A method for preparing a fluorine-free superhydrophobic self-cleaning coating

Abstract

This invention discloses a method for preparing a fluorine-free superhydrophobic self-cleaning coating, belonging to the field of functional coating materials technology. It aims to address the environmental shortcomings of existing fluorine-containing superhydrophobic coatings and the deficiencies of fluorine-free systems in terms of poor mechanical durability and reliance on thermally driven self-healing. This invention designs and synthesizes a PDMS-(HxA / TyrBn) oligomer with bis(3-aminopropyl)-terminated PDMS as the main chain. Adipic acid monohydroxyxamic acid and N-Boc-O-benzyl-L-tyrosine functional side groups are covalently grafted to both ends via an amidation reaction. A two-liquid, two-step spraying process is used to complete the coating preparation. The resulting coating exhibits superhydrophobicity, excellent mechanical durability, self-healing ability, and self-cleaning properties, making it suitable for polyester coated fabrics, nylon coated fabrics, or PVC-coated fabrics.

Description

Technical Field

[0001] This invention belongs to the field of functional coating materials technology, specifically relating to a method for preparing a fluorine-free superhydrophobic self-cleaning coating. Background Technology

[0002] Superhydrophobic self-cleaning coatings, due to their excellent water contact angle (WCA≥150°) and sliding angle (SA≤10°), have broad application prospects in fields such as building exterior wall waterproofing, food contact surface antifouling, metal corrosion protection, and textile waterproofing. Achieving superhydrophobic properties requires the simultaneous fulfillment of two conditions: first, the coverage of low surface energy materials; and second, the construction of a micro / nano dual-scale rough structure. Traditional superhydrophobic coatings heavily rely on perfluorinated or polyfluoroalkyl substances (PFAS) to reduce surface energy, including perfluorooctyltrichlorosilane (FOTS) and perfluoropolyether (PFPE). However, due to their persistent organic pollution characteristics, PFAS substances have been included in the restricted list, and their use in food contact materials and building coatings has become increasingly prohibited in Europe and the United States. Therefore, the development of fluorine-free superhydrophobic coatings has become an urgent need in this field. Current research on fluorine-free superhydrophobic coatings mainly follows two routes: one is to use low surface energy modifiers such as polydimethylsiloxane (PDMS), long-chain alkylsilanes, and stearic acid to construct a rough structure in conjunction with SiO2 nanoparticles; the other is to introduce dynamic covalent bonds or supramolecular interactions to endow the coating with self-healing capabilities. However, both routes have obvious drawbacks: the nano-rough structure of purely physically deposited coatings is easily destroyed under mechanical wear and long-term service conditions, leading to irreversible failure of superhydrophobic properties; and existing self-healing systems also have significant shortcomings in chemical design.

[0003] Existing technology CN119978856A discloses a wear-resistant transparent superhydrophobic coating and its preparation method. This method involves etching a micron-scale array of grooves on a transparent substrate using a femtosecond ultraviolet laser, followed by spraying a SiO2-based dispersion containing an alcohol solvent, a silicon source, a silane coupling agent, and a low surface energy modifier to form a film, thus obtaining a fluorine-free superhydrophobic coating that balances wear resistance and light transmittance. While this technology achieves fluorine-free superhydrophobicity on rigid transparent substrates, it requires high substrate rigidity and resistance to high-energy pulses, limiting its applicability and making it difficult to extend to substrates such as textiles that are not resistant to laser etching. Furthermore, the functional layer relies solely on the mechanical interlocking of SiO2 particles and the limited chemical anchoring of the silane coupling agent between the functional layer and the substrate, lacking a dynamic and reversible cross-linking structure at the molecular level. Once damaged during use, the coating permanently fails and lacks any self-healing capability.

[0004] In summary, existing fluorine-free superhydrophobic coating technologies generally face problems such as poor mechanical durability, demanding self-healing conditions, and lack of chemical bonding between functional layers and the framework. There is an urgent need for a method to prepare fluorine-free superhydrophobic self-cleaning coatings that can organically unify the three functions of low surface energy, dynamic reversible crosslinking, and self-assembled rough structure construction in the same molecular system, with simple construction process and applicability to various substrates. Summary of the Invention

[0005] This invention provides a method for preparing a fluorine-free superhydrophobic self-cleaning coating, aiming to solve the environmental defects of existing fluorine-containing superhydrophobic coatings, as well as the shortcomings of fluorine-free systems in terms of poor mechanical durability and reliance on thermally driven self-healing.

[0006] The specific technical solution is as follows:

[0007] A method for preparing a fluorine-free superhydrophobic self-cleaning coating includes the following steps: S1: Synthesize PDMS-(HxA / TyrBn) oligomers; the PDMS-(HxA / TyrBn) oligomers have bis(3-aminopropyl)-terminated PDMS as the main chain, and adipic acid monohydroxyoxime side groups and N-Boc-O-benzyl-L-tyrosine side groups are covalently grafted to both ends of the main chain by amidation reaction; S2: Prepare primer A and functional layer B; primer A is prepared by dispersing hexadecyltrimethoxysilane-premodified SiO2 nanoparticles and ferric nitrate nonahydrate in a mixed solvent of ethanol and deionized water; functional layer B is prepared by dispersing the PDMS-(HxA / TyrBn) oligomer and hexadecyltrimethoxysilane-premodified SiO2 particles in a mixed solvent of ethanol and tetrahydrofuran. S3: After pretreating the substrate, the primer A liquid is sprayed onto the substrate surface and dried to form a Fe-containing... 3+ A SiO2 rough skeleton base coating with enriched coordination pre-layer is formed; then the functional layer B liquid is sprayed onto the surface of the base coating, and cured after standing at room temperature to obtain the fluorine-free superhydrophobic self-cleaning coating.

