A heterogeneous-wettability film having slit-shaped pores, and a method of manufacturing and use thereof

Abstract

The present application relates to the technical field of oil-water separation materials, and particularly relates to a heterogeneous wetting film with slit-shaped pores and a preparation method and application thereof, the heterogeneous weting film is prepared by taking polyvinylidene fluoride as a base material and through a non-solvent induced phase separation technology, the surface of the heterogeneous wetting film simultaneously comprises a continuous hydrophilic region composed of a film base material and an amphiphilic polymer, discrete low-surface-energy micro-islands composed of a block copolymer additive, and slit-shaped pores formed in situ around the low-surface-energy micro-islands; wherein the block copolymer additive is polyethylene glycol methacrylate-block-poly-pentafluorostyrene. The present application realizes the synergistic optimization of high permeability and excellent antifouling performance of the film through a simple one-step phase inversion technology; meanwhile, the application of the film in gravity-driven oil-water separation is provided, and the problems of low oil-containing wastewater treatment efficiency and serious membrane fouling are solved.

Description

Technical Field

[0001] This invention relates to the field of oil-water separation materials technology, and in particular to a heterogeneous wettable membrane with slit-like pores, its preparation method, and its application. Background Technology

[0002] Currently, oily wastewater treatment technologies mainly include oil skimming, flotation, adsorption, centrifugation, chemical coagulation, and filtration. Among these, gravity-driven membrane technology based on polymer materials is increasingly widely used due to its advantages such as low cost, low energy consumption, automated operation, and environmental friendliness. However, existing gravity-driven membrane filtration technologies still have significant limitations, primarily low permeate flux and severe membrane fouling. Therefore, developing gravity-driven membranes that combine high permeability with excellent antifouling performance has become a key technological requirement in the field of oily wastewater treatment.

[0003] Theoretically, designing an ideal gravity-driven membrane for oily wastewater treatment requires meeting two key conditions: first, the membrane should possess large pore size and high porosity to reduce mass transfer resistance; second, the membrane should have antifouling physicochemical properties. Regarding pore structure optimization, while techniques such as electrospinning and steam-induced phase separation can prepare microfiltration membranes with porosities greater than 70%, these techniques are more complex to prepare and require more sophisticated equipment compared to traditional non-solvent-induced phase separation techniques, limiting their widespread application. Membranes prepared using traditional non-solvent-induced phase separation techniques, due to their limited porosity and small pore size, have seen relatively limited application research in gravity-driven oil-water separation. In terms of the membrane's physicochemical properties, enhancing its wettability helps improve its antifouling ability. Most oil in oily wastewater exists in a dispersed state in the water; therefore, promoting aqueous phase permeation is more feasible than oil phase permeation. Hydrophilic membranes not only facilitate water permeation but also reduce oil pollution by forming a hydration defense layer—a mechanism known as "fouling resistance." However, during oil-water separation, the flux of hydrophilic membranes often decreases significantly due to oil adhesion and spreading. Although the flux can be partially restored through washing, its effective flux in oil-water separation remains low.

[0004] To overcome the limitations of single hydrophilic membranes, combining low surface energy materials with hydrophilic groups to construct membrane surfaces with heterogeneous wettability has become an effective method. Low surface energy components exhibit low adhesion properties and can actively release oily contaminants; this mechanism is known as "contamination release." By integrating antifouling and release methods, the antifouling performance of membranes is often effectively improved. However, low surface energy materials (such as fluoropolymers and polysiloxanes) typically possess strong hydrophobicity, and the hydrophobic regions they form on the membrane surface occupy a portion of the effective filtration area. While using low surface energy materials to improve antifouling performance, membrane permeability is often sacrificed, which is clearly detrimental to gravity-driven filtration. Therefore, how to maintain the excellent contaminant release capacity of low surface energy materials while avoiding their negative impact on membrane permeability remains a challenging problem. Summary of the Invention

[0005] The purpose of this invention is to provide a heterogeneous wettability membrane with slit-like pores, its preparation method, and its application. Through a simple one-step phase inversion technology, the membrane achieves synergistic optimization of high permeability and excellent antifouling performance. At the same time, it provides the application of this membrane in gravity-driven oil-water separation, solving the problems of low treatment efficiency and severe membrane fouling of oily wastewater.

