Tough underwater superoleophobic gel composite coating and preparation method thereof

Abstract

The invention discloses a tough underwater superoleophobic gel composite coating and a preparation method thereof.The preparation method specifically comprises the following steps that 1, a base material is soaked in a mixed solution of tannic acid and 3-aminopropyltriethoxysilane, after a period of time, the base material is taken out and soaked in a ferric chloride solution, and a nano-particle modified filter screen is obtained after drying; (2) loading the gel precursor solution on a nanoparticle modified filter screen through a dip-coating method, and preparing a gel composite filter screen under ultraviolet initiation; and (3) soaking the gel composite filter screen in a sodium citrate aqueous solution, and taking out the gel composite filter screen to obtain the tough underwater super-oleophobic gel composite coating modified fishing net. According to the method, the tough underwater super-oleophobic gel composite coating modified fishing net is prepared by adopting an impregnation method and ultraviolet initiation, the preparation process is simple, and the prepared gel composite coating has excellent oil stain resistance, mechanical stability and chemical stability and can be applied to crude oil adhesion prevention and oil-water separation of industrial oily wastewater.

Description

Technical Field

[0001] The invention belongs to the field of polymer functional materials and polymer coatings, and in particular relates to a method for preparing a tough underwater super-oleophobic gel composite coating. Background Art

[0002] Oil is easy to transport and has high energy density, so it is the most important transportation driving energy and is indispensable in modern society. However, the high viscosity of crude oil causes great troubles in the transportation and processing of crude oil. And with the continuous growth of global energy demand, the scale of offshore oil extraction and transportation continues to expand, and oil spills occur frequently, posing a serious threat to the marine ecological environment. And the highly adhesive crude oil will contaminate oil spill recovery equipment, such as oil trawls, skimmers, etc., making them difficult to clean. In addition, the oily wastewater generated by the large-scale use of crude oil in industry and its adverse impact on the environment have become global problems that need to be solved urgently.

[0003] Hydrophilic gels can tightly bind water molecules through electrostatic interactions or hydrogen bonds, and the stable hydration layer formed around the gel establishes a barrier that repels pollutants from adhering. Therefore, taking advantage of this property, a large number of hydrophilic gels have been used in anti-oil design. However, although hydrophilic gel coatings can effectively prevent oil adhesion, in practical applications, due to their high water content, they have poor mechanical and chemical resistance and are not suitable for the intended application. Summary of the invention

[0004] In view of the problems of poor durability and poor bonding strength of gel coating, the present invention proposes to use tannic acid / silane coupling agent as the base adhesion layer, polyvinyl alcohol and covalently cross-linked [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide double network gel as the top layer, and introduces salting out method to successfully prepare a tough underwater super oleophobic gel composite coating. The constructed gel composite coating has excellent anti-oil performance, excellent toughness and wear resistance, and has great application potential in the field of oil-water separation.

[0005] The purpose of the present invention is to provide a method for preparing a tough underwater super-oleophobic gel composite coating, which adopts a dip coating method to prepare an underwater super-oleophobic gel composite coating with excellent anti-oil performance and mechanical stability, thereby solving the problem of poor mechanical and chemical tolerance of the hydrophilic gel coating. The prepared gel composite coating is non-polluting and non-toxic to the environment.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: A method for preparing a tough underwater superoleophobic gel composite coating comprises the following steps: (1) Dissolve tris(hydroxymethyl)aminomethane hydrochloride) powder in deionized water and adjust the pH value with KOH, which is referred to as reaction solution 1; (2) Dissolve tannic acid powder in reaction solution 1, and mix evenly under stirring, denoted as reaction solution 2; (3) Mix silane coupling agent and ethanol, and mix evenly under ultrasonic action, denoted as reaction solution 3; (4) Dissolve ferric chloride powder in deionized water, and mix evenly under stirring, denoted as reaction solution 4; (5) Dissolve polyvinyl alcohol powder in deionized water, heat and stir to mix evenly, denoted as reaction solution 5; (6) Weigh a certain mass of [2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, and N,N'-methylenebisacrylamide and dissolve them in reaction solution 5, heat and stir to mix evenly, denoted as reaction solution 6; (7) Dissolve sodium citrate powder in deionized water, and mix evenly under stirring, denoted as reaction solution 7; (8) Mix reaction solution 2 and reaction solution 3 in proportion and mix evenly under stirring, denoted as reaction solution 8; (9) Put the cleaned fishing net into reaction solution 8 to perform surface modification on the fishing net; (10) Immerse the fishing net obtained in step (9) in reaction solution 4, take it out and dry it; immerse it in reaction solution 6, take it out and form a gel coating under photoinitiation; (11) Immerse the gel composite fishing net obtained in step (10) in reaction solution 7 for a certain period of time, take it out to obtain a composite fishing net with a tough underwater superoleophobic gel composite coating.

