A method for preparing a laser-induced fluorine-free photo-thermal super-hydrophobic coating

Abstract

The application discloses a preparation method of a laser-induced fluorine-free photothermal super-hydrophobic coating and belongs to the technical field of photothermal super-hydrophobic coatings, laser micro-nano processing and surface anti-icing and deicing technologies. The steps comprise the following: carbon-based photothermal fillers are modified by in-situ polymerization of dopamine, compounded with fluorine-free resins to form a coating, and after spraying and curing, the nanosecond laser etching is used to remove the surface resin-rich area to construct a micro-nano hierarchical structure with synergistic micro-pillar arrays and nano-roughness. The obtained coating has a water contact angle of > 150 degrees, a rolling angle of < 10 degrees, an average light absorption rate of 250-2500 nm of > 97 percent, does not contain fluorine components, and still maintains the super-hydrophobic performance after the tape stripping, acid solution and salt solution immersion, ultraviolet aging and frosting / deicing cycles. The application has both passive anti-icing and active photothermal deicing capabilities, the process parameters are controllable, is suitable for various substrates, is environmentally friendly and durable, and has the engineering popularization value.

Description

Technical Field

[0001] This invention belongs to the fields of photothermal superhydrophobic coating, laser micro-nano processing and surface anti-icing and de-icing technology, and particularly relates to a method for preparing a laser-induced fluorine-free photothermal superhydrophobic coating. Background Technology

[0002] Icing poses a serious threat to the safe operation of power transmission lines, wind turbines, aerospace vehicles, transportation vehicles, and outdoor structures. To address this challenge, active anti-icing / de-icing strategies such as mechanical de-icing, chemical de-icing, and thermal de-icing have been widely used in engineering practice. However, while these methods can achieve a certain degree of de-icing effect in complex service environments, they generally suffer from inherent limitations such as high energy consumption, poor environmental friendliness, and insufficient long-term economic viability.

[0003] In recent years, passive anti-icing strategies have received increasing attention. Among them, superhydrophobic surfaces, with their properties of reducing droplet residence time, increasing nucleation energy barriers, and reducing solid-liquid contact area, can effectively delay icing and reduce ice adhesion strength. However, research shows that a single superhydrophobic surface cannot maintain stable anti-icing performance under long-term low-temperature and high-humidity environments: the continuous condensation process causes moisture to gradually penetrate into the surface micro-nano textures, triggering a transition from the Cassie state to the Wenzel state in the wetting state, resulting in increased ice adhesion and a significant decrease in anti-icing effect. Furthermore, superhydrophobic surfaces themselves do not possess active ice-melting capabilities and cannot eliminate existing ice layers.

[0004] Photothermal materials can convert absorbed light energy into heat energy. Combining the active heating capability of photothermal materials with the passive hydrophobic properties of superhydrophobic interfaces to construct photothermal superhydrophobic surfaces holds promise for synergistic regulation of the icing and de-icing processes. This synergistic mechanism can overcome the shortcomings of single superhydrophobic surfaces, such as easy failure in low-temperature and high-humidity environments and easy residue of meltwater on single photothermal surfaces, providing a new approach for developing efficient, low-energy-consumption, and sustainable anti-icing / de-icing interfaces. Specifically, before icing occurs, the superhydrophobic properties inhibit ice formation by promoting droplet rolling and delaying nucleation. After ice formation, the photothermal material absorbs solar radiation and converts it into heat energy, raising the surface temperature and forming a meltwater layer at the ice-solid interface. Subsequently, the low adhesion and low contact angle hysteresis characteristics of the superhydrophobic surface weaken the direct contact between the meltwater and the substrate, promoting rapid meltwater detachment and reducing the risk of secondary freezing. Furthermore, the surface micro- and nano-structures not only determine the stability of the superhydrophobic state but also significantly affect the photothermal conversion efficiency. Porous, grooved, and hierarchically roughened structures can enhance multiple reflections and reabsorptions of incident light, generating a photothermal trap effect and improving solar energy utilization. Therefore, the design of high-performance photothermal superhydrophobic anti-icing interfaces needs to consider three aspects: high absorption and high conversion efficiency of photothermal materials, dual regulation of light capture and wetting state by micro-nano structures, and low adhesion and rapid removal of meltwater during de-icing.

[0005] In existing technologies, photothermal superhydrophobic coatings are typically prepared by compounding photothermal components such as carbon materials, MXene, or metal polyphenol networks with low surface energy polymers. For example, CN122326107A discloses a carbon-coated nano-silica photothermal superhydrophobic coating; CN119286394A discloses a polydimethylsiloxane / carbon nanotube porous material; CN122406335A discloses an MXene-metal polyphenol-based photothermal superhydrophobic anti-icing coating; and CN116656235A discloses an anti-icing and de-icing coating containing photothermal components and fluorinated silanes. Laser processing is also a common method for constructing micro-nano rough structures. CN114211121A discloses a processing method that first performs femtosecond laser ablation on the substrate surface and then coats it with a hydrophobic film.

