An antifouling coating material, an antifouling coating, and a method for producing and using the same

Abstract

The application provides an antifouling coating material, an antifouling coating and a preparation method and application thereof. The antifouling coating prepared from the antifouling coating material provided by the application has a water contact angle of 105.8-161.5 degrees and a sliding angle of 1.5-24.1 degrees in a wavelength range of 200-2500 nm; a light absorption rate of 65.7-98.3 %; and a maximum light-heat surface temperature of 45.1-82.8 DEG C under 1 solar light intensity. Moreover, the antifouling coating has synergistic antifouling of superhydrophobic low adhesion and biological repellence, wide-spectrum high-efficiency and controllable light-heat antifouling capacity, all-weather antifouling capacity facing the air-water interface of the sea, and excellent mechanical durability and light-heat / wetting performance stability.

Description

Technical Field

[0001] This invention relates to the field of coating materials technology, specifically to an antifouling coating material, an antifouling coating, its preparation method, and its application. Background Technology

[0002] Marine biofouling refers to the process by which micro and macro marine organisms, such as bacteria, microalgae, barnacles, oysters, and mussels, attach and grow on the surfaces of engineering components such as ship hulls, offshore platforms, buoys, aquaculture cages, and marine sensor housings. Biofouling significantly increases ship drag and fuel consumption, accelerates the corrosion and failure of metal and alloy components, shortens service life, and increases cleaning and maintenance costs, making it one of the key issues restricting the reliability and economy of marine engineering equipment.

[0003] To mitigate biofouling, various antifouling coating technologies have been developed. Traditional antifouling coatings often rely on the slow leaching of organotin, organocopper, or quaternary ammonium salt biocides into seawater, inhibiting attachment and growth by releasing toxic ions or organic matter. While these coatings offer good antifouling effects in the short term, the long-term accumulation of biocides in the marine environment can cause serious harm to non-target organisms and ecosystems. Many organotin antifouling agents have been strictly restricted or banned by international conventions. With increasingly stringent environmental regulations, the development of non-toxic, low-toxic, and environmentally friendly antifouling coatings has become a research hotspot.

[0004] However, most existing antifouling coatings are still primarily designed for fully submerged solid-liquid interfaces. For components such as buoys, aquaculture ropes, and sensor housings that operate for extended periods at the marine air-water interface, experiencing frequent wet-dry cycles and intense sunlight exposure, suitable antifouling coating systems remain limited. Furthermore, the nutrient salts and gas concentration gradients enriched in the air-sea interface microenvironment easily induce the aggregation of microorganisms and algae. Traditional coatings relying solely on low surface energy or a single antibacterial mechanism have limitations in terms of antifouling effectiveness and stability. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an antifouling coating material, an antifouling coating, a preparation method thereof, and its application.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides an antifouling coating material, the antifouling coating material comprising the following raw material components by mass: 40-84 parts of polysulfurized urethane, 15-45 parts of a fluorinated low surface energy monomer, 1-15 parts of a capsaicin analog functional monomer, and 0.05-3 parts of a photothermal filler; wherein the total amount of the polysulfurized urethane, the fluorinated low surface energy monomer, and the capsaicin analog functional monomer is 100 parts; the polysulfurized urethane is obtained by an addition reaction of a polyfunctional thiol compound and a polyisocyanate compound; wherein the amount of the polyfunctional thiol compound is 28-54 parts (preferably 38-48 parts), and the amount of the polyisocyanate compound is 12-30 parts (preferably 18-26 parts).

[0007] Preferably, the amount of the fluorinated monomer is 24-36 parts, the amount of the capsaicin analog functional monomer is 2-8 parts, and the amount of the photothermal filler is 0.1-1.5 parts.

[0008] Furthermore, the polyfunctional thiol compound is at least one of pentaerythritol tetrakis(3-mercaptopropionic acid) ester (PETMP) and polymethylolpropane tris(3-mercaptopropionic acid) ester; the polyisocyanate compound is at least one of hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), and isophorone diisocyanate (IPDI).

[0009] Specifically, polyurethane thioester is used as a matrix resin to provide sufficient mechanical strength and adhesion to substrates. It is formed by the addition reaction of a thiol-containing polyfunctional thiol compound and a polyisocyanate compound, thereby forming a cross-linked network, preferably a polyurethane thioester backbone formed primarily of pentaerythritol tetrakis(3-mercaptopropionic acid) and hexamethylene diisocyanate. This backbone provides excellent mechanical strength, flexibility, and adhesion to metal substrates.

[0010] Furthermore, the fluorinated low surface energy monomer is one or more of fluorinated acrylates, fluorinated olefins, fluorinated silanes, and fluorinated long-chain alkyl groups; preferably, the fluorinated low surface energy monomer is 1H,1H,2H,2H-17 fluorodecyl acrylate (HDFDA).

