A wear-resistant super-hydrophobic radiative cooling coating based on reactive blending phase separation and a preparation method thereof

Abstract

This invention discloses a method for preparing a wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blending phase separation. First, hydrophobic fumed silica is modified using a silane coupling agent. Then, epoxy resin and fluorosilicone resin are blended in an organic solvent, and modified silica is added to the blend. The mixture is then ultrasonically dispersed in an ice bath to obtain a uniform dispersion. A non-solvent is added dropwise to the dispersion to induce phase separation in the resin system. Next, a curing agent that reacts with the epoxy resin and a silane crosslinking agent or condensation catalyst that reacts with the fluorosilicone resin are sequentially added to the phase-separated system to obtain a composite sol. The composite sol is coated onto a substrate surface and cured by stepwise temperature increases to finally obtain the target coating. This method achieves a synergistic improvement in the coating's high radiation-cooling performance, high hydrophobicity, and high mechanical wear resistance by constructing a reactive epoxy-fluorosilicone interpenetrating polymer matrix and using chemically bonded modified silica at the interface.

Description

Technical Field

[0001] This invention relates to the field of radiation cooling functional coating technology, and in particular to a wear-resistant superhydrophobic radiation cooling coating based on reactive blended phase separation and its preparation method. Background Technology

[0002] Radiative cooling refers to the technology where an object reflects sunlight in the 0.3–2.5 μm solar wavelength range and simultaneously dissipates heat into the cold outer space through radiation in the 8–13 μm "atmospheric transparency window" wavelength range. High reflectivity in the solar wavelength range and high emissivity in the atmospheric transparency window wavelength range are two crucial conditions for ensuring radiative cooling of materials. Coating materials, on the other hand, are solid continuous films obtained by applying a coating in a single coat. They can be loaded onto any substrate, are easy to process, have fewer restrictions on the substrate and coating material, and are readily scalable for mass production.

[0003] Radiative cooling coatings utilize high solar reflectance and high infrared emissivity to achieve spontaneous cooling, showing great promise in fields such as construction, outdoor equipment, and personal thermal management. However, long-term exposure to the complex outdoor environment, including rain, dust accumulation, sunlight, and bacterial growth, can damage the surface microstructure of radiative cooling coatings, leading to decreased reflectivity and reduced cooling effectiveness. Furthermore, these coatings suffer from poor mechanical stability, insufficient abrasion resistance, short outdoor lifespan, limited functionality, and difficulty in achieving synergistic performance, ultimately failing to meet the demands of long-term outdoor use.

[0004] Therefore, the preparation of a composite coating that achieves the synergistic effect of superhydrophobic self-cleaning, high radiation cooling performance, and high wear resistance and mechanical stability is of great research significance and application value. Summary of the Invention

[0005] To address the problems of poor mechanical stability, insufficient wear resistance, short outdoor service life, limited functionality, and difficulty in achieving synergistic performance in current radiative cooling coatings, this invention provides a wear-resistant, superhydrophobic radiative cooling coating based on reactive blended phase separation. This coating is a multifunctional synergistic coating with an interpenetrating network structure and interfacial chemical bonding, offering wear resistance, superhydrophobicity, and radiative cooling capabilities.

[0006] The wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation provided by this invention is prepared by the following steps: S1. Disperse hydrophobic fumed silica in anhydrous ethanol, add silane coupling agent, and reflux at 60-80℃ for 6-12 hours under nitrogen protection. After reaction, centrifuge, wash and dry to obtain modified silica, abbreviated as m-SiO2.

[0007] The preferred particle size of the hydrophobic fumed silica is 15-30 nm.

[0008] The mass ratio of silica to anhydrous ethanol is 1:15 to 1:25.

[0009] The silane coupling agent is KH-560 or γ-glycidoxypropyltrimethoxysilane, and its amount is 5%-15% of the mass of silicon dioxide.

[0010] The methoxy group (-OCH3) of the silane coupling agent hydrolyzes to generate silanol groups (Si-OH), which undergo a condensation reaction with the silanol groups on the surface of SiO2 to form a strong Si-O-Si covalent bond, thereby grafting the silane coupling agent onto the surface of SiO2 and enabling it to carry reactive epoxy groups.

[0011] S2. Epoxy resin and fluorosilicone resin are mixed in an organic solvent and stirred until homogeneous to form a homogeneous mixture; m-SiO2 is added to the mixture and ultrasonically dispersed in an ice bath to obtain a uniform dispersion.