[0006] To achieve the above objectives, the present invention provides a heterogeneous wetting membrane with slit-like pores. The heterogeneous wetting membrane is prepared using polyvinylidene fluoride as the matrix material and a non-solvent-induced phase separation technique. The surface of the heterogeneous wetting membrane simultaneously includes a continuous hydrophilic region composed of the matrix material and an amphiphilic polymer, discrete low surface energy micro-islands composed of block copolymer additives, and slit-like pores formed in situ around the low surface energy micro-islands. The block copolymer additive is polyethylene glycol methacrylate-block-polypentafluorostyrene.

[0007] Preferably, the hydrophilic polymer is Pluronic F127.

[0008] The method for preparing the above-mentioned heterogeneous wettability membrane with slit-like pores includes the following steps:

[0009] S1. Preparation of block copolymer additive: A continuous atom transfer radical polymerization method was adopted, using xylene as solvent, pentaerythritol-α-bromo(PENTA-α-Br) as initiator, and bipyridine and CuBr as catalytic system, to sequentially polymerize polyethylene glycol methacrylate and 2,3,4,5,6-pentafluorostyrene. After purification, polyethylene glycol methacrylate-block-polypentafluorostyrene was obtained.

[0010] S2. Preparation of casting solution: Polyvinylidene fluoride as the matrix material, N,N-dimethylacetamide as the solvent, Pranic F127 as the hydrophilic reinforcing agent, and polyethylene glycol methacrylate-block-polypentafluorostyrene prepared in S1 as the low surface energy modifier are mixed, heated and stirred and degassed to form a uniform casting solution.

[0011] S3. Preparation of heterogeneous wettability membrane: The casting solution is coated onto a glass plate and then immersed in a non-solvent coagulation bath. After phase transformation, a heterogeneous wettability membrane is obtained.

[0012] Preferably, the polymerization of polyethylene glycol methacrylate in S1 is carried out under nitrogen protection, the reaction temperature is 60-80℃, and the reaction time is 0.8-1.2h.

[0013] Preferably, the polymerization of 2,3,4,5,6-pentafluorostyrene in S1 is carried out under nitrogen protection, at a reaction temperature of 100-120℃, and for a reaction time of 5.5-6.5h.

[0014] Preferably, the weight parts of each component in the casting solution in S2 are: 14-18 parts of polyvinylidene fluoride, 4-6 parts of Pranic F127, 2.0-8.0 parts of polyethylene glycol methacrylate-block-polypentafluorostyrene, and 90-110 parts of N,N-dimethylacetamide.

[0015] Preferably, the concentration of polyethylene glycol methacrylate-block polypentafluorostyrene in the casting solution in S2 is 3.0-7.0 wt%.

[0016] Preferably, after heating to 65-75℃ in S2, the mixture is stirred and mixed, and the degassing time is 5.5-6.5h.

[0017] Preferably, the coating thickness in S3 is 250 μm, the non-solvent coagulation bath is deionized water, and the temperature of the non-solvent coagulation bath is 25-30℃.

[0018] The above-mentioned application of a heterogeneous wetting membrane with slit-like pores is that the heterogeneous wetting membrane is used for gravity-driven oil-water emulsion separation, and the oil-water separation object is one of hexane-water, diesel-water or soybean oil-water emulsions.

[0019] Therefore, the present invention, employing the above-mentioned heterogeneous wettability membrane with slit-like pores, its preparation method, and its application, has the following beneficial effects:

[0020] (1) The present invention adopts a one-step non-solvent-induced phase separation technology, which does not require complex equipment and high-precision process control, has low production cost, is easy to scale up production, and has greater potential for industrial application compared with electrospinning, steam-induced phase separation and other technologies.

[0021] (2) The membrane surface prepared by the present invention has a structure of continuous hydrophilic regions (polyvinylidene fluoride and Pluronic F127), discrete low surface energy micro islands (PEGMA-b-PPFS) and slit-like pores: the continuous hydrophilic regions reduce the initial adhesion of oil droplets through the "fouling resistance" mechanism; the discrete low surface energy micro islands inhibit the spread of oil droplets through the "fouling release" mechanism, while promoting the release of oil droplets, and the two work together to achieve excellent antifouling performance; the slit-like pore structure formed in situ can effectively trap oil droplets and significantly reduce the water phase permeation resistance, thus solving the adverse effects of low surface energy materials on membrane permeability;

[0022] (3) This invention combines the construction of heterogeneous wetting surfaces and the formation of slit-like pores in the same process through a one-step phase transformation method, realizing the synergistic design of membrane structure (slit pores) and surface chemistry (heterogeneous wetting), and solving the contradiction in traditional technology that the use of low surface energy materials to improve antifouling performance must sacrifice permeability.