[0008] Furthermore, the synthesis of the PDMS-(HxA / TyrBn) oligomer in step S1 includes the following sub-steps: 1) Adipic acid monomethyl ester was reacted with hydroxylamine hydrochloride and potassium hydroxide in ethanol at 50°C for 8 hours to convert the methyl ester end to hydroxamic acid, yielding adipic acid monohydroxyxamic acid; the adipic acid monohydroxyxamic acid was dissolved in anhydrous ethyl acetate with N-hydroxysuccinimide and dicyclohexylcarbodiimide, stirred at room temperature in the dark for 12 hours, filtered, the filtrate was concentrated and purified by precipitation with diethyl ether to obtain the active succinimide ester of adipic acid monohydroxyxamic acid; 2) Dissolve the bis(3-aminopropyl)-terminated polydimethylsiloxane in anhydrous N,N-dimethylformamide, and add the succinimide active ester of adipic acid monohydroxyoxime acid dropwise at room temperature, stirring at room temperature in the dark for 6 hours. 3) Add N-Boc-O-benzyl-L-tyrosine, EDC·HCl, HOBt and DIPEA to the reaction solution obtained in step 2), stir at room temperature in the dark for 24 hours; after the reaction is completed, dialyze to purify, freeze dry under vacuum to obtain the PDMS-(HxA / TyrBn) oligomer.

[0009] Furthermore, in step 1), the molar ratio of monomethyl adipic acid, hydroxylamine hydrochloride, and potassium hydroxide is 1.0:1.1:2.2.

[0010] Further, in step 2), the molar ratio of the succinimide active ester of adipic acid monohydroxyoxime to the bis(3-aminopropyl)-terminated polydimethylsiloxane is 0.90:1.0; the number average molecular weight of the bis(3-aminopropyl)-terminated polydimethylsiloxane is 1000 g / mol.

[0011] Further, the molar ratios of N-Boc-O-benzyl-L-tyrosine, EDC·HCl, HOBt, and DIPEA in step 3) to the bis(3-aminopropyl)-terminated polydimethylsiloxane in step 2) are 1.10:1.20:1.20:2.00:1.0, respectively.

[0012] Further, the preparation method of the primer A solution in step S2 is as follows: based on 100 parts by weight of a mixed solvent of ethanol and deionized water, wherein the volume ratio of ethanol to deionized water is 95:5, weigh 2.0-3.0 parts by weight of hexadecyltrimethoxysilane pre-modified SiO2 nanoparticles and 0.08 parts by weight of ferric nitrate nonahydrate, and disperse them intermittently by ultrasonication in an ice bath using a probe ultrasonicator with a power of 200W and an ultrasonication time of 15 minutes to obtain the primer A solution; the primer A solution is to be used within 4 hours after preparation.

[0013] Further, the preparation method of the functional layer B solution in step S2 is as follows: based on 100 parts by weight of a mixed solvent of ethanol and tetrahydrofuran, wherein the volume ratio of ethanol to tetrahydrofuran is 4:1, weigh 1.8-2.2 parts by weight of the PDMS-(HxA / TyrBn) oligomer and 0.2-0.5 parts by weight of hexadecyltrimethoxysilane pre-modified SiO2 particles, and disperse them intermittently by ultrasonication in an ice bath with a probe ultrasonicator at a power of 150W for 10 minutes to obtain the functional layer B solution.

[0014] Further, the substrate mentioned in step S3 includes polyester coated fabric, nylon coated fabric, or polyvinyl chloride mesh fabric; the specific method for pre-treating the substrate is as follows: for polyester coated fabric and nylon coated fabric substrates, ultrasonic cleaning with ethanol and deionized water for 5 minutes each, pre-drying in a 60°C oven for 10 minutes to fully dehumidify, and finally activation with 30W air plasma for 60 seconds; for polyvinyl chloride mesh fabric substrates, ultrasonic cleaning with ethanol and deionized water for 5 minutes each, drying with nitrogen, and finally activation with 20W air plasma for 30 seconds.

[0015] Furthermore, the construction parameters for spraying the primer A liquid in step S3 are as follows: nozzle diameter 1.0mm, air pressure 0.2-0.25MPa, distance between the spray gun and the substrate surface 15cm, pause for 10 seconds after each spray, spray a total of 2-3 coats, and control the wet film thickness of the primer to be 20-30μm; after spraying, dry at 50℃ for 20 minutes.

[0016] Further, in step S3, the functional layer B liquid is sprayed after the primer A liquid has dried and cooled to room temperature. The spraying conditions are the same as those for the primer A liquid. Two coats are applied, and the wet film thickness is controlled to be 15-25 μm. After spraying, the coating is left to stand at room temperature for 10 minutes, and then cured at 60℃-70℃ for 2-3 hours. After cooling to room temperature, the fluorine-free superhydrophobic self-cleaning coating is obtained.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, PDMS-(HxA / TyrBn) molecules are synthesized and introduced, wherein the hydroxamic acid group of the HxA side group reacts with the Fe pre-placed in the SiO2 undercoat. 3+ A tridentate coordination complex is formed, and the functional layer and the framework are connected by chemical bonding rather than physical stacking. The overall wear resistance and adhesion of the coating are significantly improved compared with similar physically stacked coatings. During the solvent evaporation and film formation process, the TyrBn side groups are self-assembled into a nanofiber network through benzyl π-π stacking and amide hydrogen bonding. This network is superimposed on the micron-scale roughness of SiO2 particles, forming a lotus leaf-like micro-nano dual-scale structure. No template or etching process is required, making the process simple.