[0006] However, the existing solutions still have the following shortcomings: (1) Carbon-based photothermal fillers are prone to agglomeration in the polymer matrix, and the interfacial bonding strength between them and the organic polymer matrix is ​​insufficient; at the same time, hydrophobic chemical components are prone to aging and degradation under environmental factors such as acid and alkali corrosion and ultraviolet irradiation, resulting in poor coating durability. (2) Some technical solutions rely on fluorine-containing low surface energy components to improve hydrophobicity, but fluorine-containing compounds are difficult to degrade in the environment, posing potential ecological risks. (3) The superhydrophobic performance of the coating is highly dependent on the integrity of the micro-nano hierarchical structure. During long-term de-icing and defrosting service, the surface structure is prone to wetting state changes, and droplets are difficult to maintain a stable Cassie-Baxter state, resulting in a sharp decline in anti-icing performance.

[0007] Therefore, there is a need for a method to prepare photothermal superhydrophobic coatings that are durable, fluorine-free, adaptable to a variety of substrates, and have controllable process parameters, so that the laser-induced micro-nano hierarchical structure can simultaneously play the role of stabilizing the low-adhesion wetting state and enhancing light capture. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention proposes a method for preparing a laser-induced fluorine-free photothermal superhydrophobic coating.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a laser-induced fluorine-free photothermal superhydrophobic coating includes the following steps: (1) The carbon-based photothermal filler was dispersed in Tris-HCl buffer to obtain a suspension, and dopamine (DA) was added to carry out in-situ self-polymerization reaction to obtain polydopamine (PDA) modified carbon-based composite photothermal filler. (2) The polydopamine-modified carbon-based composite photothermal filler is dispersed in a coating solvent to obtain a suspension, and fluorine-free resin and curing agent are added and mixed evenly to obtain a photothermal superhydrophobic coating. (3) The photothermal superhydrophobic coating is sprayed onto the substrate surface and then thermo-cured to obtain a composite coating; (4) The composite coating after curing is laser-etched using a nanosecond laser to remove the resin-rich area on the surface and construct a micro-nano hierarchical structure composed of micron-level columnar structure and nano-level roughness, thereby obtaining a laser-induced fluorine-free photothermal superhydrophobic coating.

[0010] This invention modifies the interface of carbon-based photothermal fillers with polydopamine to improve the dispersion stability and filler-matrix bonding force of the fillers in polymers and organic solvents, thereby reducing the risk of agglomeration and coating peeling and effectively improving the durability of the coating. Simultaneously, nanosecond lasers are used to precisely control the polymer coverage state and micro / nano-layer morphology of the composite coating surface. Laser etching forms micron-scale column arrays and nanoscale textures, constructing a stable micron-nano-layer structure. A process window is established between frequency, scanning speed, number of scans, power, and line spacing, ensuring sufficient laser energy to activate the coating surface without excessive ablation or substrate exposure. This laser-induced structure can simultaneously stabilize the low-adhesion Cassie-Baxter state and form light-harvesting microcavities, achieving synergistic effects of passive anti-icing, photothermal heating, and active de-icing. Furthermore, the preparation method is applicable to planar, flexible, or curved substrates and maintains good hydrophobic properties under mechanical, chemical, ultraviolet, outdoor aging, and freeze-thaw environments.

[0011] Further, in step (1), the pH of the Tris-HCl buffer is 8.5, the molar concentration of the Tris-HCl buffer itself is 0.05-1 mol / L; the concentration of the carbon-based photothermal filler in the suspension is 1-10 g / L; the concentration of the dopamine in the suspension is 1-10 g / L; and the conditions for the in-situ self-polymerization reaction are: mechanical stirring at 300-1000 rpm for 8-40 h at room temperature.

[0012] Further, in step (1), the carbon-based photothermal filler is one of carbon nanotubes, graphene, graphene oxide, carbon fiber, and carbon powder.

[0013] Further, in step (2), the coating solvent is one of ethyl acetate, n-hexane, n-heptane, n-butyl acetate, and isobutyl acetate; the concentration of the polydopamine-modified carbon-based composite photothermal filler in the suspension is 0.025–0.15 g / g; the fluorine-free resin is one of polydimethylsiloxane, epoxy resin, and two-component polyurethane, and the mass ratio of the fluorine-free resin to the curing agent is (1–10):1; the mass ratio of the polydopamine-modified carbon-based composite photothermal filler to the fluorine-free resin is (5–18):100.

[0014] Further, in step (3), the substrate is a rigid substrate or a flexible substrate; the rigid substrate is selected from one of copper, aluminum, stainless steel, carbon steel, glass, polyethylene plastic and ABS (acrylonitrile-butadiene-styrene copolymer) board, and is sandblasted before spraying; the flexible substrate is selected from one of fabric, paper and tape, and is not specially treated before spraying; the spraying parameters are: the spraying operation distance is 5-30cm, the atomization pressure is 0.1-0.6MPa; the curing temperature is 40-150℃, and the curing time is 6-40h.

[0015] Further, in step (4), the laser etching process parameters are: laser power 3-20W, laser scanning speed 350-600mm / s, laser frequency 40-80kHz, pulse width 2-20ns, and number of scans 7-19; the laser parameters are adjusted in a coordinated manner to determine the operable process window based on the surface states of under-etching, moderate etching, and over-etching.