[0023] (4) The heterogeneous wetting membrane prepared by the present invention exhibits excellent permeation and antifouling properties in gravity-driven oil-water separation; and after multiple oil-water separation-cleaning cycles, the membrane flux recovery rate can reach more than 99%, showing good reusability and stability, long service life, and reduced processing costs.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a surface SEM image of the M-PO film in Comparative Example 1 of this invention;

[0026] Figure 2 This is a surface SEM image of membrane M-P5 in Embodiment 4 of the present invention;

[0027] Figure 3 This is a schematic diagram showing the change of surface water contact angle of the membranes prepared in Examples 3-5 and Comparative Example 1 within 60 seconds.

[0028] Figure 4 This is a comparison chart of the membrane pure water flux obtained in Examples 3-5 and Comparative Example 1 of the present invention;

[0029] Figure 5 This is a comparison chart of the permeation flux of the membranes prepared in Examples 3-5 and Comparative Example 1 to hexane-water (H / W), diesel-water (D / W), and soybean oil-water (S / W) emulsions.

[0030] Figure 6 This is a comparison chart of the flux recovery rates of the membranes prepared in Examples 3-5 and Comparative Example 1 after cleaning. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0032] This invention provides a heterogeneous wetting membrane with slit-like pores, which is prepared by non-solvent-induced phase separation technology using polyvinylidene fluoride as the matrix material. The surface of the heterogeneous wetting membrane simultaneously includes a continuous hydrophilic region composed of the matrix material and an amphiphilic polymer, discrete low surface energy micro-islands composed of block copolymer additives, and slit-like pores formed in situ around the low surface energy micro-islands; wherein, the block copolymer additive is polyethylene glycol methacrylate-block-polypentafluorostyrene.

[0033] In this invention, during the phase transformation process, the hydrophilic segments (polyethylene glycol methacrylate) in the block copolymer additive spontaneously segregate to the membrane surface. At the same time, the polypentafluorostyrene segments, due to their similar structure and intermolecular forces, self-assemble to form discrete low surface energy micro-islands. The shrinkage effect generated during the formation of micro-islands leads to the generation of slit-like pores.

[0034] The synergistic effect between the continuous hydrophilic regions and discrete low surface energy micro-islands in the heterogeneous wetting membrane of this invention enables the membrane to exhibit excellent antifouling and defouling capabilities. Furthermore, the slit-like pores surrounding the low surface energy micro-islands can trap oil droplets while allowing rapid water permeation, thereby eliminating the potential adverse effects of low surface energy materials on membrane permeability. This results in the heterogeneous wetting membrane performing exceptionally well in treating oil / water emulsions, achieving ultra-high separation flux under gravity-driven conditions, and exhibiting excellent antifouling and reusability.

[0035] Preferably, the amphiphilic polymer is Pluronic F127.

[0036] In this invention, Pluronic F127 spontaneously segregates onto the surface of the polyvinylidene fluoride (PVDF) membrane during the phase inversion process, and physically crosslinks with PVDF to form a continuous hydrophilic region.

[0037] The method for preparing the above-mentioned heterogeneous wettability membrane with slit-like pores includes the following steps:

[0038] S1. Preparation of block copolymer additive: A continuous atom transfer radical polymerization method was used, with xylene as solvent, pentaerythritol-α-bromo(PENTA-α-Br) as initiator, and bipyridine (Bpy) and CuBr as catalysts. Polyethylene glycol methacrylate (PEGMA) and 2,3,4,5,6-pentafluorostyrene (PFS) polymerization were carried out sequentially. After purification, polyethylene glycol methacrylate-block-polypentafluorostyrene (PEGMA-b-PPFS) was obtained. The reaction principle equation is as follows:

[0039] ;

[0040] In the formula, the value of m ranges from 20 to 40, the value of n ranges from 42 to 96, and the value of y ranges from 6 to 89.

[0041] S2. Preparation of casting solution: Polyvinylidene fluoride (PVDF) is used as the matrix material, N,N-dimethylacetamide (DMAc) is used as the solvent, Pluronic F127 is used as the hydrophilic reinforcing agent, and polyethylene glycol methacrylate-block-polypentafluorostyrene prepared in S1 is used as the low surface energy modifier. The mixture is heated, stirred and degassed to form a uniform casting solution.

