Composite material with asymmetric wettability structure and preparation method and application thereof

Abstract

The present invention discloses a composite material with an asymmetric wettability structure, a preparation method and an application thereof. The method comprises modifying MXene and chitosan on the surface of a PU nanofiber membrane by a simple immersion method to obtain a hydrophilic chitosan / MXene@PU composite membrane, and then spinning a layer of hydrophobic PU / PVP fiber on the surface of the composite membrane by electrospinning. The composite material prepared by the present invention has asymmetric superwetting properties, with a water contact angle of 122° on one side and a contact angle of 72° on the other side, and has excellent mechanical properties. In addition, the composite fiber membrane has the ability to transport water in one direction, which can transport water from the hydrophobic side to the hydrophilic side, and water cannot penetrate in the reverse direction; the composite material also has excellent photothermal conversion performance and has broad application prospects in the fields of flexible wearable materials, health monitoring and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of functional polymer material preparation, and relates to a composite material with an asymmetric wettability structure, a preparation method and an application thereof. Background Art

[0002] Electrically conductive fiber / fabric composites (ECFC) have the advantages of light weight, excellent air permeability, low cost and easy processing, and show broad application prospects in the field of flexible wearable electronic materials. One of the most commonly used methods for preparing ECFC is to modify conductive nanofillers (such as metals and carbon nanomaterials) to the fiber surface through physical or chemical interfacial interactions (such as hydrogen bonds and electrostatic interactions). For example, two-dimensional graphene oxide (GO) and MXene have abundant oxygen-containing groups, which can be assembled onto the fiber through hydrogen bonds to form a conductive network with a wrinkled morphology on the fiber surface. For nanofillers with a small amount of functional groups on the surface, such as pristine carbon nanotubes (CNT) and reduced graphene oxide (RGO), they can also be fixed on the fiber surface through methods such as ultrasonic induction and interfacial sintering.

[0003] Existing ECFC technologies primarily focus on the construction and application of their conductive networks, while less research has focused on the wettability of materials, which plays an important role in practical applications. To achieve superhydrophobicity, existing studies typically use low-surface-energy agents such as fluorine- or silicon-containing molecules to modify the surface of ECFCs. Gu et al. grafted a layer of TiO2 particles onto a PU membrane to create a rough surface and improve the hydrophobicity of the PU membrane (Gu, H.; Li, G.; Li, P.; et al, Superhydrophobic and breathable SiO2 / polyurethane porous membrane for durable water repellent application and oil-water separation. Applied Surface Science 2020, 512, 144837.). Xu et al. designed a biomimetic hierarchical structure by electrospinning PU fibers and electrostatically spraying PU microspheres. During the preparation of microspheres, fluorine-free hexadecyltrimethoxysilane (HDTMS) was added to the electrospray solution to improve the hydrophobicity of the PU membrane (Xu, Y.; Li, Y.; Zhang, Y.; et al, Superhydrophobic Polyurethane Membrane with a Biomimetically Hierarchical Structure for Self-Cleaning. ACS Applied Materials & Interfaces 2022, 14(43), 49274-49283.)(Gu, H.; Li, G.; Li, P.; et al, Superhydrophobic and breathable SiO2 / polyurethane porous membrane for durable water repellent application and oil-water separation. Applied Surface Science 2020, 512, 144837.). On the one hand, the excellent hydrophobicity of superhydrophobic ECFC can prevent water from penetrating the material; on the other hand, if superhydrophobic ECFC is used as a wearable fabric, sweat will be blocked and cannot smoothly diffuse to the outer layer, which greatly reduces the wearing comfort of the clothing. To this end, scientists have developed a fiber composite material with asymmetric wettability, that is, the structure has the properties of a hydrophilic surface on one side and a hydrophobic surface on the other.