[0012] The preferred mass ratio of epoxy resin to fluorosilicone resin is 1:1.2 to 1:2. The preferred epoxy resin is E-51 or E-44. The preferred fluorosilicone resin is perfluoropolyether silane or fluorinated vinyl silicone resin.

[0013] The organic solvent is ethyl acetate, butanone, or a mixture of both. The mass ratio of the total mass of epoxy resin and fluorosilicone resin to the organic solvent is 1:5 to 1:10.

[0014] The amount of m-SiO2 added is 5%-15% of the total mass of epoxy resin and fluorosilicone resin.

[0015] S3. Add non-solvent dropwise to the dispersion in step S2 under continuous stirring to induce phase separation in the resin system, forming a continuous phase rich in polymer and a microdroplet phase rich in organic solvent and non-solvent, thus obtaining a phase-separated system.

[0016] The non-solvent is selected from at least one of n-propanol, isopropanol, and water, and the amount added accounts for 4%-8% of the total mass of the phase separation system.

[0017] S4. Add a curing agent that can react with epoxy resin and a silane crosslinking agent or condensation catalyst that can react with fluorosilicone resin to the phase separation system in sequence. After stirring evenly, let it stand for 5-10 minutes to degas and obtain a composite sol solution.

[0018] The curing agent is an amine or anhydride curing agent, and its dosage is 20%-40% of the epoxy resin mass.

[0019] The preferred silane crosslinking agent is Si-PH (a siloxane crosslinking agent containing an aromatic ring).

[0020] The condensation catalyst is an organotin or titanate compound.

[0021] The amount of silane crosslinking agent or condensation catalyst used is 1%-5% of the mass of fluorosilicone resin.

[0022] S5. Apply the composite sol solution to the substrate surface, and then perform step-by-step temperature increase curing to finally obtain the target coating.

[0023] The preferred process for the stepped temperature curing is as follows: The first stage involves maintaining a constant temperature of 25-40℃ for 0.5-1 hour. This stage is used to slowly evaporate most of the solvent / non-solvent, allowing the stationary phase to separate and form micro / nano porous structures. The second stage involves heating to 60-80℃ and holding at that temperature for 1-2 hours. During this stage, the epoxy resin primarily undergoes a curing reaction, with the epoxy groups reacting with the amine curing agent in a ring-opening crosslinking reaction to form a rigid crosslinked network. Simultaneously, the epoxy groups on the surface of m-SiO2 also participate in this reaction, anchoring the SiO2 particles covalently within the epoxy network.

[0024] The third stage involves heating to 100-120℃ and holding at that temperature for 1-2 hours. During this stage, the fluorosilicone resin crosslinks, forming an epoxy-fluorosilicone interpenetrating network. The fluorosilicone resin undergoes silanol condensation crosslinking under the action of a crosslinking agent or catalyst. The silane coupling agent acts as a crucial chemical bridge: the silane coupling agent grafted onto the epoxy network undergoes a condensation reaction with the silanols of the fluorosilicone resin (forming Si-O-Si bonds) at its other end via methoxy hydrolysis, thus covalently connecting the epoxy and fluorosilicone networks to form an interpenetrating polymer network structure.

[0025] The resulting coating has a structure comprising a micro-nano hierarchical porous surface, an epoxy-fluorosilicone interpenetrating network polymer matrix, and silica nanoparticles chemically anchored in the network by covalent bonds.

[0026] Compared with the prior art, the advantages of the present invention are: (1) Epoxy-fluorosilicone interpenetrating network brings a synergistic enhancement of wear resistance with a combination of rigidity and flexibility: Epoxy resin is hard and brittle, while fluorosilicone resin is soft and tough. If the two are simply physically blended, the performance may be compromised, or even the performance may be reduced due to the separation of the two phases. In this invention, a silane coupling agent is used as a "chemical bridge". Its epoxy end participates in the crosslinking of epoxy resin, and its silanol end condenses with fluorosilicone resin, connecting the two originally incompatible networks with covalent bonds to form an interpenetrating polymer network. The rigid epoxy resin network provides high wear resistance (hardness support); the flexible fluorosilicone resin network provides stress buffering and crack propagation resistance. The two networks are connected by chemical bonds to produce a synergistic effect, so that the wear resistance of the coating is far superior to that of a single epoxy coating (brittle peeling) or a single fluorosilicone coating (easily scratched), and is also better than a simple physical blend of the two. This is a "1+1>2" effect that cannot be achieved by a single resin system or a simple physical blend.