[0018] (2) The present invention uses a two-liquid two-step spraying process to complete the coating preparation. The construction process is simple. The flexible fabric substrate only needs conventional cleaning, pre-drying and mild plasma activation treatment. No special chemical modification is required. The pretreatment parameters have good universality for different fabric materials. The prepared coating is suitable for polyester coated fabric, nylon coated fabric or polyvinyl chloride (PVC) mesh fabric. It has good cross-substrate versatility and has strong industrial application potential. Attached Figure Description

[0019] Figure 1This is a synthetic route diagram for the PDMS-(HxA / TyrBn) oligomer of the present invention; Figure 2 Stacked comparison of Fourier transform infrared spectra of adipic acid monohydroxyxamic acid, N-Boc-O-benzyl-L-tyrosine, bis(3-aminopropyl)-terminated PDMS, and PDMS-(HxA / TyrBn). Detailed Implementation

[0020] This invention proposes a method for preparing a fluorine-free superhydrophobic self-cleaning coating, which consists of three stages: the first stage is the synthesis of the core functional oligomer PDMS-(HxA / TyrBn), as shown in the attached figure. Figure 1 The synthesis route is shown; the second stage is the preparation of primer A and functional layer B; the third stage is coating application and curing. The following provides a detailed description of each stage: Synthesis of S1.PDMS-(HxA / TyrBn) oligomers (1) Add monomethyl adipic acid (1.0 equiv) and ethanol (8 v) to a reaction flask equipped with mechanical stirring, nitrogen protection and thermometer, add hydroxylamine hydrochloride (1.1 equiv) and potassium hydroxide (2.2 equiv), react at 50°C for 8 hours to convert the methyl ester end to hydroxamic acid, while the free acid end remains unchanged. After the reaction is complete, adjust the pH to 3-4 with dilute hydrochloric acid, extract with ethyl acetate, dry the organic phase with anhydrous sodium sulfate and concentrate under reduced pressure to obtain monohydroxyxamic adipic acid (HxA). Take the obtained HxA (1.0 equiv), N-hydroxysuccinimide (NHS, 1.1 equiv) and dicyclohexylcarbodiimide (DCC, 1.1 equiv) and dissolve in anhydrous ethyl acetate (5 v), stir at room temperature in the dark for 12 hours, filter to remove dicyclohexylurea precipitate, concentrate the filtrate and purify with diethyl ether precipitation to obtain the active succinimide ester of HxA (HxA-OSu). Store HxA-OSu in a sealed container at -20°C and prepare a solution immediately before use.

[0021] (2) Add bis(3-aminopropyl)-terminated PDMS (Mn=1000g / mol, 1.0equiv) and anhydrous N,N-dimethylformamide (DMF, 8v) to a reaction flask equipped with mechanical stirring, nitrogen protection, and a thermometer, and stir at room temperature until completely dissolved. Dissolve the obtained HxA-OSu (0.90equiv) in anhydrous DMF (2v) beforehand, and slowly add it dropwise to the reaction solution at room temperature. After the addition is complete, continue stirring at room temperature in the dark for 6 hours to covalently graft the HxA unit to one end of the PDMS chain via an amide bond. After the reaction is complete, use the reaction solution directly for the next step.

[0022] (3) In the reaction solution from the previous step, N-Boc-O-benzyl-L-tyrosine (Boc-Tyr(Bn)-OH, 1.1 equiv), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl, 1.20 equiv), 1-hydroxybenzotriazole (HOBt, 1.20 equiv), and N,N-diisopropylethylamine (DIPEA, 2.00 equiv) were added. The mixture was stirred at room temperature in the dark for 24 hours. The free carboxyl group of Boc-Tyr(Bn)-OH was activated by EDC / HOBt and underwent amidation condensation with the free primary amine of the system, covalently grafting the TyrBn unit onto the other end of the PDMS chain via an amide bond. After the reaction was completed, the reaction solution was transferred to a dialysis bag with a molecular weight cutoff (MWCO) of 500 Da and dialyzed thoroughly in DMF, ethanol, and deionized water in sequence to completely remove unreacted small molecule reagents. After dialysis, the solution in the dialysis bag was freeze-dried under vacuum at -50°C for 48 hours to obtain the final product PDMS-(HxA / TyrBn).

[0023] The resulting PDMS-(HxA / TyrBn) structure is as follows: .

[0024] The terminal hydroxyoxime group of the HxA unit is related to Fe. 3+ It has extremely high coordination affinity and can interact with Fe pre-placed in the SiO2 layer of the undercoat. 3+ A stable tripentate chelate coordination complex is formed, chemically anchoring the PDMS-(HxA / TyrBn) functional layer molecular network to the inorganic framework, thus endowing the coating with mechanical durability; simultaneously, Fe... 3+ The α-hydroxyoxime acid coordination bond exhibits dynamic reversibility in the presence of moisture. When damaged, the coordination bond dissociates under the combined action of local stress and moisture, allowing the PDMS chain segment to gain temporary mobility and migrate to the damaged area. After the ambient humidity recovers, the coordination bond is spontaneously rebuilt, re-anchoring the migrated chain segment and realizing a self-repair function triggered by room temperature and humidity. The repair process does not require heating or other external stimuli.

[0025] The TyrBn unit retains the benzyl protection of the phenolic hydroxyl group, which, during the solvent evaporation and film formation process of the coating, drives the orderly self-assembly of the side groups through the synergistic effect of the π-π stacking between the benzyl aromatic rings and the directional hydrogen bonding of the amide bonds, forming a nanofiber-like ordered rough structure. This structure can significantly reduce the solid-liquid contact area, keeping the water droplets in a stable Cassie–Baxter wetting state, thereby endowing the coating with excellent superhydrophobic properties while ensuring the stability of the surface rough structure.

[0026] In addition to the target structure PDMS-(HxA / TyrBn) obtained through the above preparation process, the product also contains a small amount of PDMS-(HxA / HxA) byproducts with both ends grafted with adipic acid monohydroxyxamic acid, and a very small amount of PDMS-(TyrBn / TyrBn) byproducts with both ends grafted with N-Boc-O-benzyl-L-tyrosine. These byproducts do not require additional separation and purification: because PDMS-(HxA / HxA) contains biterminal hydroxamic acid groups, it can react with Fe2+ pre-placed in the SiO2 undercoat layer. 3+ The formation of two-point coordination anchorage has a certain positive contribution to the overall crosslinking density and adhesion of the functional layer; PDMS-(TyrBn / TyrBn) has no substantial negative impact on the construction of the superhydrophobic structure of the coating because of its extremely low proportion and its ability to participate in the π-π stacking self-assembly of TyrBn side groups.