[0007] Further, in the reaction solution 1 described in step (1), the content of tris(hydroxymethyl)aminomethane hydrochloride accounts for 0.5 wt%-1 wt% of the solution.

[0008] Further, in the reaction solution 2 described in step (2), the content of tannic acid accounts for 0.5 wt%-1 wt% of the solution.

[0009] Further, in the reaction solution 3 described in step (3), the content of silane coupling agent accounts for 0.5 wt%-2 wt% of the solution. Further, in the reaction solution 4 described in step (4), the content of ferric chloride accounts for 0.5 wt%-2 wt% of the solution.

[0010] Further, in the reaction solution 5 described in step (5), the content of polyvinyl alcohol accounts for 5 wt%-20 wt% of the solution.

[0011] Further, in the reaction solution 6 described in step (6), the content of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide in the solution is 5 wt% - 20 wt%, the content of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone in the solution is 0.1 wt% - 1 wt%, and the content of N,N'-methylenebisacrylamide in the solution is 0.1 wt% - 1 wt%.

[0012] Further, in the reaction solution 7 described in step (7), the content of sodium citrate in the solution is 10 wt% - 30 wt%.

[0013] Further, in the reaction solution 8 described in step (8), the volume ratio of the reaction solution 2 to the reaction solution 3 is 5:1.

[0014] Further, the specific operation of the surface modification in step (9) is impregnation at room temperature for 12 - 48 h.

[0015] Further, in step (10), the immersion time in the reaction solution 4 is 0.5 - 5 h, the drying temperature is 60 °C, the drying time is 6 h, the immersion time in the reaction solution 6 is 10 - 50 s, and the photoinitiation operation is ultraviolet lamp irradiation for 2 - 8 h.

[0016] Further, in step (11), the immersion time in the reaction solution 7 is 24 - 72 h.

[0017] The beneficial effects of the present invention are as follows: (1) The dip-coating method and ultraviolet light initiation process used in the preparation process are simple and convenient to operate, without the need for toxic reagents, solving the problems of complex preparation processes, high energy consumption, environmental harm, etc. in many traditional methods.

[0018] (2) Through a simple dip-coating method, tannic acid-3-aminopropyltriethoxysilane-iron ion nanoparticles with rich active sites and polyvinyl alcohol-[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide are assembled in layers, enabling the wettability of the substrate material to change, having underwater superoleophobic properties. And salting-out treatment greatly improves the mechanical properties of the gel in a seawater environment. This is because the salting-out treatment process effectively enhances the structural stability of the gel in a marine environment by regulating the compactness and cross-linking uniformity of the gel network structure.

[0019] (3) The prepared coating has self-cleaning properties, enabling crude oil droplets to spontaneously detach underwater. And it has long-term stability. After tests such as 5000 times of cotton cloth friction, 100 times of tape adhesion, and extreme environments (pH = 1 - 13), it shows excellent anti-oil adhesion performance. Description of the Drawings

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings. Among them, Figure 1 Shows the dynamic process of contact - detachment of a tough underwater super - oleophobic gel coating of Example 1 of the present invention with an underwater oil droplet (dichloromethane).

[0021] Figure 2 Shows the mechanical property test results of the tough underwater super - oleophobic gel coating of Example 1 of the present invention and Comparative Example 1 after 48 h of seawater immersion.

[0022] Figure 3 Shows the underwater oil contact angle test of the tough underwater super - oleophobic gel coating of Example 1 of the present invention at different modification stages.

[0023] Figure 4 Shows the lap - shear strength test of the gel coating of the present invention on a polyethylene substrate (Comparative Example 2) and a hydrophilic nanoparticle - modified polyethylene substrate (Example 1).

