Self-cleaning, cooling flexible transparent film and preparation method thereof

Abstract

The application discloses a self-cleaning and cooling flexible transparent film and a preparation method thereof. The flexible film is mainly composed of PVDF and PMMA polymer monomers, and the preparation method comprises the following steps: mixing PVDF and PMMA, adding a solvent DMAc or DMF, and fully stirring to obtain a colorless transparent solution; adding a low surface energy modifier trimethoxy (1H, 1H, 2H, 2H-heptadecafluorodecyl) silane or octadecyl trimethoxysilane into the colorless transparent solution and fully dispersing by magnetic stirring; placing the prepared solution at room temperature for 2-4 hours, transferring the solution to a cleaned glass, coating a film on the surface of the substrate by an adjustable scraper, forming a flat coating, and placing the coating into a 70-130 DEG C oven to completely solidify. The film is a flexible and bendable film, has good light transmittance, a hydrophobic rolling angle, and has remarkable refrigeration and cooling performance, and can be widely used in the outer surfaces of objects, such as special-shaped curved surfaces, solar cell panels and building glasses, which need light transmission and cooling.

Description

Technical Field

[0001] This invention belongs to the fields of energy and coating technology, and specifically relates to a self-cleaning, cooling flexible transparent film and its preparation method. Background Technology

[0002] In recent years, self-cleaning transparent surfaces have been widely studied and applied in smart windows, solar panels, camera lenses, and other optoelectronic devices. Self-cleaning properties can extend the lifespan of these products, reduce or even eliminate the need for chemical detergents and the high labor costs of cleaning, slow down or even inhibit the accumulation of dirt and bacterial growth on these surfaces, and improve the overall efficiency of outdoor optoelectronic devices. High optical transparency is crucial for optical and electronic devices such as solar panels, automotive glass, goggles, smart windows, greenhouses, camera lenses, and electronic screens. Flexible films can be bent, rolled, and deformed, thus adapting to various unconventional shapes and curved surfaces. Therefore, exploring a flexible, transparent, and hydrophobic membrane material is of great significance for materials with unconventional shapes that require transparency and hydrophobicity. Simultaneously, a certain degree of radiative cooling performance without additional resource consumption has practical value for devices that are inherently low-temperature friendly. Summary of the Invention

[0003] This invention provides a method for preparing a self-cleaning, cooling, flexible transparent film, comprising the following steps:

[0004] (1) Preparation of PVDF / PMMA mixed solution: PVDF and PMMA of different molecular weights are added to the solvent and stirred thoroughly to form a transparent solution. The solution is placed in an oven at 50-80℃ and left to stand for 6-24 h to obtain PVDF / PMMA mixed solution.

[0005] (2) Preparation of modified PVDF / PMMA mixed solution: Add the low surface energy modifier to the mixed solution obtained in step (1), stir evenly, and let stand at room temperature for 2-4 h to obtain the modified PVDF / PMMA mixed solution;

[0006] (3) Film formation: The modified PVDF / PMMA mixed solution obtained in step (2) is coated onto the substrate by a blade coating method, and a self-cleaning, cooling and cooling flexible transparent film is obtained by high temperature curing.

[0007] Furthermore, the molecular weight of the PVDF mentioned in step (1) is 400,000-534,000.

[0008] Further, the different molecular weight PMMA mentioned in step (1) includes high molecular weight PMMA and low molecular weight PMMA; the molecular weight of the high molecular weight PMMA is 180,000-220,000, and the molecular weight of the low molecular weight PMMA is 120,000-140,000.

[0009] Furthermore, the total amount of PVDF and PMMA added is 60%-90%; the amount of high molecular weight PMMA added is 5%-35% of the total amount of PVDF and PMMA added; the amount of high molecular weight PMMA added is 5%-35% of the total amount of PVDF and PMMA added.

[0010] Further, the solvent in step (1) is at least one of DMAc or DMF, and the amount added is 6.3wt% to 18.8wt% of the total amount of polymer PVDF and PMMA added.