[0027] S2. Preparation of coating liquid (1) Preparation of primer A: Weigh 2.0-3.0 parts by weight of SiO2 nanoparticles pre-modified with 0.5 wt% hexadecyltrimethoxysilane (HDTMS), add 0.08 parts by weight of ferric nitrate nonahydrate (Fe(NO3)3·9H2O), and disperse them together in 100 parts by weight of ethanol / deionized water mixed solvent (95:5, v / v). Use a probe sonicator to ultrasonically disperse the particles in an ice bath at 200 W for intermittent sonication for 15 minutes to obtain a uniform suspension of primer A. The prepared suspension of primer A should be used within 4 hours to prevent Fe from accumulating. 3+ Hydrolysis and precipitation. The surface of the HDTMS-premodified SiO2 particles is hydrophobic, which is beneficial for uniform dispersion in organic solvent / water mixtures, while retaining some surface hydroxyl groups as Fe. 3+ The weak coordination anchoring point. Fe(NO3)3 in the ethanol / water system is Fe 3+ It exists in the form of free ions and simple hydrates, and does not immediately form a strong precipitate with SiO2. Instead, it forms Fe on the SiO2 surface after the primer dries. 3+ The enriched layer provides reaction sites for subsequent HxA coordination.

[0028] (2) Preparation of functional layer B solution: 1.8-2.2 parts by weight of PDMS-(HxA / TyrBn) and an additional 0.2-0.5 parts by weight of HDTMS pre-modified SiO2 particles for roughness supplementation were dissolved / dispersed in 100 parts by weight of ethanol / tetrahydrofuran (THF) mixed solvent (4:1, v / v), and ultrasonically dispersed with a probe at a power of 150W for intermittent sonication for 10 minutes to obtain a uniform B solution coating solution. The high volatility of ethanol in the obtained B solution helps the solvent evaporate rapidly during the film formation process, promoting the π-π stacking self-assembly of TyrBn side groups.

[0029] S3. Coating Application and Curing (1) The substrate to be coated is subjected to the following standard treatments in sequence: First, solvent ultrasonic cleaning, using ethanol and deionized water for 5 minutes each to thoroughly remove grease, dust and residual finishing agent from the surface of the flexible fabric; Second, pre-drying and dehumidification, placing the cleaned substrate in a 60℃ oven for 10 minutes to fully remove the moisture remaining due to moisture absorption of the fabric, ensuring uniform spreading of the subsequent A solution; Third, air plasma activation in a plasma cleaner to introduce a large number of active groups such as hydroxyl and carbonyl groups on the surface of the substrate, significantly improving the wetting and spreading properties of the A solution and the adhesion of the coating; Coating is applied within 30 minutes after activation. The substrate is a flexible fabric, including polyester coated fabric, nylon coated fabric or PVC mesh fabric. For polyester coated fabric and nylon coated fabric substrates, 30W air plasma activation is used for 60 seconds; for PVC mesh fabric substrates, 20W air plasma activation is used for 30 seconds to avoid thermal degradation or surface damage of the PVC substrate. Flexible fabric substrates should be laid flat and fixed on a rigid carrier plate during spraying to avoid wrinkles affecting the uniformity of the coating.

[0030] (2) Application of Liquid A Primer: Pour the prepared Liquid A into the material cup of the pneumatic spray gun. The nozzle diameter is 1.0 mm, and the air pressure is set to 0.2-0.25 MPa. Spray evenly onto the pretreated substrate surface at room temperature, keeping the spray gun 15 cm away from the substrate surface. Pause for 10 seconds after each coat before applying the next coat. Apply a total of 2-3 coats, controlling the wet film thickness of the primer to 20-30 μm. After spraying, place the substrate in a 50°C oven to dry for 20 minutes, allowing the ethanol / water to evaporate and SiO2 particles to deposit on the substrate surface to form a micron-scale rough skeleton. At the same time, Fe... 3+ A coordination pre-layer is enriched and formed on the surface of SiO2 particles.

[0031] (3) Application of the functional layer of liquid B: After the primer of liquid A has dried, cool the substrate to room temperature, pour liquid B into the spray gun cup, and spray it evenly onto the surface of the primer under the same conditions as the application of liquid A. Apply two coats, controlling the wet film thickness to 15-25 μm. After spraying, let it stand at room temperature for 10 minutes to allow the solvent to initially evaporate and the TyrBn side groups to begin self-assembly. Then, transfer it to a 60°C-70°C oven for curing for 2-3 hours, and finally cool it to room temperature to obtain the coating sample. During the curing process, the hydroxamic acid of the HxA side group in PDMS-(HxA / TyrBn) reacts with the Fe pre-placed in the primer. 3+ A tridentate coordination complex is formed, chemically anchoring the functional layer molecular network to the SiO2 framework. The TyrBn side groups complete π-π self-assembly driven by continuous solvent evaporation, forming a nanofiber network that is superimposed on the roughness of the SiO2 particles, constructing a micro / nano dual-scale superhydrophobic structure. After curing, the coating can be used after natural cooling to room temperature.

[0032] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] The preferred embodiments of the present invention are described in detail below; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

[0034] Example 1 Synthesis of PDMS-(HxA / TyrBn) oligomers: (1) To a reaction flask equipped with mechanical stirring, nitrogen protection, and a thermometer, add monomethyl adipic acid (1.46 g, 9.11 mmol, 1.0 equiv) and 12 mL of ethanol, then add hydroxylamine hydrochloride (0.70 g, 10.1 mmol, 1.1 equiv) and potassium hydroxide (1.12 g, 20.0 mmol, 2.2 equiv), heat to 50°C and stir for 8 hours. After the reaction is complete, cool to room temperature, adjust the pH to 3.5 with 1 mol / L dilute hydrochloric acid, extract with 3 × 30 mL of ethyl acetate, combine the organic phases, dry with anhydrous sodium sulfate for 30 minutes, filter, and concentrate under reduced pressure to obtain crude HxA. The obtained HxA (1.41 g, 8.75 mmol, 1.0 equiv), NHS (1.11 g, 9.62 mmol, 1.1 equiv), and DCC (1.98 g, 9.62 mmol, 1.1 equiv) were dissolved in 7 mL of anhydrous ethyl acetate and stirred at room temperature in the dark for 12 hours. The mixture was filtered, and the filtrate was slowly added dropwise to 150 mL of ice-cold diethyl ether. The precipitated solid was collected, filtered under reduced pressure, and HxA-OSu was obtained and stored in a sealed container at -20°C for later use.

