A method for one-step preparation of a fully hydrophobic film using electrostatic synergy and spray-assisted phase separation.

Abstract

This invention discloses a one-step method for preparing a fully hydrophobic membrane using electrostatic synergy and spray-assisted phase separation, comprising the following steps: (1) preparation of a positively charged electroforming solution; (2) preparation of an anionic fluorinated surfactant solution; (3) scraping the casting solution in step (1) into a liquid film of a certain thickness; (4) spraying the aqueous solution of the anionic fluorinated surfactant onto the surface of the liquid film in step (3) using a spray gun; (5) placing the liquid film in an aqueous coagulation bath, allowing it to fully complete phase transformation, and then freeze-drying to obtain the fully hydrophobic membrane. This method utilizes a spray coating process to construct the micro / nano structure on the membrane surface and utilizes the electrostatic interaction between the positively charged electroforming solution and the anionic fluorinated surfactant to achieve "persistent fluorination" of the membrane surface. Therefore, this method can achieve one-step synergistic construction of micro / nano structures and fluorination modification during the phase transformation membrane formation process, which is of great significance for the large-scale preparation of fully hydrophobic membranes.

Description

Technical Field

[0001] This invention relates to a method for preparing a fully hydrophobic film, and more particularly to a method for preparing a fully hydrophobic film in one step by electrostatic synergy and spraying-assisted phase separation. Background Technology

[0002] Membrane distillation technology has broad prospects in the treatment of high-salinity wastewater, but it faces the problems of membrane fouling and wetting, which have become the main obstacles to the industrial application of membrane distillation technology. Due to its unique wetting properties, fully hydrophobic membranes exhibit good antifouling and antiwetting effects during membrane distillation. At present, fully hydrophobic membranes are mainly constructed by depositing nanoparticles (such as SiO2, ZnO, TiO2) on the surface of hydrophobic membranes to build micro-nano structures, and further reducing the surface energy through surface fluorination modification. Elimelech et al. first developed fully hydrophobic membranes in 2014 (Environ. Sci. Technol. Lett., 2014, 1(11): 443-447), which attached nano-silica particles to hydrophilic glass fiber (GF) membranes, and then modified the GF membranes with fluorinated alkylsilanes to obtain fully hydrophobic membranes. The aggregation of nano-silica particles on the GF surface and within the membrane pores constructs a multi-scale recessed structure. Simultaneously, fluorination modification reduces the surface energy of the GF membrane, significantly improving its anti-wetting properties. The modified fully hydrophobic membrane exhibits contact angles of approximately 150° and 110° with water and mineral oil, respectively. Inspired by this work, many researchers have further optimized fully hydrophobic membranes to achieve even better anti-wetting properties. In summary, current methods for preparing fully hydrophobic membranes generally involve post-film formation modifications, resulting in complex processes that hinder the large-scale preparation and application of fully hydrophobic membranes.

[0003] Patent (CN 202210258170.4) discloses a method for the synergistic preparation of a fully hydrophobic membrane using spray-induced solvent-based phase conversion and click chemistry. This method uses a polymer with polyvinylidene fluoride (PVDF) as the main structure as the raw material, and constructs a base film with a micro / nano-level structure through spray-induced solvent-based phase conversion. Subsequently, the base film is hydroxylated on the surface using a strong alkaline NaOH solution, and then fluorinated under strong ultraviolet irradiation and a photoinitiator to achieve full hydrophobicity. While this method also utilizes spraying to generate micro / nano structures on the film surface, it requires complex processes and a large amount of chemical reagents for fluorination modification to obtain a fully hydrophobic membrane, thus failing to achieve a one-step synergistic construction of the micro / nano structure and fluorination modification. Summary of the Invention

[0004] Purpose of the invention: The present invention aims to provide a method for preparing a fully hydrophobic membrane in one step by electrostatic synergy and spraying-assisted phase separation. This method utilizes the electrostatic interaction between the positively charged electroforming solution and the anionic fluorinated surfactant to achieve "persistent fluorination" on the membrane surface, thus enabling the one-step synergistic construction of micro-nano structures and fluorination modification during the phase transformation membrane formation process.

[0005] Technical solution: The method for preparing a fully hydrophobic film in one step by electrostatic synergy and spray-assisted phase separation as described in this invention includes the following steps:

[0006] (1) Preparation of positively charged casting solution: Using polymers with C-Cl bonds as film-forming materials, amine compounds as hydrophilic and charged modifiers, and polyvinylpyrrolidone (PVP) as conventional pore-forming additives, the above substances are dissolved in an organic solvent to prepare a uniform and transparent positively charged casting solution.

[0007] (2) Preparation of anionic fluorinated surfactant solution: Dissolve the anionic fluorinated surfactant in water to prepare a homogeneous surfactant solution, and place it in a spray gun;

[0008] (3) Pour the positively charged electroforming liquid onto a glass plate and scrape it to form a liquid film;

[0009] (4) Use a spray gun to spray the anionic fluorinated surfactant solution onto the liquid film surface in step (3);

[0010] (5) Place the liquid film obtained in step (4) in an aqueous phase coagulation bath, wait for it to fully complete the phase transformation, freeze dry, and a fully hydrophobic film can be obtained.