[0011] Further, the low surface energy modifier mentioned in step (2) is at least one of trimethoxy(1H,1H,2H,2H-heptadecylfluorodecyl)silane or octadecyltrimethoxysilane, and the amount added is 0.1%-1% of the total amount of polymer PVDF and PMMA added.

[0012] Furthermore, the curing temperature in step (3) is 70-130℃ and the curing time is 5-30 min.

[0013] Furthermore, the coating thickness described in step (3) is 0.5mm-3mm.

[0014] A self-cleaning, cooling flexible transparent film, prepared by the above method, has a visible light transmittance of ≥93%.

[0015] The beneficial effects of this invention are as follows:

[0016] The flexible transparent film prepared by the technical solution of this invention is composed of two polymers, PVDF and PMMA, cured by thermally induced phase separation. By introducing PMMA of different molecular weights, the film's transmittance of visible light is improved while maintaining good mechanical strength. This flexible film has good visible light transmittance, superior hydrophobic self-cleaning properties, and allows water droplets to slide freely at a certain tilt angle. It also has strong atmospheric transparency and radiation capacity, meeting light transmittance requirements while possessing self-cleaning and radiative cooling properties. Compared with bare glass, glass coated with the film of this invention can achieve a daytime temperature reduction of up to 5.8°C. Attached Figure Description

[0017] Figure 1 Transmittance diagrams of membranes obtained with different PVDF / PMMA ratios in Examples 1-4.

[0018] Figure 2 a: Actual image of the membrane obtained in Example 5; b: Actual image of the membrane obtained in Example 6.

[0019] Figure 3 Transmittance of membranes obtained by adding 7 to 9 different amounts of low surface energy modifiers.

[0020] Figure 4 Transmittance diagrams of films with different coating thicknesses prepared in Examples 10 and 11.

[0021] Figure 5 Transmittance diagrams of membranes prepared at different drying temperatures in Examples 12 and 13.

[0022] Figure 6 The self-cleaning performance of the membrane obtained in Example 1 is shown in the following diagrams: a: before water droplets are added; b: during water droplet sliding; c: after water droplet sliding.

[0023] Figure 7 A diagram illustrating the flexibility properties of the membrane obtained in Example 1.

[0024] Figure 8 Outdoor temperature test site of the membrane obtained in Example 1.

[0025] Figure 9 Temperature change of the membrane obtained in Example 1 during outdoor testing. Detailed Implementation

[0026] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0027] Example 1

[0028] (1) Preparation of PVDF / PMMA mixed solution: PVDF (molecular weight 400,000), high molecular weight PMMA (molecular weight 180,000), and low molecular weight PMMA (molecular weight 120,000) were added to DMAc in sequence, with a mass ratio of 8:1:1. The mass ratio of DMAc to PVDF / PMMA mixture was 14.1:1. The mixture was magnetically stirred at 60℃ for 2 h to form a transparent solution.

[0029] (2) PVDF / PMMA solution aging: The prepared transparent solution was sealed and placed in a 60℃ oven and left to stand for 12 hours.

[0030] (3) Preparation of PVDF / PMMA / 17F mixed solution: Weigh 10g of PVDF / PMMA mixed solution, add 0.22wt% of trimethoxy(1H,1H,2H,2H-heptadecylfluorodecyl)silane solution, stir at room temperature for 30min under magnetic stirrer, and then let stand at room temperature for 3h.

[0031] (4) Coating film formation: Place a clean glass slide on a horizontal table, adjust the adjustable scraper, and set the film coating thickness to 0.5 mm. Use a plastic dropper to evenly drop the prepared solution onto the substrate, and slowly slide it across the substrate at a uniform speed to form a smooth coating. Finally, place the sample in a 100℃ oven to dry for about 15 minutes. Remove the sample immediately after the film is completely cured to obtain a PPF flexible film with a contact angle of 107.5°.

[0032] Example 2

[0033] The method is the same as in Example 1, except that the high molecular weight PMMA has a molecular weight of 220,000 and the low molecular weight PMMA has a molecular weight of 140,000. The contact angle of the PPF film is 105.5°.