[0035] (2) To a reaction flask equipped with a mechanical stirrer, nitrogen protection, and a thermometer, add bis(3-aminopropyl)-terminated PDMS (Mn=1000g / mol, 2.00g, 2.00mmol, 1.0equiv) and 8mL of anhydrous DMF, and stir at room temperature until completely dissolved. Dissolve the obtained HxA-OSu (0.46g, 1.80mmol, 0.90equiv) in 4mL of anhydrous DMF, and slowly add it dropwise to the above reaction solution at room temperature. After the addition is complete, continue stirring at room temperature in the dark for 6 hours. The reaction solution is used directly in the next step without purification.

[0036] (3) Add Boc-Tyr(Bn)-OH (0.82 g, 2.2 mmol, 1.10 equiv), EDC·HCl (0.46 g, 2.40 mmol, 1.20 equiv), HOBt (0.32 g, 2.40 mmol, 1.20 equiv), and DIPEA (0.52 g, 4.00 mmol, 2.00 equiv) sequentially to the reaction solution from the previous step, and stir at room temperature in the dark for 24 hours. Transfer the reaction solution to a dialysis bag with a MWCO of 500 Da, and dialyze thoroughly in DMF, ethanol, and deionized water sequentially. Then freeze-dry the solution in the dialysis bag under vacuum at -50°C for 48 hours to obtain PDMS-(HxA / TyrBn).

[0037] Preparation of Solution A: Weigh 2g of HDTMS pre-modified SiO2 nanoparticles and 0.08g of Fe(NO3)3·9H2O into an Erlenmeyer flask, add 95mL of ethanol / 5mL of deionized water mixed solvent, and disperse intermittently by ultrasonication in an ice bath using a probe sonicator at a power of 200W, working for 3 seconds and then intermittently for 3 seconds, for a total of 15 minutes to obtain a uniform suspension of Solution A. Use within 4 hours after preparation.

[0038] Preparation of solution B: Weigh 1.80g of PDMS-(HxA / TyrBn) and 0.50g of HDTMS pre-modified SiO2 nanoparticles and add them to an Erlenmeyer flask. Add 80mL of ethanol / 20mL of THF mixed solvent and disperse the solution intermittently by ultrasonication in an ice bath with a probe sonicator at a power of 150W for 3 seconds on and 3 seconds off, for a total of 10 minutes to obtain a homogeneous solution B.

[0039] Application: Take a 50mm×50mm polyester coated fabric, ultrasonically clean it for 5 minutes each with ethanol and deionized water, pre-dry it in a 60°C oven for 10 minutes, then activate it with 30W air plasma for 60 seconds in a plasma cleaner. After activation, lay the substrate flat and fix it on a rigid carrier plate. Apply the coating within 30 minutes. Pour liquid A into the slurry cup of a pneumatic spray gun with a nozzle diameter of 1.0mm. Spray two coats evenly at a distance of 15cm from the substrate under a pressure of 0.20MPa, with a 10-second interval between each coat. Control the wet film thickness of the primer to 20-30μm. Then dry it in a 50°C oven for 20 minutes and remove it to cool to room temperature. Immediately pour liquid B into the slurry cup of the spray gun and spray two coats evenly under the same conditions, controlling the wet film thickness to 15-25μm. Let it stand at room temperature for 10 minutes, then cure it in a 60°C oven for 3 hours. Cool to room temperature to obtain the coated sample.

[0040] Example 2 The synthesis of PDMS-(HxA / TyrBn) and the preparation of solutions A and B were the same as in Example 1. A 50mm × 50mm nylon coated fabric was used as the substrate. The substrate was treated as follows: ultrasonically cleaned with ethanol and deionized water for 5 minutes each, pre-dried in a 60°C oven for 10 minutes, and then activated with 30W air plasma for 60 seconds in a plasma cleaner. The activated substrate was then laid flat and fixed onto a rigid carrier plate. The remaining steps were the same as in Example 1.

[0041] Example 3 The synthesis of PDMS-(HxA / TyrBn) and the preparation of solutions A and B were the same as in Example 1. A 50mm × 50mm PVC mesh fabric was used as the substrate. The substrate was treated by ultrasonically cleaning it with ethanol and deionized water for 5 minutes each, drying it with nitrogen, and then activating it with 20W air plasma for 30 seconds in a plasma cleaner. The activated substrate was then flattened and fixed onto a rigid carrier plate. The remaining steps were the same as in Example 1.

[0042] Example 4 The synthesis of PDMS-(HxA / TyrBn) and the preparation of solution B were the same as in Example 1. Solution A preparation: 3.00 g of HDTMS-modified SiO2 and 0.08 g of Fe(NO3)3·9H2O were dispersed in a 95 mL ethanol / 5 mL deionized water mixed solvent and ultrasonically dispersed. The substrate selection and other steps were the same as in Example 1.

[0043] Example 5 The synthesis of PDMS-(HxA / TyrBn) and the preparation of solution A were the same as in Example 1. Solution B preparation: 2.20 g of PDMS-(HxA / TyrBn) and 0.50 g of HDTMS-modified SiO2 were dispersed in 80 mL of ethanol / 20 mL of THF mixed solvent and ultrasonically dispersed. The substrate selection and other steps were the same as in Example 1.

[0044] Example 6 The synthesis of PDMS-(HxA / TyrBn) and the preparation of solution A were the same as in Example 1. Solution B preparation: 1.80 g of PDMS-(HxA / TyrBn) and 0.20 g of HDTMS-modified SiO2 were dispersed in 80 mL of ethanol / 20 mL of THF mixed solvent and ultrasonically dispersed. The substrate selection and other steps were the same as in Example 1.

