Sandwich structure composite membrane with asymmetric wettability and preparation method thereof

Abstract

This invention discloses a sandwich-structured composite membrane with asymmetric wettability, comprising, from bottom to top, a hydrophilic cellulose nanofiber layer, a conductive MXene@copper sulfide heterojunction layer, and a superhydrophobic CNF@silica@polydimethylsiloxane composite layer. The hydrophilic cellulose nanofiber layer has a water contact angle of less than 90°, and the superhydrophobic CNF@silica@polydimethylsiloxane composite layer has a water contact angle of greater than 150° and a roll-off angle of less than 5°. This invention also discloses a method for preparing this composite membrane. The layers are prepared using a vacuum-assisted layer-by-layer filtration method, and the top layer is treated with polydimethylsiloxane for superhydrophobicity. The resulting composite membrane exhibits asymmetric wettability and adhesion, and combines advantages such as efficient electromagnetic shielding, selective antibacterial / anti-adhesion properties, and good mechanical flexibility.

Description

Technical Field

[0001] This invention belongs to the field of functional composite materials technology, specifically relating to sandwich structure composite membranes with asymmetric wettability. This invention also relates to a method for preparing sandwich structure composite membranes with asymmetric wettability. Background Technology

[0002] With the rapid development of 5G mobile communication technology and the Internet of Things (IoT), wearable electronic devices face severe electromagnetic interference (EMI) problems. High-performance EMI shielding materials are crucial for solving the increasingly serious problem of electromagnetic pollution. Traditional metal-based shielding materials have drawbacks such as high density, susceptibility to corrosion, and poor flexibility. Transition metal carbides / nitrides (MXenes) have shown great potential in the field of electromagnetic shielding due to their excellent metallic conductivity and layered structure. However, monolayer MXenes are prone to oxidation and self-stacking, leading to a decline in the performance of their conductive networks.

[0003] On the other hand, wearable devices used in the medical and health field also face unique dual biosafety risks: first, the device-skin contact surface may lead to infection due to skin microbiome dysbiosis; second, the device-environment contact surface may be colonized by airborne pathogens. Therefore, an ideal electromagnetic shielding material not only needs highly efficient shielding performance, but also needs to have asymmetric antibacterial capabilities, that is, it should be able to actively kill bacteria on the skin contact surface, and effectively resist bacterial adhesion on the air contact surface.

[0004] While some multilayer composite films have been reported for electromagnetic shielding, there is still a lack of integrated materials that can simultaneously achieve efficient electromagnetic shielding, asymmetric wettability, selective antibacterial and anti-adhesion functions. Summary of the Invention

[0005] The purpose of this invention is to provide a sandwich structure composite film with asymmetric wettability, which solves the problem that existing wearable electronic materials cannot simultaneously satisfy electromagnetic shielding and directional antibacterial properties.

[0006] Another object of the present invention is to provide a method for preparing a sandwich-structured composite film with asymmetric wettability.

[0007] The technical solution adopted in this invention is a sandwich structure composite membrane with asymmetric wettability, comprising, from bottom to top, a hydrophilic cellulose nanofiber layer, a conductive MXene@copper sulfide heterojunction layer, and a superhydrophobic CNF@silica@polydimethylsiloxane composite layer. The hydrophilic cellulose nanofiber layer has a water contact angle of less than 90°, and the superhydrophobic CNF@silica@polydimethylsiloxane composite layer has a water contact angle of greater than 150° and a roll-off angle of less than 5°.

[0008] The invention is further characterized by: MXene@copper sulfide heterojunctions were prepared by in-situ growth of copper sulfide nanocrystals on the surface of monolayer or few-layer MXene nanosheets via a hydrothermal method. The average diameter of the copper sulfide nanocrystals was 30 nm, and they were bonded to the MXene matrix through S-Ti-C chemical bonds.

[0009] Another technical solution adopted in this invention is a method for preparing a sandwich-structured composite membrane with asymmetric wettability, specifically implemented according to the following steps: Step 1: Prepare MXene@copper sulfide heterojunction dispersion; Step 2: Prepare cellulose nanofibers@silica dispersion; Step 3: Vacuum-assisted layer-by-layer filtration is used to form a three-layer structure; Step 4: Spray polydimethylsiloxane onto the upper surface of the three-layer structure obtained in Step 3, and then dry and cure it to obtain the final product.

