3 (i.e., the hydrophobic side and hydrophilic side of Example 1) are shown in the attached figures. Figure 2 As shown, PAN nanofibers and TA / PAN nanofibers exhibit smooth surfaces with average diameters of 258 and 283 nm, respectively. For F-TiO2 / PAN nanofibers, F-TiO2 particles form small aggregates distributed within and on the fiber surface, resulting in uniformly visible protrusions that increase surface roughness and enhance hydrophobicity, with an average diameter of 353 nm. The changes in the hydrophilic side water contact angle of the PAN nanofiber membrane prepared in Comparative Example 1 and the pore / wetting dual-gradient monolayer fiber membranes prepared in Examples 1, 4-7 are shown in the attached figure. Figure 3 As shown in the figure, the PAN nanofiber membrane exhibits relatively weak hydrophilicity, with a final water contact angle of 58°. The addition of TA can effectively enhance the hydrophilicity of the PAN nanofiber membrane. This enhancement trend tends to slow down when the TA addition reaches 12%, and the time for water to completely wet the fiber membrane (water contact angle of 0) is shortened from 7 s to 1.5 s.

[0050] The pore size distribution and gas flux of the F-TiO2 / PAN, TA / PAN, and pore / wetting dual-gradient monolayer fiber membranes prepared in Comparative Examples 2-3 and Example 1 are shown in the attached figures. Figure 4 As shown, the average pore size of the F-TiO2 / PAN nanofiber membrane is 2.35 μm, and that of the TA / PAN nanofiber membrane is 1.47 μm. Compared to TA / PAN, the average pore size of the pore / wetting dual-gradient monolayer fiber membrane shows a slight increase to 1.67 μm, which may be due to the presence of hydrophobic and transition regions within the membrane. In terms of gas permeability, the values ​​for F-TiO2 / PAN and TA / PAN membranes are 897 and 746 μm, respectively. 3 ·m -2 ·h -1 ·kPa -1 The value of Janus PAN membrane is 785 m. 3 ·m -2 ·h -1 ·kPa -1This is consistent with the change in aperture.

[0051] During the preparation process of Example 1 above, the states of spinning solutions A and B after vertical assembly of spinning solution C are shown in the attached figure. Figure 5 As shown, spinning solution A and spinning solution B initially have a clear interface. Over time, the PAN molecular chains in the two solutions permeate and intertwine with each other, forming a physically cross-linked diffusion zone, which effectively "binds" the two originally separate solutions together.

[0052] Laser confocal microscopy images along the thickness direction of the pore / wetting-gradient monolayer fiber membrane prepared in Example 1 above are attached. Figure 6 As shown, red fluorescence highlights the hydrophobic region, clearly depicting the distribution of hydrophobic components within the membrane, while green fluorescence depicts the hydrophilic region. When both detection channels are activated simultaneously, partial overlap of the red and green fluorescent regions can be observed. This overlap indicates the existence of a transition zone between the hydrophobic and hydrophilic regions, with partial mixing of the two spinning solutions, ultimately forming an asymmetric wettable fiber membrane based on a continuous distribution of PAN.

[0053] The dynamic water contact angle images of the pore / wettability dual-gradient monolayer fiber membranes with different ratios of hydrophilic / hydrophobic layers prepared in Comparative Example 4 and Examples 1-3 are attached. Figure 7 As shown, when the ratio of hydrophobic to hydrophilic spinning solution is 1:50, a 3 μL water droplet completely penetrates the membrane within 4 seconds after contacting the hydrophobic surface, and its WCA rapidly decreases from 146 ° to 0 °. With increasing volume of the hydrophobic solution, Examples 1 and 2 maintain water transport capability; however, due to the thickened hydrophobic region hindering droplet transport, the penetration time increases to 6 seconds and 18 seconds, respectively. In Comparative Example 4, due to the relatively excessive thickness of the hydrophobic region, water droplets have difficulty penetrating.

[0054] The breakthrough pressures on both sides of the bilayer Janus membrane, the wetted single-gradient monolayer fiber membrane, and the pore / wetting dual-gradient monolayer fiber membrane prepared in Comparative Examples 5-6 and Example 1 are shown in the attached figures. Figure 8 As shown, the breakthrough pressure here refers to the minimum critical pressure required for a liquid to first penetrate the pores of the fiber membrane and be transported to the other side. The breakthrough pressure of each membrane from the hydrophobic side to the hydrophilic side is consistently lower than that in the opposite direction, confirming unidirectional water transport. However, due to potential interfacial defects, the breakthrough pressure of the bilayer Janus membrane is generally lower, which may affect the stability of unidirectional liquid transport. Conversely, the positive breakthrough pressure of the wetting single-gradient fiber membrane is significantly higher than that of the pore / wetting dual-gradient membrane, indicating a weakened unidirectional liquid transport capability. This is due to the single liquid transport driving force of the wetting single-gradient fiber membrane.

[0055] The water vapor transmission rate (WVTR) of the pore / wetting dual-gradient monolayer fiber membrane prepared in Example 1 above under different humidity conditions is shown in the attached figure. Figure 9As shown, the WVTR in the positive direction (from the hydrophobic side to the hydrophilic side) reaches 1295 g·m. -2 ·d -1 The WVTR decreased to 889 g·m⁻¹ in the reverse direction (from the hydrophilic side to the hydrophobic side). -2 ·d -1 This indicates a significant directional difference. When the ambient humidity increased to 80%RH, the WVTR of all membranes decreased, which can be attributed to the suppression of vapor volatilization under high humidity.