[0016] The present invention also provides a laser-induced fluorine-free photothermal superhydrophobic coating, which is prepared by the above-described method.

[0017] Furthermore, the surface of the fluorine-free photothermal superhydrophobic coating has a micro-nano hierarchical structure composed of a micron-level columnar array and a nano-level roughness; the water contact angle of the fluorine-free photothermal superhydrophobic coating is greater than 150° and the roll-off angle is less than 10°; the average light absorption rate of the fluorine-free photothermal superhydrophobic coating in the wavelength range of 250 to 2500 nm is not less than 97%.

[0018] Furthermore, the fluorine-free photothermal superhydrophobic coating does not contain fluorine-containing low surface energy components, and the fluorine-free photothermal superhydrophobic coating still maintains its superhydrophobic properties after repeated tape peeling, acid / salt solution immersion, ultraviolet aging, outdoor exposure, and frost / defrost cycle testing.

[0019] The present invention also provides the application of a laser-induced fluorine-free photothermal superhydrophobic coating in the fields of anti-icing and / or de-icing.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects: (1) This invention utilizes polydopamine to modify the interface of carbon-based photothermal filler, which improves the dispersion uniformity of functionalized composite filler in organic resin and the bonding between filler and matrix, reduces agglomeration, interfacial voids and coating peeling, and effectively improves the mechanical stability of photothermal superhydrophobic coating; at the same time, relying on the excellent chemical stability of the material itself, it ensures the long-term durability of the coating in mechanical wear, corrosive solution immersion, ultraviolet aging and outdoor real environment.

[0021] (2) This invention uses a solidified composite coating containing functionalized photothermal fillers as the target for laser processing. The laser selectively removes the resin-rich surface layer and exposes the internal photothermal framework, which differs from the scheme of etching the bare substrate first and then coating. By coordinating the adjustment of power, frequency, scanning speed, number of scans and line spacing, and using the surface state of under-etching and over-etching as feedback, a reproducible parameter window can be established between the degree of resin layer removal, the micron-level columnar array morphology and the nano-level roughness.

[0022] (3) This invention utilizes the excellent hydrophobic properties of the resin itself, combined with the air layer captured by the laser-induced hierarchical structure, to obtain stable Cassie-state superhydrophobic properties. No additional superhydrophobic modification step is required, the coating does not require fluorine-containing low surface energy modifiers, and the water contact angle of the coating exceeds 150° and the roll-off angle is less than 10°. The use of an environmentally friendly fluorine-free system avoids the long-term accumulation of fluorides in the environment and potential pollution problems, meeting the requirements of green and sustainable development.

[0023] (4) This invention introduces carbon-based photothermal fillers and polydopamine photothermal components, enabling the coating to possess excellent photothermal conversion performance under sunlight. The same laser-induced hierarchical structure can simultaneously form a stable, low-adhesion superhydrophobic state and a light-harvesting microcavity, reducing the steps required to separately construct the hydrophobic layer and the photothermal layer, thereby enhancing the coating's ability to capture and convert sunlight. The broad-spectrum absorption rate in the 250–2500 nm range can reach up to 99.3%, and it exhibits passive delayed icing and active photothermal de-icing capabilities.

[0024] (5) This invention can be used on glass, metal, wood, paper, fabric and polymer sheets, and can also be prefabricated on a flexible carrier and then transferred to tubular or other curved substrates. The preparation method is simple, the raw materials are readily available and the cost is low. It is suitable for spray coating and has good engineering feasibility and industrial promotion value.

[0025] In summary, this invention provides a method for preparing a laser-induced fluorine-free photothermal superhydrophobic coating, which is environmentally friendly, sustainable, has high mechanical and chemical stability, and combines photothermal and superhydrophobic properties. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 SEM images of the coatings prepared in Example 1 and Comparative Examples 1-6; Figure 2 The contact angle and roll-off angle of the coatings prepared in Example 1 and Comparative Examples 1-6 are shown. Figure 3The adhesion test results are for the coatings prepared in Example 1 and Comparative Example 1. Figure 4 The absorption spectra of the coatings prepared in Example 1, Comparative Example 2, and Comparative Example 3 are shown. Figure 5 The actual temperature rise of the coatings prepared in Example 1, Comparative Example 2 and Comparative Example 3 after 300 seconds of exposure to standard sunlight in an environment of -15°C. Figure 6 The graph shows the freezing time of the coatings prepared in Example 1, Comparative Example 2 and Comparative Example 3 when 50 μL droplets were placed on the surface in an environment of -15°C. Figure 7 The graph shows the de-icing time of the coatings prepared in Example 1, Comparative Example 2 and Comparative Example 3 under one standard sunlight irradiation condition after a 50 μL droplet of liquid is frozen on a 20° inclined surface in an environment of -15°C and the coatings utilize the photothermal superhydrophobic properties. Figure 8 The coating prepared in Example 1 was subjected to various durability tests, and the results of the measurement of the contact angle and roll-off angle of the coating surface were obtained. Figure 9 This is a flowchart illustrating the preparation of a laser-induced fluorine-free photothermal superhydrophobic coating according to the present invention. Detailed Implementation