[0004] Existing studies believe that fiber membranes with asymmetric wettability can be prepared by interfacial modification technology. Yang et al. chemically grafted an ultra-thin hydrophobic layer on one side of the TiO2@PPS membrane. The resulting membrane showed super-hydrophobicity on the chemically modified side and super-hydrophilicity on the untreated side (Yang, C.; Han, N.; Han, C.; et al, Design of a Janus F-TiO2@PPS Porous Membrane with Asymmetric Wettability for Switchable Oil / Water Separation. ACS Applied Materials & Interfaces 2019, 11 (25), 22408-22418.). However, the introduced low surface energy reagent will inevitably diffuse or migrate from the hydrophobic side to the hydrophilic side, which may destroy the asymmetric wettability of the fiber membrane. In addition to chemical modification, Yang et al. also designed a hydrophilic / hydrophobic superimposed double-layer structure to achieve asymmetric wettability. However, because the bilayer structure typically has very different wettability and chemical composition, which inevitably leads to interfacial incompatibility, the bilayer structure is prone to delamination when the fiber membrane undergoes mechanical deformation (such as torsion and stretching). In summary, there is an urgent need to develop an asymmetric wettable composite membrane that combines excellent mechanical durability and unidirectional water transport performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite material with an asymmetric wettability structure that has excellent unidirectional water transport performance and photothermal conversion performance, as well as its preparation method and application. This method modifies a hydrophobic polyurethane (PU) nanofiber membrane into a hydrophilic film using MXene and chitosan. A layer of hydrophobic TPU and polyvinylpyrrolidone (PVP) is electrospun on one side of the membrane by electrospinning. By adjusting the PVP content in the electrospinning solution and the electrospinning time, the TPU / PVP side has better hydrophobic properties. When constructing the hydrophobic layer, PVP is innovatively added. This improvement not only enhances the interfacial interaction between the two-layer structure, but also effectively improves the durability of the material.

[0006] The technical solutions for achieving the purpose of the present invention are as follows:

[0007] A method for preparing a composite material having an asymmetric wettability structure comprises the following steps:

[0008] Step 1: soaking the PU nanofiber membrane in a dispersion of MXene for a period of time, taking it out and drying it, repeating the soaking-drying steps multiple times to obtain a PU nanofiber membrane with a surface coated with MXene;

[0009] Step 2: Soaking the PU nanofiber membrane coated with MXene in a chitosan solution for a period of time, taking it out and drying it to obtain a PU nanofiber membrane coated with chitosan and MXene;

[0010] Step 3, using a mixed dispersion of TPU and PVP as the spinning liquid, electrospinning is performed on the surface of the PU nanofiber membrane coated with chitosan and MXene, the spinning voltage is 14kV~16kV, the liquid feed rate is 1ml / h~3ml / h, the distance between the needle and the receiver is 12cm, and the electrospinning time is 2~3 hours to obtain a composite material with an asymmetric wettability structure. The solvent of the mixed dispersion is tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) with a volume ratio of 4:1, the TPU concentration is 10wt.%, and the PVP concentration is 0.1wt.%.

[0011] In step 1, the surface of the PU membrane treated with MXene has abundant hydrophilic groups, which makes the hydrophobic surface hydrophilic.

[0012] Furthermore, in step 1, the MXene concentration in the MXene dispersion is 3 mg / ml to 7 mg / ml, preferably 5 mg / ml.

[0013] Furthermore, in step 1, the soaking treatment time is 10 minutes and the number of repetitions is 3 times.

[0014] Furthermore, in step 2, the mass fraction of the chitosan solution is 0.3 wt.% to 0.7 wt.%, preferably 0.5 wt.%.

[0015] Furthermore, in step 2, the soaking treatment time is 15 to 45 seconds, preferably 30 seconds.

[0016] Furthermore, in step 2, the drying temperature is 40°C.

[0017] Furthermore, in step 3, the spinning voltage is 15 kV and the liquid feeding speed is 2 ml / h.

[0018] The present invention provides a composite material with an asymmetric wettability structure obtained by the above preparation method.

