Differential surface wettability films, their preparation methods and applications

Abstract

This invention relates to the field of surface modification technology, and discloses a surface wettability differential membrane, its preparation method, and its application. The porous membrane comprises a framework and a modifying material with opposite wettability to the framework, loaded onto the framework; wherein, based on the area of ​​the porous membrane, the loading area of ​​the modifying material is 30-80%. The membrane material provided by this invention, loaded with an appropriate amount of modifying material, exhibits significantly higher water collection efficiency.

Description

Technical Field

[0001] This invention relates to the field of material surface modification technology, specifically to a surface wettability differential film, its preparation method, and its application. Background Technology

[0002] Many plants and animals can effectively collect water and survive under extreme conditions. The surface structures of these organisms contain multiple synergistic effects that lead to surface energy gradients or Laplace pressures, resulting in differences in surface wettability. This allows for the directionality of small-scale droplets, enabling highly efficient water collection.

[0003] However, artificially obtaining surface wettability differential structures typically involves modifying the surface's microstructure or altering some of its chemical composition. Existing methods include electrochemical etching, photolithography, photografting, plasma processing, micromilling, and laser ablation. However, existing technologies largely rely on expensive equipment and consumables. For example, plasma processors and femtosecond laser technology have extremely high equipment costs. Photografting and photolithography techniques require expensive consumables such as photoresists or micromasks during surface modification, and also suffer from drawbacks such as cumbersome procedures, time-consuming processes, and high energy consumption, limiting the large-scale fabrication of products. All of these factors hinder the industrial promotion and application of products with surface wettability differentials.

[0004] Therefore, there is an urgent need to develop a method for preparing materials with efficient water or fog collection performance that is simple in process, low in cost, and has a wide selection of raw materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in the prior art and to provide a surface wettability differential membrane, its preparation method, and its application. This method is simple, low-cost, and uses a wide variety of raw materials, and can obtain materials with efficient water or fog collection performance.

[0006] To achieve the above objectives, a first aspect of the present invention provides a porous membrane having a surface wettability difference, the porous membrane comprising a framework and a modified material with the opposite wettability to the framework loaded on the framework;

[0007] The area of ​​the modified material is 30-80% based on the area of ​​the porous membrane.

[0008] In a second aspect, the present invention provides a method for preparing a porous membrane with different surface wettability, the method comprising: using a modifying liquid containing a modifying substance to modify and atomize the framework of the porous membrane, so that the framework is loaded with a modifying substance with opposite wettability to the framework, thereby obtaining the porous membrane.

[0009] The modified atomization time is 1-80 seconds; relative to 1m 2The porous membrane has a droplet consumption rate of 0.5-200 g·h. -1 .

[0010] Thirdly, the present invention provides a surface wettability differential film prepared by the method described above.

[0011] Fourthly, the present invention provides the application of the surface wettability difference membrane described in the first or third aspect in water collection or fog collection.

[0012] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0013] 1. The membrane material provided by this invention is loaded with an appropriate amount of modified substances. The modified substances are dispersed relatively evenly, which can better adsorb water in water vapor or fog environments and condense into small water droplets. It continuously circulates adsorption and condensation, and can efficiently collect water.

[0014] 2. The method of the present invention does not require expensive equipment or complex processes, and has the advantages of strong universality, rich selection of raw materials, simple process and easy large-scale preparation, which is conducive to practical application and production, low production cost and wide applicability. Attached Figure Description

[0015] Figure 1 These are scanning electron microscope (SEM) images of the porous membrane prepared in Example 1;

[0016] Figure 2 These are scanning electron microscope images of the porous membrane prepared in Example 4;

[0017] Figure 3 This is a scanning electron microscope image of the porous membrane prepared in Example 11. Detailed Implementation

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] In a first aspect, the present invention provides a porous membrane having a surface wettability difference, the porous membrane comprising a framework and a modified material loaded on the framework having a wettability opposite to that of the framework;

[0020] The area of ​​the modified material is 30-80% based on the area of ​​the porous membrane.

[0021] The porous membranes described above are generally used for water or mist collection; therefore, wettability refers to wettability in water. The inventors of this invention discovered that when using the porous membrane described above in a water vapor or mist environment, the more wettable portions of the membrane can adsorb and condense water into small droplets, while the hydrophobic portions repel this liquid. This continuous cycle of adsorption, condensation, and repulsion on the membrane adjusts the high-water environment to a low-water environment, achieving the purpose of water collection. In particular, when the loading area of ​​the modified material is within the specified range, the modified material and the framework can work together to achieve even better water collection results.

