A method for preparing a hydrophilic-oleophobic coating in air

Abstract

This invention discloses a method for preparing an air-based hydrophilic-oleophobic coating, comprising the following steps: a) adding a silane coupling agent to ethanol to obtain solution A; b) first adding perfluorooctanoic acid and sodium hydroxide to ethanol to obtain a sodium perfluorooctanoate ethanol solution, then adding at least two types of hydrophilic nanoparticles of the same particle size to the sodium perfluorooctanoate ethanol solution to obtain solution B; c) adding a fluorinated surfactant and at least two types of hydrophilic nanoparticles of the same particle size to ethanol to obtain solution C; d) first mixing solution B and solution C uniformly to obtain solution D, then slowly adding solution A dropwise to solution D to obtain suspension E; e) spraying suspension E onto the surface of a substrate and drying at 55-65°C for 1-3 hours to obtain an air-based hydrophilic-oleophobic coating. The preparation method of this invention is simple, and the resulting coating exhibits excellent hydrophilicity and oleophobicity, acid and alkali resistance, salt resistance, and oil stain resistance.

Description

Technical Field

[0001] This invention relates to a method for preparing a hydrophilic-oleophobic coating in air, belonging to the field of functional material preparation technology. Background Technology

[0002] Oily wastewater is characterized by large volume, complex water quality, and difficulty in biodegradation, which can cause significant harm to the surrounding environment. Therefore, membrane separation materials are needed to separate oil and water in oily wastewater.

[0003] Hydrophilic-oleophobic coatings can achieve "oil removal and water flushing" during oil-water separation by taking advantage of the different wettability of water droplets and oil droplets on their surface. Compared with the commonly used "water removal and oil flushing" separation materials on the market, they have better oil resistance, higher throughput, and are more suitable for treating oily wastewater.

[0004] Currently, there are two main methods for using hydrophilic-oleophobic coatings to treat oily wastewater. One method is underwater oleophobic coating: for example, Chinese patent CN114405287A first constructs a hydrophilic polymer hydrogel layer in situ, and then grafts a hydrophilic polymer brush onto the surface of the hydrophilic polymer hydrogel layer to obtain a hydrophilic and underwater oleophobic coating. However, in practical applications, since the coating itself does not have oleophobic properties, it only absorbs a large amount of water onto the rough surface, thereby reducing the contact area with oil and reducing the adhesion of oil. This type of membrane is limited by the environment in which it is used, has weak anti-oil performance, and low separation efficiency. The other method is airborne oleophobic coating: for example, Chinese patent CN109825179A stirs waterborne fluorocarbon surfactant, polyether modified organosilicon leveling agent, dispersant, thickener, deionized water, and hydrophilic fumed silica nanoparticles and silica powder, and then adds waterborne resin to make a coating. However, this method is complex to prepare and has weak anti-oil performance. Summary of the Invention

[0005] In view of the above-mentioned problems in the existing technology, the purpose of this invention is to provide a method for preparing a hydrophilic-oleophobic coating in air that is simple to prepare, has good chemical stability, and strong resistance to oil stains.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing an air-sensitive hydrophilic-oleophobic coating includes the following steps:

[0008] a) Add the silane coupling agent to ethanol and mix thoroughly to obtain solution A;

[0009] b) First, add perfluorooctanoic acid and sodium hydroxide to ethanol and mix them evenly to obtain a sodium perfluorooctanoic acid ethanol solution. Then, add at least two types of hydrophilic nanoparticles of the same size to the sodium perfluorooctanoic acid ethanol solution and mix them evenly to obtain solution B.

[0010] c) Add a fluorinated surfactant and at least two types of hydrophilic nanoparticles of the same size to ethanol and mix them evenly to obtain solution C;

[0011] d) First, mix solution B obtained in step b) with solution C obtained in step c) to obtain solution D. Then, slowly add solution A obtained in step a) to solution D to obtain suspension E.

[0012] e) Spray suspension E onto the surface of the substrate and dry it at 55-65°C for 1-3 hours to obtain an air-hydrophilic-oleophobic coating.