[0011] The fluorinated low surface energy monomer can be a fluorinated acrylate monomer, such as HDFDA, which forms side chains in the polyurethane network. During curing, the fluorinated segments spontaneously accumulate on the coating surface, significantly reducing surface free energy and providing a chemical basis for the formation of a superhydrophobic interface. This fluorinated low surface energy monomer is not limited to HDFDA; it can also be other fluorinated acrylates, fluorinated olefins, fluorinated silanes, fluorinated long-chain alkyl groups, etc., as long as they can form a fluorine-rich layer on the coating surface, significantly reducing surface free energy and achieving similar superhydrophobic / low-adhesion effects.

[0012] Furthermore, the capsaicin analog functional monomer is a functional monomer or prepolymer with capsaicin structural characteristics, including at least one of 1-hydroxy-2,4-bis(methyleneacrylamide)naphthalene (HMN), 1-[(propenyloyl)amino]methyl-4-methoxynaphthalene, and 1-[(propenyloyl)amino]methyl-2-ethoxynaphthalene.

[0013] The structural formula of 1-hydroxy-2,4-bis(methyleneacrylamide)naphthalene (HMN) is as follows: ; The structural formula of 1-[(propenyloyl)amino]methyl-4-methoxynaphthalene is: ; The structural formula of 1-[(propenoyl)amino]methyl-2-ethoxynaphthalene is: .

[0014] It should be noted that capsaicin analog functional monomers, i.e., functional monomers with capsaicin structural characteristics (such as capsaicin analogs containing naphthalene rings and amide structures), are further introduced into the coating material and fixed in the polyurethane network by covalent bonds through copolymerization or grafting, forming a non-exudative bio-repellent interface. Capsaicin analog fragments can interfere with the adhesion behavior of microorganisms and attached organisms, exhibiting biorepulsion and adhesion inhibition effects on bacteria, microalgae, and mollusks.

[0015] Furthermore, the photothermal filler is one or more of carbon-based materials, MXene materials, and metal compound nanomaterials; wherein, the carbon-based material is selected from one or more of carbon nanotubes, graphene, carbon black, carbon nanofibers, carbon nanospheres, and carbon quantum dots; and the MXene material is selected from Ti3C2T. x Ti2CT x Nb2CT x V2CT x One or more of two-dimensional transition metal carbon / nitrides; the metal compound nanomaterial is selected from one or more of titanium dioxide, iron oxide, copper oxide, copper sulfide, molybdenum sulfide, tungsten sulfide, gold nanomaterials, and silver nanomaterials.

[0016] To endow the coating with broad-spectrum light absorption and photothermal conversion capabilities, this invention preferably uses hydroxylated carbon nanotubes (CNT-OH) with hydroxyl functional groups on their surface as a photothermal filler. CNT-OH possesses high absorption capacity in the visible-near-infrared spectral range, and under illumination, it can rapidly convert absorbed light energy into heat energy, achieving localized interfacial heating. Hydroxylation facilitates its dispersion in the polyurethane matrix and allows it to form a certain interfacial bond with polyurethane through hydrogen bonds or other interactions. By adjusting its doping amount, different tunable photothermal effects and rough structures can be achieved.

[0017] Photothermal fillers can be hydroxylated carbon nanotubes (CNT-OH), or other nanomaterials with broad-spectrum light absorption and high photothermal conversion efficiency, such as: oxidized or carboxylated carbon nanotubes, graphene and its oxides, reduced graphene oxide; carbon-based photothermal materials such as carbon black, conductive carbon black, carbon spheres, and carbon quantum dots; and other inorganic photothermal materials such as MXene, black titanium dioxide, copper oxide / iron oxide nanoparticles, metal sulfides, or metal nanoparticles.

[0018] The surface of the photothermal filler can contain functional groups such as hydroxyl, carboxyl, and amino groups, which can be bonded to polyurethane via hydrogen bonds or chemical bonds to improve dispersibility and interfacial stability. As long as it can effectively absorb light within the solar spectrum and convert light energy into heat energy, thereby generating the localized temperature rise required for antifouling on the coating surface, it can be considered an equivalent substitute for the photothermal filler of this invention.

[0019] A second aspect of the present invention provides a method for preparing the above-mentioned antifouling coating material, the method comprising: (1) The polyfunctional thiol compound, the fluorine-containing low surface energy monomer and the capsaicin analog functional monomer are dissolved together in an organic solvent and prepolymerized under the action of an initiator to obtain a prepolymer solution. (2) Add the photothermal filler to the prepolymer solution and mix evenly to obtain a photothermal filler dispersion; wherein the photothermal filler and carbonyl, amino and other groups in the prepolymer can form hydrogen bonds or other secondary interactions, which is beneficial to the construction of a stable crosslinking network.

[0020] (3) Add a polyisocyanate compound to the photothermal filler dispersion and mix thoroughly to obtain the antifouling coating material.

[0021] Furthermore, in step (1), the temperature of the prepolymerization reaction is 80~90℃ and the time is 2~5 h; the organic solvent includes ethyl acetate; the initiator includes azobisisobutyronitrile (AIBN), and the amount used is 0.5~3 parts (preferably 0.7~1.8 parts); in step (2), the mixing method is ultrasonic dispersion and mechanical stirring.