[0022] The loading area of ​​the modified material can be determined by the following method: placing the porous membrane in water and taking a picture. Since the hydrophobic part appears silver and the hydrophilic part appears gray in the picture, the loading area of ​​the modified material can be calculated by calculating the proportion of pixels that represent the color of the modified material in the image processing software.

[0023] According to the present invention, in order to better match the modified material and the skeleton and further improve the water collection effect, preferably, the loading area of ​​the modified material is 40-60% based on the area of ​​the porous membrane.

[0024] According to the present invention, preferably, the distribution particle size of the modified material is 0.5-50 μm, more preferably 3-30 μm. It is understood that the modified material is dispersed on the porous membrane in the form of dots, and the particle size of the corresponding dots is also known as the distribution particle size of the modified material. The inventors of the present invention have discovered in their research that when the distribution particle size range described above is met, the modified material can be fully exposed and distributed relatively uniformly, thus fully utilizing the effect of the modified material.

[0025] According to the present invention, preferably, the average pore size of the porous membrane is 0.05-8 μm, more preferably 0.1-2.5 μm.

[0026] According to the present invention, preferably, the thickness of the porous membrane is 20-350 μm, more preferably 80-220 μm.

[0027] According to the present invention, preferably, the porous membrane has micro-protrusion structures distributed on it, and the diameter of the micro-protrusion at its maximum cross-sectional area is 0.01-10 μm. The diameter at the maximum cross-sectional area of ​​the micro-protrusion refers to the average diameter of the maximum cross-sectional area of ​​all micro-protrusions on the membrane, which can be calculated by processing scanning electron microscopy images using Nano Measure software. The micro-protrusion structure can increase the specific surface area of ​​the membrane, further improving its water collection capacity. The diameter at the maximum cross-sectional area of ​​the protrusions can be observed using a scanning electron microscope.

[0028] According to the present invention, preferably, the skeleton is composed of one of a hydrophilic substance and a hydrophobic substance.

[0029] It is understandable that when the skeleton is composed of hydrophilic substances, the modified substance is hydrophobic; when the skeleton is composed of hydrophobic substances, the modified substance is hydrophilic.

[0030] According to the present invention, preferably, the weight-average molecular weight of the hydrophilic substance is 10,000-500,000 g / mol.

[0031] According to the present invention, preferably, the weight-average molecular weight of the hydrophobic substance is 10,000-800,000 g / mol.

[0032] The specific selection of the hydrophilic and hydrophobic substances is not particularly limited and can be substances commonly used in the art. However, preferably, the hydrophilic substance is selected from at least one of polyacrylonitrile, sulfonated polyethersulfone, polyvinylidene fluoride-grafted polyacrylic acid, polyvinyl alcohol, cellulose acetate, polydopamine, polyacrylic acid, polymaleic anhydride, and polyamide, and more preferably from at least one of polyacrylonitrile, sulfonated polyethersulfone, and polyvinylidene fluoride-grafted polyacrylic acid.

[0033] Preferably, the hydrophobic substance is selected from at least one of fluorosilane polymers, polyvinylidene fluoride, polysulfone, polyethersulfone, polystyrene, polyolefins, polychlorotrifluoroethylene, polyvinyl chloride, alkylsilane polymers, and polydimethylsiloxane, more preferably at least one of fluorosilane polymers, polyvinylidene fluoride, and polydimethylsiloxane. The fluorosilane polymer can be obtained by condensation of substances that are easily hydrolyzed and condensed, such as trichloroalkylfluorosilane, trimethoxyalkylfluorosilane, dichloroalkylfluorosilane, and dimethoxyalkylfluorosilane.

[0034] According to the present invention, preferably, the porous membrane further includes an additive.

[0035] Preferably, the content of the additive is 0.1-20% by weight, based on the total weight of the porous membrane.