[0010] Another feature of the technical solution of this invention is that: Step 1 specifically involves mixing a single-layer or few-layer MXene suspension with a copper source and a sulfur source, and then growing copper sulfide nanocrystals in situ on the MXene surface via a hydrothermal reaction to obtain an MXene@copper sulfide heterojunction dispersion.

[0011] In step 1, the copper source is copper chloride, the sulfur source is L-cysteine, the hydrothermal reaction temperature is 100℃, and the reaction time is 8h.

[0012] Step 2 specifically involves dispersing cellulose nanofibers in an alcohol-water mixed solvent, then sequentially adding tetraethyl orthosilicate and methyltrimethoxysilane to carry out a hydrolysis-condensation reaction, thereby obtaining a surface-modified cellulose nanofibers@silica dispersion.

[0013] Step 3 specifically involves using a vacuum-assisted layer-by-layer filtration method to sequentially filter the cellulose nanofiber dispersion, the MXene@copper sulfide heterojunction dispersion prepared in step 1, and the cellulose nanofiber@silica dispersion prepared in step 2 onto a filter membrane to form a three-layer structure.

[0014] In step 3, vacuum-assisted layer-by-layer filtration uses a filter membrane with a pore size of 0.45 μm.

[0015] In step 4, the drying and curing conditions are: drying in an oven at 60°C for 2 hours.

[0016] The beneficial effects of this invention are: This invention presents a sandwich-structured composite membrane with asymmetric wettability. By integrating a hydrophilic bottom layer, a conductive middle layer, and a superhydrophobic top layer, it achieves a "interface separation defense" functional design. The hydrophilic bottom layer effectively captures bacteria on the skin surface, while the superhydrophobic top layer resists the adhesion of airborne pollutants. The MXene@copper sulfide heterojunction in the middle layer not only provides excellent electromagnetic shielding performance (total shielding efficiency up to 33.64 dB in the X-band) but also enhances electromagnetic wave absorption loss through the highly conductive network of MXene and the heterojunction introduced by copper sulfide. Simultaneously, under near-infrared light irradiation, this heterojunction can synergistically generate photothermal, photodynamic, and chemodynamic effects, achieving highly efficient killing of captured bacteria (inhibition rates of over 99% for both Staphylococcus aureus and Escherichia coli). This composite membrane exhibits good mechanical flexibility and deformation stability, capable of withstanding bending, folding, and a certain weight of suspension load without breaking, making it suitable for flexible wearable electronic devices. Attached Figure Description

[0017] Figure 1 This is an electron microscope image of the cross-section of the composite film prepared in Example 5 of the present invention; Figure 2 This is an electron microscope image of the upper surface (CSP) of the composite film prepared in Example 5 of the present invention; Figure 3 This is an electron microscope image of the lower surface (CNF) of the composite film prepared in Example 5 of the present invention. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0019] Example 1 A sandwich-structured composite membrane with asymmetric wettability comprises, from bottom to top, a hydrophilic cellulose nanofiber layer, a conductive MXene@copper sulfide heterojunction layer, and a superhydrophobic CNF@silica@polydimethylsiloxane composite layer. The hydrophilic cellulose nanofiber layer has a water contact angle of less than 90°, and the superhydrophobic CNF@silica@polydimethylsiloxane composite layer has a water contact angle of greater than 150° and a roll-off angle of less than 5°. The bottom layer is the hydrophilic cellulose nanofiber layer, the middle layer is the conductive MXene@copper sulfide heterojunction layer, and the top layer is the superhydrophobic CNF@silica@polydimethylsiloxane composite layer.

[0020] Example 2 A sandwich-structured composite membrane with asymmetric wettability is constructed, in which MXene@copper sulfide heterojunctions are prepared by in-situ growth of copper sulfide nanocrystals on the surface of monolayer or few-layer MXene nanosheets via a hydrothermal method. The copper sulfide nanocrystals have an average diameter of 30 nm and are bonded to the MXene matrix through S-Ti-C chemical bonds. The hydrophilic cellulose nanofiber layer has a smooth, flat surface, while the superhydrophobic CNF@silica@polydimethylsiloxane composite layer has a micro-nano binary rough structure composed of silica nanoparticles and cellulose nanofibers.

[0021] Example 3 The preparation method of the sandwich structure composite membrane with asymmetric wettability is carried out according to the following steps: Step 1: Prepare MXene@copper sulfide heterojunction dispersion; Step 2: Prepare cellulose nanofibers@silica dispersion; Step 3: Vacuum-assisted layer-by-layer filtration is used to form a three-layer structure; Step 4: Spray polydimethylsiloxane onto the upper surface of the three-layer structure obtained in Step 3, and then dry and cure it to obtain the final product.