[0022] The third aspect of the present invention provides a method for preparing an anti-fouling coating, the method comprising: applying the anti-fouling coating material as described above to the surface of a substrate by spraying, brushing or dipping, and curing it at a temperature of 20~60 ℃ for 12~48 h to obtain the anti-fouling coating.

[0023] Understandably, the substrate surface was subjected to rust removal, cleaning, and / or primer treatment before spraying, brushing, or dipping. After coating, curing is performed, allowing the mercapto groups to undergo an addition reaction with the isocyanate, forming a cross-linked polysulfururethane network. This simultaneously fixes the positions of fluorinated segments, capsaicin analogs, and photothermal fillers, resulting in a dense and well-adhered photothermal superhydrophobic antifouling coating.

[0024] During curing and film formation, due to the low surface energy effect of fluorinated segments, they spontaneously migrate and accumulate on the outermost surface of the coating. Simultaneously, crosslinking shrinkage and stress release caused by component inhomogeneity "push" the surface into micron-scale wrinkles and protrusions. The presence of photothermal fillers further enhances local stiffness and stress concentration, resulting in a micro / nano-level rough structure with multi-scale wrinkles, folds, and peaks. Capsaicin analogue fragments are uniformly distributed throughout the network and exposed on the surface, forming a chemical functional interface.

[0025] The fourth aspect of the present invention provides an antifouling coating prepared by the above-described method, wherein the antifouling coating has a water contact angle of 105.8° to 161.5° and a sliding angle of 1.5° to 24.1° in the wavelength range of 200 to 2500 nm; a light absorption rate of 65.7% to 98.3%; and a maximum photothermal surface temperature of 45.1 to 82.8 °C under one solar irradiance.

[0026] The fifth aspect of the present invention provides the application of the above-described antifouling coating in marine engineering components located at the air-sea interface.

[0027] Compared with the prior art, the technical solution provided by the present invention has at least the following advantages: (1) Non-leaching, environmentally friendly antifouling mechanism.

[0028] This invention utilizes capsaicin analog functional monomers covalently introduced into a polysulfuric acid ester network to form a non-exudative, contact-active biorepellent interface. It achieves long-term inhibition of bacteria, microalgae, and large fouling organisms without relying on the continuous release of highly toxic biocides such as organotin and organocopper. Compared to traditional exudative antifouling coatings, it effectively reduces the potential toxicity and bioaccumulation risk to the marine ecosystem, meeting green environmental protection and regulatory requirements.

[0029] (2) Synergistic antifouling effect of superhydrophobic low adhesion and bio-repellency.

[0030] This invention utilizes the stress mismatch caused by the enrichment of fluorinated monomers on the surface and curing shrinkage to spontaneously construct a micron / nano-level rough structure on the coating surface. This allows the coating to achieve a superhydrophobic state with a water contact angle ≥150° and a roll-off angle ≤10° over a wide range of formulations. Simultaneously, the exposed capsaicin analog groups on the surface exhibit both repulsive and inhibitory effects on fouling bioadhesion. Compared to existing coatings that rely solely on low surface energy or a single superhydrophobic mechanism, this invention maintains lower adhesion and higher inhibition efficiency even under static, low-flow-rate, and alternating wet and dry conditions.

[0031] (3) Broad spectrum, high efficiency and adjustable photothermal antifouling capability.

[0032] The antifouling coating material formulation of this invention uses photothermal filler, preferably hydroxylated carbon nanotubes, which have high absorption rates in the visible-near-infrared band and achieve uniform dispersion and stable interlocking through interfacial interaction with the polyurethane matrix. Under simulated sunlight irradiation, the coating can achieve significant temperature rise in a short time, and the maximum temperature and heating rate can be controlled by the dosage of the photothermal filler and the light intensity, achieving photothermal killing or weakening of attached fouling organisms. Compared with existing coatings that only possess photothermal or superhydrophobic functions, this invention achieves a synergistic antifouling effect of "superhydrophobic low adhesion + photothermal active killing" within the same system, significantly broadening the effective antifouling operating window.

[0033] (4) All-weather antifouling capability for the marine air-water interface.

[0034] This invention's coating specifically considers the microenvironmental characteristics of the marine air-water interface under alternating wet and dry conditions and strong sunlight. In the absence of light or low light, it achieves passive antifouling through superhydrophobicity, low adhesion, and biorepellency via capsaicin analogues. Under daylight conditions, it transitions to active antifouling mode through the photothermal effect of the photothermal filler, thus maintaining good antifouling performance throughout the diurnal cycle. Compared to traditional antifouling coatings primarily targeting fully submerged solid-liquid interfaces, this invention is more suitable for marine engineering components such as buoys, monitoring equipment, and aquaculture cables that are constantly exposed to the air-sea interface.

[0035] (5) Excellent mechanical durability and photothermal / wetting performance stability.