[0042] S3. Preparation of heterogeneous wettability membrane: The casting solution is coated onto a glass plate and then immersed in a non-solvent coagulation bath. After phase transformation, a heterogeneous wettability membrane is obtained.

[0043] In this invention, the casting solution is a homogeneous solution. When the casting solution is immersed in a non-solvent coagulation bath, the amphiphilic polymer Pluronic F127 will spontaneously segregate to the membrane surface and physically entangle with polyvinylidene fluoride to form a continuous hydrophilic region. The prepared polyethylene glycol methacrylate-block-polypentafluorostyrene, due to having the same structure and intermolecular forces, will self-assemble to form low surface energy micro-islands. At the same time, the shrinkage effect of the micro-islands will lead to the formation of crack-like pores.

[0044] In this invention, the casting solution is a homogeneous solution. When the casting solution is immersed in a non-solvent coagulation bath, the amphiphilic polymer Pluronic F127 will spontaneously segregate to the membrane surface and physically entangle with polyvinylidene fluoride to form a continuous hydrophilic region. The prepared polyethylene glycol methacrylate-block-polypentafluorostyrene, due to having the same structure and intermolecular forces, will self-assemble to form low surface energy micro-islands. At the same time, the shrinkage effect of the micro-islands will lead to the formation of crack-like pores.

[0045] In this invention, PENTA-α-Br is a star-shaped initiator, which is prepared by the method described in the Journal of Membrane Science (2021, 638: 119648).

[0046] Preferably, the polymerization of polyethylene glycol methacrylate in S1 is carried out under nitrogen protection, the reaction temperature is 60-80℃, and the reaction time is 0.8-1.2h.

[0047] Preferably, the polymerization of 2,3,4,5,6-pentafluorostyrene in S1 is carried out under nitrogen protection, at a reaction temperature of 100-120℃, and for a reaction time of 5.5-6.5h.

[0048] In a further preferred embodiment, the purification process in S1 involves filtration using an alumina column to remove residual catalyst, followed by precipitation with ethanol, filtration, and drying.

[0049] Preferably, the weight parts of each component in the casting solution in S2 are: 14-18 parts of polyvinylidene fluoride, 4-6 parts of Pluronic F127, 2.0-8.0 parts of polyethylene glycol methacrylate-block-polypentafluorostyrene, and 90-110 parts of N,N-dimethylacetamide.

[0050] Preferably, the concentration of polyethylene glycol methacrylate-block polypentafluorostyrene in the casting solution in S2 is 3.0-7.0 wt%.

[0051] This invention controls the amount of polyethylene glycol methacrylate-block-polypentafluorostyrene within the aforementioned range to enable the formation of discrete low surface energy micro-islands of suitable size, uniform distribution, and appropriate quantity. When the amount is below 3.0 wt%, the number of micro-islands may be insufficient, failing to form effective dirt release points. When the amount is above 7.0 wt%, excessive aggregation and connectivity of micro-islands may occur, disrupting the heterogeneous wetting structure and weakening the membrane's synergistic antifouling ability.

[0052] Preferably, after heating to 65-75℃ in S2, the mixture is stirred and mixed, and the degassing time is 5.5-6.5h.

[0053] Preferably, the coating thickness in S3 is 250 μm, the non-solvent coagulation bath is deionized water, and the temperature of the non-solvent coagulation bath is 25-30℃.

[0054] In a further preferred embodiment, the post-treatment in S3 involves storing the membrane detached through the non-solvent-induced phase separation process in deionized water and periodically changing the water to ensure complete removal of residual solvent.

[0055] The above-mentioned application of a heterogeneous wetting membrane with slit-like pores is that the heterogeneous wetting membrane is used for gravity-driven oil-water emulsion separation, and the oil-water separation object is one of hexane-water, diesel-water or soybean oil-water emulsions.