[0019] Furthermore, the present invention provides the use of the above-mentioned composite material with an asymmetric wettability structure in the preparation of human body temperature monitoring materials, photothermal conversion materials, liquid unidirectional transport materials or flexible wearable devices.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) The method of the present invention adds PVP when preparing the hydrophobic fiber layer, which enhances the interfacial interaction and thus increases the durability of the material.

[0022] (2) The composite material with an asymmetric wettability structure prepared by the present invention has excellent unidirectional transport performance, which can reach as fast as 30 seconds, and the contact angle of the hydrophobic side can reach 122°, and the contact angle of the hydrophilic side can reach 72°.

[0023] (3) The composite material with asymmetric wettability prepared by the present invention has excellent photothermal conversion performance. 2 It can be heated to 85℃ at a low optical density and can be used in extreme environments, greatly expanding its application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the preparation of composite materials with asymmetric wettability structure.

[0025] Figure 2a a, b, c, and d are scanning electron microscope images of the hydrophilic side surface, hydrophilic side single fiber, hydrophobic side surface and cross-section of the composite material with asymmetric wettability structure prepared in Example 1, respectively.

[0026] Figure 3 This is a graph showing the relationship between the contact angle of the hydrophobic side and time during unidirectional transport of the composite material with an asymmetric wettability structure prepared in Example 1, and a comparison graph of the hydrophobic side and the hydrophilic side after unidirectional transport.

[0027] Figure 4 This is a graph showing the relationship between the contact angle of the hydrophilic side and time during unidirectional transport of the composite material with an asymmetric wettability structure prepared in Example 1, and a comparison graph between the hydrophilic side and the hydrophobic side after unidirectional transport.

[0028] Figure 5 This is a relationship diagram of the time from the hydrophobic side to the hydrophilic side of the material droplets of Example 1, Example 2, Example 3, and Comparative Example 1.

[0029] Figure 6 This is a relationship diagram of the one-way transport time of the hydrophobic side of the materials in Example 1, Comparative Example 2, and Comparative Example 3.

[0030] Figure 7 This is a comparison of the materials of Example 1 and Comparative Example 2 after being stretched 20% and cycled 400 times.

[0031] Figure 8 This is a graph showing the relationship between temperature and time for the composite material with an asymmetric wettability structure prepared in Example 1 under 2.5 solar rays.

[0032] Figure 9This is a graph showing the relationship between the heating and cooling cycles and time for the composite material with an asymmetric wettability structure prepared in Example 1 under 2.5 solar rays.

[0033] Figure 10 This is a temperature-resistance relationship diagram of the composite material with an asymmetric wettability structure prepared in Example 1.

[0034] Figure 11 This is a graph showing the relationship between temperature, resistance and time for the composite material with an asymmetric wettability structure prepared in Example 1 under 2.5 solar rays.

[0035] Figure 12 This is a physical picture of the one-way transport from the hydrophobic side to the hydrophilic side in Example 1.

[0036] Figure 13 This is a real picture of the one-way transport hydrophilic side absorption in Example 1.

[0037] Figure 14 This is a real picture of a water droplet from the hydrophobic side to the hydrophilic side in comparative example 1.

[0038] Figure 15 This is a real picture of the water droplet from the hydrophobic side to the hydrophilic side in comparative example 3. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0040] Example 1

[0041] (1) Soak the PU film in a MXene solution with a concentration of 5 mg / ml for 10 minutes, take it out and place it in a 40°C oven for drying, and repeat the soaking-drying process three times. Weigh a certain mass of chitosan and dissolve it in water to make a 0.5wt.% solution. Place the above-mentioned surface-modified PU film in a chitosan solution with a concentration of 0.5wt.% for 30 seconds, take it out and place it in a 40°C oven for drying. Add a certain amount of TPU and PVP to THF and DMF with a volume ratio of 4:1, heat and stir at 65°C for 6 hours, the mass fraction of TPU is 10wt.%, the mass fraction of PVP is 0.1wt.%, set the electrospinning parameters, the voltage is 15kV, the distance from the needle to the collection device is 12cm, the liquid feed rate is 2ml / h, and the spinning time is 2 hours to obtain a composite material with an asymmetric wettability structure with unidirectional transport and photothermal conversion properties. The preparation process is as follows Figure 1 As shown, the microstructure of the composite material with asymmetric wettability structure is shown in Figure 2.