[0056] The pore / wettability dual-gradient monolayer fiber membrane prepared in Example 1 above was placed on a beaker containing hot water (95 ºC) to test its water vapor permeation and the membrane surface wettability after the test, as shown in the attached figure. Figure 10 As shown, when the hydrophobic side faces downwards, significantly more condensed water vapor is observed on the inner wall of the upper beaker compared to the opposite direction. For the corresponding images of the membrane after testing, a large wetted area is visible on the upper surface (hydrophilic) of the membrane in the forward direction, confirming effective water vapor transport from the hydrophobic side to the hydrophilic side. In the opposite direction, only sporadic wetted spots are observed, indicating limited water vapor transport. The results demonstrate that the pore / wetting-gradient monolayer fiber membrane exhibits excellent unidirectional vapor transport capability, which is beneficial for transport from the hydrophobic side to the hydrophilic side.

[0057] This demonstrates that the technical solution proposed in this embodiment enables the pore / wetting-gradient monolayer fiber membrane to possess excellent unidirectional liquid transport capabilities, which is likely due to: (1) The single-layer nanofiber membrane prepared by continuous electrospinning is obtained by pre-assembling hydrophilic and hydrophobic spinning solutions. The fiber distribution is regular and the structure is stable. (2) Based on the continuous gradient distribution of PAN component concentration in the spinning solution, the fiber membrane has a continuous gradient pore structure. (3) The single-layer fiber membrane with a wetting gradient structure can avoid the interference of the step-like wetting difference between the layers of multilayer Janus wetting materials, and effectively improve the unidirectional water transport rate of the membrane.

[0058] This invention relates to a single-layer Janus fiber membrane with a gradient in porosity and wettability, and a one-step electrospinning method for its preparation. It should be noted that the specific embodiments described above are merely preferred embodiments and not the sole limitation on the technical solution of this invention. Without departing from the core principles of this invention, those skilled in the art can make several adjustments, modifications, or changes, and these modifications should also fall within the protection scope defined by the claims of this invention. Furthermore, all components not specifically described in this specification can be implemented using existing technologies.

Claims

1. A single-layer Janus fiber membrane with a dual gradient of pore size and wettability, characterized in that, The fiber membrane is a single-layer membrane with an integrated structure composed of PAN fibers. The monolayer membrane comprises continuously distributed hydrophobic regions, transition regions, and hydrophilic regions along its thickness direction; the fibers in the hydrophobic regions are loaded with hydrophobic particles, and the fibers in the hydrophilic regions are loaded with hydrophilic additives; the monolayer membrane exhibits a pore gradient and wettability gradient with the average pore size gradually decreasing from the hydrophobic regions to the hydrophilic regions.

2. The monolayer Janus fiber membrane with dual gradients of pore size and wettability according to claim 1, characterized in that, The hydrophobic particles are F-TiO2 particles, and the hydrophilic additive is TA.

3. The monolayer Janus fiber membrane with dual gradients of pore size and wettability according to claim 1, characterized in that, The pore size of the hydrophobic region is 2.0~3.0 μm; the pore size of the hydrophilic region is 1.0~1.6 μm.

4. A method for preparing a single-layer Janus fiber membrane with a dual gradient of pore size and wettability as described in any one of claims 1-3, characterized in that: Step S1: Prepare a hydrophobic electrospinning solution A, which contains PAN at a first concentration, hydrophobic particles, and a solvent. Step S2: Prepare a hydrophilic electrospinning solution B, which contains a second concentration of PAN, a hydrophilic additive, and a solvent, wherein the first concentration is higher than the second concentration; Step S3: The spinning solution A and spinning solution B are sequentially drawn into the same syringe. The two spinning solutions are allowed to stand so that the interface between the two solutions merges and forms a gradient transition zone, thereby obtaining the pre-electrostatic spinning solution C. Step S4: The pre-electrospinning solution C is continuously electrospinned. Hydrophilic fibers, mixed fibers and hydrophobic fibers are received sequentially on the surface of the roller receiver. After drying, a target pore / wetting dual-gradient monolayer fiber membrane is obtained.

5. The method for preparing a monolayer Janus fiber membrane with dual gradients of pore size and wettability according to claim 4, characterized in that: In step S1, the concentration of PAN in solution A in the solvent is 12-14 wt%; the concentration of PAN in solution B in the solvent is 9-11 wt%.

6. The method for preparing a monolayer Janus fiber membrane with dual gradients of pore size and wettability according to claim 4, characterized in that: In solution A, the mass ratio of F-TiO2 particles to PAN is 1:20 to 3:20; in solution B, the mass ratio of TA to PAN is 3:50 to 9:

50.

7. The method for preparing a monolayer Janus fiber membrane with dual gradients of pore size and wettability according to claim 4, characterized in that, In step S3, the volume ratio of electrospinning solutions A and B in the pre-electrospinning solution C is 1:50 to 3:

50.

8. The method for preparing a monolayer Janus fiber membrane with dual gradients of pore size and wettability according to claim 4, characterized in that, In step S3, the settling time is 0.1 to 2 hours.

9. The method for preparing a monolayer Janus fiber membrane with dual gradients of pore size and wettability according to claim 4, characterized in that, In step S4, the electrospinning voltage is 10~20 kV, the roller collection speed is 250~500 r / min, the receiving distance is 10~15 cm, the spinning solution injection speed is 1.0~1.5 mL / h, the ambient temperature is 23~30 ºC, and the ambient relative humidity is 45~60%.

10. The application of a fiber membrane as described in any one of claims 1-3 in face masks, outdoor sportswear, or protective clothing.

Images