[0027] (2) Superior interfacial durability resulting from the "chemical anchoring" of functionalized nanoparticles (m-SiO2): This invention modifies SiO2 by grafting onto the surface of a silane coupling agent, enabling the SiO2 particles to carry reactive epoxy groups. During the coating curing process, the epoxy groups directly participate in the cross-linking reaction of the epoxy resin, making the SiO2 particles covalently bonded to the epoxy network rather than being physical fillers. Each m-SiO2 particle has thousands of active sites on its surface, which can simultaneously connect with multiple polymer molecular chains, becoming a multifunctional cross-linking center. The particles and the matrix are covalently bonded, thus achieving a qualitative leap in the wear resistance and impact resistance of the coating, avoiding inorganic / organic interface defects, eliminating the weak interfacial layer between the particles and the resin, improving the overall density of the coating and its resistance to corrosive media penetration; ensuring the durability of the superhydrophobic rough structure, even if the surface is worn, the exposed particles in the lower layer are still firmly connected by chemical bonds and will not fall off, thus maintaining the superhydrophobic properties for a long time.

[0028] (3) The coating prepared by the present invention has a static contact angle with water droplets greater than 155° and a roll-off angle less than 10°; the reflectivity of the solar band is greater than 95% and the infrared emissivity of the atmospheric transparent window is greater than 95%, and it can achieve a cooling of more than 8°C outdoors; after being polished with 1000-grit sandpaper for 10 m or continuously impacted by water flow for 30 min, it can still maintain a stable radiative cooling effect and superhydrophobic properties (contact angle still >150°).

[0029] (4) This invention resolves the contradiction between coating porosity and strength: In the prior art, coatings must sacrifice mechanical strength to achieve high cooling performance (high porosity), which is a long-standing technical contradiction. To address this, this invention utilizes the high toughness of the epoxy-fluorosilicone interpenetrating network matrix and the pinning effect of chemically anchored particles to achieve a coating that maintains or even increases porosity (through precise phase separation control) while surpassing the damage resistance of conventional coatings with the same porosity. The macroscopic physical contradiction (the contradiction between porosity and wear resistance) is resolved through the control of the microstructure of the material matrix (epoxy-fluorosilicone interpenetrating network + chemical bonding).

[0030] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0031] Figure 1 is a scanning electron microscope image of coating A in Example 1.

[0032] Figure 2 The image shows the reflectance of coating A in Example 1 in the solar band and the infrared emissivity spectrum of the 8-13 μm atmospheric transparent window.

[0033] Figure 3The curve shows the radiation cooling effect of coating A in Example 1 over time in an outdoor environment. Detailed Implementation

[0034] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0035] Example 1 A wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation is prepared by the following steps: (1) Hydrophobic gaseous SiO2 (particle size 15-30 nm) was dispersed in anhydrous ethanol at a mass ratio of 1:15. Then KH-560 was added at a mass of 10% of SiO2. The mixture was heated to 70 °C and refluxed for 10 hours under nitrogen protection. After the reaction, the mixture was washed three times with alternating anhydrous ethanol and deionized water. The mixture was then dried under vacuum at 60 °C for 12 hours to obtain m-SiO2.

[0036] (2) Epoxy resin E-51 and perfluoropolyether silane (Momentive FS-2200) are mixed in ethyl acetate at a mass ratio of 1:1.6. The total mass ratio of epoxy resin E-51 and perfluoropolyether silane to ethyl acetate is 1:5. The mixture is stirred until homogeneous to form a homogeneous blend. m-SiO2 is added to the blend. The amount of m-SiO2 added is 10% of the total mass of epoxy resin and fluorosilicone resin. The mixture is ultrasonically dispersed in an ice bath at a power of 200-300W for 15-20 minutes to obtain a uniform dispersion.

[0037] (3) Under continuous stirring (stirring speed of 300 r / min), non-solvent isopropanol is added dropwise to the dispersion to form a continuous phase rich in polymer and a micro-droplet phase rich in organic solvent and non-solvent, thus obtaining a phase separation system. The amount of isopropanol added accounts for 8% of the total mass of the phase separation system.

[0038] (4) First, add polyamide curing agent (model: Huntsman Aradur 115) to the phase separation system, the amount of which is 30% of the mass of epoxy resin. Then add tetrabutyl titanate, the amount of which is 4% of the mass of perfluoropolyether silane. After stirring evenly, let stand for 10 minutes to degas and obtain composite sol solution.