[0022] Example 4 The preparation method of the sandwich structure composite membrane with asymmetric wettability is carried out according to the following steps: Step 1: Prepare MXene@copper sulfide heterojunction dispersion; Step 1 specifically involves mixing a single-layer or few-layer MXene suspension with a copper source and a sulfur source, and then growing copper sulfide nanocrystals in situ on the MXene surface via a hydrothermal reaction to obtain an MXene@copper sulfide heterojunction dispersion. In step 1, the copper source is copper chloride, the sulfur source is L-cysteine, the hydrothermal reaction temperature is 100℃, and the reaction time is 8h. Step 2: Prepare cellulose nanofibers@silica dispersion; Step 2 specifically involves dispersing cellulose nanofibers in an alcohol-water mixed solvent, then sequentially adding tetraethyl orthosilicate and methyltrimethoxysilane to carry out a hydrolysis-condensation reaction, thereby obtaining a surface-modified cellulose nanofibers@silica dispersion. Step 3: Vacuum-assisted layer-by-layer filtration is used to form a three-layer structure; Step 3 specifically involves using a vacuum-assisted layer-by-layer filtration method to sequentially filter the cellulose nanofiber dispersion, the MXene@copper sulfide heterojunction dispersion prepared in step 1, and the cellulose nanofiber@silica dispersion prepared in step 2 onto a filter membrane to form a three-layer structure. In step 3, a filter membrane with a pore size of 0.45 μm is used for vacuum-assisted layer-by-layer filtration; Step 4: Spray polydimethylsiloxane onto the upper surface of the three-layer structure obtained in Step 3, and then dry and cure it to obtain the final product. In step 4, the drying and curing conditions are: drying in an oven at 60°C for 2 hours.

[0023] Example 5 The preparation method of the sandwich structure composite membrane (CSP / MXC / CNF15) with asymmetric wettability is specifically implemented according to the following steps: Step 1: Synthesis of MXene Nanosheets 3.2 g of LiF was added to 40 mL of 9M HCl and stirred until homogeneous. Then, 2 g of Ti3AlC2MAX phase powder was slowly added while stirring. The reaction system was stirred at 500 rpm for 48 hours at 40°C. After the reaction was complete, the resulting slurry was centrifuged at 5000 rpm for 1 minute to remove the supernatant. Deionized water was added to the precipitate, and the mixture was washed repeatedly until the supernatant turned black. The washed precipitate was sonicated in an ice bath for 30 minutes, then centrifuged at 3500 rpm for 15 minutes, and the supernatant was collected to obtain a monolayer Ti3C2T. x MXene dispersion (concentration approximately 10 mg / mL).

[0024] Step 2: Preparation of MXene@copper sulfide heterojunction Take 5 mL of the MXene dispersion (approximately 10 mg / mL) obtained in step 1 and add it to a solution containing 0.3 g CuCl2·2H2O and 0.52 g L-cysteine, and mix thoroughly. Transfer the mixture to a 150 mL stainless steel autoclave lined with polytetrafluoroethylene and react at 100 °C for 8 h. After the reaction is complete, allow it to cool naturally to room temperature. Separate the product by centrifugation and wash it three times each with deionized water and ethanol to obtain the MXene@copper sulfide heterojunction dispersion.

[0025] Step 3: Preparation of cellulose nanofibers@silica A cellulose nanofiber gel containing 21.6 mg dry weight (2% solids content) was dispersed in 40 mL of 82% isopropanol aqueous solution and sonicated for 5 minutes. While stirring at 300 rpm, 960 μL of tetraethyl orthosilicate was added dropwise, followed by the slow addition of 272 μL of 26.5% ammonia aqueous solution. The pH was adjusted to 10, and the reaction was continued at room temperature for 1 hour. The reaction product was centrifuged at 8000 rpm for 5 minutes and washed three times with ethanol and deionized water. The resulting precipitate was redispersed in 40 mL of 82% isopropanol solution containing 960 μL of methyltrimethoxysilane and 544 μL of 26.5% ammonia, and stirred at 50 °C for 2 hours. After cooling to room temperature, the precipitate was collected by centrifugation and washed three times with deionized water and ethanol to obtain a cellulose nanofiber@silica dispersion.