[0036] It is understood that additives can be used to assist in the formation of pores and microprotrusions, and the additives can be pore-forming agents, inorganic fillers, etc. Preferably, the additives are selected from at least one of polyvinylpyrrolidone (weight-average molecular weight can be 15000-60000 g / mol), graphene, nano-silica, α-hydrogen-ω-hydroxy poly(oxyethylene)a-poly(oxypropylene)b-poly(oxyethylene)a block copolymer (weight-average molecular weight can be 1000-7000 g / mol, for example, F127) and polyoxyethylene (weight-average molecular weight can be 20000-50000 g / mol).

[0037] In a second aspect, the present invention provides a method for preparing a porous membrane with different surface wettability, the method comprising: using a modifying liquid containing a modifying substance to modify and atomize the framework of the porous membrane, so that the framework is loaded with a modifying substance with opposite wettability to the framework, thereby obtaining the porous membrane.

[0038] The modified atomization time is 1-80 seconds; relative to 1m 2 The porous membrane has a droplet consumption rate of 0.5-200 g·h. -1 .

[0039] The inventors of this invention discovered in their research that using a modified liquid to modify and atomize the framework allows the modified material to be uniformly distributed on the porous membrane framework, thus minimizing performance differences across the membrane. When the modification atomization time and droplet consumption range described above are met, a suitable loading area of ​​the modified material on the framework can be ensured, resulting in better performance when the porous membrane is used for water collection.

[0040] Furthermore, the processes for artificially preparing structures with differential surface wettability often employ techniques such as electrochemical etching, photolithography, and photografting. However, these techniques rely on expensive equipment, resulting in high equipment costs, cumbersome procedures, and demanding skilled operators. The method provided by this invention, on the other hand, enables the production of materials with highly efficient water or fog collection capabilities while maintaining a simple process and low cost.

[0041] According to the present invention, preferably, the modified atomization time is 3-40 s; relative to 1 m 2 The porous membrane has a droplet consumption rate of 2-100 g·h. -1 When the above range is met, the loading area of ​​the modified material can be 40-60% based on the area of ​​the porous membrane. The loading area of ​​the modified material is more suitable, and a better water collection effect can be obtained.

[0042] According to the present invention, preferably, the droplet size of the modified atomized liquid is 0.5-48 μm, thus enabling the distribution particle size of the modified material to be 0.5-50 μm. More preferably, the droplet size of the modified atomized liquid is 3-28 μm, and when the above range is satisfied, the distribution particle size of the modified material can be 3-30 μm. It is understood that the size of the droplets sprayed by the atomizing device is not a fixed value, but a range. The inventors of the present invention have further discovered in their research that when the range described above is satisfied, it is possible to further ensure that the distribution particle size of the modified material is within a suitable range and to fully expose the modified material, thereby obtaining a better water collection effect.

[0043] According to the present invention, preferably, the method further includes: coating a substrate with a hydrophilic or hydrophobic substance solution as a casting solution, pre-atomizing the substrate coated with the casting solution with water or alcohol as an atomizing liquid, and placing the pre-atomized product in a coagulation bath to remove the solvent introduced by the casting solution, thereby obtaining the framework of a porous membrane.

[0044] The substrate can be a commonly used substrate in casting, such as copper mesh, non-woven fabric, and glass plate. The mesh count of the copper mesh can be 150-300 mesh.

[0045] It is understood that a certain coating thickness can be set when coating the casting solution, but the thickness of the porous membrane obtained after preparation is generally about 20-150 μm lower than the thickness set during coating. According to the present invention, preferably, the coating results in a porous membrane thickness of 20-350 μm, more preferably 80-220 μm. It is understood that the thickness of the porous membrane does not include the thickness of the substrate.

[0046] The coating speed is not particularly limited, for example, it can be 0.5-10 m / min. The specific coating operation method is also not particularly limited, for example, a doctor blade can be used for coating.

[0047] When water or alcohol is used as the atomizing fluid, the solvent in the atomizing fluid and the casting solution generally have better miscibility, enabling the solvent to be initially extracted from the casting solution. During the extraction process, a porous structure can be formed on the membrane. Preferably, the pre-atomization time is 20-50 seconds; relative to 1m 2 The porous membrane has a droplet consumption rate of 3-40 g·h during pre-atomization. -1 The droplet size is 3-28 μm. The inventors of this invention have discovered that when the above range, especially the time range, is met, it is possible to further ensure the formation of a uniform porous structure on the membrane.