[0024] Figure 5 Shows the dynamic process of underwater self - cleaning of the tough underwater super - oleophobic gel coating (b) of Example 1 of the present invention and a blank fishing net (a).

[0025] Figure 6 Shows the underwater oil contact angle of the tough underwater super - oleophobic gel coating (a) of Example 1 of the present invention at different friction times (artificial seawater immersion for 24 h), (b) optical micrographs of the modified fishing net before and after wear test, (c) multi - oil - droplet (dichloromethane) spraying experiment (sample after wear test).

[0026] Figure 7 Shows the (a) separation flux and (b) separation efficiency of the tough underwater super - oleophobic gel coating of Example 1 of the present invention for toluene / water emulsion (v: v = 1:99) cycle, (c) optical pictures and optical micrographs of the oil - in - water emulsion and filtrate.

[0027] Figure 8 Are (a) optical image of solid crude oil; (b) optical images of the modified filter screen of the tough underwater super - oleophobic gel coating of Example 1 of the present invention before and after recovering solid crude oil; (c) continuous optical images during the process of recovering solid crude oil. Detailed implementation manners

[0028] A preparation method of a tough underwater super - oleophobic gel composite coating, comprising the following steps: (1) Preparation of hydrophilic nanoparticle coating Immerse the substrate in a mixed solution of tannic acid and 3-aminopropyltriethoxysilane. After a certain period of time, take it out and immerse it in a ferric chloride solution. After drying, a preliminarily hydrophilic modified filter screen is obtained. (2) Preparation of polyvinyl alcohol-poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide double network gel coating Load the gel precursor solution onto the hydrophilic modified filter screen by dip coating method, and obtain a gel composite filter screen under ultraviolet initiation. (3) Salting-out treatment Immerse the gel composite filter screen in an aqueous solution of sodium citrate, and a tough underwater superoleophobic gel composite coating modified filter screen can be obtained after taking it out.

[0029] Furthermore, in step (1), the specific configuration of the mixed solution of tannic acid and 3-aminopropyltriethoxysilane is as follows: 100 mL of tris(hydroxymethyl)aminomethane hydrochloride buffer solution with tannic acid content of 0.5 wt%-1 wt% and 20 mL of ethanol solution with 3-aminopropyltriethoxysilane content of 0.5 wt%-2 wt% are mixed evenly under magnetic stirring.

[0030] Furthermore, in step (1), the substrate is immersed in the solution at room temperature for 12 - 48 h.

[0031] Furthermore, in step (1), the specific configuration of the ferric chloride solution is as follows: dissolve a certain amount of ferric chloride powder in deionized water, and mix evenly under magnetic stirring to obtain a 0.5 wt%-2 wt% aqueous solution of ferric chloride. Immerse the filter screen modified by tannic acid-3-aminopropyltriethoxysilane in the ferric chloride solution for 0.5 - 5 h.

[0032] Furthermore, in step (2), the gel precursor solution is configured as follows: in 18 g of 5 wt%-20 wt% polyvinyl alcohol solution, add 5 wt%-20 wt% of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 0.1 wt%-1 wt% of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, and 0.1 wt%-1 wt% of N,N'-methylenebisacrylamide, and mix evenly under magnetic stirring at 60°C.

[0033] Furthermore, in step (2), the specific steps of the dip coating method are as follows: immerse the substrate modified by nanoparticles in the gel precursor solution for 10 - 50 s.

[0034] Further, the specific conditions for ultraviolet initiation in step (2) are as follows: the substrate loaded with the gel precursor solution is irradiated with ultraviolet light for 2 - 8 h.

[0035] Further, the specific preparation of the sodium citrate aqueous solution in step (3) is as follows: a certain amount of sodium citrate is mixed with deionized water and stirred evenly under magnetic stirring to obtain a 10 wt% - 30 wt% sodium citrate aqueous solution.

[0036] Further, the specific steps of the salting - out treatment in step (3) are as follows: the gel - composite filter is immersed in the sodium citrate aqueous solution at room temperature for 24 - 72 h. After taking it out, the modified substrate coated with a tough underwater super - oleophobic gel - composite coating can be obtained.