[0036] Thanks to the highly adhesive polyurethane network and the mechanical framework formed by the photothermal filler, the coating of this invention maintains its complete and dense morphology even after repeated friction, seawater immersion, and multiple light-dark cycles. Although the surface roughness structure evolves somewhat, the superhydrophobic contact angle and low roll-off angle are basically maintained, and the photothermal heating curve shows only a slight decay. Compared with some existing photothermal or superhydrophobic coatings that are prone to failure after mechanical damage, this invention has a longer effective protective life and lower maintenance costs under actual marine service conditions. Attached Figure Description

[0037] Figure 1 This is a synthesis route diagram of the antifouling coating provided in the embodiments of the present invention; Figure 2 This is a fluorescence image of a coating containing capsaicin and dibenzyl capsaicin analogues under ultraviolet light irradiation, provided in an embodiment of the present invention. Figure 2 (a) Fluorescence image of coatings containing capsaicin and dibenzyl capsaicin analogues in air. Figure 2 (b) is a fluorescent image of a coating containing capsaicin and dibenzyl capsaicin analogues underwater; Figure 3 3(a) is a scanning image of the antifouling coating provided in the embodiments of the present invention; 3(a) is a scanning electron microscope (SEM) image of the coating. Figure 3 (b) is a confocal laser scanning microscope (CLSM) image; Figure 4 This is a SEM image of carbon nanotubes anchored in a polymer matrix, provided in an embodiment of the present invention. Figure 5 This is the UV-vis-NIR absorption spectrum of the antifouling coating provided in the embodiments of the present invention; Figure 6 This is the highest photothermal conversion temperature of the antifouling coating provided in the embodiments of the present invention; Figure 7 These are fluorescence microscope images of Chlorella on the antifouling coating provided in this embodiment of the invention; Figure 8 These are fluorescence microscopic images of live and dead Escherichia coli on the antifouling coating provided in this embodiment of the invention; Figure 9 These are optical photographs of the mussel distribution and byssal protein adhesion on the antifouling coating provided in this embodiment of the invention before and after the test. Detailed Implementation

[0038] The inventors' research revealed the following prominent problems with existing marine antifouling coating technologies: First, traditional antifouling coatings containing biocides such as organotin, organocopper, or quaternary ammonium salts rely on the continuous seepage of toxic components into seawater to suppress fouling, easily causing marine ecological pollution and bioaccumulation, which does not meet current green environmental protection and regulatory requirements; Second, non-toxic / low-toxic antifouling coatings, represented by fluorosilicone resins and low surface energy polymers, mostly adopt a passive "easy desorption" mechanism, mainly relying on reducing surface energy and superhydrophobic effects to weaken adhesion, making it difficult to remove fouling organisms in a timely manner under static or low shear conditions. First, existing photothermal antibacterial or photothermal antifouling coatings, while incorporating light-absorbing fillers, generally suffer from low photothermal conversion efficiency, non-superhydrophobic surfaces, and performance degradation under long-term seawater immersion and mechanical friction, making it difficult to balance efficient photothermal response with long-term durability. Second, existing coating designs often fail to achieve the organic synergy of three mechanisms: biological repulsion, superhydrophobic low adhesion, and photothermal killing, lacking an all-weather interface system with stable antifouling capabilities under both light and dark conditions.

[0039] To address the aforementioned shortcomings, the technical problem to be solved by this invention is to provide an antifouling coating material, an antifouling coating, a preparation method thereof, and its application. This coating, in alternating wet and dry environments such as the marine air-water interface, simultaneously possesses the following performance characteristics: First, without relying on soluble biocides, a specific structural design is used to achieve long-term inhibition and easy desorption of bacteria, microalgae and large attached organisms, thereby reducing the potential toxic risks to the marine ecological environment. Secondly, by constructing a superhydrophobic interface that combines low surface energy with hierarchical roughness, it can still maintain low adhesion and excellent self-cleaning ability under complex working conditions such as static, low flow rate and periodic wetting. Furthermore, by introducing highly efficient broadband light-absorbing components, the light absorption and photothermal conversion efficiency of the coating in the visible-near-infrared solar spectrum range is improved, and localized interface heating is rapidly generated under sunlight irradiation, thereby achieving photothermal killing or weakening of attached fouling organisms. Finally, even under long-term seawater immersion, mechanical friction, and multiple photothermal cycles, it can still maintain a high contact angle, a low roll-off angle, and stable photothermal heating performance, exhibiting good mechanical durability and thermal stability, making it suitable for large-area applications on the surfaces of actual marine engineering equipment.

[0040] As can be seen, the present invention aims to construct a coating system that combines environmental friendliness, superhydrophobicity and low adhesion, and photothermal active antifouling capability, providing a new material solution for all-weather antifouling of marine engineering components at the air-water interface.

[0041] The present invention will now be described in detail with reference to specific embodiments.

[0042] This invention provides an antifouling coating material, specifically a polyurethane sulfide synthesized from PETMP and HDI, a fluorinated low surface energy monomer HDFDA, a capsaicin analog functional monomer HMN, and a photothermal filler CNT-OH. The synthetic route for preparing the antifouling coating using the above raw materials is as follows: Figure 1 As shown.