[0013] In one embodiment, in step a), the silane coupling agent is at least one of 3-aminopropyltriethoxysilane, bis(3-trimethoxysilyl)propylamine, and diethoxydimethylsilane.

[0014] In one embodiment, in step a), the mass ratio of silane coupling agent to ethanol is 1:(15-30).

[0015] In one embodiment, in step b), the mass ratio of perfluorooctanoic acid to sodium hydroxide is 10:1; the mass ratio of perfluorooctanoic acid to hydrophilic nanoparticles is 1:(6-10); and the mass ratio of perfluorooctanoic acid to ethanol is 1:(20-30).

[0016] In one embodiment, in step c), the mass ratio of fluorinated surfactant to hydrophilic nanoparticles is 1:(1-2.5); the mass ratio of fluorinated surfactant to ethanol is 1:(4-12).

[0017] In one embodiment, in step c), the fluorosurfactant is an amphoteric fluorocarbon surfactant, preferably DuPont Capstone FS-50.

[0018] In one embodiment, in steps b) and c), the hydrophilic nanoparticles are any one of silicon dioxide, silicon carbide, and titanium dioxide.

[0019] In one embodiment, in steps b) and c), the hydrophilic nanoparticles of different sizes have the same mass.

[0020] In one embodiment, in steps b) and c), the hydrophilic nanoparticles have a particle size range of 10–500 nm, preferably 10–100 nm.

[0021] In one embodiment, in step d), the mass ratio of solution B to solution C is 1:(1-1.5), preferably 1:(1-1.2); the mass ratio of solution A to solution D is 1:(1-1.5), preferably 1:(1.2-1.4).

[0022] In one embodiment, in step e), the suspension E is sprayed onto the surface of the substrate using a spray gun. The spraying pressure is 0.2 to 0.8 MPa, the spraying distance is 10 to 20 cm, and the nozzle inner diameter of the spray gun is 0.3 to 2 μm.

[0023] In one embodiment, in step e), the substrate includes, but is not limited to, a glass slide and a silicon carbide film.

[0024] Compared with the prior art, the present invention has the following significant advantages:

[0025] 1. This invention first prepares solution B by mixing sodium perfluorooctanoate ethanol solution with hydrophilic nanoparticles, then prepares solution C by mixing fluorinated surfactant, hydrophilic nanoparticles, and ethanol, and then prepares solution D by mixing solution B and solution C. Next, solution A, obtained by mixing silane coupling agent and ethanol, is mixed with solution D to prepare suspension E. Finally, suspension E is sprayed onto the surface of a substrate to obtain an air-sensitive hydrophilic-oleophobic coating. The hydrophilic nanoparticles of different sizes in suspension E contain a large number of hydrophilic hydroxyl groups on their surfaces, which can construct a rough structure on the substrate surface. Simultaneously, under the action of the silane coupling agent and sodium ion bonds, fluorinated materials (perfluorooctanoic acid and fluorinated surfactant) are bound to the surface of the hydrophilic nanoparticles, giving them oleophobic properties. The remaining hydroxyl groups on the surface of the hydrophilic nanoparticles still exhibit good hydrophilic properties. This reduces the dispersion component in the surface energy of the coating and increases the polar component, resulting in a coating with excellent hydrophilic-oleophobic properties, acid and alkali resistance, salt resistance, and oil resistance, making it suitable for oil-water separation applications.

[0026] 2. The present invention only requires simple mixing of the liquid materials to obtain solutions A, B, C, D and suspension E. The preparation method is simple, the conditions are mild, and it is suitable for large-scale production. Attached Figure Description

[0027] Figure 1 These are scanning electron microscope (SEM) images of the hydrophilic-oleophobic coating in air in Example 1 of the present invention at different image scales; wherein, (a) image scale is 50 μm, (b) image scale is 20 μm, (c) image scale is 10 μm, (d) image scale is 100 nm, (e) image scale is 200 nm, and (f) image scale is 500 nm.