[0045] Example 7 The synthesis of PDMS-(HxA / TyrBn), and the preparation of solutions A and B were the same as in Example 1. The selection of the substrate and the other steps were the same as in Example 1, except that after two coats of solution B were sprayed, the mixture was left to stand at room temperature for 10 minutes and then cured in a 70°C oven for 3 hours.

[0046] Example 8 The synthesis of PDMS-(HxA / TyrBn), and the preparation of solutions A and B were the same as in Example 1. The selection of the substrate and the other steps were the same as in Example 1, except that after two coats of solution B were sprayed, the mixture was left to stand at room temperature for 10 minutes and then cured in a 60°C oven for 2 hours.

[0047] Example 9 The synthesis of PDMS-(HxA / TyrBn), and the preparation of solution A and solution B were the same as in Example 1. The selection of the substrate and the other steps were the same as in Example 1, except that after two coats of solution B were sprayed, the mixture was left to stand at room temperature for 10 minutes and then cured in a 70°C oven for 2 hours.

[0048] Comparative Example 1 The HxA-OSu grafting step is omitted in the synthesis process. PDMS-TyrBn is used instead of PDMS-(HxA / TyrBn) to prepare solution B of the same concentration. Fe(NO3)3·9H2O is not added to solution A, i.e., Fe is not pre-placed. 3+ The remaining steps are the same as in Example 1.

[0049] Comparative Example 2 The Boc-Tyr(Bn)-OH grafting step was omitted in the synthesis process. PDMS-HxA was used instead of PDMS-(HxA / TyrBn) to prepare solution B of the same concentration. The remaining steps were the same as in Example 1.

[0050] Performance testing: 1. Water contact angle (WCA) and sliding angle (SA) test Refer to GB / T 30693-2014 "Measurement of the contact angle between plastic film and water".

[0051] Testing Procedure: Each 50mm × 50mm coated sample was left to stand at room temperature for 24 hours before testing. Flexible samples were flattened and adhered to a rigid glass slide before testing to avoid substrate deformation affecting the test results. Five different locations were tested for each sample. A contact angle meter was used, with a 5μL volume of deionized water droplet. Static wC was calculated using Young-Laplace fitting. SA was determined using the tilting stage method, with a 20μL volume of deionized water droplet. The minimum tilt angle at which the droplet began to slide was defined as SA. Each group of samples was tested three times, and the average value was taken.

[0052] 2. Sandpaper abrasion durability test Referring to the basic principle of the reciprocating friction test method described in GB / T 9266-2009 "Determination of Washability of Architectural Coatings", and using sandpaper as the wear medium to construct a dry reciprocating wear condition, the wear resistance of the coating under high mechanical stress conditions was evaluated.

[0053] Testing Procedure: A 50mm × 50mm coated sample was flatly pasted and fixed onto a rigid glass slide. Cw-2000 sandpaper was placed on the coated surface, and a 100g load was applied. The sample was pushed 15cm at a time, once horizontally and once vertically, constituting one cycle. After every 10 wear cycles, the wear resistance coefficient (WCA) was measured, and the change in WCA with the number of wear cycles was recorded until the WCA was below 150°. The final number of wear cycles was then recorded.

[0054] 3. Self-healing performance test Testing Procedure: Before testing, the flexible sample was flattened and fixed onto a rigid glass slide to ensure test stability. A constant pressure was applied to the coating surface with Cw-100 sandpaper, pushing it three times until the WCA dropped below 150°. The sample was then placed in a constant temperature and humidity chamber at 25°C and 60% ± 5% relative humidity. The WCA was measured every 4 hours until it recovered to above 150°, and the recovery time was recorded. This damage-repair cycle was repeated, and the number of cycles in which the WCA stably recovered to ≥150° was recorded.

[0055] 4. Adhesion test Refer to GB / T 9286-2021 "Cross-cut test for paints and varnishes".

[0056] Testing process: A 2mm × 2mm grid is drawn on the coating with a knife, for a total of 25 grids. The knife marks only penetrate the coating to the surface of the substrate, without piercing the substrate. Special adhesive tape is applied and then peeled off vertically. The number of grids that do not come off is recorded, and the grid is graded according to the grid method (0 is the best, 5 is the worst).

[0057] 5. Self-cleaning performance test Testing Procedure: Before testing, the flexible sample is flattened and fixed onto a rigid glass slide to ensure test stability. Carbon black powder, approximately 10 mg / cm³, is evenly sprinkled onto the coating surface. 2 Rinse the surface with 10 mL of deionized water slowly dripped from a height of 10 cm. The cleaning rate is evaluated by the percentage of residual carbon black area on the surface after drying.

[0058] 6. Fourier Transform Infrared Spectroscopy (FTIR) Characterization (1) Parameter setting and detection process: Fourier transform infrared spectroscopy (FTIR) was used to analyze the chemical structure and grafting bonding characteristics of adipic acid monohydroxyoxime (HxA), N-Boc-O-benzyl-L-tyrosine (Boc-Tyr(Bn)-OH), bis(3-aminopropyl)-terminated PDMS, and PDMS-(HxA / TyrBn) oligomers. Test parameters: KBr pellet method was used for sample preparation, and the scanning wavenumber range was set to 4000-500 cm⁻¹. -1 The resolution is set to 4cm. -1 The data was collected at room temperature.

[0059] (2) Characterization results: as shown in the appendix Figure 2 The image shows a stacked comparison of the Fourier transform infrared (FTIR) spectra of HxA, Boc-Tyr(Bn)-OH, bis(3-aminopropyl)-terminated PDMS, and the product PDMS-(HxA / TyrBn). The bis(3-aminopropyl)-terminated PDMS spectrum at 3450 cm⁻¹... -1 and 3370cm -1 The characteristic bimodal peaks of the primary amine completely disappeared in the product, indicating that the primary amine at the PDMS chain end had been completely consumed; the product at 1630 cm⁻¹... -1 A new amide I band C=O stretching vibration peak appears at HxA (1700 cm⁻¹). -1 ) and Boc-Tyr(Bn)-OH (1740cm) -1 The disappearance of the free carboxylic acid C=O peak indicates that the carboxyl groups of both raw materials have been converted into amide bonds, and HxA and Boc-Tyr(Bn)-OH have been successfully covalently grafted onto the PDMS chain ends. The product also retains the 1260 cm⁻¹ peak intact. -1 and 1030cm -1 The Si-CH3 bending vibration peak and the Si-O-Si stretching vibration peak at 750 cm⁻¹ demonstrate that the PDMS siloxane backbone did not degrade during the reaction; -1 The retention of the out-of-plane bending vibration peak of the benzene ring further confirms the complete structure of the benzene ring on the TyrBn side group, thus introducing it into the product. In summary, the FTIR results confirm the successful synthesis of the target product PDMS-(HxA / TyrBn).