[0037] To make the content of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0038] Example 1 (1) Preparation of the hydrophilic nanoparticle coating First, the polyethylene fishing net is ultrasonically cleaned with industrial alcohol for 10 min and then placed in an oven at 60 °C for drying. 0.2 g of tannic acid is added to a buffer solution (Tris - HCl, pH = 8.5, 50 mL), and then 10 mL of ethanol containing 0.1 g of 3 - aminopropyltriethoxysilane is added to the tannic acid solution. The fishing net is immediately immersed in the mixture and left standing at room temperature for 24 h for surface modification. The modified fishing net is washed with distilled water and ethanol, and then immersed in a ferric chloride hexahydrate solution (5.0 mg / mL, 100 mL) at room temperature. After soaking for 1 h, it is washed with deionized water and dried in an oven at 60 °C to obtain the hydrophilic nanoparticle - modified fishing net.

[0039] (2) Preparation of the poly(vinyl alcohol) - poly[2 - (methacryloyloxy)ethyl]dimethyl - (3 - sulfopropyl) ammonium hydroxide double - network gel coating Weigh 20 g of PVA and add it to 180 mL of deionized water. Heat and stir it in a water bath (800 rpm, 80 °C) until it is completely dissolved. 2.0 g of [2 - (methacryloyloxy)ethyl]dimethyl - (3 - sulfopropyl) ammonium hydroxide, 0.040 g of 2 - hydroxy - 4' - (2 - hydroxyethoxy) - 2 - methylpropiophenone (photoinitiator), and 0.060 g of N,N' - methylenebisacrylamide (cross - linker) are successively added to 18 g of a 10 wt% PVA solution. Heat and stir it in a water bath (600 rpm, 60 °C) until it is completely dissolved. The hydrophilic nanoparticle - modified fishing net is immersed in the above - mentioned gel precursor solution for 30 s, and then transferred to a rack and irradiated with ultraviolet light (365 nm, 20 w) for 4 h.

[0040] (3) Salting-out treatment The gel composite coating modified fishing net was immersed in a 1M sodium citrate solution for 48 h.

[0041] Example 2 (1) Preparation of hydrophilic nanoparticle coating First, the polyethylene fishing net was ultrasonically cleaned with industrial alcohol for 10 min and then placed in an oven at 60 °C for drying. 0.4 g of tannic acid was added to a buffer solution (Tris-HCl, pH = 8.5, 100 mL), and then 20 mL of ethanol containing 0.2 g of 3-aminopropyltriethoxysilane was added to the tannic acid solution. The fishing net was immediately immersed in the mixture and left standing at room temperature for 24 h for surface modification. The modified fishing net was washed with distilled water and ethanol, and then immersed in a ferric chloride hexahydrate solution (5.0 mg / mL, 200 mL) at room temperature. After soaking for 1 h, it was washed with deionized water and dried in an oven at 60 °C to obtain the hydrophilic nanoparticle modified fishing net.

[0042] (2) Preparation of polyvinyl alcohol-poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide double network gel coating 40 g of PVA was weighed and added to 360 mL of deionized water, and it was stirred under water bath heating (800 rpm, 80 °C) until it was completely dissolved. 4.0 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 0.080 g of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (photoinitiator), and 0.120 g of N,N'-methylenebisacrylamide (crosslinker) were successively added to 36 g of 10 wt% PVA solution. It was stirred under water bath heating (600 rpm, 60 °C) until it was completely dissolved. The hydrophilic nanoparticle modified fishing net was immersed in the above gel precursor solution for 30 s and then transferred to a rack and irradiated with ultraviolet light (365 nm, 20 w) for 4 h.

[0043] (3) Salting-out treatment The gel composite coating modified fishing net was immersed in a 1M sodium citrate solution for 48 h.

[0044] Example 3 (1) Preparation of hydrophilic nanoparticle coating First, the polyethylene fishing net was ultrasonically cleaned with industrial alcohol for 10 min and then placed in an oven at 60 °C for drying. 0.8 g of tannic acid was added to a buffer solution (Tris-HCl, pH = 8.5, 200 mL), and then 40 mL of ethanol containing 0.4 g of 3-aminopropyltriethoxysilane was added to the tannic acid solution. The fishing net was immediately immersed in the mixture and allowed to stand at room temperature for 24 h for surface modification. The modified fishing net was washed with distilled water and ethanol, and then immersed in a ferric chloride hexahydrate solution (5.0 mg / mL, 400 mL) at room temperature. After soaking for 1 h, it was washed with deionized water and dried in an oven at 60 °C to obtain a hydrophilic nanoparticle-modified fishing net.