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0030] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0031] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0032] This invention provides a method for preparing a laser-induced fluorine-free photothermal superhydrophobic coating, comprising the following steps: (1) Preparation of polydopamine (PDA) modified carbon-based composite photothermal filler: The carbon-based photothermal filler is dispersed in Tris-HCl buffer solution with pH 8.5 and ultrasonically treated for 10-60 min (e.g., 30 min) to form a uniform suspension; then dopamine (DA) is added to it and mechanically stirred at 300-1000 rpm (e.g., 500 rpm) at room temperature for 8-40 h (e.g., 24 h) to promote in-situ self-polymerization of DA on the surface of the carbon-based filler. The functionalized composite filler generated is collected by centrifugation, and then placed in an oven at 40-100℃ (e.g., 80℃) to dry it thoroughly and grind it into fine powder for later use. The molar concentration of the Tris-HCl buffer solution is 0.05–1 mol / L (e.g., 0.05 mol / L); the concentration of the carbon-based photothermal filler in the suspension is 1–10 g / L (e.g., 2 g / L); the concentration of the dopamine in the suspension is 1–10 g / L (e.g., 2 g / L); the carbon-based photothermal filler is one of carbon nanotubes, graphene, graphene oxide, carbon fiber, and carbon powder (e.g., graphene oxide).

[0033] (2) Preparation of photothermal superhydrophobic coating: When preparing the coating, the polydopamine-modified carbon-based composite photothermal filler is dispersed in the coating solvent and ultrasonically treated for 5-30 min (e.g., 10 min) to form a uniform suspension; then, the fluorine-free resin and its curing agent (at a certain standard mass ratio) are added to the suspension to prepare a series of coating slurries with a mass ratio of polydopamine-modified carbon-based composite photothermal filler to fluorine-free resin of (5-18):100 (e.g., 10:100); after mechanical stirring at 500-1200 rpm (e.g., 800 rpm) to mix the components evenly, a uniformly dispersed photothermal superhydrophobic coating is obtained. The coating solvent is one of ethyl acetate, n-hexane, n-heptane, n-butyl acetate, and isobutyl acetate (e.g., ethyl acetate); the concentration of PDA@C in the suspension is 0.025–0.15 g / g (e.g., 0.03 g / g); the fluorine-free resin is one of polydimethylsiloxane, epoxy resin, and two-component polyurethane (e.g., polydimethylsiloxane), and the mass ratio of resin to curing agent is (1–10):1 (e.g., 10:1). The resin can be a polydimethylsiloxane system, and the curing agent is its matching organosilicon crosslinking curing agent containing silanium groups.

[0034] (3) Application of photothermal superhydrophobic coating: Before spraying, for rigid substrates, use 80-300 mesh quartz sand to sandblast the smooth rigid substrates to enhance surface roughness and interfacial adhesion. Then, ultrasonically clean these substrates in acetone, anhydrous ethanol and deionized water for 5 minutes each to remove surface grease and impurities, and finally blow dry for later use. For flexible substrates, no special treatment is required. Use an air spray gun to spray the coating onto the pretreated substrate surface. The operating distance during spraying is controlled at 5-30cm (e.g., 20cm), and the atomization pressure is set at 0.1-0.6MPa (e.g., 0.25MPa). After spraying, place the sample in an oven at 40-150℃ (e.g., 80℃) for heat curing. The heat curing time is 6-40h (e.g., 18h).

[0035] The rigid substrate includes one of copper, aluminum, stainless steel, carbon steel, glass, polyethylene plastic and ABS board (such as copper); the flexible substrate includes one of fabric, paper and tape.

[0036] (4) Micro-nano hierarchical structure processing: The cured composite coating is laser-etched using a nanosecond laser. This process can construct regularly arranged micron-level columnar structures, thereby forming a hierarchical morphology composed of micron-confined channels and nano-roughness, and obtaining a laser-induced fluorine-free photothermal superhydrophobic composite interface. The processing endpoint is determined by the surface state of the coating: when a continuous resin-rich layer still exists on the surface and the micro-nano hierarchical structure has not been formed, it is judged as under-etching, and the cumulative energy input or pulse space coverage is improved by reducing the scanning speed, increasing the number of scans, or coordinating the frequency; when the hierarchical structure collapses, through ablation occurs, or the substrate is exposed, it is judged as over-etching, and it is corrected by increasing the scanning speed, reducing the number of scans, or reducing the cumulative energy input; when the resin-rich surface layer is removed, the micron-level columnar structure is etched and rich nano-roughness is formed, it is determined as an operable window.

[0037] The laser power is 3-20W (e.g., 6W), the laser scanning speed is 350-600mm / s (e.g., 450mm / s), the laser frequency is 40-80kHz (e.g., 50kHz), the pulse width is 2-20ns (e.g., 20ns), and the number of scans is 7-19 (e.g., 9).

[0038] Unless otherwise specified, "room temperature" in this invention refers to 25±2℃.

[0039] All raw materials used in this invention were purchased from the market.