[0060] Table 1. Results of WCA, SA, and sandpaper abrasion durability tests for each embodiment and comparative example.

[0061] Table 2. Test results of self-healing performance, adhesion, and self-cleaning performance for each embodiment and comparative example.

[0062] Results analysis: (1) As shown in Tables 1 and 2, Example 1 is the optimal formulation, with a WCA of 156.8° and an SA of 5.5°. After 36 abrasions with Cw-2000 sandpaper, the WCA is still ≥150°. The self-healing time at room temperature is 16 hours, with 8 repair cycles. The adhesion is grade 0, and the self-cleaning rate is 96.4%. All performance indicators are the best in the group. The performance of Examples 2 and 3 is similar to that of Example 1, proving that the two-liquid two-step process of the coating of the present invention is also applicable to different flexible fabrics such as nylon coated fabric and PVC mesh fabric, and has good cross-substrate versatility. In Example 4, increasing the SiO2 content in liquid A increased the roughness of the primer skeleton, slightly increased the number of abrasion cycles to 38, and the WCA was comparable to that in Example 1, indicating that moderately increasing the SiO2 content in the primer has a positive effect on coating durability. In Example 5, increasing the oligomer concentration in liquid B increased the density of the functional layer, and the overall performance was close to that of Example 1. In Example 6, reducing the amount of supplementary SiO2 in liquid B weakened the contribution of nano-roughness, reduced the WCA to 152.4°, reduced the number of abrasion cycles to 28, and reduced the self-cleaning rate to 91.5%, indicating the necessity of supplementing SiO2 in liquid B to maintain the micro-nano dual-scale rough structure. In Examples 7-9, adjusting the curing parameters resulted in varying degrees of decrease in WCA and abrasion resistance: In Example 7, the curing temperature was too high, which interfered with the self-assembly order of TyrBn, resulting in a decrease in WCA and abrasion cycles, and a decrease in adhesion to level 1; In Example 8, the curing time was shortened, and Fe... 3+ -HxA coordination was not fully completed, and the number of repair cycles was reduced to 6. Example 9 had the lowest overall performance, but still met the basic requirements for superhydrophobicity.

[0063] (2) The WCA of Comparative Example 1 was 152.9°, and its initial superhydrophobicity was close to that of the Example group, indicating that the TyrBn self-assembled rough structure can still be formed normally in a system without HxA. However, the abrasion resistance of Comparative Example 1 was only 11 times, which is 31% of that of Example 1, with an adhesion level of 3, and it could not self-repair after damage. The comparative results directly prove that Fe 3+ -HxA coordination crosslinking is the core of the functional layer chemically anchored to the SiO2 framework. Without this chemical bond, the coating is maintained only by the physical contact between PDMS and SiO2. Under the deformation of the flexible substrate, mechanical wear is more likely to cause overall peeling. At the same time, the lack of dynamic reversibility of coordination bonds makes the coating completely lose its self-healing ability, which verifies the irreplaceable nature of HxA units in this invention.

[0064] (3) Although Comparative Example 2 contains Fe 3+The coordination crosslinking system exhibited a WCA of only 143.2°, failing to meet the superhydrophobic standard, while the SA reached 16.2°, resulting in a self-cleaning rate of only 75.4%. These results indicate that without TyrBn self-assembly units, the coating relies solely on SiO2 particles to provide a single micrometer-scale roughness, failing to form a micro / nano dual-scale composite structure. Consequently, water droplets cannot stably maintain a Cassie-Baxter wettability, leading to substandard WCA and self-cleaning performance. While Comparative Example 2 demonstrated some self-healing capability, its practical value was limited due to its WCA benchmark being below the superhydrophobic threshold. The comparison between Comparative Example 2 and Comparative Example 1 further illustrates that HxA ensures mechanical durability and self-healing capability, while TyrBn ensures the micro / nano rough structure and superhydrophobic performance; only through their synergy can a comprehensive high-performance fluorine-free superhydrophobic self-cleaning coating be achieved.

[0065] In summary, this invention designs PDMS-(HxA / TyrBn) oligomers with Fe... 3+ Using adipic acid monohydroxyoxime as a dynamic metal coordination bond and N-Boc-O-benzyl-L-tyrosine covalently grafted side groups as self-assembly units, a superhydrophobic self-cleaning coating with three functions—dynamic reversible crosslinking, self-assembly of a nano-rough structure, and continuous low surface energy coverage—was successfully prepared using a two-liquid, two-step spraying process.

Claims

1. A method for preparing a fluorine-free superhydrophobic self-cleaning coating, characterized in that, Includes the following steps: S1: Synthesize PDMS-(HxA / TyrBn) oligomers; the PDMS-(HxA / TyrBn) oligomers have bis(3-aminopropyl)-terminated PDMS as the main chain, and adipic acid monohydroxyoxime side groups and N-Boc-O-benzyl-L-tyrosine side groups are covalently grafted to both ends of the main chain by amidation reaction; S2: Prepare primer A and functional layer B; primer A is prepared by dispersing hexadecyltrimethoxysilane-premodified SiO2 nanoparticles and ferric nitrate nonahydrate in a mixed solvent of ethanol and deionized water; functional layer B is prepared by dispersing the PDMS-(HxA / TyrBn) oligomer and hexadecyltrimethoxysilane-premodified SiO2 particles in a mixed solvent of ethanol and tetrahydrofuran. S3: After pretreating the substrate, the primer A liquid is sprayed onto the substrate surface and dried to form a Fe-containing... 3+ A SiO2 rough skeleton base coating with enriched coordination pre-layer is formed; then the functional layer B liquid is sprayed onto the surface of the base coating, and cured after standing at room temperature to obtain the fluorine-free superhydrophobic self-cleaning coating.