[0039] (5) The composite sol is sprayed onto the surface of the glass substrate and then cured by step heating. First, it is kept at 30℃ for 1 hour, then heated to 70℃ for 1.5 hours, and finally heated to 110℃ for 1 hour to obtain the target coating A.

[0040] The microstructure of coating A was observed using scanning electron microscopy, such as... Figure 1 As shown in the figure, coating A has a micro-nano hierarchical porous rough structure.

[0041] Figure 2 The image shows the reflectance of coating A in the solar band and the infrared emissivity of the atmospheric transparent window in the 8-13 μm range for Example 1. It can be seen that coating A has a reflectance greater than 95% in the solar band and an infrared emissivity greater than 95% in the atmospheric transparent window.

[0042] Figure 3 The figure shows the radiative cooling effect test curve of coating A in Example 1 under outdoor conditions over time. It can be seen that the temperature of the cavity below coating A is significantly lower than the air temperature, with a temperature difference of more than 8°C. This indicates that coating A can achieve a cooling effect of more than 8°C outdoors.

[0043] Example 2 A wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation is prepared by the following steps: (1) Hydrophobic gaseous SiO2 (particle size 15-30 nm) was dispersed in anhydrous ethanol at a mass ratio of 1:25. γ-glycidyl etheroxypropyltrimethoxysilane was added at a mass of 5% of the SiO2 mass. The mixture was heated to 60 °C and refluxed for 12 hours under nitrogen protection. After the reaction, the mixture was washed three times with alternating anhydrous ethanol and deionized water and dried under vacuum at 80 °C for 10 hours to obtain m-SiO2.

[0044] (2) Epoxy resin E-44 and fluorinated vinyl silicone resin (LS-8722) are mixed in methyl ethyl ketone at a mass ratio of 1:1.4. The mass ratio of the total mass of epoxy resin E-44 and fluorinated vinyl silicone resin to methyl ethyl ketone is 1:10. The mixture is stirred until homogeneous to form a homogeneous blend. m-SiO2 is added to the blend. The amount of m-SiO2 added is 5% of the total mass of epoxy resin and fluorosilicone resin. The mixture is ultrasonically dispersed in an ice bath at a power of 200-300W for 15-20 minutes to obtain a uniform dispersion.

[0045] (3) Under continuous stirring (stirring speed of 400 r / min), non-solvent n-propanol is added dropwise to the dispersion to form a continuous phase rich in polymer and a micro-droplet phase rich in organic solvent and non-solvent, thus obtaining a phase separation system. The amount of n-propanol added accounts for 5% of the total mass of the phase separation system.

[0046] (4) First, add the curing agent isophorone diamine to the phase separation system. The amount is 30% of the mass of epoxy resin. Then add dibutyltin dilaurate. The amount is 2% of the fluorinated vinyl silicone resin. After stirring evenly, let stand for 10 minutes to remove bubbles and obtain the composite sol solution.

[0047] (5) The composite sol is sprayed onto the surface of the aluminum alloy substrate and then cured by step heating. First, it is kept at 40℃ for 1 hour, then heated to 80℃ for 1 hour, and finally heated to 100℃ for 2 hours to obtain the target coating B.

[0048] Comparative Example 1 Based on Example 1, step (1) is omitted, and unmodified hydrophobic vapor phase SiO2 is directly added to step (2) to replace m-SiO2, with the same amount. Subsequent steps are kept consistent, and finally coating C is obtained.

[0049] Comparative Example 2 Based on Example 1, step (3) is omitted. In step (4), curing agent and tetrabutyl titanate are directly added to the dispersion obtained in step (2). Subsequent steps remain the same, and finally coating D is obtained.

[0050] Comparative Example 3 Based on Example 1, in step (2), perfluoropolyether silane is replaced with an equal amount of epoxy resin E-51, that is, a single epoxy resin material is used, and the other subsequent steps are kept consistent, and finally coating E is obtained.

[0051] Comparative Example 4 Based on Example 1, in step (2), epoxy resin E-51 is replaced with an equal amount of perfluoropolyether silane, that is, a single perfluoropolyether silane material is used, and other subsequent steps remain the same, finally obtaining coating F.

[0052] Comparative Example 5 Based on Example 1, in step (5), the heating and curing method is adjusted as follows: first, the temperature is kept constant at 30°C for 1 hour, then the temperature is raised to 110°C and kept constant for 1 hour, and finally the coating G is obtained.