[0048] During pre-atomization, the non-solvent (atomizing liquid) slowly enters the casting solution. The solvent is initially extracted from the casting solution, but it is not completely extracted or separated from the membrane. The coagulation bath refers to placing the membrane in a liquid with strong miscibility with the solvent, allowing for thorough solvent extraction and more complete separation between the solvent and the membrane, resulting in membrane solidification. This process also forms porous structures and microprotrusions on the membrane. The liquid is typically water. For example, the pre-atomized product can be immersed in water to obtain the framework of a porous membrane.

[0049] Among them, the equipment for pre-atomization and modified atomization is not particularly restricted, and high-pressure airflow atomization equipment, ultrasonic atomization equipment, etc. can be used.

[0050] Among them, the spray pressure and inlet air temperature of pre-atomization and modified atomization are not particularly limited. The spray pressure can be 5-60 bar and the inlet air temperature can be 20-80℃.

[0051] According to the present invention, preferably, the weight-average molecular weight of the hydrophilic substance is 10,000-500,000 g / mol.

[0052] According to the present invention, preferably, the weight-average molecular weight of the hydrophobic substance is 10,000-800,000 g / mol.

[0053] According to the present invention, preferably, the hydrophilic substance is selected from at least one of polyacrylonitrile, sulfonated polyethersulfone, polyvinylidene fluoride-grafted polyacrylic acid, polyvinyl alcohol, cellulose acetate, polydopamine, polyacrylic acid, polymaleic anhydride, and polyamide, and more preferably from at least one of polyacrylonitrile, sulfonated polyethersulfone, and polyvinylidene fluoride-grafted polyacrylic acid. Some substances, such as dopamine, can undergo self-polymerization in an alkaline solution to obtain polydopamine. During preparation, dopamine can be directly dissolved in an alkaline solution to obtain polydopamine through self-polymerization. Other similar substances can also be obtained by monomer self-polymerization to obtain the corresponding polymers.

[0054] According to the present invention, preferably, the hydrophobic substance is selected from at least one of fluorosilane polymers, polyvinylidene fluoride, polysulfone, polyethersulfone, polystyrene, polyolefins, polychlorotrifluoroethylene, polyvinyl chloride, alkylsilane polymers and polydimethylsiloxane, more preferably at least one of fluorosilane polymers, polyvinylidene fluoride and polydimethylsiloxane.

[0055] According to the present invention, preferably, the concentration of hydrophilic or hydrophobic substances in the casting solution is 5-28 wt%, more preferably 8-20 wt%. When the above range is met, the casting solution has a suitable viscosity, which is more conducive to film formation and obtaining a suitable pore structure. When preparing the casting solution, it can be heated to 50-80°C to better dissolve the solute. For substances that obtain corresponding polymers through monomer self-polymerization, since the mass of the polymer formed after self-polymerization is basically not different from the mass of the monomer before self-polymerization, it is sufficient to ensure that the monomer concentration is within the above range during preparation.

[0056] According to the present invention, preferably, the concentration of the modified substance in the modified liquid is 0.05-4 wt%, more preferably 0.1-2 wt%.

[0057] According to the present invention, preferably, the casting solution further contains additives.

[0058] Preferably, the concentration of the additives in the casting solution is 0.5-15 wt%.

[0059] Preferably, the additive is selected from at least one of polyvinylpyrrolidone, graphene, nano-silica, α-hydro-ω-hydroxy poly(oxyethylene)a-poly(oxypropylene)b-poly(oxyethylene)a block copolymer (such as F127) and polyoxyethylene.

[0060] The inventors of this invention also discovered in their research that using pre-atomization in conjunction with additives can collectively form suitable pores and micro-protrusions on the membrane, thereby giving the porous membrane better water collection and mist collection effects. Since the additives in the casting solution are generally dispersed relatively uniformly, they are uniformly dispersed inside the membrane during film formation, just like the film-forming polymer. If pre-atomization or a coagulation bath is performed, some of the additives that help form the pores and micro-protrusions will leave the membrane. Therefore, even when additives are present in the casting solution, the additives will not affect the accuracy of the measurement of the loaded area of ​​the modified material according to the aforementioned method.

[0061] According to the present invention, preferably, the solvents of the casting solution and the modification solution are each independently selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, ethanol, water, acetone and toluene.

[0062] According to the present invention, the method further includes drying the modified product.

[0063] Preferably, the drying temperature is 23-28°C. Drying can be carried out by allowing the air to stand still.