[0045] (2)Preparation of Polyvinyl Alcohol-Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium Hydroxide Double Network Gel Coating Weigh 20 g of PVA and add it to 180 mL of deionized water. Heat and stir in a water bath (800 rpm, 80 °C) until it is completely dissolved. 4.0 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 0.160 g of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (photoinitiator), and 0.240 g of N,N'-methylenebisacrylamide (crosslinker) were successively added to 72 g of 10 wt% PVA solution. Heat and stir in a water bath (600 rpm, 60 °C) until it is completely dissolved. The hydrophilic nanoparticle-modified fishing net was immersed in the above gel precursor solution for 30 s and then transferred to a rack and irradiated with ultraviolet light (365 nm, 20 w) for 4 h.

[0046] (3)Salting-Out Treatment The gel composite coating-modified fishing net was placed in a 1 M sodium citrate solution and soaked for 48 h.

[0047] Example 4 (1)Preparation of Hydrophilic Nanoparticle Coating First, the polyethylene fishing net was ultrasonically cleaned with industrial alcohol for 10 min and then placed in an oven at 60 °C for drying. 0.6 g of tannic acid was added to a buffer solution (Tris-HCl, pH = 8.5, 150 mL), and then 30 mL of ethanol containing 0.3 g of 3-aminopropyltriethoxysilane was added to the tannic acid solution. The fishing net was immediately immersed in the mixture and allowed to stand at room temperature for 24 h for surface modification. The modified fishing net was washed with distilled water and ethanol, and then immersed in a ferric chloride hexahydrate solution (5.0 mg / mL, 300 mL) at room temperature. After soaking for 1 h, it was washed with deionized water and dried in an oven at 60 °C to obtain a hydrophilic nanoparticle-modified fishing net.

[0048] (2)Preparation of Polyvinyl Alcohol-Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium Hydroxide Double Network Gel Coating Weigh 20 g of PVA and add it to 180 mL of deionized water. Stir it in a water bath (800 rpm, 80 °C) until it is completely dissolved. Then, add 6.0 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 0.120 g of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (photoinitiator), and 0.180 g of N,N'-methylenebisacrylamide (crosslinker) to 54 g of 10 wt% PVA solution in sequence. Stir it in a water bath (600 rpm, 60 °C) until it is completely dissolved. Immerse the hydrophilic nanoparticle-modified fishing net into the above gel precursor solution for 30 s, then transfer it to a rack and irradiate it with ultraviolet light (365 nm, 20 w) for 4 h.

[0049] (3)Salting-out Treatment Place the gel composite coating-modified fishing net in 1M sodium citrate solution and soak it for 48 h.

[0050] Comparative Example 1 (without salting-out treatment) (1)Preparation of Hydrophilic Nanoparticle Coating First, ultrasonically clean the polyethylene fishing net with industrial alcohol for 10 min, and then place it in an oven at 60 °C to dry. Add 0.2 g of tannic acid to a buffer solution (Tris-HCl, pH = 8.5, 50 mL), and then add 10 mL of ethanol containing 0.1 g of 3-aminopropyltriethoxysilane to the tannic acid solution. Immediately immerse the fishing net into the mixture and let it stand at room temperature for 24 h for surface modification. Wash the modified fishing net with distilled water and ethanol, and then immerse it in ferric chloride hexahydrate solution (5.0 mg / mL, 100 mL) at room temperature. After soaking for 1 h, wash it with deionized water and dry it in an oven at 60 °C to obtain the hydrophilic nanoparticle-modified fishing net.