[0043] This invention employs a two-stage, step-by-step preparation method: first, under isocyanate-free conditions, a thiol-olefin click prepolymerization reaction is completed with polyfunctional thiols, fluorinated monomers, and capsaicin analog functional monomers to obtain a functionalized prepolymer; then, photothermal fillers are introduced and crosslinked with polyisocyanates for curing, thereby achieving efficient fixation of functional components, uniform dispersion of fillers, and stable construction of a fluorine-rich surface layer and hierarchical structure. This step-by-step process avoids the competitive consumption of -NCO by -SH and inhibits premature curing. The resulting coating exhibits a more uniform distribution of functional components, a more stable superhydrophobic interface, and a higher photothermal conversion retention rate. Even after tribological durability testing, it maintains its superhydrophobic properties, with only a slight decrease in the maximum photothermal temperature, demonstrating excellent long-term service stability.

[0044] See Figure 2 The biaromatic capsaicin analogue used in this invention possesses both biorepellent groups and luminescent chromophores, making it more conducive to generating a fluorescence response (requiring photoexcitation) than monoaromatic / natural capsaicin. Under illumination, the fluorescence response can serve as an interfacial optical signal, interfering with the attachment behavior of fouling organisms such as microalgae (preferring photosynthesis and interfering with attachment mechanisms), thereby synergistically improving the antifouling effect with superhydrophobic low adhesion and photothermal heating effects.

[0045] See Figure 3 In addition to providing photothermal conversion driven by light, photothermal fillers can also play a synergistic role as structural and mechanical reinforcing phases of coatings: firstly, fillers induce and strengthen surface undulations and micro / nano-level rough structures during the curing process, promoting the formation of stable superhydrophobic interfaces. Figure 3 As shown in the SEM and CLSM data, the micro-wrinkle morphology and surface roughness of the coating interface increase with the increase of photothermal filler; secondly, the filler forms a mechanically anchored skeleton in the cross-linked network, dispersing the frictional load and inhibiting crack propagation, thereby improving wear resistance and anti-stripping performance. Figure 4 As shown, carbon nanotubes are firmly anchored to the polymer matrix.

[0046] Example 1 Weigh out 52 parts PETMP, 20 parts HDFDA, and 3 parts HMN by weight, add ethyl acetate to form a homogeneous and stirable system, and add 1 part AIBN initiator; react at 85 °C for 4 h to obtain a prepolymer. Mix the prepolymer with 25 parts HDI and 0.05 parts carbon black, and disperse under stirring for 3 h to obtain a coating material. Apply the coating material to the surface of the pretreated substrate by spraying, and cure at 60 °C for 12 h to form a film, thus obtaining an antifouling coating.

[0047] Example 2 Weigh out the following components by weight: 48 parts PETMP, 25 parts HDFDA, and 3 parts HMN. Add ethyl acetate and 0.8 parts AIBN initiator. React at 85 °C for 4 h to obtain the prepolymer. Mix the prepolymer with 24 parts HDI and Ti3C2T... x Mix 0.10 parts and stir and disperse for 5 h to obtain a coating material; apply the coating material to the surface of the pretreated substrate and cure at 60 ℃ for 20 h to form a film.

[0048] Example 3 Weigh out 44 parts PETMP, 30 parts HDFDA, and 4 parts HMN by weight, add ethyl acetate and 1 part AIBN initiator; react at 85 °C for 4 h to obtain a prepolymer. Mix the prepolymer with 22 parts HDI and 0.30 parts graphene, stir and disperse for 6 h to obtain a coating material; coat the coating material onto the surface of the pretreated substrate and cure at 60 °C for 24 h to form a film.

[0049] Example 4 Weigh out 40 parts PETMP, 34 parts HDFDA, and 6 parts HMN by weight, add ethyl acetate and 1.2 parts AIBN initiator; react at 85 °C for 5 h to obtain a prepolymer. Mix the prepolymer with 20 parts HDI and 0.80 parts tungsten sulfide, stir and disperse for 6 h to obtain a coating material; coat the coating material onto the surface of the pretreated substrate and cure at 60 °C for 24 h to form a film.

[0050] Example 5 Weigh out the following components by weight: 42.5 parts PETMP, 31 parts HDFDA, and 4.5 parts HMN. Add ethyl acetate and 1.2 parts AIBN initiator. React at 85 °C for 5 h to obtain a prepolymer. Mix the prepolymer with 22 parts HDI and 1.50 parts carbon nanotubes, and stir and disperse for 6 h to obtain a coating material. Apply the coating material to the surface of the pretreated substrate and cure at 60 °C for 30 h to form a film.

[0051] Effect test: The water contact angle of the coating surface was measured using a contact angle meter. A droplet of deionized water (2 μL) was slowly added to the sample surface. After the droplet stabilized (5 s), the droplet profile was captured and the static contact angle was calculated. Measurements were taken at least five times at different locations for each sample, and the average value was taken as the water contact angle for that sample. The results are shown in Table 1.

[0052] The roll-off angle (slip angle) of the coating surface was determined using a tilting table contact angle measuring device. A droplet of deionized water (2 μL) was added to the sample surface, and the tilt angle was slowly increased at a constant rate. The minimum tilt angle at which the droplet began to roll / slip continuously was recorded as the roll-off angle. Each sample was measured at at least five times at different locations, and the average value was taken. The results are shown in Table 1.