[0064] Preferably, the drying time is 0.5-10 hours.

[0065] Thirdly, the present invention provides a surface wettability differential film prepared by the method described above.

[0066] Fourthly, the present invention provides the application of the surface wettability difference membrane described in the first or third aspect in water collection or fog collection.

[0067] According to a particularly preferred embodiment of the present invention, a porous membrane is prepared according to the following method:

[0068] Take polyvinylidene fluoride-grafted polyacrylic acid (weight average molecular weight of 200,000-300,000 g / mol), use N,N-dimethylformamide as solvent, and prepare a casting solution with a concentration of 13-18 wt% of polyvinylidene fluoride-grafted polyacrylic acid at 50-58℃. Apply the casting solution evenly to the nonwoven fabric with a doctor blade, so that the thickness of the final film is about 90-100 μm.

[0069] Then, using an ultrasonic atomization device with water as the atomizing liquid, the substrate coated with the casting solution was pre-atomized for 22-28 seconds, relative to 1m. 2The porous membrane has a droplet consumption rate of 17-20 g / h and a droplet size of 9-23 μm during pre-atomization.

[0070] The pre-atomized product is then immersed in deionized water for solidification to obtain the framework of the porous membrane.

[0071] An ethanol solution of polydimethylsiloxane (polydimethylsiloxane concentration of 0.1-0.3 wt%) was prepared as the modification solution. The modification solution was atomized onto the porous membrane framework using an ultrasonic atomization device; this modification atomization was performed for 5-10 seconds, relative to 1 m... 2 The porous membrane has a droplet consumption rate of 8-15 g / h and a droplet size of 15-22 μm.

[0072] The modified atomized product was placed in air at 25-27°C and left to stand for 1-2.5 hours to obtain the porous membrane with different surface wettability.

[0073] The present invention will be described in detail below through embodiments. In the following embodiments,

[0074] 200# copper wire mesh, which is a copper wire mesh with a mesh count of 200;

[0075] The ultrasonic atomizing equipment, model HQ-JS130H, was purchased from Zhongshan Haoqi Electric Co., Ltd.

[0076] Polyacrylonitrile, with a weight-average molecular weight of 75,000 g / mol;

[0077] Polyvinylidene fluoride, with a weight-average molecular weight of 350,000 g / mol;

[0078] Polydimethylsiloxane, with a weight-average molecular weight of 40,000 g / mol.

[0079] Example 1

[0080] Polyacrylonitrile was used as a solvent, and a casting solution with a polyacrylonitrile concentration of 8 wt% and a polyoxyethylene concentration of 0.5 wt% was prepared at 60 °C. The casting solution was then uniformly coated onto a 200# copper grid using a doctor blade (coating speed of 10 m / min) to achieve a final film thickness of approximately 180 μm.

[0081] Then, using an ultrasonic atomization device with water as the atomizing liquid, the substrate coated with the casting solution was pre-atomized for 30 seconds, relative to 1m. 2 The porous membrane has a droplet consumption rate of 15 g / h and a droplet size of 5-15 μm during pre-atomization.

[0082] The pre-atomized product is then immersed in deionized water for solidification to obtain the framework of the porous membrane.

[0083] A methylpyrrolidone solution of polyvinylidene fluoride (PVC) with a concentration of 0.5 wt% was prepared as the modifying solution. The modifying solution was atomized onto the porous membrane framework using an ultrasonic atomizing device; this modification atomization was performed for 3 seconds, relative to 1 m... 2 The porous membrane had a droplet consumption rate of 2 g / h and a droplet size of 8-13 μm. The inlet air temperature for pre-atomization and modified atomization was 20 °C, and the spray pressure was 5 bar.

[0084] The modified atomized product was placed in air at 25°C and allowed to stand for 0.5 hours to obtain the porous membrane with different surface wettability.

[0085] Example 2

[0086] Polyvinylidene fluoride (PVDF) was used as a solvent, and a casting solution with a PVDF concentration of 18 wt% and a polyoxyethylene concentration of 0.5 wt% was prepared at 80 °C. The casting solution was then uniformly coated onto a glass plate using a doctor blade (coating speed of 8 m / min) to achieve a final film thickness of approximately 220 μm.