[0040] The technical solution of the present invention will be further illustrated by the following embodiments.

[0041] Example 1 A method for preparing a laser-induced fluorine-free photothermal superhydrophobic coating includes the following steps: (1) Preparation of polydopamine (PDA) modified carbon-based composite photothermal filler: 0.4 g of graphene oxide was dispersed in 200 mL of Tris-HCl buffer solution with a concentration of 0.05 mol / L and a pH of 8.5, and ultrasonically treated for 30 min to form a suspension with a concentration of 2 g / L. Then, 0.4 g of dopamine (DA) was added to it and mechanically stirred at 500 rpm for 24 h at room temperature to promote in-situ self-polymerization of DA on the surface of the carbon-based filler. The functionalized composite filler generated was collected by centrifugation, dried thoroughly in an oven at 80 °C, and ground and dispersed into powder to obtain polydopamine modified carbon-based composite photothermal filler (denoted as PDA@C). (2) Preparation of photothermal superhydrophobic coating: When preparing the coating, 0.5g of PDA@C was dispersed in 15g of ethyl acetate and ultrasonically treated for 10min to form a uniform suspension; then 5.0g of polydimethylsiloxane and 0.5g of the matching silicone crosslinking curing agent containing silane groups were mixed in a mass ratio of 10:1 and added to the suspension. The mass ratio of PDA@C to PDMS base adhesive in the coating slurry was 10:100. After mechanical stirring at 800rpm to make the components uniformly mixed, a uniformly dispersed photothermal superhydrophobic coating was obtained. (3) Construction of photothermal superhydrophobic coating: Before spraying, a smooth copper plate of 3cm×3cm×2mm was sandblasted with 150-mesh quartz sand to enhance surface roughness and interfacial adhesion. Then, these substrates were ultrasonically cleaned for 5 minutes each in acetone, anhydrous ethanol and deionized water to remove grease and impurities from the surface. Finally, they were dried for later use. The coating was sprayed onto the pretreated substrate surface using an air spray gun. The operating distance during spraying was controlled at 20cm and the atomization pressure was set at 0.25MPa. After spraying, the sample was placed in an 80℃ oven for heat curing for 18 hours. (4) Micro-nano hierarchical structure processing: The solidified composite coating is laser etched using a nanosecond laser. The laser power is controlled at 6W, the laser scanning speed is 450mm / s, the laser frequency is 50kHz, the pulse width is 20ns, and the number of scans is 9, to obtain a laser-induced fluorine-free photothermal superhydrophobic coating.

[0042] Example 2 Similar to Example 1, except that in step (2), the amount of PDA@C was adjusted to 5 wt% of the PDMS base adhesive, i.e., the mass ratio of PDA@C to PDMS base adhesive was 5:100. All other conditions were the same as in Example 1. The resulting coating exhibited a water contact angle of 158° and a roll-off angle of 8.8°, demonstrating superhydrophobic properties. The average light absorption rate of the coating in the wavelength range of 250–2500 nm was measured to be 96.1%.

[0043] Example 3 Similar to Example 1, except that in step (1), 0.4g of carbon nanotubes replaced 0.4g of graphene oxide, and the polydopamine modification conditions were the same as in Example 1, resulting in PDA@CNT; in step (2), 0.3g of PDA@CNT was dispersed in 15g of ethyl acetate, and 5.0g of PDMS base adhesive and 0.5g of matching curing agent were added, so that the mass ratio of PDA@CNT to PDMS base adhesive was 6:100; in step (4), the laser power was 6W, the scanning speed was 350mm / s, the frequency was 50kHz, the pulse width was 13ns, the number of scans was 11, and the scan line spacing was 50μm, with the remaining conditions being the same as in Example 1. The resulting coating had a water contact angle of 161°, a roll-off angle of 4.5°, and an average light absorption rate of 97.7% in the wavelength range of 250–2500nm.

[0044] Example 4 Similar to Example 1, the difference is that in step (3), a fabric is used as a flexible substrate, and no special treatment such as sandblasting is performed before spraying. The spraying, curing, and subsequent laser processing parameters are the same as in Example 1. The resulting fabric-based photothermal superhydrophobic coating has a water contact angle of 163.3° and a roll-off angle of 4.4°, indicating that the preparation method is also applicable to flexible substrates.

[0045] To further verify the applicability of the preparation method described in this invention to different amounts of polydopamine-modified carbon-based photothermal fillers, different carbon-based photothermal fillers, and different substrates, the wetting properties and light absorption properties of the coatings obtained in Examples 1 to 4 were tested, and the results are shown in Table 1.

[0046] Table 1 Performance test results of coatings obtained from different embodiments Comparative Example 1 Same as Example 1, except that step (1) is omitted, and the mass of PDA@C in step (2) is replaced with graphene oxide that has not been modified by polydopamine.

[0047] Comparative Example 2 Same as Example 1, except that in step (2), the mass ratio of PDA@C to fluorine-free resin is 0.1wt%.

[0048] Comparative Example 3 Similar to Example 1, except that step (4) is not performed, and the composite coating is not laser-treated after curing. The surface retains a continuous resin-rich layer and no effective micro-nano hierarchical structure is formed on the coating.