[0053] The diffuse reflectance spectrum of the coating was measured using a UV-Vis-NIR spectrophotometer equipped with an integrating sphere attachment. Barium sulfate (BaSO4) was used as a reference white plate, and the test wavelength range was 200–2500 nm. The diffuse reflectance of the sample was recorded, and the absorbance was calculated. The results are as follows: Figure 5 As shown.

[0054] A solar simulator was used as the light source, and the light intensity was set to 1 sun (1000 W·m). -2 The sample was placed horizontally in a fixed position, ensuring the light spot completely covered the test area. An infrared thermal imager was used to record the temperature change curve of the sample surface over time during illumination until a stable plateau was reached. The highest surface temperature during the stable plateau phase was taken as the highest photothermal surface temperature of the sample under 1 sun conditions. The results are as follows: Figure 6 As shown.

[0055] To evaluate the superhydrophobic stability and photothermal performance changes of the coating under mechanical wear, a tribological durability test was conducted. During the test, the coating surface was placed in contact with 1000-grit sandpaper, and a 100 g load was applied to the back of the coating. Horizontal reciprocating friction was performed along a straight line. One cycle was defined as pushing forward 10 cm and then backward 10 cm (total travel 20 cm). This was repeated for 100 cycles. After 100 cycles, the water roll-off angle and photothermal performance of the coating were further measured to comprehensively evaluate the coating's superhydrophobic retention and photothermal conversion stability after the durability test. The results are shown in Table 2.

[0056] Prepare a Chlorella suspension and adjust the initial algal cell concentration to 1×10⁻⁶. 5The algae were cultured at approximately 1000 mL / mL under conditions of 4000 lux light intensity, 20 ± 2 °C, and a 12:12 h light-dark cycle. The coated samples were then immersed in an equal volume of algal suspension for static culture for 72 h. After culture, the samples were removed, irradiated for 5 minutes under a sunlight simulator, and gently rinsed with deionized water to remove any unattached algal cells. The algal cell coverage area on the sample surface was quantified using fluorescence microscopy, and the algae resistance rate was calculated. The results are shown below. Figure 7 As shown.

[0057] Prepare an Escherichia coli suspension and bring its initial concentration to 10. 7 At approximately CFU / mL, the samples were cultured at 37°C. The coated samples were immersed in the bacterial suspension and cultured on a constant-temperature shaker for 18 hours. After culture, the samples were removed and irradiated under a sunlight simulator for 5 minutes, followed by gentle rinsing with buffer to remove any unattached bacteria. Fluorescent live / dead staining combined with fluorescence microscopy was used to quantify the bacterial coverage area on the sample surface and calculate the antibacterial rate. The results are as follows: Figure 8 As shown.

[0058] The mussels were fed natural spirulina powder, fed regularly every two days, with timely water changes to maintain a stable rearing environment. The rearing temperature was maintained at 20±2 ℃. Healthy mussels were placed on the surface of the coated sample. During the experiment, the mussels were allowed to move and stack. After the four-week experimental period, the mussels were removed from the incubator, and the amount of byssal protein attached to the coating surface was recorded. The results are as follows: Figure 9 As shown.

[0059] The test results for the above-mentioned parts are shown in Table 1, and the durability test results are shown in Table 2.

[0060] Table 1. Test results of water contact angle, roll-off angle, light absorptivity, maximum photothermal conversion temperature, anti-algae rate, antibacterial rate, and anti-mussel adhesion rate for Examples 1 to 5.

[0061] Table 2 Durability test results of Examples 1 to 5

[0062] As can be seen, embodiments of the present invention provide a series of capsaicin-functionalized PTU-based superhydrophobic photothermal coatings (PHF / CNT-x) for marine structures operating at dynamic air-water interfaces. These coatings are constructed on a PTU framework with high mechanical strength and strong adhesion, incorporating fluorinated acrylates and covalently linked capsaicin analogs to form a low surface energy interface with graded roughness, achieving a contact-based and environmentally friendly repulsion mechanism. CNT-OH is further dispersed within this framework. Low-load carbon nanotubes (CNTs) can serve as broadband light absorbers and thermally conductive frameworks, enabling rapid and reversible photothermal conversion under sunlight irradiation. Under light-free conditions, the combination of the capsaicin analog repulsion effect and the superhydrophobic state holds promise for passively inhibiting the attachment of bacteria, microalgae, and mussels. Under light irradiation, CNT-mediated heating can synergistically inactivate or remove residual fouling organisms. This invention integrates covalently bonded capsaicin analogues, fluorinated superhydrophobicity, and CNT-mediated photothermal activity into a PTU matrix to construct a sunlight-responsive and environmentally friendly marine antifouling coating suitable for dynamic air-water interface structures.

[0063] Referring to Table 1, the superhydrophobic properties of the coating are mainly due to the introduction of fluorinated functional monomers and aromatic groups, which reduces surface polarity. Furthermore, microphase separation creates localized circular regions, leading to partial chemical heterogeneity and further enhancing the apparent hydrophobicity. The added photothermal fillers (such as carbon nanotubes) form a robust multi-scale network, enhancing the surface morphology and promoting air trapping, thus producing a superhydrophobic state.