2. The method for preparing a fluorine-free superhydrophobic self-cleaning coating as described in claim 1, characterized in that, The synthesis of the PDMS-(HxA / TyrBn) oligomer in step S1 includes the following sub-steps: 1) Adipic acid monomethyl ester was reacted with hydroxylamine hydrochloride and potassium hydroxide in ethanol at 50°C for 8 hours to convert the methyl ester end to hydroxamic acid, yielding adipic acid monohydroxyxamic acid; the adipic acid monohydroxyxamic acid was dissolved in anhydrous ethyl acetate with N-hydroxysuccinimide and dicyclohexylcarbodiimide, stirred at room temperature in the dark for 12 hours, filtered, the filtrate was concentrated and purified by precipitation with diethyl ether to obtain the active succinimide ester of adipic acid monohydroxyxamic acid; 2) Dissolve the bis(3-aminopropyl)-terminated polydimethylsiloxane in anhydrous N,N-dimethylformamide, and add the succinimide active ester of adipic acid monohydroxyoxime acid dropwise at room temperature, stirring at room temperature in the dark for 6 hours. 3) Add N-Boc-O-benzyl-L-tyrosine, EDC·HCl, HOBt and DIPEA to the reaction solution obtained in step 2), stir at room temperature in the dark for 24 hours; after the reaction is completed, dialyze to purify, freeze dry under vacuum to obtain the PDMS-(HxA / TyrBn) oligomer.

3. The method for preparing a fluorine-free superhydrophobic self-cleaning coating as described in claim 2, characterized in that, In step 1), the molar ratio of monomethyl adipic acid, hydroxylamine hydrochloride, and potassium hydroxide is 1.0:1.1:2.

2.

4. The method for preparing a fluorine-free superhydrophobic self-cleaning coating as described in claim 2, characterized in that, In step 2), the molar ratio of the succinimide active ester of adipic acid monohydroxyoxime to the bis(3-aminopropyl)-terminated polydimethylsiloxane is 0.90:1.0; the number average molecular weight of the bis(3-aminopropyl)-terminated polydimethylsiloxane is 1000 g / mol.

5. The method for preparing a fluorine-free superhydrophobic self-cleaning coating as described in claim 2, characterized in that, The molar ratios of N-Boc-O-benzyl-L-tyrosine, EDC·HCl, HOBt, and DIPEA in step 3) to the bis(3-aminopropyl)-terminated polydimethylsiloxane in step 2) are 1.10:1.20:1.20:2.00:1.0, respectively.

6. The method for preparing a fluorine-free superhydrophobic self-cleaning coating as described in claim 1, characterized in that, The preparation method of the primer A solution in step S2 is as follows: Based on 100 parts by weight of a mixed solvent of ethanol and deionized water, wherein the volume ratio of ethanol to deionized water is 95:5, weigh 2.0-3.0 parts by weight of hexadecyltrimethoxysilane pre-modified SiO2 nanoparticles and 0.08 parts by weight of ferric nitrate nonahydrate, and disperse them intermittently by ultrasonication in an ice bath with a probe ultrasonicator at a power of 200W for 15 minutes to obtain the primer A solution; the primer A solution should be used within 4 hours after preparation.

7. The method for preparing a fluorine-free superhydrophobic self-cleaning coating as described in claim 1, characterized in that, The preparation method of the functional layer B solution in step S2 is as follows: Based on 100 parts by weight of a mixed solvent of ethanol and tetrahydrofuran, wherein the volume ratio of ethanol to tetrahydrofuran is 4:1, weigh 1.8-2.2 parts by weight of the PDMS-(HxA / TyrBn) oligomer and 0.2-0.5 parts by weight of hexadecyltrimethoxysilane pre-modified SiO2 particles, and disperse them intermittently by ultrasonication in an ice bath with a probe ultrasonicator at a power of 150W for 10 minutes to obtain the functional layer B solution.

8. The method for preparing a fluorine-free superhydrophobic self-cleaning coating as described in claim 1, characterized in that, The substrate mentioned in step S3 includes polyester coated fabric, nylon coated fabric, or polyvinyl chloride mesh fabric; the specific method for pre-treating the substrate is as follows: for polyester coated fabric and nylon coated fabric substrates, ultrasonic cleaning with ethanol and deionized water for 5 minutes each, pre-drying in a 60°C oven for 10 minutes to fully dehumidify, and finally activation with 30W air plasma for 60 seconds; for polyvinyl chloride mesh fabric substrates, ultrasonic cleaning with ethanol and deionized water for 5 minutes each, drying with nitrogen, and finally activation with 20W air plasma for 30 seconds.

9. The method for preparing a fluorine-free superhydrophobic self-cleaning coating as described in claim 1, characterized in that, The construction parameters for spraying primer A liquid in step S3 are as follows: nozzle diameter 1.0mm, air pressure 0.2-0.25MPa, distance between spray gun and substrate surface 15cm, pause for 10 seconds after each spray, spray 2-3 times in total, control the wet film thickness of primer to be 20-30μm; after spraying, dry at 50℃ for 20 minutes.

10. The method for preparing a fluorine-free superhydrophobic self-cleaning coating as described in claim 1, characterized in that, In step S3, the functional layer B liquid is sprayed after the primer A liquid has dried and cooled to room temperature. The spraying conditions are the same as those for the primer A liquid. Two coats are applied, and the wet film thickness is controlled to be 15-25 μm. After spraying, the coating is left to stand at room temperature for 10 minutes, and then cured at 60℃-70℃ for 2-3 hours. After cooling to room temperature, the fluorine-free superhydrophobic self-cleaning coating is obtained.

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