[0051] (2)Preparation of Polyvinyl Alcohol-Poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium Hydroxide Double Network Gel Coating Weigh 20 g of PVA and add it to 180 mL of deionized water. Stir while heating in a water bath (800 rpm, 80 °C) until it is completely dissolved. Add 2.0 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 0.040 g of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (photoinitiator), and 0.060 g of N,N'-methylenebisacrylamide (crosslinker) to 18 g of 10 wt% PVA solution in sequence. Stir while heating in a water bath (600 rpm, 60 °C) until it is completely dissolved. Immerse the hydrophilic nanoparticle-modified fishing net in the above gel precursor solution for 30 s, then transfer it to a rack and irradiate it with ultraviolet light (365 nm, 20 w) for 4 h.

[0052] Comparative Example 2 (the polyethylene base is not modified with hydrophilic nanoparticles) (1) Preparation of polyvinyl alcohol-poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide double-network gel coating Weigh 20 g of PVA and add it to 180 mL of deionized water. Stir while heating in a water bath (800 rpm, 80 °C) until it is completely dissolved. Add 2.0 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 0.040 g of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (photoinitiator), and 0.060 g of N,N'-methylenebisacrylamide (crosslinker) to 18 g of 10 wt% PVA solution in sequence. Stir while heating in a water bath (600 rpm, 60 °C) until it is completely dissolved. Immerse the polyethylene fishing net in the above gel precursor solution for 30 s, then transfer it to a rack and irradiate it with ultraviolet light (365 nm, 20 w) for 4 h.

[0053] (2) Salting-out treatment Place the gel-coated and modified fishing net in 1 M sodium citrate solution and soak it for 48 h.

[0054] Figure 1 This is the dynamic experiment of the contact-detachment of oil droplets on the tough underwater superoleophobic gel coating of Example 1 of the present invention. As Figure 1 shown, when the droplet in the syringe descends and contacts the fishing net, the oil droplet changes from spherical to oval; after moving the syringe away from the modified fishing net, the oil droplet remains on the syringe and does not adhere to the sample surface. This phenomenon is attributed to the sufficient formation of the hydration layer, which significantly reduces the adhesion force of the oil droplet to the coating surface.

[0055] Figure 2 This is the mechanical property test of the tough underwater superoleophobic gel coating of Example 1 of the present invention and Comparative Example 1; as Figure 2As shown, the fracture strength of the sample in the seawater environment reached 0.759 MPa, which was 37.0% higher than 0.554 MPa of Comparative Example 1. To characterize the impact resistance of the material, it was calculated from the linear region of the stress-strain curve that the Young's modulus of the sample in the seawater environment reached 0.517 MPa, which was nearly 289% higher than 0.133 MPa of Comparative Example 1. The experimental results show that the salting-out treatment process effectively enhances the structural stability of the sample in the marine environment by regulating the compactness and cross-linking uniformity of the gel network structure.

[0056] Figure 3 This is the underwater oil contact angle test of the tough underwater superoleophobic gel coating at different modification stages in Example 1 of the present invention; as Figure 3 shown, the bare net could not form a stable hydration layer due to the hydrophobic property of the polyethylene material itself, resulting in the rapid spreading of dichloromethane oil droplets on its surface, and the contact angle approaching 0°. After being modified with a hydrophilic nanoparticle coating, a stable hydrophilic defense layer was formed on the surface of the fishing net, and its underwater oil contact angle was significantly increased to 128.3° ± 1.2°. This was attributed to the micro-nano rough structure formed by the organic-inorganic hybrid network in the coating and the abundant hydrophilic groups. It should be noted that the hydrophilic nanoparticles not only endow the material with underwater oleophobic properties, but also the exposed amino active sites on their surface provide an ideal reaction interface for the in-situ loading of the subsequent polyvinyl alcohol-poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide double network gel. When a polyvinyl alcohol-poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide double network gel composite coating was constructed by the step-by-step modification method, the wettability of the fishing net surface changed significantly, reaching the underwater superoleophobic state (contact angle 151.2° ± 1.1°). Particularly noteworthy is that the sample after salting-out treatment still maintains the superoleophobic property of 150.5° ± 1.0°, indicating that the modified coating has excellent salt tolerance stability, which ensures the efficient self-cleaning separation of oil droplets in the marine environment.