[0064] See Figure 5 The UV-Vis-NIR diffuse reflectance spectroscopy showed that the introduction of CNTs significantly enhanced the absorption in the 200–2500 nm range, with the total absorbance remaining above 96%. The near-complete light absorption is due to the combined effect of the carbon nanotube π-electron network capturing broadband light and the multiple reflections within the rough surface of the micro / nanostructure.

[0065] See Figure 6 In simulated sunlight (1 sun, 1000 W·m), -2 Under these conditions, the surface temperature of the coating increases significantly. This phenomenon stems from the inherently high absorption rate of carbon nanotubes and the ultrafast nonradiative relaxation of photoexcited electrons via phonon coupling. Furthermore, the percolating carbon nanotube network promotes lateral heat transfer within the polymer matrix, thereby achieving a uniform temperature distribution and rapid thermal equilibrium.

[0066] Referring to Table 2, the mechanical durability of the coating was evaluated by simulating long-term surface wear through repeated wear cycles. After the above-mentioned friction durability test (100 cycles), the photothermal superhydrophobic and antifouling coating obtained in the preferred embodiment maintained a stable superhydrophobic state. This was demonstrated by the static water contact angle remaining within the superhydrophobic range and the roll-off angle remaining low. This indicates that its hierarchical rough structure and low surface energy components stabilized the Cassie state by trapping air below the water droplet and maintaining an extremely low solid-liquid contact rate after mechanical wear. Simultaneously, the highest photothermal surface temperature of the coating under simulated sunlight irradiation showed only a slight decrease after the durability test, indicating that the photothermal filler has a good embedding and fixation effect in the polymer network, and the overall light absorption and photothermal conversion functions did not significantly decrease. This slight decrease can be attributed to the local wear of the surface photothermal filler caused by friction and the change in heat dissipation conditions caused by changes in surface microstructure. The durability of the coating of this invention originates from the synergistic effect of "mechanical support of the matrix resin network - stable enrichment of low surface energy components - non-exudation fixation of functional components - embedding enhancement of photothermal filler". First, the polyurethane matrix resin forms a continuous and dense network structure through cross-linking and curing, endowing the coating with high cohesive strength and adhesion to the substrate. Under frictional loads, it is less prone to large-area peeling, thus providing a stable load-bearing foundation for the surface microstructure. Second, the fluorinated low surface energy monomers are chemically bonded to the matrix resin structure, maintaining low surface free energy and reducing the adhesion of dirt and water droplets even during slight wear. Simultaneously, the capsaicin analog functional monomers are fixed in the network through copolymerization via chemical bonds, preventing the migration and loss of physically blended components during friction or immersion, ensuring the long-term effectiveness of the functional interface. Furthermore, the photothermal filler is uniformly dispersed in the matrix resin and forms a stable interface with the polymer network through physical interlocking and hydrogen bonding / polar interactions. This improves local modulus and shear resistance while maintaining a certain level of light absorption and photothermal conversion capacity after wear. Therefore, even after mechanical wear, the coating retains its superhydrophobic properties, and the maximum photothermal conversion temperature only decreases slightly.

[0067] See Figure 7 , Figure 8 and Figure 9The preferred embodiment coating exhibits high inhibition rates in algae suppression, antibacterial, and anti-mussel adhesion tests. This is mainly attributed to the superhydrophobic interface constructed by the low surface energy components and hierarchical rough structure of the coating surface, as well as the synergistic antifouling mechanism formed by capsaicin analogs and photothermal fillers. Under no-light or low-light conditions, the coating surface maintains a stable Cassie state and forms a gas-solid composite interface, significantly reducing the actual solid-liquid contact area and effective adhesion sites, making it difficult for fouling organisms to achieve sufficient wetting and firm anchoring. Simultaneously, capsaicin analogs are covalently fixed in the polymer network, forming a contact-active repellent layer that interferes with the initial attachment and adhesion process of fouling organisms, thereby improving the overall anti-adhesion ability. Under light conditions, the photothermal fillers in the coating absorb sunlight broadly and rapidly convert it into heat energy, raising the local temperature of the interface. This further weakens or destroys the adhesion structure of residual attached organisms and promotes detachment, thus forming a day-night dual-mode synergy with the superhydrophobic low-adhesion effect and the capsaicin analog repellency effect, significantly improving the overall inhibition rate. The above mechanisms are universally applicable to typical fouling organisms of different scales. Therefore, the preferred coating can achieve a high inhibition rate in terms of algae suppression, antibacterial and anti-mussel adhesion, and this effect mainly comes from the interfacial synergistic effect rather than the release of harmful substances, which has the advantage of environmental compatibility.