[0028] Figure 2 These are photographs of water and different oil droplets on the surface of a hydrophilic-oleophobic coating in air in Example 1 of the present invention;

[0029] Figure 3 These are test images of the acid and alkali resistance and salt resistance of the hydrophilic-oleophobic coating in air in Example 1 of the present invention;

[0030] Figure 4 This is a test diagram of the separation of oil-in-water emulsion from a silicon carbide membrane and a silicon carbide membrane with an attached hydrophilic-oleophobic coating in the air, as shown in Example 1 of the present invention.

[0031] Figure 5 These are photographs of the contact angles of a glass slide and a glass slide with an air-coated hydrophilic-oleophobic coating in Embodiment 2 of the present invention; wherein, (a) is a photograph of the hydrophilic contact angle of the glass slide, (b) is a photograph of the hydrophilic contact angle of the glass slide with the air-coated hydrophilic-oleophobic coating, (c) is a photograph of the contact angle of edible oil on the glass slide, and (d) is a photograph of the contact angle of edible oil on the glass slide with the air-coated hydrophilic-oleophobic coating. Detailed Implementation

[0032] The technical solution of the present invention will be further described in detail and completely below with reference to the embodiments.

[0033] Example 1

[0034] a) Add 1.04 g of bis(3-trimethoxysilyl)propylamine to 30 mL of ethanol and stir at 300 rpm for 2 hours to mix evenly, to obtain solution A;

[0035] b) First, add 0.5g of perfluorooctanoic acid and 0.05g of sodium hydroxide to 15mL of ethanol, and stir at 300 rpm for 2 hours to mix evenly, to obtain a sodium perfluorooctanoic acid ethanol solution. Then, add 1.5g of 12nm titanium dioxide nanoparticles and 1.5g of 60nm titanium dioxide nanoparticles to the sodium perfluorooctanoic acid ethanol solution, and sonicate for 30 minutes to mix evenly, to obtain solution B.

[0036] c) Add 2.06g of fluorosurfactant (Capstone FS-50, DuPont), 1.5g of 12nm titanium dioxide nanoparticles and 1.5g of 60nm titanium dioxide nanoparticles to 15mL of ethanol. Stir at 300 rpm for 2 hours and then sonicate for 30 minutes to mix evenly to obtain solution C.

[0037] d) First, mix solution B obtained in step b) with solution C obtained in step c) to obtain solution D. Then, slowly add solution A obtained in step a) to solution D to obtain suspension E.

[0038] e) The suspension E was sprayed onto the surface of the silicon carbide film using a spray gun with an inner diameter of 0.5 μm. The spraying pressure was 0.2 MPa and the spraying distance was 10 cm. The film was then dried at 60 °C for 2 hours to obtain a hydrophilic-oleophobic coating in the air.

[0039] Figure 1These are scanning electron microscope (SEM) images of the hydrophilic-oleophobic coating in air at different image scales in this embodiment; where (a) image scale is 50 μm, (b) image scale is 20 μm, (c) image scale is 10 μm, (d) image scale is 100 nm, (e) image scale is 200 nm, and (f) image scale is 500 nm. Figure 1 It is evident that titanium dioxide nanoparticles of different particle sizes are irregularly interwoven and stacked on the membrane surface, forming a rough porous structure.

[0040] The hydrophilic-oleophobic coating obtained in this embodiment was subjected to hydrophilic-oleophobic performance testing in air:

[0041] Figure 2 These are photographs of water and different oil droplets on the surface of the hydrophilic-oleophobic coating in air in this embodiment;

[0042] The water contact angle of the hydrophilic-oleophobic coating surface in air was measured using 5 μL of water, and the result was 4.3°. The oil contact angle and roll-off angle of the hydrophilic-oleophobic coating surface in air were measured using 8 μL of edible oil, olive oil, mineral oil, and hexadecane, respectively. The results were: oil contact angles of 145.6°, 147.0°, 149.3°, and 145.8°, and oil roll-off angles of 6.2°, 7.1°, 6.0°, and 6.8°, respectively.

[0043] Therefore, the air-sensitive hydrophilic-oleophobic coating prepared in this embodiment has excellent hydrophilic and oleophobic properties.