[0042] (2) One-way transport test;

[0043] The dynamic contact angle of the composite material with asymmetric wettability structure was measured using an OCA20 contact angle meter. 5 μL of distilled water was dropped onto the hydrophobic side surface of the composite material with asymmetric wettability structure and the contact angle was recorded every 10 seconds. The test results are shown in Figure 3 As shown in the figure, the contact angle of the composite material with asymmetric wettability structure drops from 121° to 0° in just 30 seconds. The upper right corner is a comparison of the hydrophobic side before and after unidirectional transport. The dynamic contact angle of the composite material with asymmetric wettability structure was tested using the OCA20 contact angle meter. 5μL of distilled water was dropped on the hydrophilic side surface of the composite material with asymmetric wettability structure, and the results were recorded every 1s. Figure 4 The contact angle of the composite material with an asymmetric wettability structure dropped from 72° to 0° in just 2.5 seconds. The upper right corner shows a comparison of the hydrophilic side before and after unidirectional transport.

[0044] (3) Durability test:

[0045] The durability of composite materials with asymmetric wettability structures was tested using an electronic universal testing machine. The materials were cut into rectangles with a length of 20 mm and a width of 4 mm. The stretching degree was set to 20%, and the stretching cycle was repeated 400 times. The test results are shown in Fig. Figure 7 As shown in a, the composite material with asymmetric wettability structure does not show delamination.

[0046] (4) Photothermal conversion capability test:

[0047] The composite material with asymmetric wettability was placed under a simulated light source with an intensity of 2.5 suns. The illumination intensity of the xenon lamp was 2.5 kW m -2 , an infrared imager was used to record the temperature change of the surface of the composite material with asymmetric wettability structure during illumination. The test results are shown in Figure 8 As shown in Figure 1, the surface temperature of the composite material with asymmetric wettability structure rises rapidly to 85°C within 100 seconds and remains stable. The xenon lamp irradiation time is adjusted so that the composite material with asymmetric wettability structure is alternately exposed to 300 seconds of illumination and 300 seconds of non-illumination. The temperature change of the composite material surface with asymmetric wettability structure during the illumination process is recorded using an infrared imager. The test results are shown in Figure 1. Figure 9 The surface temperature of the composite material with asymmetric wettability can be raised to 85°C under illumination and lowered to room temperature (22°C) under non-illumination conditions. After multiple cycles, the composite material with asymmetric wettability can still maintain stability.

[0048] (5) Temperature sensitivity test

[0049] Place it under a light source simulating sunlight intensity, and the xenon lamp has a light intensity of 2.5kW m -2The insulation resistance tester TH2684A4A was used to record the resistance change of the composite material with asymmetric wettability structure as the temperature changed during the illumination process. The test results are as follows: Figure 10 As shown in Figure 2, the linear regression equation for the surface resistance of the composite material with asymmetric wettability structure as the temperature changes can be obtained: (R-R0) / R0=-0.36+0.64e -0.03T Adjust the xenon lamp irradiation time so that the composite material with asymmetric wettability structure is alternately exposed to light for 300s and non-illuminated for 300s. Use the insulation resistance tester TH2684A4A to record the resistance change of the composite material with asymmetric wettability structure as the temperature changes during the irradiation process. The test results are as follows: Figure 11 As shown in the figure, when the composite material with an asymmetric wettability structure is exposed to light, the surface temperature of the composite material with an asymmetric wettability structure increases and the resistance decreases accordingly. When the composite material with an asymmetric wettability structure is not exposed to light, the surface temperature of the composite material with an asymmetric wettability structure decreases and the resistance increases accordingly.