[0056] Example 1

[0057] This invention provides a heterogeneous wetting membrane with slit-like pores. The surface of the heterogeneous wetting membrane simultaneously comprises continuous hydrophilic regions composed of polyvinylidene fluoride (PVDF) proton material and the amphiphilic polymer Pluronic F127, discrete low surface energy micro-islands composed of the block copolymer additive PEGMA-b-PPFS, and slit-like pores formed in situ around the low surface energy micro-islands. It is prepared by the following steps:

[0058] S1. Preparation of block copolymer additive: 20 mL xylene, 5 mL polyethylene glycol methacrylate, 1.0 mmol star-shaped initiator PENTA-α-Br, and 8.0 mmol bipyridine were added to a Schlenk flask equipped with a stirrer. Degassing was then carried out through three cycles of freezing, evacuation, and thawing. 4.0 mmol CuBr was added under nitrogen protection, and the reaction was maintained at 60 °C for 0.8 h. After the reaction was complete, the mixture was rapidly cooled to room temperature, and 10 mL of 2,3,4,5,6-pentafluorostyrene was added to the Schlenk flask under nitrogen protection. The polymerization reaction was continued at 100 °C for 5.5 h. The mixture was filtered through an alumina column to remove residual catalyst, then precipitated with ethanol. After filtration and drying, polyethylene glycol methacrylate-block-polypentafluorostyrene (PEGMA-b-PPFS) was obtained.

[0059] S2. Preparation of casting solution: Add 14g of polyvinylidene fluoride, 90mL of N,N-dimethylacetamide, 4.0g of Pluronic F127 and 2.7g of PEGMA-b-PPFS to a round-bottom flask. Mix the mixture at 65°C using a mechanical stirrer to form a homogeneous casting solution.

[0060] S3. Preparation of heterogeneous wettability membrane: After degassing the obtained casting solution at 65°C for 5.5 h, the obtained casting solution is uniformly coated onto a glass plate with a 250 μm thick doctor blade. After standing for 30 s, the glass plate is immersed in deionized water at 25°C. After the membrane spontaneously detaches, it is stored in deionized water and the water is changed regularly to ensure that residual solvent is completely removed, thus obtaining a heterogeneous wettability membrane.

[0061] Example 2

[0062] This invention provides a heterogeneous wetting membrane with slit-like pores. The surface of the heterogeneous wetting membrane simultaneously comprises continuous hydrophilic regions composed of polyvinylidene fluoride (PVDF) propellant and the amphiphilic polymer Pluronic F127, discrete low surface energy micro-islands composed of the block copolymer additive PEGMA-b-PPFS, and slit-like pores formed in situ around the low surface energy micro-islands. It is prepared by the following steps:

[0063] S1. Preparation of block copolymer additive: 20 mL xylene, 5 mL polyethylene glycol methacrylate, 1.0 mmol star-shaped initiator PENTA-α-Br, and 8.0 mmol bipyridine were added to a Schlenk flask equipped with a stirrer. Degassing was then performed through three cycles of freezing, evacuation, and thawing. 4.0 mmol CuBr was added under nitrogen protection, and the reaction was maintained at 80 °C for 1.2 h. After the reaction was complete, the mixture was rapidly cooled to room temperature, and 10 mL of 2,3,4,5,6-pentafluorostyrene was added to the Schlenk flask under nitrogen protection. The polymerization reaction was continued at 120 °C for 6.5 h. The mixture was filtered through an alumina column to remove residual catalyst, then precipitated with ethanol. After filtration and drying, polyethylene glycol methacrylate-block-polypentafluorostyrene (PEGMA-b-PPFS) was obtained.

[0064] S2. Preparation of casting solution: Add 18g of polyvinylidene fluoride, 110mL of N,N-dimethylacetamide, 6.0g of Pluronic F127 and 7.7g of PEGMA-b-PPFS to a round-bottom flask. Mix the mixture at 75°C using a mechanical stirrer to form a homogeneous casting solution.

[0065] S3. Preparation of heterogeneous wettability membrane: After degassing the obtained casting solution at 75°C for 6.5 h, the obtained casting solution is uniformly coated onto a glass plate with a 250 μm thick doctor blade. After standing for 30 s, the glass plate is immersed in deionized water at 30°C. After the membrane spontaneously detaches, it is stored in deionized water and the water is changed regularly to ensure that residual solvent is completely removed, thus obtaining a heterogeneous wettability membrane.