[0049] Comparative Example 4 Same as in Example 1, except that in step (4), the laser scanning speed of laser etching is 50 mm / s and the laser frequency is 70 kHz.

[0050] Comparative Example 5 Same as in Example 1, except that in step (4), the number of laser etching scans is 21.

[0051] Comparative Example 6 Same as in Example 1, except that in step (4), the number of laser etching scans is 3.

[0052] 1. The surface microstructure of the coatings prepared in Example 1 (i.e., Example 1 in the figure) and Comparative Examples 1-6 was characterized using a scanning electron microscope. The results are as follows: Figure 1 As shown. From Figure 1 As can be seen, the coating prepared in Example 1 has a regular array of micron-sized columnar structures, forming high aspect ratio cavities between the arrays. Simultaneously, nanoscale rough structures are uniformly distributed on the micron-sized columns. This micro-nano hierarchical structure can effectively trap air and maintain a stable Cassie-Baxter wetting state. Furthermore, the cavities formed in the etched areas can act as light-trapping microcavities, causing multiple scattering and reflection of incident light within the cavities, thereby enhancing light absorption. In Comparative Example 1, the photothermal filler in the coating was not modified with polydopamine, resulting in severe agglomeration within the coating. This loose agglomeration led to poor coating adhesion. In Comparative Example 2, due to insufficient addition of functionalized photothermal filler, the surface of the coating did not absorb enough laser light, failing to form an effective micro-nano hierarchical structure, resulting in a smoother and flatter surface. In Comparative Example 3, the coating, without laser treatment, retained a continuous resin layer on the surface, exhibiting a highly adhesive superhydrophobic state. In Comparative Examples 4 and 5, due to inappropriate laser processing parameters, the coating was excessively ablated, destroying the formed micron-sized columnar array and exposing the substrate. The coating prepared in Comparative Example 6, due to inappropriate laser processing parameters, only formed a shallow rough structure on the surface after etching, but failed to form a micron-scale columnar array, thus failing to effectively trap the air layer and form a low-adhesion Cassie-Baxter superhydrophobic state. These results indicate that the formation of the hierarchical structure is jointly determined by polydopamine interface modification, the content of functionalized photothermal fillers, and laser processing parameters.

[0053] 2. The contact angle and roll-off angle of the coatings prepared in Example 1 and Comparative Examples 1-6 were tested using a contact angle tester. The results are as follows: Figure 2 As shown. From Figure 2 As can be seen, the contact angle and roll-off angle of the coating are significantly affected by the amount of functionalized photothermal filler and the laser processing parameters. Example 1 exhibits excellent low-adhesion superhydrophobic properties, with a contact angle of 164.3° and a roll-off angle of only 3.1°. Although Comparative Example 1 has poor coating adhesion, it also possesses superhydrophobic properties, with a contact angle of 159° and a roll-off angle of only 5.2°. The water contact angles of Comparative Examples 2 to 6 are 107°, 133°, 141°, 130°, and 118°, respectively, and the roll-off angles are 40.5°, 85°, 55°, 80.7°, and 84.5°, respectively, none of which reach the low-adhesion superhydrophobic state. In summary, to form an effective micron columnar array with a structure that combines superhydrophobicity and high light-harvesting performance, it is necessary to modify the carbon-based photothermal filler, rationally control the amount of functionalized photothermal filler added, and rationally select the processing range of laser etching.

[0054] 3. To evaluate the adhesion of the coatings prepared in Example 1 and Comparative Example 1, a cross-cut adhesion test was conducted according to the standard GB / T 9286-2021 "Paints and Varnishes Cross-cut Adhesion Test". The specific method was as follows: a 1mm × 1mm grid was cut into the coating using a multi-bladed cutter, with the cuts reaching the substrate; then 3M tape (#600, Scotch) was applied and quickly removed. The adhesion between the coating and the substrate was quantified based on the area of ​​coating remaining on the substrate. Adhesion was graded from 0 to 5, with grade 0 being the best and grade 5 the worst. The results are as follows: Figure 3 As shown. Comparing the adhesion test results of Example 1 and Comparative Example 1, the coating adhesion of Example 1, after using polydopamine-modified graphene oxide, improved from level 5 to level 0, indicating that polydopamine modification can effectively improve the dispersion and interfacial bonding performance of photothermal fillers in polymer matrices.

[0055] 4. The absorption spectra of the coatings prepared in Example 1, Comparative Example 2, and Comparative Example 3 in the wavelength range of 0.25–2.5 μm were measured using a UV-Vis-NIR spectrophotometer. The results are as follows: Figure 4 As shown. From Figure 4As can be seen, the coating prepared in Comparative Example 2 had insufficient addition of functionalized photothermal filler, resulting in poor photothermal performance. The average light absorption rate in the 0.25–2.5 μm wavelength range was only 64.9%. In Comparative Example 3, the amount of PDA@GO added was the same as in Example 1, but without laser treatment, its average light absorption rate reached 95.6%, indicating that an appropriate amount of PDA@GO can endow the coating with strong broadband absorption capabilities. Based on this, Example 1, after laser treatment to form a micro / nano hierarchical structure, further increased the average light absorption rate to 99.3%, indicating that the laser-induced grooves and hierarchical rough structures can further improve light-harvesting capabilities by enhancing multiple scattering and reflection of incident light. The results show that functionalized photothermal filler is the main source of broadband absorption, and laser-induced hierarchical structures can further enhance light harvesting.