[0011] Further, the film-forming material in step (1) is one or two of polyvinylidene fluoride-trifluorochloroethylene (PVDF-CTFE), polyvinyl chloride (PVC), etc.; the amine compound is meglumine, dopamine, serine, or tris(hydroxymethyl)methyl methylamine, etc.; in the positively charged film casting solution, the concentration of the film-forming material is 10-30 wt%, the concentration of the amine compound is 1-10 wt%, and the concentration of polyvinylpyrrolidone is 1-20 wt%.

[0012] Further, the fluorinated surfactant in step (2) is sodium perfluorononenoxybenzenesulfonate or For example, FS-66 contains fluorinated surfactants whose concentration in water exceeds their critical micelle concentration.

[0013] Furthermore, in step (4), the spray gun spraying time is controlled within 2-60 seconds.

[0014] Furthermore, the temperature of the aqueous phase coagulation bath in step (5) is 20-50℃.

[0015] Furthermore, the fully hydrophobic membrane prepared using the described method has a water contact angle ≥148° in air, a contact angle ≥98° with mineral oil, and a water flux ≥87 Lm. -2 h -1 .

[0016] Invention Principle: Due to the low bond energy of the C-Cl bonds in the molecular chains of PVDF-CTFE and PVC, they can undergo substitution reactions with meglumine amine compounds. Therefore, during the preparation of the casting solution, the introduction of meglumine amine compounds can achieve grafting of these compounds onto PVDF-CTFE and PVC, resulting in a positively charged casting solution. Furthermore, using a spray gun, a solution containing anionic fluorinated surfactants can be sprayed onto the surface of the positively charged casting solution. The solution sprayed from inside the spray gun facilitates the construction of micro / nano structures on the film surface. Simultaneously, the anionic fluorinated surfactants, through electrostatic interactions with the positively charged casting solution, form an arrangement with hydrophilic ends facing inward (towards the casting solution) and perfluorinated chain segments facing outward. This allows for the simple simultaneous implementation of micro / nano structure construction and fluorination modification. After solidifying the liquid film in an aqueous coagulation bath, a fully hydrophobic film is obtained. This method is simple, can be completed during the phase inversion process, and does not involve complex post-modification steps, thus enabling large-scale preparation.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the method is simple and easy to implement, can be completed during the phase transformation process, and does not involve complex post-modification procedures, thus enabling large-scale preparation. The prepared fully hydrophobic film exhibits high contact angles with both water and mineral oil, and reaches a superhydrophobic state with respect to water. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation process and principle of a fully hydrophobic membrane. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0020] Example 1

[0021] Using 70g dimethylacetamide (DMAC) as solvent, 18g PVDF-CTFE, 10g PVP, and 2g meglumine were uniformly dissolved at 80℃ to form a homogeneous and transparent casting solution. The casting solution was evenly coated onto a glass plate using a doctor blade, followed by spraying with a 2wt% OBS aqueous solution onto the liquid film on the glass plate over a 30s spraying time. A PVDF-CTFE membrane was prepared using a 30℃ water coagulation bath according to a conventional solvent-free phase-inducing separation method. After complete phase inversion, the membrane was removed and freeze-dried for later use. The resulting membrane had a water flux of 87 Lm. -2 h -1The contact angle between water in the air and mineral oil is 152°.

[0022] Example 2

[0023] Using 70g dimethylacetamide (DMAC) as solvent, 18g PVDF-CTFE, 10g PVP, and 2g serine were uniformly dissolved at 80℃ to obtain a homogeneous and transparent casting solution. The casting solution was evenly spread onto a glass plate using a doctor blade, followed by spraying with a spray gun for 30 seconds, applying 2wt% of the solution. FS-66 aqueous solution was uniformly sprayed onto the liquid film on a glass plate. A PVDF-CTFE membrane was prepared using a 30°C water coagulation bath via a conventional solvent-free phase-inducing separation method. After complete phase inversion, the membrane was removed and freeze-dried for later use. The water flux of the resulting membrane was 10² L / m³. -2 h -1 The contact angle between water in the air and mineral oil is 156°.

[0024] Example 3

[0025] Using 70g dimethylacetamide (DMAC) as solvent, 18g PVDF-CTFE, 10g PVP, and 2g tris(hydroxymethyl)methyl methylamine were uniformly dissolved at 80℃ to obtain a homogeneous and transparent casting solution. The casting solution was evenly spread onto a glass plate using a doctor blade, followed by spraying with a spray gun for 30 seconds, applying 2% of the solution. FS-66 aqueous solution was uniformly sprayed onto the liquid film on a glass plate. A PVDF-CTFE membrane was prepared using a conventional solvent-free phase-inducing separation method with a 30°C water coagulation bath. After complete phase inversion, the membrane was removed and freeze-dried for later use. The water flux of the resulting membrane was 195 Lm. -2 h -1 The contact angle between water in the air and mineral oil is 157°.