[0057] Figure 4 This is the lap shear strength test of the gel coating of the present invention on a polyethylene substrate (Comparative Example 2) and a hydrophilic nanoparticle-modified polyethylene substrate (Example 1); as Figure 4 shown, the polyethylene substrate modified with hydrophilic nanoparticles showed a significant interfacial enhancement effect, and its maximum shear adhesion strength with the gel coating reached 30.2 kPa, which was a 100% increase compared to 15.1 kPa of the unmodified polyethylene substrate.

[0058] Figure 5 This is the display of the underwater self-cleaning dynamic process of the tough underwater superoleophobic gel coating (b) in Example 1 of the present invention and the blank fishing net (a); as Figure 5As shown in Figure a, under standard test conditions, after the blank fishing net was contaminated with crude oil, even after 5 minutes of static immersion treatment, obvious oil stains still remained on the surface, indicating its lack of self-cleaning function. The sample, however, exhibited remarkable self-cleaning characteristics. Thanks to the strong interaction formed between the hydrophilic polymer and water molecules, the sample was able to effectively maintain a stable hydration layer structure in the wet state. When the contaminated sample was immersed in an aqueous environment, it was observed that the crude oil stains on the surface rapidly shrank and detached from the substrate surface within 50 seconds, and finally floated to the liquid surface in the form of spherical oil droplets ( Figure 5 Figure b).

[0059] Figure 6 Tough underwater superoleophobic gel coating of Example 1 of the present invention: (a) Underwater oil contact angle at different numbers of friction cycles (immersed in artificial seawater for 24 h); (b) Optical microscopic images of the modified fishing net before and after wear test; (c) Multi-oil-drop (dichloromethane) spraying experiment (sample after wear test). As Figure 6 shown in Figure a, after 4500 cycles of friction, the coating still maintained excellent underwater superoleophobic properties, and its contact angle was stable at 155.7° ± 4.7°. When the number of friction cycles increased to 5000, the contact angle decreased significantly to 147.9° ± 8.3°, indicating that the material first lost its underwater superoleophobic performance (contact angle < 150°). Through friction morphology analysis ( Figure 6 Figure b), it was found that only local damage occurred on the film layer after 5000 times of friction, and the mass wear rate was as low as 4.61%, which explained the fundamental reason why the sample still maintained high oleophobicity before the critical number of friction cycles. It should be noted that even after the superoleophobicity failed, the friction-treated sample still exhibited good oil-based liquid repellency: in the underwater environment, dichloromethane droplets remained approximately spherical after contacting the surface and could quickly roll off the substrate surface under the action of gravity.

[0060] Figure 7 Tough underwater superoleophobic gel coating of Example 1 of the present invention for toluene / water emulsion (v:v = 1:99) cycle: (a) Separation flux and (b) Separation efficiency, (c) Optical pictures and optical microscopic images of oil-in-water emulsion and filtrate; As Figure 7 shown in Figure a, the continuous 10-cycle test data showed that under an operating pressure of 0.65 bar, the separation flux of the membrane always remained in the range of (1287 ± 72) L·m⁻²·h⁻¹·bar⁻¹, demonstrating excellent flux stability. The flux fluctuation phenomenon was mainly attributed to the microstructure reorganization of the membrane filtration sites and the instrument reset deviation during the cycle cleaning process. By quantitatively analyzing the filtrate components with a UV spectrophotometer, the separation efficiency of each cycle was measured to be always higher than 99.2% (n = 10), confirming that the composite membrane still maintained excellent emulsion separation performance after multiple uses ( Figure 7 Figure b). FromFigure 7 As shown in the optical photo in c, the letters on the background paper cannot be seen through the unseparated water-in-oil emulsion, but the English on the background paper can be seen through the separated filtrate. In the microscope image, there is a clear difference before and after the emulsion is separated. The optical microscope image of the original emulsion shows a large number of tiny emulsified oil droplets, while the filtrate can hardly see the existence of emulsified oil droplets. The clear filtrate in the optical photo and the inability to observe obvious emulsion droplets under the microscope both confirm that the emulsion has been successfully separated.