[0044] The acid and alkali resistance and salt resistance of the hydrophilic-oleophobic coating prepared in this embodiment were tested.

[0045] The silicon carbide film with an attached hydrophilic-oleophobic coating was immersed in an acidic solution with pH=1, an alkaline solution with pH=12, and a 3.5% (w / w) salt solution. The change in contact angle was recorded every hour. The test results are as follows: Figure 3 As shown.

[0046] Figure 3 These are test results for the acid and alkali resistance and salt resistance of the hydrophilic-oleophobic coating in air in this embodiment; (from...) Figure 3 It is evident that regardless of the solution in which the edible oil is immersed, the contact angle remains above 144°, indicating that the hydrophilic-oleophobic coating prepared by this invention has good acid and alkali resistance, salt resistance, and good chemical stability.

[0047] The water-in-oil emulsion separation test was performed on the hydrophilic-oleophobic coating in air prepared in this embodiment:

[0048] The oil-in-water emulsions used in the tests were: edible oil in water, mineral oil in water, olive oil in water, hexadecane in water, and decane in water. The test results are as follows: Figure 4 As shown.

[0049] Figure 4 This is a test diagram of the separation of oil-in-water emulsion from a silicon carbide membrane and a silicon carbide membrane with an attached hydrophilic-oleophobic coating in the air, as shown in this embodiment; (The diagram is from...) Figure 4 It is evident that the water-in-oil emulsion separation efficiency of the silicon carbide membrane with the attached air-hydrophilic-oleophobic coating is improved compared to that of the silicon carbide membrane, indicating that the air-hydrophilic-oleophobic coating prepared in this embodiment has a good water-in-oil emulsion separation effect.

[0050] Example 2

[0051] a) Add 0.95 g of 3-aminopropyltriethoxysilane to 30 mL of ethanol and stir at 300 rpm for 2 hours to mix evenly, to obtain solution A;

[0052] b) First, add 0.5g of perfluorooctanoic acid and 0.05g of sodium hydroxide to 15mL of ethanol and stir at 300 rpm for 2 hours to mix evenly, to obtain a sodium perfluorooctanoic acid ethanol solution. Then, add 1g of 12nm titanium dioxide nanoparticles, 1g of 60nm titanium dioxide nanoparticles and 1g of 100nm titanium dioxide nanoparticles to the sodium perfluorooctanoic acid ethanol solution and sonicate for 30 minutes to mix evenly, to obtain solution B.

[0053] c) Add 2.06g of fluorosurfactant (Capstone FS-50, DuPont), 1g of 12nm titanium dioxide nanoparticles, 1g of 60nm titanium dioxide nanoparticles and 1g of 100nm titanium dioxide nanoparticles to 15mL of ethanol. Stir at 300 rpm for 2 hours and then sonicate for 30 minutes to mix evenly to obtain solution C.

[0054] d) First, mix solution B obtained in step b) with solution C obtained in step c) to obtain solution D. Then, slowly add solution A obtained in step a) to solution D to obtain suspension E.

[0055] e) The suspension E was sprayed onto the surface of a glass slide using a spray gun with an inner diameter of 0.5 μm. The spraying pressure was 0.2 MPa and the spraying distance was 10 cm. The slide was then dried at 60 °C for 2 hours to obtain a hydrophilic-oleophobic coating in the air.

[0056] The hydrophilic-oleophobic coating obtained in this embodiment was subjected to hydrophilic-oleophobic performance testing in air:

[0057] Figure 5These are photographs of the contact angles of the glass slide and the glass slide with the hydrophilic-oleophobic coating in the air in this embodiment; wherein, (a) is a photograph of the hydrophilic contact angle of the glass slide, (b) is a photograph of the hydrophilic contact angle of the glass slide with the hydrophilic-oleophobic coating in the air, (c) is a photograph of the contact angle of the glass slide with the edible oil, and (d) is a photograph of the contact angle of the glass slide with the hydrophilic-oleophobic coating in the air.