[0026] Step 4: Assembly of the composite membrane The composite membrane was prepared using a vacuum-assisted layer-by-layer filtration method. First, 10 mL of a 5 mg / mL cellulose nanofiber dispersion was mixed with 20 mL of water and magnetically stirred for 40 minutes. The mixture was then vacuum-filtered through a 0.45 μm filter membrane to form the bottom layer. Next, 5 mL of a 5 mg / mL MXene@copper sulfide heterojunction dispersion was added above the bottom layer and vacuum-filtered again to form the middle layer. Finally, 5 mL of a 10 mg / mL cellulose nanofiber@silica dispersion was added above the middle layer and vacuum-filtered again to form the top layer. The upper surface of the resulting CSP / MXC / CNF three-layer membrane was coated with polydimethylsiloxane and then dried in a 60 °C oven for 2 hours to obtain the final product, the CSP / MXC / CNF15 composite membrane.

[0027] The performance of the composite membrane prepared in this embodiment was tested: Structural characterization: such as Figure 1-3 As shown in the image, scanning electron microscopy reveals that the composite membrane exhibits a distinct sandwich structure. The bottom layer consists of relatively flat cellulose nanofibers; the middle layer shows uniformly distributed copper sulfide nanoparticles loaded onto MXene sheets; and the top layer comprises a micro-nano rough structure constructed from cellulose nanofibers and silica nanoparticles.

[0028] Wettability: The bottom layer has a water contact angle of less than 90°, exhibiting hydrophilicity; the top layer has a water contact angle of 150.5° and a roll-off angle of less than 5°, exhibiting superhydrophobicity and low adhesion.

[0029] Electromagnetic shielding performance: In the X-band of 8.2-12.4 GHz, the total electromagnetic shielding effectiveness of the composite film is 33.64 dB, with a shielding efficiency exceeding 99.9%. Absorption loss is dominant, indicating that it mainly attenuates electromagnetic waves through absorption mechanisms.

[0030] Antibacterial properties: After irradiation with near-infrared laser (808 nm, 1 W / cm²) for 15 minutes, the bottom layer of the composite membrane showed an antibacterial rate of over 99% against Staphylococcus aureus and Escherichia coli, demonstrating excellent bactericidal effect. Meanwhile, the top layer surface showed almost no bacterial adhesion (bacterial adhesion rate of 0%).

[0031] Photothermal performance: Under irradiation with 808nm near-infrared light, the temperature of the composite film can rise to about 110℃ in a short time and has good cycling stability.

[0032] Mechanical properties: The composite film has a tensile strength of 113.9 MPa and an elongation at break of 21.6%. It can be wrapped around a finger, folded, and suspended with a 500 g weight without damage, demonstrating good flexibility and mechanical strength.

[0033] Table 1 below shows the composition and conductivity of different composite membrane samples: Table 1

[0034] The MXC content in MXC / CNF and CSP / MXC / CNF is 15 mg, corresponding to sample CSP / MXC / CNF15.

[0035] Table 2 shows the electromagnetic shielding performance of different composite films in the X-band (8.2-12.4 GHz): surface

[0036]

[0037] SET = SEA + SER. When SEA > 10 dB, the multiple reflection terms SEM can be ignored. The SEA / SER ratio of CSP / MXC / CNF is approximately 1.93, indicating a significantly enhanced absorption contribution.

[0038] Table 3 shows the photothermal properties of different composite films under 808 nm near-infrared light irradiation: Table 3

[0039] Table 4 below shows the antibacterial properties of different composite films (against Staphylococcus aureus and Escherichia coli): Table 4

[0040] The antibacterial rate is calculated using the formula (Nc - Nm) / Nc × 100%, where Nc is the number of colonies in the CNF group and Nm is the number of colonies in the experimental group.

[0041] Table 5 below shows the wettability and bacterial adhesion rate of different surfaces: Table 5

[0042] The bacterial adhesion rate was defined as (Nm / Nc) × 100%, where Nc is the number of colonies adhering to the CNF group and Nm is the number of colonies adhering to the experimental group.

[0043] Table 6 below shows the mechanical properties of different composite membranes: Table 6

[0044] Example 6 This embodiment is basically the same as embodiment 1, except that in step 4, the amount of MXene@copper sulfide heterojunction dispersion used is 3 mL (corresponding to CSP / MXC / CNF10 sample) or 1 mL (corresponding to CSP / MXC / CNF5 sample).