[0056] 5. The actual photothermal temperature rise of the coatings prepared in Examples 1, 2, and 3 was investigated in a low-temperature chamber at -15°C. Irradiation was performed under 1 sun conditions, and the surface temperature rise was recorded after 300 seconds. The results are as follows: Figure 5 As shown. From Figure 5 As can be seen, the temperature rise in Example 1 was 27.3°C, with the surface temperature increasing from approximately -15°C to approximately 12.3°C; the temperature rises in Comparative Examples 2 and 3 were 15.6°C and 20.3°C, respectively. These results are consistent with the changes in the absorption spectrum, indicating that the functionalized photothermal filler and the laser-induced light-harvesting structure have a synergistic promoting effect on the photothermal temperature rise.

[0057] 6. A static droplet freezing experiment was conducted at -15℃ to evaluate the anti-icing performance of the coatings prepared in Example 1, Comparative Example 2, and Comparative Example 3, and to compare the delay capabilities of different coatings in droplet freezing. In the experiment, thermally conductive silicone grease was applied to the back of the sample to reduce back-side contact thermal resistance. After the sample surface temperature stabilized, a 50 μL droplet was added to the surface, and the time required for the droplet to freeze completely from its initial application was recorded. The results are as follows: Figure 6 As shown. From Figure 6 As can be seen, the coating prepared in Example 1 has the longest droplet freezing delay time of 712 s, indicating that the micro-nano hierarchical structure formed by the coating can effectively capture the air layer, reduce the solid-liquid contact area, increase the thermal resistance of the solid-liquid interface, and increase the nucleation energy barrier, thus significantly delaying the freezing time. In contrast, the droplet freezing times of the coatings prepared in Comparative Examples 2 and 3 are 120 s and 192 s, respectively, indicating that the surface is easily induced to freeze by ice nuclei.

[0058] 7. To evaluate the anti-icing performance and active photothermal de-icing capability of the coatings prepared in Examples 1, 2, and 3, the photothermal melting performance of the coatings on an inclined surface was further tested. The experiment was conducted in a cold chamber at -15°C, with a frozen droplet volume of 50 μL and a light intensity of 1 sun. The surface was placed on an inclined plane with an angle of only 20°. The time required for the ice droplet to be removed from the surface or completely melted after being exposed to light was recorded. The results are as follows: Figure 7 As shown, from Figure 7 As can be seen, the coating prepared in Example 1 exhibits the best photothermal de-icing performance, with a de-icing time of only 131 s. This is due to two main reasons: firstly, the surface has excellent photothermal response properties, allowing it to heat up faster and reach a higher surface temperature after being exposed to light, thus efficiently melting ice droplets; secondly, the surface possesses stable Cassie superhydrophobic properties, resulting in low adhesion to melt water, which can be quickly removed under the influence of gravity. The coatings prepared in Comparative Examples 2 and 3, due to their poor photothermal performance and less than ideal hydrophobic properties, exhibited even worse photothermal de-icing performance, with de-icing times of 613 s and 397 s, respectively.

[0059] 8. To evaluate the excellent mechanical and chemical stability of the coating prepared in Example 1, repeated tape peeling, corrosive solution immersion, ultraviolet aging, outdoor exposure, and frosting / defrosting cycle tests were conducted. After the tests, the contact angle and roll-off angle of the coating were measured, and the results are as follows: Figure 8As shown. To investigate the stability of the micro / nano hierarchical structure under continuous peeling, a high-strength tape repeated peeling test was conducted. In the test, 3M standard tape was uniformly applied to the sample surface, and a 300g standard weight was applied for rolling and compaction to ensure full interface contact. The tape was then peeled off. After 50 cycles of peeling, the contact angle and roll-off angle of the coating remained stably within the superhydrophobic range. Simulating industrial acid rain and marine salt spray environments, the composite coating was continuously immersed in 1M HCl strong acid and 3.5wt% NaCl solution for 120 hours. After immersion, no blistering, cracking, or erosion was observed in the coating, and the contact angle and roll-off angle remained within the superhydrophobic range. Accelerated ultraviolet (UV) aging tests were conducted on the coating according to ASTM G154 standard. The test results showed that after 240 hours of UV irradiation, the interfacial wettability of the coating remained almost unchanged. To evaluate the hydrophobic stability of the coating in real-world applications, the coating sample was placed at a 45° angle in an outdoor environment for a long-term exposure test lasting 127 days. During this period, the coating underwent realistic and varied complex conditions, including high-temperature sunlight exposure, wind and sand erosion, heavy rain erosion, and diurnal temperature variations. The results showed that the hydrophobic performance of the coating surface did not show significant deterioration and maintained its Cassie state superhydrophobic characteristics. During service, the coating needs to repeatedly undergo the freeze-thaw phase transition process. Frost / defrost cycle tests were systematically conducted on a cold stage. In the test, the sample was fully exposed to humid atmosphere until a dense frost layer formed on the surface. The cold source was then turned off, and the sample was placed vertically to allow the frost layer to detach under environmental and photothermal effects. The results showed that even after repeated exposure to the physical effects of expansion stress during humid air freezing and the impact of alternating temperatures during photothermal defrosting, the superhydrophobicity of the coating decreased negligibly after 20 consecutive frost / defrost cycles, and the frost layer could always be completely peeled off from the surface. Based on the test results of the above durability performance, the coating prepared in Example 1 successfully integrates strong interfacial adhesion, excellent mechanical scratch resistance, good chemical and photo-induced stability, and real-world weather resistance across seasons into this fluorine-free photothermal superhydrophobic surface.