[0087] Then, a high-pressure atomization device was used, with water as the atomizing liquid, to pre-atomize the substrate coated with the casting solution. The pre-atomization time was 40 seconds, relative to 1m. 2 The porous membrane has a droplet consumption rate of 13 g / h during pre-atomization, and the droplet size is 4-19 μm.

[0088] The pre-atomized product is then immersed in deionized water for solidification to obtain the framework of the porous membrane.

[0089] A polyacrylonitrile N,N-dimethylformamide solution (polyacrylonitrile concentration 2 wt%) was prepared as the modification solution. The modification solution was atomized onto the porous membrane framework using an ultrasonic atomization device, i.e., modification atomization was performed. The modification atomization time was 3 seconds, relative to 1 m... 2 The porous membrane had a droplet consumption rate of 13 g / h and a droplet size of 3-11 μm. The inlet air temperature for both pre-atomization and modified atomization was 60 °C, and the spray pressure was 30 bar.

[0090] The modified atomized product was placed in air at 28°C and left to stand for 3 hours to obtain the porous membrane with different surface wettability.

[0091] Example 3

[0092] Sulfonated polyethersulfone (weight-average molecular weight of 90,000 g / mol) and polyvinylpyrrolidone (as an auxiliary agent, weight-average molecular weight of 40,000 g / mol) were used as solvents. At 60°C, a casting solution with a sulfonated polyethersulfone concentration of 10 wt% and a polyvinylpyrrolidone concentration of 10 wt% was prepared. The casting solution was then uniformly coated onto a nonwoven fabric using a doctor blade (coating speed of 10 m / min). The coating resulted in a final film thickness of approximately 120 μm.

[0093] Then, using an ultrasonic atomization device with water as the atomizing liquid, the substrate coated with the casting solution was pre-atomized for 20 seconds, relative to 1m. 2 The porous membrane has a droplet consumption rate of 40 g / h and a droplet size of 6-15 μm during pre-atomization.

[0094] The pre-atomized product is then immersed in deionized water for solidification to obtain the framework of the porous membrane.

[0095] An ethanol solution of polydimethylsiloxane (polydimethylsiloxane concentration 1 wt%) was prepared as the modification solution. The modification solution was atomized onto the porous membrane framework using an ultrasonic atomization device; this modification atomization was performed for 20 seconds, relative to 1 m... 2 The porous membrane has a droplet consumption rate of 80 g / h and a droplet size of 6-15 μm.

[0096] The modified atomized product was placed in air at 23°C and left to stand for 10 hours to obtain the porous membrane with different surface wettability.

[0097] Example 4

[0098] Polyacrylonitrile and polyvinylpyrrolidone (as an auxiliary agent with a weight-average molecular weight of 40,000 g / mol) were used as solvents. At 50 °C, a casting solution with a polyacrylonitrile concentration of 8 wt% and a polyvinylpyrrolidone concentration of 10 wt% was prepared. The casting solution was then uniformly coated onto a nonwoven fabric using a doctor blade (coating speed of 3 m / min) to achieve a final film thickness of approximately 80 μm.

[0099] Then, using an ultrasonic atomization device with water as the atomizing liquid, the substrate coated with the casting solution was pre-atomized for 40 seconds, relative to 1m. 2 The porous membrane has a droplet consumption rate of 20 g / h during pre-atomization, and the droplet size is 8-14 μm.

[0100] The pre-atomized product is then immersed in deionized water for solidification to obtain the framework of the porous membrane.

[0101] An ethanol solution of polydimethylsiloxane (0.1 wt% polydimethylsiloxane concentration) was prepared as the modification solution. The modification solution was atomized onto the porous membrane framework using an ultrasonic atomization device; this modification atomization was performed for 70 seconds, relative to 1 m... 2 The porous membrane has a droplet consumption rate of 16 g / h and a droplet size of 8-14 μm.

[0102] The modified atomized product was placed in air at 25°C and left to stand for 3 hours to obtain the porous membrane with different surface wettability.

[0103] Example 5

[0104] Polyvinylidene fluoride-grafted polyacrylic acid (weight average molecular weight of 230,000 g / mol) was used as a solvent. At 50°C, a casting solution with a concentration of 15 wt% was prepared. The casting solution was then uniformly coated onto a nonwoven fabric using a doctor blade (coating speed of 9 m / min). The coating resulted in a final film thickness of approximately 90 μm.