[0026] Example 4

[0027] Using 70g dimethylacetamide (DMAC) as solvent, 18g PVDF-CTFE, 10g PVP, and 2g meglumine were uniformly dissolved at 80℃ to form a homogeneous and transparent casting solution. The casting solution was evenly coated onto a glass plate using a doctor blade, followed by spraying with a 2wt% OBS aqueous solution onto the liquid film on the glass plate over a 35s spraying time. A PVDF-CTFE membrane was prepared using a 30℃ water coagulation bath according to a conventional solvent-free phase-inducing separation method. After complete phase inversion, the membrane was removed and freeze-dried for later use. The resulting membrane had a water flux of 214 Lm. -2 h -1 The contact angle between water in the air and mineral oil is 158°.

[0028] Comparative Example 1

[0029] Using dimethylacetamide (DMAC) as a solvent, 18 g of PVDF-CTFE, 10 g of PVP, and 2 g of meglumine were uniformly dissolved at 80 °C to obtain a homogeneous and transparent casting solution. The casting solution was then uniformly spread onto a glass plate using a doctor blade. A PVDF-CTFE membrane was prepared using a conventional solvent-free phase-inducing separation method with a 30 °C water coagulation bath. After complete phase inversion, the membrane was removed and freeze-dried for later use. The resulting membrane had a water flux of 369 Lm³. -2 h -1 The contact angle between water in the air and mineral oil is 47°.

[0030] Comparative Example 2

[0031] Using dimethylacetamide (DMAC) as a solvent, 18 g of PVDF-CTFE, 10 g of PVP, and 2 g of serine were uniformly dissolved at 80 °C to obtain a homogeneous and transparent casting solution. The casting solution was evenly coated onto a glass plate using a doctor blade, followed by spraying with water onto the liquid film on the glass plate over a 30-second spraying time using a 30 °C water coagulation bath. The PVDF-CTFE membrane was prepared using a conventional solvent-free phase-inducing separation method. After complete phase inversion, the membrane was removed and freeze-dried for later use. The water flux of the obtained membrane was 194 Lm. -2 h -1 The contact angle between water in the air and mineral oil is 36°.

Claims

1. A method of electrostatically synergistic, spray-assisted phase separation one-step fabrication of omniphobic membranes, characterized in that, Includes the following steps: (1) Preparation of positively charged casting solution: A polymer with C-Cl bonds is used as the film-forming material, an amine compound is used as a hydrophilic and charge-modifying agent, and polyvinylpyrrolidone is used as a conventional pore-forming additive. The above substances are dissolved in an organic solvent to prepare a positively charged casting solution; the film-forming material is one or two of polyvinylidene fluoride-trifluorochloroethylene or polyvinyl chloride; the amine compound is meglumine, dopamine, serine, or tris(hydroxymethyl)methyl methylamine; the concentration of the film-forming material is 10-30 wt%, the concentration of the amine compound is 1-10 wt%, and the concentration of polyvinylpyrrolidone is 1-20 wt%; (2) Preparation of anionic fluorinated surfactant solution: Dissolve the anionic fluorinated surfactant in water to prepare a homogeneous surfactant solution, and place it in the spray gun; (3) Pour the positively charged electroforming solution onto a glass plate and scrape it to form a liquid film; (4) Use a spray gun to spray the anionic fluorinated surfactant solution onto the liquid film surface in step (3); (5) Place the liquid film obtained in step (4) in an aqueous phase coagulation bath, wait for it to fully complete the phase transformation, freeze dry, and then obtain a fully hydrophobic film.

2. The method for preparing a fully hydrophobic film in one step by electrostatic synergy and spraying-assisted phase separation according to claim 1, characterized in that, The fluorinated surfactant in step (2) is sodium perfluorononenoxybenzenesulfonate or Capstone® FS-66.

3. The method for preparing a fully hydrophobic film in one step by electrostatic synergy and spraying-assisted phase separation according to claim 1, characterized in that, In step (2), the concentration of the fluorinated surfactant in water is greater than its critical micelle concentration.

4. The method for preparing a fully hydrophobic film in one step by electrostatic synergy and spraying-assisted phase separation according to claim 1, characterized in that, Step (4) The spray gun spraying time should be controlled within 2-60 seconds.

5. The method for preparing a fully hydrophobic film in one step by electrostatic synergy and spraying-assisted phase separation according to claim 1, characterized in that, The temperature of the aqueous phase coagulation bath in step (5) is 20-50 ℃.

6. The method for preparing a fully hydrophobic film in one step by electrostatic synergy and spraying-assisted phase separation according to claim 1, characterized in that, The fully hydrophobic membrane has a water contact angle of ≥148° in air and a contact angle of ≥98° with mineral oil.

7. The method for preparing a fully hydrophobic film in one step by electrostatic synergy and spraying-assisted phase separation according to claim 1, characterized in that, The water flux of the omniphobic membrane is > 87 Lm -2 h -1 .

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