[0058] The water contact angle of the hydrophilic-oleophobic coating surface in air was measured using 5 μL of water, and the result was 4.1°. The oil contact angle and roll-off angle of the hydrophilic-oleophobic coating surface in air were measured using 8 μL of edible oil, olive oil, mineral oil, and hexadecane, respectively. The results showed oil contact angles of 147.6°, 147.4°, 148.3°, and 146.8°, and oil roll-off angles of 5.2°, 6.1°, 6.7°, and 6.9°, respectively. This indicates that the hydrophilic-oleophobic coating prepared in this example exhibits excellent hydrophilic and oleophobic properties in air.

[0059] The acid and alkali resistance and salt resistance of the hydrophilic-oleophobic coating prepared in this embodiment were tested.

[0060] Glass slides with an air-adhered hydrophilic-oleophobic coating were immersed in an acidic solution with pH=1, an alkaline solution with pH=12, and a 3.5% salt solution. The change in contact angle was recorded every hour. After 5 hours, the water contact angle was 4.1°, while the edible oil contact angle was still above 144°. This indicates that the air-adhered hydrophilic-oleophobic coating prepared by this invention has good acid and alkali resistance, salt resistance, and good chemical stability.

[0061] Comparative Example 1

[0062] a) Add 1.04 g of bis(3-trimethoxysilyl)propylamine to 30 mL of ethanol and stir at 300 rpm for 2 hours to mix evenly, to obtain solution A;

[0063] b) First, add 1g of perfluorooctanoic acid and 0.1g of sodium hydroxide to 30mL of ethanol and stir at 300 rpm for 2 hours to mix evenly, to obtain a sodium perfluorooctanoic acid ethanol solution. Then, add 3g of 12nm titanium dioxide nanoparticles and 3g of 60nm titanium dioxide nanoparticles to the sodium perfluorooctanoic acid ethanol solution and sonicate for 30 minutes to mix evenly, to obtain solution B.

[0064] c) Slowly add solution A obtained in step a) to solution B to obtain suspension C;

[0065] d) The suspension C was sprayed onto the surface of the silicon carbide film using a spray gun with an inner diameter of 0.5 μm. The spraying pressure was 0.2 MPa and the spraying distance was 10 cm. The film was then dried at 60 °C for 2 hours to obtain a comparative coating.

[0066] The hydrophilic-oleophobic properties of the comparative coating prepared in this comparative example were tested:

[0067] The water contact angle of the comparison coating surface was measured with 5 μL of water, and the result was 6°. The oil contact angle and roll-off angle of the comparison coating surface were measured with 8 μL of edible oil, olive oil, mineral oil, and hexadecane, respectively. The results were: oil contact angles of 140.2°, 141.0°, 139.3°, and 140.7°, respectively, and oil roll-off angles of 36.7°, 37.2°, 36.0°, and 36.9°, respectively. All oil roll-off angles were greater than 10°.

[0068] As can be seen from Example 1 and Comparative Example 1, the air-coated hydrophilic-oleophobic coating prepared using two fluorinated materials (perfluorooctanoic acid and fluorinated surfactants) has a lower water contact angle, a higher oil contact angle, and a lower oil roll-off angle than the comparative coating prepared using one fluorinated material (perfluorooctanoic acid). It also exhibits significantly reduced oil adhesion and superior anti-oil properties.

[0069] Comparative Example 2

[0070] a) Add 1.04 g of bis(3-trimethoxysilyl)propylamine to 30 mL of ethanol and stir at 300 rpm for 2 hours to mix evenly, to obtain solution A;

[0071] b) Add 4.12g of fluorosurfactant (Capstone FS-50, DuPont), 3g of 12nm titanium dioxide nanoparticles and 3g of 60nm titanium dioxide nanoparticles to 30ml of ethanol. Stir at 300 rpm for 2 hours and then sonicate for 30 minutes to mix evenly to obtain solution B.

[0072] c) Slowly add solution A obtained in step a) to solution B to obtain suspension C;

[0073] d) The suspension C was sprayed onto the surface of the silicon carbide film using a spray gun with an inner diameter of 0.5 μm. The spraying pressure was 0.2 MPa and the spraying distance was 10 cm. The film was then dried at 60 °C for 2 hours to obtain a comparative coating.