[0053] The main performance test results of the coatings prepared in the above embodiments and comparative examples are shown in Table 1.

[0054] Table 1. Performance test results of the coatings prepared in Examples 1-2 and Comparative Examples 1-5

[0055] As shown in Table 1, the coatings prepared in Examples 1 and 2 of this invention possess ultra-high hydrophobic self-cleaning properties, high solar reflectivity and atmospheric window infrared emissivity, and excellent outdoor cooling effect. Furthermore, even after long-distance sanding and prolonged water flow impact, they can still stably maintain their superhydrophobic structure and radiative cooling capability. Comparative Examples 1-5, due to defects such as unmodified nanoparticles, omission of phase separation process, single resin system, and elimination of stepped temperature curing, all exhibited problems such as decreased hydrophobicity, reduced optical radiation performance, and poor wear resistance and durability. This fully demonstrates that the reactive blended phase separation, silica chemical modification, epoxy-fluorosilicone interpenetrating network, and stepped temperature curing technical solutions of this invention are the core key to achieving the synergistic stability of superhydrophobicity, radiative cooling, and high wear resistance in the coating.

[0056] In summary, the coating preparation method of the present invention achieves a synergistic improvement in high porosity, high hydrophobicity, and high mechanical wear resistance by constructing a reactive epoxy-fluorosilicone interpenetrating polymer matrix and using modified nanoparticles with interfacial chemical bonding. The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation, characterized in that, Includes the following steps: S1. Disperse hydrophobic fumed silica in anhydrous ethanol, add silane coupling agent, heat to 60-80℃ under nitrogen protection and reflux for 6-12 hours. After reaction, centrifuge, wash and dry to obtain modified silica, abbreviated as m-SiO2. S2. Epoxy resin and fluorosilicone resin are mixed in an organic solvent and stirred until homogeneous to form a homogeneous mixture; m-SiO2 is added to the mixture and ultrasonically dispersed in an ice bath to obtain a uniform dispersion. S3. Add non-solvent dropwise to the dispersion in step S2 under continuous stirring to induce phase separation in the resin system, forming a continuous phase rich in polymer and a micro-droplet phase rich in organic solvent and non-solvent, thus obtaining a phase-separated system. S4. Add curing agent that can react with epoxy resin and silane crosslinking agent or condensation catalyst that can react with fluorosilicone resin to the phase separation system in sequence. After stirring evenly, let stand for 5-10 minutes to degas and obtain composite sol solution. S5. Apply the composite sol solution to the substrate surface, and then perform step-by-step temperature increase curing to finally obtain the target coating.

2. The method for preparing a wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation as described in claim 1, characterized in that, In step S5, the stepwise temperature curing process is as follows: first, the temperature is kept constant at 25-40℃ for 0.5-1h, then the temperature is increased to 60-80℃ and kept constant for 1-2h, and finally the temperature is increased to 100-120℃ and kept constant for 1-2h to obtain the target coating.

3. The method for preparing a wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation as described in claim 1, characterized in that, The silane coupling agent is KH-560 or γ-glycidoxypropyltrimethoxysilane, and its amount is 5%-15% of the mass of silicon dioxide.

4. The method for preparing a wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation as described in claim 1, characterized in that, The hydrophobic fumed silica has a particle size of 15-30 nm.

5. The method for preparing a wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation as described in claim 1, characterized in that, In step S2, the mass ratio of epoxy resin to fluorosilicone resin is 1:1.2 to 1:

2.

6. The method for preparing a wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation as described in claim 5, characterized in that, The organic solvent is ethyl acetate or butanone or a mixture of both.

7. The method for preparing a wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation as described in claim 5, characterized in that, The amount of m-SiO2 added is 5%-15% of the total mass of epoxy resin and fluorosilicone resin.

8. The method for preparing a wear-resistant, superhydrophobic, radiation-cooling coating based on reactive blended phase separation as described in claim 1, characterized in that, In step S3, the non-solvent is selected from at least one of n-propanol, isopropanol, and water, and the amount added accounts for 4%-8% of the total mass of the phase separation system.

9. A wear-resistant, superhydrophobic, radiation-cooling coating, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The wear-resistant superhydrophobic radiation cooling coating as described in claim 9, characterized in that, The coating structure includes a micro-nano hierarchical porous surface, an epoxy-fluorosilicone interpenetrating network polymer matrix, and silica nanoparticles chemically anchored in the network via covalent bonds.

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