[0034] Example 3

[0035] The method is the same as in Example 1, except that the mass ratio of PVDF, high molecular weight PMMA, and low molecular weight PMMA is 7:1:2. The contact angle of the PPF membrane is 103.5°.

[0036] Example 4

[0037] The method is the same as in Example 1, except that the molecular weight of PVDF is 540,000, the molecular weight of high molecular weight PMMA is 250,000, and the molecular weight of low molecular weight PMMA is 150,000. The contact angle of the PPF film is 100°.

[0038] Example 5

[0039] The method is the same as in Example 1, except that the mass ratio of PVDF, high molecular weight PMMA, and low molecular weight PMMA is 6:4:0. The contact angle of the PPF membrane is 99.0°.

[0040] Example 6

[0041] The method is the same as in Example 1, except that the mass ratio of PVDF, high molecular weight PMMA, and low molecular weight PMMA is 8:0:2, and the molecular weight of the low molecular weight PMMA is 120,000. The contact angle of the PPF film is 104°.

[0042] The visible light transmittance results of the films obtained in Examples 1-4 are as follows: Figure 1 As shown, PMMA can improve the transmittance of the membrane to visible light, and the effect of improving transmittance is even better with PMMA of smaller molecular weight.

[0043] The PPF films obtained in Examples 5 and 6 are respectively as follows: Figure 2 As shown in a and b, the membrane surface obtained in Example 5 has a wavy pattern, while the membrane surface obtained in Example 6 has small protrusions. Figure 2 (b circle part) This is because: (1) PMMA and PVDF have a large difference in curing shrinkage rate. When a higher proportion of high molecular weight PMMA is added, the shrinkage rate difference is obvious, resulting in uneven film surface; (2) Low molecular weight PMMA has poor heat resistance and is prone to shrinkage during drying, leading to unevenness.

[0044] Example 7

[0045] The method is the same as in Example 1, except that the amount of trimethoxy(1H,1H,2H,2H-heptadecyl)silane solution added in step (3) is 0.20 wt%. The contact angle of the PPF film is 100.25°.

[0046] Example 8

[0047] The method is the same as in Example 1, except that the amount of trimethoxy(1H,1H,2H,2H-heptadecyl)silane solution added in step (3) is 0.24 wt%. The contact angle of the PPF film is 103.25°.

[0048] Example 9

[0049] The method is the same as in Example 1, except that the amount of trimethoxy(1H,1H,2H,2H-heptadecyl)silane solution added in step (3) is 0.26 wt%. The contact angle of the PPF membrane is 100.5°.

[0050] The UV-Vis transmittance of films prepared in Examples 7-9 with different amounts of low surface energy modifiers was tested. Figure 3 As shown in Example 1, in the range of 300-900nm, the highest transmittance of the film is achieved when the 17F doping amount is 0.22wt%, with the visible light transmittance reaching up to 94%.

[0051] Example 10

[0052] The method is the same as in Example 1, except that in step (4), the film coating thickness is set to 1.25 mm and the PPF film contact angle is 106.5°.

[0053] Example 11

[0054] The method is the same as in Example 1, except that the coating thickness in step (4) is 2 mm. The contact angle of the PPF film is 104°.

[0055] The ultraviolet-visible light transmittance of films with different coating thicknesses prepared in Examples 10 and 11 was tested, such as... Figure 4As shown, the transmittance of films with different coating thicknesses ranges from 300 to 900 nm. As can be seen from Example 1, the thicker the coating, the lower the transmittance of the film.

[0056] Example 12

[0057] The method is the same as in Example 1, except that the oven temperature in step (4) is set to 90°C. The contact angle of the PPF film is 103.5°.

[0058] Example 13

[0059] The method is the same as in Example 1, except that the oven temperature in step (4) is set to 110°C and the PPF film contact angle is 102°.

[0060] The UV-Vis transmittance of the films prepared in Examples 12 and 13 at different drying temperatures was tested. Figure 5 The transmittance of the film in the range of 300-900nm at different drying temperatures is shown in Example 1. It can be seen that the film has the highest transmittance when the wet film drying temperature is 100℃ and the film has the largest hydrophobic angle when the wet film drying temperature is 100℃.