[0074] The hydrophilic-oleophobic properties of the comparative coating prepared in this comparative example were tested:

[0075] The water contact angle of the comparison coating surface was measured with 5 μL of water, and the result was 6.5°. The oil contact angle and roll-off angle of the comparison coating surface were measured with 8 μL of edible oil, olive oil, mineral oil, and hexadecane, respectively. The results were: oil contact angles of 138.6°, 142.0°, 139.5°, and 139.2°, respectively, and oil roll-off angles of 45.2°, 42.2°, 46.1°, and 42.9°, respectively. All oil roll-off angles were greater than 10°.

[0076] As can be seen from Example 1 and Comparative Example 2, the air-coated hydrophilic-oleophobic coating prepared using two fluorinated materials (perfluorooctanoic acid and fluorinated surfactant) has a lower water contact angle, a higher oil contact angle, and a lower oil roll-off angle than the comparative coating prepared using one fluorinated material (fluorinated surfactant). It also exhibits significantly reduced oil adhesion and superior anti-oil properties.

[0077] Comparative Example 3

[0078] a) Add 1.04 g of bis(3-trimethoxysilyl)propylamine to 30 mL of ethanol and stir at 300 rpm for 2 hours to mix evenly, to obtain solution A;

[0079] b) First, add 0.5g of perfluorooctanoic acid and 0.05g of sodium hydroxide to 30mL of ethanol, and stir at 300 rpm for 2 hours to mix evenly, to obtain a sodium perfluorooctanoic acid ethanol solution. Then, add 2.06g of fluorosurfactant (Capstone FS-50, DuPont), 3g of 12nm titanium dioxide nanoparticles and 3g of 60nm titanium dioxide nanoparticles to the sodium perfluorooctanoic acid ethanol solution, stir at 300 rpm for 2 hours and then ultrasonically disperse for 30 minutes to mix evenly, to obtain solution B.

[0080] c) Slowly add solution A obtained in step a) to solution B to obtain suspension C;

[0081] d) The suspension C was sprayed onto the surface of the silicon carbide film using a spray gun with an inner diameter of 0.5 μm. The spraying pressure was 0.2 MPa and the spraying distance was 10 cm. The film was then dried at 60 °C for 2 hours to obtain a comparative coating.

[0082] The hydrophilic-oleophobic properties of the comparative coating prepared in this comparative example were tested:

[0083] The water contact angle of the comparison coating surface was measured with 5 μL of water, and the result was 8.5°. The oil contact angle and roll-off angle of the comparison coating surface were measured with 8 μL of edible oil, olive oil, mineral oil, and hexadecane, respectively. The results were: oil contact angles of 130.2°, 132.3°, 130.8°, and 121.9°, respectively, and oil roll-off angles of 20.8°, 18.6°, 21.2°, and 26.5°, respectively.

[0084] As can be seen from Example 1 and Comparative Example 3, the hydrophilic-oleophobic coating in air prepared by modifying hydrophilic nanoparticles with two fluorinated materials (perfluorooctanoic acid and fluorinated surfactants) has a lower water contact angle, a higher oil contact angle, and a lower oil roll-off angle than the comparative coating prepared by simultaneously modifying hydrophilic nanoparticles with a mixture of the two fluorinated materials (perfluorooctanoic acid and fluorinated surfactants). It also has significantly reduced oil adhesion and superior anti-oil properties.

[0085] Comparative Example 4

[0086] a) Add 1.04 g of bis(3-trimethoxysilyl)propylamine to 30 mL of ethanol and stir at 300 rpm for 2 hours to mix evenly, to obtain solution A;

[0087] b) First, add 0.5g of perfluorooctanoic acid and 0.05g of sodium hydroxide to anhydrous ethanol and stir at 300 rpm for 2 hours to mix them evenly, so as to obtain a sodium perfluorooctanoic acid ethanol solution. Then, add 3g of 12nm titanium dioxide nanoparticles to the sodium perfluorooctanoic acid ethanol solution and ultrasonically disperse for 30 minutes to mix them evenly, so as to obtain solution B.