[0066] Example 3

[0067] This invention provides a heterogeneous wetting membrane with slit-like pores. The surface of the heterogeneous wetting membrane simultaneously comprises continuous hydrophilic regions composed of polyvinylidene fluoride (PVDF) propellant and the amphiphilic polymer Pluronic F127, discrete low surface energy micro-islands composed of the block copolymer additive PEGMA-b-PPFS, and slit-like pores formed in situ around the low surface energy micro-islands. It is prepared by the following steps:

[0068] S1. Preparation of block copolymer additive: 20 mL xylene, 5 mL polyethylene glycol methacrylate, 1.0 mmol star-shaped initiator PENTA-α-Br, and 8.0 mmol bipyridine were added to a Schlenk flask equipped with a stirrer. Degassing was then performed through three cycles of freezing, evacuation, and thawing. 4.0 mmol CuBr was added under nitrogen protection, and the reaction was maintained at 70 °C for 1 h. After the reaction was complete, the mixture was rapidly cooled to room temperature, and 10 mL of 2,3,4,5,6-pentafluorostyrene was added to the Schlenk flask under nitrogen protection. The polymerization reaction was continued at 110 °C for 6 h. The mixture was filtered through an alumina column to remove residual catalyst, then precipitated with ethanol. After filtration and drying, polyethylene glycol methacrylate-block-polypentafluorostyrene (PEGMA-b-PPFS) was obtained.

[0069] S2. Preparation of casting solution: Add 16g of polyvinylidene fluoride, 100mL of N,N-dimethylacetamide, 5.0g of Pluronic F127 and 3.0g of PEGMA-b-PPFS to a round-bottom flask. Mix the mixture at 70°C using a mechanical stirrer to form a homogeneous casting solution.

[0070] S3. Preparation of heterogeneous wettability membrane: After degassing the obtained casting solution at 70℃ for 6 hours, the obtained casting solution is uniformly coated onto a glass plate with a 250μm thick doctor blade. After standing for 30 seconds, the glass plate is immersed in deionized water at 25℃. After the membrane spontaneously detaches, it is stored in deionized water and the water is changed regularly to ensure that the residual solvent is completely removed, thus obtaining a heterogeneous wettability membrane, denoted as M-P3.

[0071] Example 4

[0072] Based on Example 3, the difference from Example 3 is that the amount of PEGMA-b-PPFS added is 5.0g, and the rest is the same as in Example 3. The resulting heterogeneous wettability membrane is denoted as M-P5.

[0073] Example 5

[0074] Based on Example 3, the difference from Example 3 is that the amount of PEGMA-b-PPFS added is 7.0g, and the rest is the same as in Example 3. The resulting heterogeneous wettability membrane is denoted as M-P7.

[0075] Comparative Example 1

[0076] Based on Example 3, the difference from Example 3 is that PEGMA-b-PPFS was not added, but everything else is the same as in Example 3. The resulting membrane is denoted as M-PO.

[0077] Performance testing

[0078] Surface morphology observation: The surface morphology of the films prepared in Comparative Example 1 and Example 4 was observed by scanning electron microscopy (SEM).

[0079] like Figures 1-2 As shown, the surface of the M-P0 membrane in Comparative Example 1 is a uniform structure composed of membrane substrate and Pluronic F127, while the surface of the M-P5 membrane in Example 4 of the present invention exhibits a unique structure: a continuous hydrophilic region formed by membrane substrate and Pluronic F127, discrete micro-islands formed by PEGMA-b-PPFS aggregation, and obvious slit-like pores generated around the micro-islands.

[0080] Surface energy test: The surface energy of the films prepared in Examples 3-5 and Comparative Example 1 was calculated using a contact angle measuring instrument, and the results are shown in Table 1.

[0081] Table 1 Surface energy parameters of heterogeneous wettability membranes with different PEGMA-b-PPFS addition amounts

[0082]

[0083] As shown in Table 1, with the increase of PEGMA-b-PPFS doping, the total surface energy (γ) of the film decreases. s The surface energy was significantly reduced, demonstrating the successful construction of low surface energy micro-islands, enabling the prepared heterogeneous wettable membrane to possess both low surface energy (antifouling release) and certain hydrophilicity (fouling resistance).

[0084] Wettability test: A contact angle meter was used to measure the contact angle of water on the membrane surface at 0s, 10s, 20s, 30s, 40s, 50s and 60s by adding a certain volume of deionized water to the membrane surface. The wettability of the membrane was evaluated in this way. The membrane samples tested included the membranes prepared in Examples 3-5 and Comparative Example 1.

[0085] The results are as follows Figure 3 As shown, the M-P0 membrane had the lowest initial contact angle of 67.4°. The initial contact angle increased after the addition of PEGMA-b-PPFS, primarily due to the increased surface coverage of the fluorinated microislands. After 60 seconds, the contact angle of the M-P0 membrane decreased to 5.2°. In contrast, the wettability of the M-P3, M-P5, and M-P7 membranes was significantly enhanced. Specifically, the WCA of the M-P5 membrane decreased rapidly with increasing droplet age, with water completely penetrating the membrane within 30 seconds. This rapid wettability is attributed to the formation of slit-like pores. The slit-like pore structure significantly enhanced capillary action, allowing for faster water penetration. Simultaneously, the slit-like pores interconnected with the continuous hydrophilic regions containing Pluronic F127 promoted water diffusion and transport.