[0068] In summary, this invention provides a photoresponsive capsaicin-functionalized polythiourethane superhydrophobic photothermal coating for controlling marine biofouling at the air-water interface. This coating achieves a stable bioactive interface, superhydrophobicity, and efficient solar-to-thermal energy conversion by covalently linking capsaicin analogs and fluorinated acrylates to the polythiourethane backbone and dispersing photothermal fillers as photothermal conversion agents. The composite coating retains its superhydrophobicity, elemental homogeneity, and basic photothermal response after repeated abrasion, exhibiting good mechanical durability. Although the composite coating shows slight fading and a slight decrease in the maximum photothermal conversion temperature after abrasion, its heating-cooling curve remains highly repeatable under multiple light-on / off cycles and different irradiance levels, indicating a robust and reversible photothermal conversion process. Biological experiments show that the composite coating effectively inhibits the attachment and colonization of marine fouling organisms under both dark and light conditions, while exhibiting negligible acute toxicity to brine shrimp larvae. These results support a dual-mode antifouling mechanism: the superhydrophobic state and capsaicin-functionalized interface provide passive fouling release and bio-attraction avoidance; while photothermal heating mediated by the solar photothermal filler actively damages and removes residual fouling organisms. In conclusion, the composite coating system represents a promising and environmentally friendly strategy for protecting marine structures operating at dynamic air-water interfaces.

[0069] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of the present invention. Any person skilled in the art can make their own modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A stain-resistant coating material, characterized in that, The antifouling coating material comprises the following raw material components by weight: 40-84 parts polysulfide urethane, 15-45 parts fluorinated low surface energy monomer, 1-15 parts capsaicin analog functional monomer, and 0.05-3 parts photothermal filler; wherein the total amount of the polysulfide urethane, fluorinated low surface energy monomer, and capsaicin analog functional monomer is 100 parts. The polysulfuric acid ester is obtained by an addition reaction of a polyfunctional thiol compound and a polyisocyanate compound; wherein the amount of the polyfunctional thiol compound is 28-54 parts and the amount of the polyisocyanate compound is 12-30 parts.

2. The anti-fouling coating material according to claim 1, characterized in that, The polyfunctional thiol compound is at least one of pentaerythritol tetrakis(3-mercaptopropionic acid) ester and polymethylolpropane tris(3-mercaptopropionic acid) ester; The polyisocyanate compound is at least one of hexamethylene diisocyanate, diphenylmethane diisocyanate, and isophorone diisocyanate.

3. The anti-fouling coating material according to claim 1, characterized in that, The fluorinated low surface energy monomer is one or more of fluorinated acrylates, fluorinated olefins, fluorinated silanes, and fluorinated long-chain alkyl groups.

4. The anti-fouling coating material according to claim 1, characterized in that, The capsaicin analog functional monomer is a functional monomer with capsaicin structural characteristics, including at least one of 1-hydroxy-2,4-bis(methyleneacrylamide)naphthalene, 1-[(propenyloyl)amino]methyl-4-methoxynaphthalene, and 1-[(propenyloyl)amino]methyl-2-ethoxynaphthalene.

5. The anti-fouling coating material according to claim 1, characterized in that, The photothermal filler is one or more of carbon-based materials, MXene materials, and metal / metal compound nanomaterials; The carbon-based material is selected from one or more of carbon nanotubes, graphene, carbon black, carbon nanofibers, carbon nanospheres, and carbon quantum dots. The MXene material is selected from Ti3C2T. x Ti2CT x Nb2CT x V2CT x One or more of the two-dimensional transition metal carbides / nitrides; The metal compound nanomaterials are selected from one or more of titanium dioxide, iron oxide, copper oxide, copper sulfide, molybdenum sulfide, tungsten sulfide, gold nanomaterials, and silver nanomaterials.

6. A method for preparing an antifouling coating material according to any one of claims 1 to 5, characterized in that, The preparation method includes: (1) The polyfunctional thiol compound, the fluorine-containing low surface energy monomer and the capsaicin analog functional monomer are dissolved together in an organic solvent and prepolymerized under the action of an initiator to obtain a prepolymer solution. (2) Add the photothermal filler to the prepolymer solution and mix evenly to obtain a photothermal filler dispersion; (3) Add a polyisocyanate compound to the photothermal filler dispersion and mix thoroughly to obtain the antifouling coating material.

7. The method for preparing the antifouling coating material according to claim 6, characterized in that, In step (1), the temperature of the prepolymerization reaction is 80~90 ℃ and the time is 2~5 h; The organic solvent includes ethyl acetate; The initiator includes azobisisobutyronitrile, and the amount used is 0.5 to 3 parts; In step (2), the method of uniform mixing is ultrasonic dispersion and mechanical stirring.

8. A method for preparing an anti-fouling coating, characterized in that, The preparation method includes: applying the anti-fouling coating material as described in any one of claims 1 to 5 to the surface of a substrate by spraying, brushing or dipping, and curing it at a temperature of 20 to 60°C for 12 to 48 hours to obtain the anti-fouling coating.

9. An antifouling coating prepared by the method of claim 8, characterized in that, The antifouling coating has a water contact angle of 105.8°~161.5° and a sliding angle of 1.5°~24.1° in the wavelength range of 200~2500 nm; a light absorption rate of 65.7%~98.3%; and a maximum photothermal surface temperature of 45.1~82.8 °C under one solar irradiance.

10. The application of the antifouling coating according to claim 9 in marine engineering components at the air-sea interface.

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