[0050] Example 2

[0051] (1) Soak the PU film in a 5mg / ml MXene solution for 10 minutes, remove it and place it in a 40℃ oven to dry, and repeat three times. Weigh a certain amount of chitosan and dissolve it in water to make a 0.5wt.% solution. Place the above surface-modified PU film in the 0.5wt.% chitosan solution for 30 seconds, remove it and place it in a 40℃ oven to dry for use. Add a certain amount of TPU and PVP to THF and DMF with a volume ratio of 4:1, heat and stir at 65℃ for 6 hours, the mass fraction of TPU is 10wt.%, the mass fraction of PVP is 0.1wt.%, set the electrospinning parameters, voltage is 15kV, the distance from the needle to the collection device is 12cm, and the spinning time is 2.5 hours, to obtain a composite material with an asymmetric wettability structure with unidirectional transport and photothermal conversion properties.

[0052] (2) Contact angle test: The contact angle of the multifunctional composite material was tested using an OCA20 contact angle meter. 5 μL of distilled water was dropped onto the surface of the material. To ensure the accuracy of the results, the test was repeated three times and the average value was taken. The test results are shown in Figure 5 The unidirectional transport time of the composite material with asymmetric wettability structure is 32 seconds.

[0053] Example 3

[0054] (1) Soak the PU film in a MXene solution with a concentration of 5 mg / ml for 10 minutes, take it out and place it in a 40°C oven to dry, and repeat three times. Weigh a certain amount of chitosan and dissolve it in water to make a 0.5wt.% solution. Place the above surface-modified PU film in the chitosan solution with a concentration of 0.5wt.% for 30 seconds, take it out and place it in a 40°C oven to dry for use. Add a certain amount of TPU and PVP to THF and DMF with a volume ratio of 4:1, heat and stir at 65°C for 6 hours, the mass fraction of TPU is 10wt.%, the mass fraction of PVP is 0.1wt.%, set the electrospinning parameters, voltage is 15kV, the distance from the needle to the collection device is 12cm, and the spinning time is 3 hours, to obtain a composite material with an asymmetric wettability structure with unidirectional transport and photothermal conversion properties.

[0055] (2) Contact angle test:

[0056] The contact angle of the composite material with asymmetric wettability structure was tested using OCA20 contact angle meter. 5 μL of distilled water was dropped on the surface of the material. To ensure the accuracy of the results, the test was performed 3 times and the average value was taken. The test results are shown in Figure 5 The composite material with an asymmetric wettability structure has a one-way transport time of 35 seconds.

[0057] Comparative Example 1

[0058] The PU film was immersed in a MXene solution with a concentration of 5 mg / ml for 10 minutes, taken out and placed in a 40°C oven to dry, and repeated three times. A certain mass of chitosan was weighed and dissolved in water to make a 0.5wt.% solution. The above surface-modified PU film was placed in a chitosan solution with a concentration of 0.5wt.% for 30 seconds, then taken out and placed in a 40°C oven to dry for use. A certain amount of TPU and PVP were added to THF and DMF with a volume ratio of 4:1, heated and stirred at 65°C for 6 hours, the mass fraction of TPU was 10wt.%, and the mass fraction of PVP was 0.1wt.%. The electrospinning parameters were set, the voltage was 15kV, the distance from the needle to the collection device was 12cm, and the spinning time was 1.5 hours. After the contact angle test, the test results are shown in FIG. Figure 14 The droplets diffused on the hydrophobic side surface, which did not meet the definition of unidirectional transport. It was found that this composite material could not meet the unidirectional transport requirements.

[0059] Comparative Example 2

[0060] The PU film was immersed in a MXene solution with a concentration of 5 mg / ml for 10 minutes, taken out and placed in a 40°C oven to dry, and repeated three times. A certain mass of chitosan was weighed and dissolved in water to make a 0.5wt.% solution. The above surface-modified PU film was placed in a chitosan solution with a concentration of 0.5wt.% for 30 seconds, then taken out and placed in a 40°C oven to dry for use. A certain amount of TPU was added to THF and DMF with a volume ratio of 4:1, heated and stirred at 65°C for 6 hours, the mass fraction of TPU was 10wt.%, and the electrospinning parameters were set, the voltage was 15kV, the distance from the needle to the collection device was 12cm, and the spinning time was 2 hours. After the contact angle test, the test results are shown in FIG. Figure 6 It takes 90 seconds for the contact angle to drop from 130° to 0°. After durability testing, the present invention found that the interface bonding force of the composite material was weak. The test results are shown in Figure 7 b. When the stretching degree is 20%, delamination occurs after 400 cycles of stretching, which does not meet the requirements.