[0088] c) Add 2.06g of fluorosurfactant (Capstone FS-50, DuPont) and 3g of 12nm titanium dioxide nanoparticles to ethanol. Stir at 300 rpm for 2 hours and then ultrasonically disperse for 30 minutes to mix evenly, to obtain solution C.

[0089] d) First, mix solution B obtained in step b) with solution C obtained in step c) to obtain solution D. Then, slowly add solution A obtained in step a) to solution D to obtain suspension E.

[0090] e) The suspension E was sprayed onto the surface of the silicon carbide film using a spray gun with an inner diameter of 0.5 μm. The spraying pressure was 0.2 MPa and the spraying distance was 10 cm. The film was then dried at 60 °C for 2 hours to obtain a comparative coating.

[0091] The hydrophilic-oleophobic properties of the comparative coating prepared in this comparative example were tested:

[0092] The water contact angle of the comparison coating surface was measured with 5 μL of water, and the result was 10.5°. The oil contact angle and roll-off angle of the comparison coating surface were measured with 8 μL of edible oil, olive oil, mineral oil, and hexadecane, respectively. The results were: oil contact angles of 134.2°, 132.2°, 129.8°, and 129.1°, and oil roll-off angles of 12.5°, 13.6°, 14.4°, and 15.2°, respectively.

[0093] As can be seen from Example 1 and Comparative Example 4, the air-based hydrophilic-oleophobic coating prepared using hydrophilic nanoparticles of the same type with multiple particle sizes has a lower water contact angle, a higher oil contact angle, and a lower oil roll-off angle than the comparative coating prepared using hydrophilic nanoparticles with a single particle size. It also has significantly reduced oil adhesion and superior anti-oil properties.

[0094] Finally, it should be noted that the above are only some preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for the preparation of a hydrophilic-oleophobic coating in air, characterized in that, The method comprises the following steps: a) adding a silane coupling agent into ethanol and mixing to obtain solution A; b) adding perfluorooctanoic acid and sodium hydroxide into ethanol and mixing to obtain a perfluorooctanoic acid sodium ethanol solution, and then adding at least two types of hydrophilic nanoparticles with different particle sizes into the perfluorooctanoic acid sodium ethanol solution and mixing to obtain solution B; c) adding a fluorine surfactant and at least two types of hydrophilic nanoparticles with different particle sizes into ethanol and mixing to obtain solution C; the fluorine surfactant is DuPont Capstone FS-50; d) mixing solution B obtained in step b) and solution C obtained in step c) to obtain solution D, and then slowly adding solution A obtained in step a) into solution D to obtain suspension E; the mass ratio of solution B to solution C is 1: (1-1.5); the mass ratio of solution A to solution D is 1: (1-1.5); e) spraying suspension E on the surface of a substrate and drying at 55-65°C for 1-3 hours to obtain a hydrophilic-oleophobic coating in air.

2. The method of claim 1, wherein: In step a), the silane coupling agent is at least one of 3-aminopropyltriethoxysilane, bis (3-trimethoxysilyl) propylamine, and diethoxydimethylsilane.

3. The method of claim 1, wherein: In step a), the mass ratio of the silane coupling agent to ethanol is 1: (15-30).

4. The method of claim 1, wherein: In step b), the mass ratio of perfluorooctanoic acid to sodium hydroxide is 10:1; the mass ratio of perfluorooctanoic acid to hydrophilic nanoparticles is 1: (6-10); and the mass ratio of perfluorooctanoic acid to ethanol is 1: (20-30).

5. The method of claim 1, wherein: In step c), the mass ratio of the fluorine surfactant to hydrophilic nanoparticles is 1: (1-2.5); and the mass ratio of the fluorine surfactant to ethanol is 1: (4-12).

6. The method of claim 1, wherein: In steps b) and c), the hydrophilic nanoparticles are any one of silicon dioxide, silicon carbide, and titanium dioxide.

7. The method of claim 1, wherein: In steps b) and c), the particle size of the hydrophilic nanoparticles ranges from 10 nm to 500 nm.

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