[0105] Then, using an ultrasonic atomization device with water as the atomizing liquid, the substrate coated with the casting solution was pre-atomized for 25 seconds, relative to 1m. 2 The porous membrane has a droplet consumption rate of 18 g / h and a droplet size of 9-23 μm during pre-atomization.

[0106] The pre-atomized product is then immersed in deionized water for solidification to obtain the framework of the porous membrane.

[0107] An ethanol solution of polydimethylsiloxane (0.1 wt% polydimethylsiloxane concentration) was prepared as the modification solution. The modification solution was atomized onto the porous membrane framework using an ultrasonic atomization device; this modification atomization was performed for 5 seconds, relative to a 1m... 2 The porous membrane has a droplet consumption rate of 11 g / h and a droplet size of 15-22 μm.

[0108] The modified atomized product was placed in air at 25°C and left to stand for 1 hour to obtain the porous membrane with different surface wettability.

[0109] Example 6

[0110] Porous membranes were prepared according to the method of Example 1, except that the modified atomization time was 1 second; relative to 1m 2 The porous membrane has a droplet consumption rate of 0.5 g / h.

[0111] Example 7

[0112] Porous membranes were prepared according to the method of Example 1, except that the modified atomization time was 80 s; relative to 1 m 2 The porous membrane has a droplet consumption rate of 200 g / h.

[0113] Example 8

[0114] A porous membrane was prepared according to the method of Example 1, except that the coating was used to make the thickness of the final membrane approximately 30 μm and the concentration of the hydrophilic substance in the casting solution was 5 wt%.

[0115] Example 9

[0116] The porous membrane was prepared according to the method of Example 1, except that the coating resulted in a final membrane thickness of approximately 325 μm; the concentration of the hydrophilic substance in the casting solution was 28 wt%.

[0117] Example 10

[0118] Porous membranes were prepared according to the method of Example 1, except that the casting solution did not contain any additives.

[0119] Example 11

[0120] The porous membrane was prepared according to the method of Example 1, except that pre-atomization was not performed, and the substrate coated with casting solution was directly placed in the coagulation bath.

[0121] Comparative Example 1

[0122] The method is the same as in Example 1, except that the porous membrane skeleton obtained after the coagulation bath is used directly as the product without further processing.

[0123] Test case

[0124] The porous membranes prepared in Examples 1-11 and Comparative Example 1 were subjected to tests on the loaded area of ​​the modified material, the particle size distribution of the modified material, the average pore size of the porous membrane, the thickness of the porous membrane, and the water collection. The results are shown in Tables 1-2.

[0125] The presence of microprotrusions on the membrane was observed using scanning electron microscopy (SEM), and the diameter at the point of maximum cross-sectional area of ​​the microprotrusions was measured. SEM images of the porous membranes from Examples 1, 4, and 11 are shown below. Figure 1-3 As shown in the figure. The method for testing the loading area of ​​the modified material is as follows: the optical photograph of the porous membrane after it has been immersed in water is processed using Photoshop software. Since the hydrophobic part appears silver and the hydrophilic part appears gray in the photograph, the pixels of the color corresponding to the modified material are obtained, and the proportion of the modified material to the total number of pixels is calculated, which is the loading area of ​​the modified material.

[0126] The particle size distribution of the modified material was tested using a Bettersize2000S spray particle size analyzer from Dandong Bettersize.

[0127] The average pore size of the porous membrane was measured using a PSMA-30 instrument purchased from Nanjing Gaoqian Functional Materials Technology Co., Ltd.

[0128] The thickness of the porous membrane was measured using a Q / ILBN2-2006 benchtop thin film thickness gauge purchased from Shanghai Precision Instruments Co., Ltd.

[0129] The method for testing water collection capacity is as follows: cut the prepared membrane sample into 2×2cm pieces. 2 A square sample is fixed to a support. The membrane sample is placed vertically to the ground, and a container for collecting water droplets is placed under the support, maintaining a distance of 20 cm from the nozzle of the nebulizer. The nebulizer is then turned on to collect water droplets. After 20 minutes, the weight of the water collected in the container is measured. The formula for calculating the water collection volume η is η = m / st, where s and t are the actual area of ​​the sample and the water collection time, respectively, and m is the mass of water collected at time t.