[0045] Test results show that the conductivity and electromagnetic shielding effectiveness of the composite film increase with the increase of the MXene@copper sulfide content in the intermediate layer. The electromagnetic shielding effectiveness of CSP / MXC / CNF10 and CSP / MXC / CNF5 are approximately [missing information]. dB and dB. Other properties (such as asymmetric wettability, antibacterial properties, etc.) are consistent with the examples. Basically the same.

[0046] This invention prepares each layer using a vacuum-assisted layer-by-layer filtration method and applies a superhydrophobic treatment to the top layer using polydimethylsiloxane. The resulting composite membrane exhibits asymmetric wettability and adhesion: the hydrophilic bottom layer actively captures and kills bacteria on the skin surface, while the superhydrophobic top layer effectively resists the adhesion of airborne bacteria; simultaneously, the MXene@copper sulfide heterojunction in the middle layer endows the composite membrane with excellent electromagnetic shielding and photothermal conversion properties. This composite membrane combines the advantages of highly efficient electromagnetic shielding, selective antibacterial / anti-adhesion, and good mechanical flexibility.

Claims

1. A sandwich-structured composite membrane with asymmetric wetting properties, characterized in that, It includes, from bottom to top, a hydrophilic cellulose nanofiber layer, a conductive MXene@copper sulfide heterojunction layer, and a superhydrophobic CNF@silica@polydimethylsiloxane composite layer. The hydrophilic cellulose nanofiber layer has a water contact angle of less than 90°, and the superhydrophobic CNF@silica@polydimethylsiloxane composite layer has a water contact angle of greater than 150° and a roll-off angle of less than 5°.

2. The sandwich-structured composite membrane with asymmetric wetting properties according to claim 1, characterized in that, The MXene@copper sulfide heterojunction is prepared by in-situ growth of copper sulfide nanocrystals on the surface of monolayer or few-layer MXene nanosheets via a hydrothermal method. The average diameter of the copper sulfide nanocrystals is 30 nm, and they are bonded to the MXene matrix through S-Ti-C chemical bonds.

3. The method for preparing a sandwich-structured composite membrane with asymmetric wettability according to any one of claims 1-2, characterized in that, The specific steps are as follows: Step 1: Prepare MXene@copper sulfide heterojunction dispersion; Step 2: Prepare cellulose nanofibers@silica dispersion; Step 3: Vacuum-assisted layer-by-layer filtration is used to form a three-layer structure; Step 4: Spray polydimethylsiloxane onto the upper surface of the three-layer structure obtained in Step 3, and then dry and cure it to obtain the final product.

4. The method for preparing a sandwich-structured composite membrane with asymmetric wettability according to claim 3, characterized in that, Step 1 specifically involves mixing a single-layer or few-layer MXene suspension with a copper source and a sulfur source, and then growing copper sulfide nanocrystals in situ on the MXene surface via a hydrothermal reaction to obtain an MXene@copper sulfide heterojunction dispersion.

5. The method for preparing a sandwich-structured composite membrane with asymmetric wettability according to claim 4, characterized in that, In step 1, the copper source is copper chloride, the sulfur source is L-cysteine, the hydrothermal reaction temperature is 100℃, and the reaction time is 8h.

6. The method for preparing a sandwich-structured composite membrane with asymmetric wetting properties according to claim 3, characterized in that, Step 2 specifically involves dispersing cellulose nanofibers in an alcohol-water mixed solvent, then sequentially adding tetraethyl orthosilicate and methyltrimethoxysilane to carry out a hydrolysis-condensation reaction, thereby obtaining a surface-modified cellulose nanofibers@silica dispersion.

7. The method for preparing a sandwich-structured composite membrane with asymmetric wettability according to claim 3, characterized in that, Step 3 specifically involves using a vacuum-assisted layer-by-layer filtration method to sequentially filter the cellulose nanofiber dispersion, the MXene@copper sulfide heterojunction dispersion prepared in step 1, and the cellulose nanofiber@silica dispersion prepared in step 2 onto a filter membrane to form a three-layer structure.

8. The method for preparing a sandwich-structured composite membrane with asymmetric wettability according to claim 7, characterized in that, In step 3, the vacuum-assisted layer-by-layer filtration uses a filter membrane with a pore size of 0.45 μm.

9. The method for preparing a sandwich-structured composite membrane with asymmetric wettability according to claim 3, characterized in that, In step 4, the drying and curing conditions are drying in an oven at 60°C for 2 hours.

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