[0061] Comparative Example 3

[0062] Immerse the PU film in a MXene solution with a concentration of 5 mg / ml for 10 minutes, take it out and place it in a 40°C oven to dry, and repeat three times. Weigh a certain mass of chitosan and dissolve it in water to make a 0.5wt.% solution. Place the above-mentioned surface-modified PU film in a chitosan solution with a concentration of 0.5wt.% for 30 seconds, take it out and place it in a 40°C oven to dry for use. Add a certain amount of TPU and PVP to THF and DMF with a volume ratio of 4:1, heat and stir at 65°C for 6 hours, the mass fraction of TPU is 10wt.%, and the mass fraction of PVP is 0.4wt.%. Set the electrospinning parameters, the voltage is 15kV, the distance from the needle to the collection device is 12cm, the spinning time is 2 hours, and the contact angle test shows the test results. Figure 15 The droplets diffused on the hydrophobic side surface, which did not meet the definition of unidirectional transport. It was found that this composite material could not meet the unidirectional transport requirements.

Claims

1. A method for preparing a composite material having an asymmetric wettability structure, characterized in that: The steps include: Step 1: soaking the PU nanofiber membrane in a dispersion of MXene for a period of time, taking it out and drying it, repeating the soaking-drying steps multiple times to obtain a PU nanofiber membrane with a surface coated with MXene; Step 2: Soaking the PU nanofiber membrane coated with MXene in a chitosan solution for a period of time, taking it out and drying it to obtain a PU nanofiber membrane coated with chitosan and MXene; Step 3, using a mixed dispersion of TPU and PVP as the spinning liquid, electrospinning is performed on the surface of the PU nanofiber membrane coated with chitosan and MXene. The spinning voltage is 14kV~16kV, the liquid feed rate is 1ml / h~3ml / h, the distance between the needle and the receiver is 12cm, and the electrospinning time is 2~3 hours to obtain a composite material with an asymmetric wettability structure. The solvent of the mixed dispersion is THF and DMF with a volume ratio of 4:1, the TPU concentration is 10wt.%, and the PVP concentration is 0.1 wt.%.

2. The preparation method according to claim 1, characterized in that In step 1, the MXene concentration in the MXene dispersion is 3 mg / ml to 7 mg / ml.

3. The preparation method according to claim 1, wherein In step 1, the MXene concentration in the MXene dispersion is 5 mg / ml.

4. The preparation method according to claim 1, characterized in that In step 1, the soaking treatment time is 10 minutes and the number of repetitions is 3 times.

5. The preparation method according to claim 1, characterized in that In step 2, the mass fraction of the chitosan solution is 0.3 wt.% to 0.7 wt.%.

6. The preparation method according to claim 1, characterized in that In step 2, the soaking treatment time is 15 to 45 seconds.

7. The preparation method according to claim 1, wherein In step 1, the MXene concentration in the MXene dispersion is 5 mg / ml; in step 2, the mass fraction of the chitosan solution is 0.5 wt.%, and the immersion treatment time is 30 seconds.

8. The preparation method according to claim 1, characterized in that In step 2, the drying temperature is 40°C.

9. The preparation method according to claim 1, characterized in that In step 3, the spinning voltage is 15 kV and the liquid feeding rate is 2 ml / h.

10. A composite material with an asymmetric wettability structure obtained according to the preparation method according to any one of claims 1 to 9.

11. Use of the composite material with an asymmetric wettability structure according to claim 10 in preparing a human body temperature monitoring material, a photothermal conversion material, a liquid unidirectional transport material, or a flexible wearable device.

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