[0061] Figure 8 (a) Optical image of solid crude oil; (b) Optical image of the tough underwater superoleophobic gel coating modified filter of Example 1 of the present invention before and after recovering solid crude oil; (c) Continuous optical image of the process of recovering solid crude oil. Figure 8 Figure a shows that solid crude oil can stick to the spoon tightly and not fall off. When placed on the water surface, it does not spread like liquid crude oil. The hydrophilic filter can be used to directly scoop out the solid crude oil blocks floating on the water surface. The process is simple and efficient ( Figure 8 c). Compared with traditional filters, this hydrophilic filter exhibits excellent anti-pollution performance, effectively solving the surface contamination and cleaning difficulties caused by crude oil adhesion of conventional materials. The experimental results show that after the hydrophilic treated filter is completed, it only needs a simple water rinse to achieve complete surface cleaning without crude oil residue ( Figure 8 (b)

[0062] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a tough underwater superoleophobic gel composite coating, which is mainly characterized in that the method comprises the following steps: (1) Dissolve the powder of tris(hydroxymethyl)aminomethane hydrochloride in deionized water and adjust the pH value with KOH, denoted as reaction solution 1; (2) Dissolve the powder of tannic acid in reaction solution 1 and mix evenly under stirring, denoted as reaction solution 2; (3) Mix the silane coupling agent and ethanol and mix evenly under ultrasonic action, denoted as reaction solution 3; (4) Dissolve the powder of ferric chloride in deionized water and mix evenly under stirring, denoted as reaction solution 4; (5) Dissolve the powder of polyvinyl alcohol in deionized water, heat and stir to mix evenly, denoted as reaction solution 5; (6) Weigh a certain mass of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, and N,N'-methylenebisacrylamide and dissolve them in reaction solution 5, heat and stir to mix evenly, denoted as reaction solution 6; (7) Dissolve the powder of sodium citrate in deionized water and mix evenly under stirring, denoted as reaction solution 7; (8) Mix reaction solution 2 and reaction solution 3 in proportion and mix evenly under stirring, denoted as reaction solution 8; (9) Put the cleaned fishing net into reaction solution 8 to perform surface modification on the fishing net; (10) Immerse the fishing net obtained in step (9) in reaction solution 4, take it out and dry it; immerse it in reaction solution 6, take it out and form a gel coating under photoinitiation; (11) Immerse the gel composite fishing net obtained in step (10) in reaction solution 7 for a certain period of time, take it out to obtain a composite fishing net with a tough underwater superoleophobic gel composite coating.

2. The preparation method according to claim 1, characterized in that: In the reaction solution 1 described in step (1), the content of tris(hydroxymethyl)aminomethane hydrochloride accounts for 0.5 wt%-1 wt% of the solution.

3. The preparation method according to claim 1, wherein: In the reaction solution 2 described in step (2), the content of tannic acid accounts for 0.5 wt%-1 wt% of the solution.

4. The preparation method according to claim 1, wherein: In the reaction solution 3 described in step (3), the content of the silane coupling agent accounts for 0.5 wt%-2 wt% of the solution.

5. The preparation method according to claim 1, wherein: In the reaction solution 4 described in step (4), the content of ferric chloride accounts for 0.5 wt%-2 wt% of the solution.

6. The preparation method according to claim 1, wherein: In the reaction solution 5 described in step (5), the content of polyvinyl alcohol accounts for 5 wt%-20 wt% of the solution.

7. The preparation method according to claim 1, characterized in that: In the reaction solution 6 described in step (6), the content of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide accounts for 5 wt%-20 wt% of the solution, the content of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone accounts for 0.1 wt%-1 wt% of the solution, and the content of N,N'-methylenebisacrylamide accounts for 0.1 wt%-1 wt% of the solution.

8. The preparation method according to claim 1, characterized in that: In the reaction solution 7 described in step (7), the content of sodium citrate accounts for 10 wt%-30 wt% of the solution.

9. The preparation method according to claim 1, characterized in that: In the reaction solution 8 described in step (8), the volume ratio of reaction solution 2 to reaction solution 3 is 5:

1.

10. The preparation method according to claim 1, characterized in that: The specific operation of surface modification in step (9) is impregnation at room temperature for 12 - 48 h; the immersion time in reaction solution 4 in step (10) is 0.5 - 5 h, the drying temperature is 60 °C, the drying time is 6 h, the immersion time in reaction solution 6 is 10 - 50 s, and the photoinitiation operation is ultraviolet lamp irradiation for 2 - 8 h; the immersion time in reaction solution 7 in step (11) is 24 - 72 h.

Images