[0061] Figure 6 This demonstrates the self-cleaning performance of the PPF membrane obtained in Example 1. Water droplets can flow smoothly down the PPF membrane, and the water droplets can also carry away dirt from the membrane surface after flowing through the PPF membrane. Figure 7 This demonstrates the flexibility of the PPF film obtained in Example 1, showing that it can be bent arbitrarily and has excellent flexibility.

[0062] Outdoor temperature testing was conducted on the PPF film prepared in Example 1. The test was conducted on April 23, 2024, at an unobstructed outdoor location in the Simulation Building of Three Gorges University, Xiling District, Yichang. The highest daytime temperature on the day of the test was 29°C, and the weather was sunny. The test chamber was made of polystyrene foam wrapped with aluminum foil to avoid interference from external convection and conduction heat transfer. The overall dimensions of the chamber were 15cm × 15cm × 15cm. Six uniformly sized cavities, each 5cm × 5cm × 5cm and 2cm deep, were cut into the top. Coated / uncoated glass slides were placed in their respective independent, non-interfering cavities to test the sample temperature under outdoor light-insulated conditions. Figure 8 shows a picture of the outdoor temperature test site. Figure 9 Temperature tests show that the PPF film has a certain radiative cooling effect. Compared with glass, the film's maximum temperature drop is 5.8℃, proving that the film has a certain radiative cooling effect.

Claims

1. A method for preparing a self-cleaning, cooling, flexible transparent film, characterized in that, Includes the following steps: (1) Preparation of PVDF / PMMA mixed solution: PVDF and PMMA of different molecular weights are added to the solvent and stirred thoroughly to form a transparent solution. The solution is placed in an environment of 50-80℃ and allowed to stand for 6-24 h to obtain PVDF / PMMA mixed solution. (2) Preparation of modified PVDF / PMMA mixed solution: Add the low surface energy modifier to the mixed solution obtained in step (1), stir evenly, and let stand at room temperature for 2-4 h to obtain the modified PVDF / PMMA mixed solution; (3) Film formation: The modified PVDF / PMMA mixed solution obtained in step (2) is coated onto the substrate by a blade coating method, and a self-cleaning, cooling and cooling flexible transparent film is obtained by high temperature curing. The solvent in step (1) is at least one of DMAc or DMF; Step (1) The different molecular weights of PMMA include high molecular weight PMMA and low molecular weight PMMA; the molecular weight of high molecular weight PMMA is 180,000-220,000, and the molecular weight of low molecular weight PMMA is 120,000-140,000. The amount of PVDF added is 60%-90% of the total amount of PVDF and PMMA added; the amount of high molecular weight PMMA added is 5%-35% of the total amount of PVDF and PMMA added.

2. The method for preparing a self-cleaning, cooling, flexible transparent film according to claim 1, characterized in that, The PVDF molecular weight mentioned in step (1) is 400,000-534,000.

3. The method for preparing a self-cleaning, cooling, flexible transparent film according to claim 1, characterized in that, The amount of solvent added in step (1) is 6.3wt% to 18.8wt% of the total amount of PVDF and PMMA added.

4. The method for preparing a self-cleaning, cooling, flexible transparent film according to claim 1, characterized in that, The low surface energy modifier mentioned in step (2) is at least one of trimethoxy(1H,1H,2H,2H-heptadecylfluorodecyl)silane or octadecyltrimethoxysilane, and the amount added is 0.1%-1% of the total amount of polymer PVDF and PMMA added.

5. The method for preparing a self-cleaning, cooling, flexible transparent film according to claim 1, characterized in that, The curing temperature in step (3) is 70-130℃ and the curing time is 5-30 min.

6. The method for preparing a self-cleaning, cooling, flexible transparent film according to claim 1, characterized in that, The coating thickness described in step (3) is 0.5mm-3mm.

7. A self-cleaning, cooling, flexible transparent film, characterized in that, The sample is prepared by any one of the preparation methods described in claims 1-6, and has a visible light transmittance of ≥93%.

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