[0130] Table 1

[0131]

[0132] Table 2

[0133]

[0134] As can be seen from the results in Table 1, Examples 1-11 using the technical solution of this invention achieve better water collection results. In particular, Examples 1-5 show higher water collection capacity and better results. Combined with... Figure 1-3 It can also be seen that when the porous membrane has micro-protrusions, the water collection performance of the membrane can be further improved.

[0135] Furthermore, the method of this invention does not require expensive equipment or complex processes when preparing porous membranes, is suitable for a variety of raw materials, is easy to prepare on a large scale, has low production costs, is conducive to practical application production, and has good prospects for industrialization.

[0136] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing porous membranes with differences in surface wettability, characterized in that, The method includes: using a modifying liquid containing a modifying substance to modify and atomize the framework of a porous membrane, so that the framework is loaded with a modifying substance with the opposite wettability to the framework, thereby obtaining the porous membrane; The modified atomization time is 1-80 seconds; relative to 1m 2 The porous membrane has a droplet consumption rate of 0.5-200 g·h. -1 ; The skeleton is composed of one of hydrophilic and hydrophobic substances; The hydrophilic substance is selected from at least one of polyacrylonitrile, sulfonated polyethersulfone, polyvinylidene fluoride-grafted polyacrylic acid, polyvinyl alcohol, cellulose acetate, polydopamine, polyacrylic acid, polymaleic anhydride and polyamide. The hydrophobic material is selected from at least one of fluorosilane polymers, polyvinylidene fluoride, polysulfone, polyethersulfone, polystyrene, polyolefins, polychlorotrifluoroethylene, polyvinyl chloride, alkylsilane polymers, and polydimethylsiloxane. The method further includes: coating a substrate with a hydrophilic or hydrophobic solution as a casting solution, using water or alcohol as an atomizing liquid to pre-atomize the substrate coated with the casting solution, and placing the pre-atomized product in a coagulation bath to remove the solvent introduced by the casting solution, thereby obtaining the framework of a porous membrane.

2. The method according to claim 1, wherein, The modified atomization time is 3-40 seconds; relative to 1m 2 The porous membrane has a droplet consumption rate of 2-100 g·h. -1 ; And / or, the modified atomized droplet size is 0.5-48 μm.

3. The method according to claim 2, wherein, The modified atomized droplet size is 3-28 μm.

4. The method according to claim 1, wherein, The coating process results in a porous membrane thickness of 20-350 μm.

5. The method according to claim 4, wherein, The coating results in a porous membrane thickness of 80-220 μm.

6. The method according to claim 1, wherein, The pre-atomization time is 20-50 seconds; relative to 1m 2 The porous membrane has a droplet consumption rate of 3-40 g·h during pre-atomization. -1 The droplet size is 3-28 μm.

7. The method according to claim 1, wherein, The weight-average molecular weight of the hydrophilic substance is 10,000-500,000 g / mol.

8. The method according to claim 1, wherein, The weight-average molecular weight of the hydrophobic substance is 10,000-800,000 g / mol.

9. The method according to claim 1, wherein, The concentration of hydrophilic or hydrophobic substances in the casting solution is 5-28 wt%.

10. The method according to claim 9, wherein, The concentration of hydrophilic or hydrophobic substances in the casting solution is 8-20 wt%.

11. The method according to claim 1, wherein, The concentration of the modified substance in the modified liquid is 0.05-4 wt%.

12. The method according to claim 11, wherein, The concentration of the modified substance in the modified liquid is 0.1-2 wt%.

13. The method according to claim 1, wherein, The casting solution also contains additives.

14. The method according to claim 13, wherein, The concentration of additives in the casting solution is 0.5-15 wt%.

15. The method according to claim 13, wherein, The additive is selected from at least one of polyvinylpyrrolidone, graphene, nano-silica, α-hydro-ω-hydroxy poly(oxyethylene)a-poly(oxypropylene)b-poly(oxyethylene)a block copolymer and polyoxyethylene.

16. The method according to claim 1, wherein, The solvents of the casting solution and the modification solution are each independently selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, ethanol, water, acetone and toluene.

17. The method according to claim 1, wherein, The method further includes drying the modified product.

18. The method according to claim 17, wherein, The drying temperature is 23-28℃.

19. The method according to claim 17, wherein, The drying time is 0.5-10 hours.

20. The porous membrane prepared by the method according to any one of claims 1-19.

21. The application of the porous membrane according to claim 20 in water collection or mist collection.

Images