[0086] Permeability testing: A gravity-driven pure water flux test method was used. Under room temperature conditions, the water depth above the membrane was maintained at 60 cm (using gravity to provide the driving force, without additional pressure). The volume of pure water passing through a unit membrane area per unit time was measured to evaluate the membrane's permeability performance. The membrane samples tested included those prepared in Examples 3-5 and Comparative Example 1.

[0087] The results are as follows Figure 4 As shown, the pure water flux of membranes M-P3, M-P5, and M-P7 is significantly increased compared to membrane M-P0, indicating that the introduction of the low surface energy modifier PEGMA-b-PPFS can significantly enhance membrane permeability. Furthermore, with increasing PEGMA-b-PPFS dosage, the pure water flux further increases, demonstrating that PEGMA-b-PPFS plays a crucial role in optimizing the membrane pore structure (slit-like pores). The improved membrane permeability stems from the synergistic effect of the slit-like pores and the heterogeneous wettability structure: the slit-like pores reduce the aqueous phase permeation resistance, which corresponds to the heterogeneous wettability mechanism observed in previous contact angle tests. This proves that the heterogeneous wettability membrane prepared in this invention exhibits excellent permeability under gravity-driven conditions.

[0088] Oil-water separation performance testing: A gravity-driven oil-water emulsion permeation flux test was conducted. Under gravity-driven conditions of room temperature and a water depth of 60 cm above the membrane, the permeation flux of the membrane for three oil-containing emulsions (hexane-water emulsion (H / W), diesel-water emulsion (D / W), and soybean oil-water emulsion (S / W)) was measured. The membrane samples tested included those prepared in Examples 3-5 and Comparative Example 1.

[0089] The results are as follows Figure 5 As shown, membrane M-P0 exhibits the lowest permeation flux for the three emulsions. In comparison, membranes M-P3, M-P5, and M-P7 show significantly improved permeation flux for all three emulsions, with the highest flux for hexane-water emulsion (H / W), followed by diesel-water emulsion (D / W), and slightly lower flux for soybean oil-water emulsion (S / W). This is because there are differences in oil droplet size and viscosity (hexane droplets are small and have low viscosity, while soybean oil droplets are the opposite), and oil emulsions with smaller droplets and lower viscosity are more likely to pass through the membrane pores.

[0090] With increasing PEGMA-b-PPFS addition, the permeation flux of membrane emulsions M-P3, M-P5, and M-P7 all significantly increased, with M-P5 exhibiting the highest flux for H / W emulsions. The flux of M-P7 decreased slightly but remained significantly higher than that of M-P3, consistent with the pure water flux test, demonstrating the regulatory effect of modifier concentration on membrane pore structure and wettability. The high permeation flux of the membrane stems from the synergistic effect of slit-like pores and heterogeneous wettability: the slit-like pores effectively trap oil droplets while reducing aqueous phase resistance, and the hydrophilic regions promote water permeation, thereby achieving efficient oil-water separation under gravity-driven conditions.

[0091] Antifouling and reusability testing: The flux recovery rate test method was used. A cycle of pure water filtration, oil-water separation, deionized water washing, and further oil-water separation was performed. The ratio of the membrane's permeate flux after washing to its initial flux (i.e., flux recovery rate) was measured to evaluate the membrane's antifouling performance and reusability. The membrane samples tested included those prepared in Examples 3-5 and Comparative Example 1.

[0092] The results are as follows Figure 6 As shown, membrane M-P0 exhibits the lowest flux recovery rate, indicating that its flux is difficult to restore after fouling through simple cleaning, resulting in poor reusability. Membranes M-P3, M-P5, and M-P7 show significantly improved flux recovery rates, especially M-P5, which exceeds 99%. This demonstrates that the introduction of the low surface energy modifier PEGMA-b-PPFS enhances the membrane's antifouling performance and reusability. The high flux recovery rate stems from the heterogeneous structure composed of continuous hydrophilic regions and discrete low surface energy micro-islands on the membrane surface. The hydration layer formed by the hydrophilic regions reduces initial oil adhesion, while the low surface energy micro-islands facilitate the desorption of adhered oil droplets through low interfacial energy interactions. The synergistic effect of these two factors achieves an efficient cycle of antifouling and defouling, enabling the membrane to maintain excellent performance even after multiple separation and cleaning cycles.