[0060] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a laser-induced fluorine-free photothermal superhydrophobic coating, characterized in that, Includes the following steps: (1) The carbon-based photothermal filler was dispersed in Tris-HCl buffer to obtain a suspension, and dopamine was added to carry out in-situ self-polymerization reaction to obtain polydopamine modified carbon-based composite photothermal filler. (2) The polydopamine-modified carbon-based composite photothermal filler is dispersed in a coating solvent to obtain a suspension, and fluorine-free resin and curing agent are added and mixed evenly to obtain a photothermal superhydrophobic coating. (3) The photothermal superhydrophobic coating is sprayed onto the substrate surface and then thermo-cured to obtain a composite coating; (4) The composite coating after curing is laser-etched using a nanosecond laser to remove the resin-rich area on the surface and construct a micro-nano hierarchical structure composed of micron-level columnar structure and nano-level roughness, thereby obtaining a laser-induced fluorine-free photothermal superhydrophobic coating.

2. The preparation method according to claim 1, characterized in that, In step (1), the pH of the Tris-HCl buffer is 8.5, the molar concentration of the Tris-HCl buffer is 0.05-1 mol / L, the concentration of the carbon-based photothermal filler in the suspension is 1-10 g / L, the concentration of the dopamine in the suspension is 1-10 g / L, and the conditions for the in-situ self-polymerization reaction are: mechanical stirring at 300-1000 rpm for 8-40 h at room temperature.

3. The preparation method according to claim 1, characterized in that, In step (1), the carbon-based photothermal filler is one of carbon nanotubes, graphene, graphene oxide, carbon fiber, and carbon powder.

4. The preparation method according to claim 1, characterized in that, In step (2), the coating solvent is one of ethyl acetate, n-hexane, n-heptane, n-butyl acetate, and isobutyl acetate; the concentration of the polydopamine-modified carbon-based composite photothermal filler in the suspension is 0.025–0.15 g / g; the fluorine-free resin is one of polydimethylsiloxane, epoxy resin, and two-component polyurethane, and the mass ratio of the fluorine-free resin to the curing agent is (1–10):1; the mass ratio of the polydopamine-modified carbon-based composite photothermal filler to the fluorine-free resin is (5–18):

100.

5. The preparation method according to claim 1, characterized in that, In step (3), the substrate is either a rigid substrate or a flexible substrate; the rigid substrate is selected from one of copper, aluminum, stainless steel, carbon steel, glass, polyethylene plastic and acrylonitrile-butadiene-styrene copolymer, and is sandblasted before spraying; the flexible substrate is selected from one of fabric, paper and tape, and is not specially treated before spraying; the spraying parameters are: spraying operation distance of 5-30cm, atomization pressure of 0.1-0.6MPa; the curing temperature of 40-150℃, and the curing time of 6-40h.

6. The preparation method according to claim 1, characterized in that, In step (4), the laser etching process parameters are: laser power 3-20W, laser scanning speed 350-600mm / s, laser frequency 40-80kHz, pulse width 2-20ns, and number of scans 7-19. The laser parameters are adjusted in a coordinated manner to determine the operable process window, based on the surface states of under-etching, moderate etching, and over-etching.

7. A laser-induced fluorine-free photothermal superhydrophobic coating, characterized in that, It is prepared by any one of claims 1 to 6.

8. The laser-induced fluorine-free photothermal superhydrophobic coating according to claim 7, characterized in that, The surface of the laser-induced fluorine-free photothermal superhydrophobic coating has a micro-nano hierarchical structure composed of a micron-level columnar array and a nano-level roughness; the water contact angle is greater than 150° and the roll-off angle is less than 10°; the average light absorption rate in the wavelength range of 250 to 2500 nm is not less than 97%.

9. The laser-induced fluorine-free photothermal superhydrophobic coating according to claim 7, characterized in that, The laser-induced fluorine-free photothermal superhydrophobic coating does not require the use of fluorine-containing low surface energy modifiers and retains its superhydrophobic properties after repeated tape peeling, acid / salt solution immersion, ultraviolet aging, outdoor exposure, and frost / defrost cycle testing.

10. The application of the laser-induced fluorine-free photothermal superhydrophobic coating according to any one of claims 7 to 9 in the fields of anti-frost and / or defrosting and phase change heat transfer enhancement.

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