[0093] Therefore, the present invention employs the above-mentioned heterogeneous wettability membrane with slit-like pores, its preparation method, and its application. Through a one-step phase transformation method, it ingeniously combines the construction of the heterogeneous wettability surface with the formation of slit-like pores in the same process, realizing the synergistic design of membrane structure (slit pores) and surface chemistry (heterogeneous wetting), and simultaneously achieving high permeation flux and excellent antifouling performance, which is particularly suitable for gravity-driven oil-water emulsion separation.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a heterogeneous wettable membrane with slit-like pores, characterized in that: A heterogeneous wetting membrane is prepared using polyvinylidene fluoride as the matrix material and a solvent-inducible phase separation technique. The surface of the heterogeneous wetting membrane simultaneously includes continuous hydrophilic regions composed of the matrix material and the amphiphilic polymer, discrete low surface energy micro-islands composed of block copolymer additives, and slit-like pores formed in situ around the low surface energy micro-islands; wherein, the block copolymer additive is polyethylene glycol methacrylate-block-polypentafluorostyrene. The amphiphilic polymer is Pranic F127; The heterogeneous wettable membrane with slit-like pores is prepared by the following steps: S1. Preparation of block copolymer additive: A continuous atom transfer radical polymerization method was adopted, with xylene as solvent, pentaerythritol-α-bromine as initiator, and bipyridine and CuBr as catalytic system, to sequentially initiate the polymerization of polyethylene glycol methacrylate and 2,3,4,5,6-pentafluorostyrene. After purification, polyethylene glycol methacrylate-block-polypentafluorostyrene was obtained. S2. Preparation of casting solution: Polyvinylidene fluoride as the matrix material, N,N-dimethylacetamide as the solvent, Pranic F127 as the hydrophilic reinforcing agent, and polyethylene glycol methacrylate-block-polypentafluorostyrene prepared in S1 as the low surface energy modifier are mixed, heated and stirred and degassed to form a uniform casting solution. S3. Preparation of heterogeneous wettability membrane: The casting solution is coated onto a glass plate and then immersed in a non-solvent coagulation bath. After phase transformation, a heterogeneous wettability membrane is obtained.

2. The method for preparing a heterogeneous wettable membrane with slit-like pores according to claim 1, characterized in that: The polymerization of polyethylene glycol methacrylate in S1 is carried out under nitrogen protection at a reaction temperature of 60-80℃ for a reaction time of 0.8-1.2h.

3. The method for preparing a heterogeneous wettable membrane with slit-like pores according to claim 1, characterized in that: The polymerization of 2,3,4,5,6-pentafluorostyrene in S1 was carried out under nitrogen protection at a reaction temperature of 100-120°C. The reaction time is 5.5-6.5 hours.

4. The method for preparing a heterogeneous wettable membrane with slit-like pores according to claim 1, characterized in that: The weight percentages of each component in the casting solution of S2 are as follows: 14-18 parts of polyvinylidene fluoride, 4-6 parts of Pranic F127, 2.0-8.0 parts of polyethylene glycol methacrylate-block-polypentafluorostyrene, and 90-110 parts of N,N-dimethylacetamide.

5. The method for preparing a heterogeneous wettable membrane with slit-like pores according to claim 1, characterized in that: The incorporation concentration of polyethylene glycol methacrylate-block polypentafluorostyrene in the casting solution of S2 is 3.0-7.0 wt%.

6. The method for preparing a heterogeneous wettable membrane with slit-like pores according to claim 1, characterized in that: After heating to 65-75℃ in S2, stir and mix, and degas for 5.5-6.5 hours.

7. The method for preparing a heterogeneous wettable membrane with slit-like pores according to claim 1, characterized in that: The coating thickness in S3 is 250μm, the non-solvent coagulation bath is deionized water, and the temperature of the non-solvent coagulation bath is 25-30℃.

8. A heterogeneous wettable membrane having slit-like pores, characterized in that: It is prepared by the method for preparing a heterogeneous wettable membrane with slit-like pores as described in any one of claims 1-7.

9. The application of a heterogeneous wettable membrane with slit-like pores as described in claim 8, characterized in that: Heterogeneous wettability membranes are used for gravity-driven oil-water emulsion separation.

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