A capsaicin / sodium alginate-polyacrylamide hydrogel-modified PDMS antifouling coating, its preparation method and application

Abstract

This invention provides a capsaicin / sodium alginate-polyacrylamide hydrogel-modified PDMS antifouling coating, its preparation method, and its application, belonging to the field of marine antifouling materials technology. It comprises three components: hydrogel, the natural antifouling agent capsaicin, and polydimethylsiloxane. The synthesis process consists of three steps: first, adding natural capsaicin to the acrylamide hydrogel synthesis process; second, mixing sodium alginate solution with capsaicin to form a precursor solution, which is then added to an initiator for polymerization; and third, slowly adding the polymerized and dried capsaicin-hydrogel powder to a degassed PDMS prepolymer mixture. This invention effectively inhibits the growth of marine fouling organisms with natural capsaicin, utilizes the hydrogel as a toughening reservoir to continuously release an environmentally friendly antifouling agent, and achieves low surface energy antifouling through the polydimethylsiloxane layer, resulting in synergistic benefits. By intervening in the biofouling process from multiple angles, the composite material jointly addresses marine biofouling.

Description

Technical Field

[0001] This invention relates to the field of marine antifouling materials technology, specifically to a capsaicin / sodium alginate-polyacrylamide hydrogel modified PDMS antifouling coating, its preparation method, and its application. Background Technology

[0002] my country boasts abundant marine resources and possesses enormous potential for the development of marine engineering equipment and shipbuilding industries. Applying antifouling coatings is currently the most economical and effective method for protecting against marine biofouling.

[0003] Traditional antifouling coatings primarily rely on the leaching of toxic biocides, such as organotin compounds and cuprous oxide, to prevent biofouling. However, these coatings are prone to rapid loss of antifouling agents in dynamic marine environments, resulting in a limited protective lifespan. Therefore, the development of environmentally friendly, long-lasting antifouling coatings has become an urgent need in this field.

[0004] To address these issues, low surface energy fouling-releasing antifouling coatings, such as polydimethylsiloxane (PDMS) coatings, have been extensively studied. These coatings, with their extremely low surface energy and elastic modulus, make it difficult for fouling organisms to adhere firmly and allow them to easily detach under water flow, achieving non-biogenic antifouling. However, pure PDMS coatings suffer from poor mechanical properties, such as insufficient toughness, susceptibility to cracking, and weak adhesion to the substrate. They are prone to physical damage under complex marine conditions, leading to failure of their antifouling function.

[0005] On the other hand, researchers have attempted to combine natural antifouling agents, such as capsaicin, with polymer carriers to construct environmentally friendly controlled-release antifouling systems. However, natural antifouling agents, when used alone, suffer from problems such as uncontrollable release, easy decomposition, and short antifouling lifespan. Although microencapsulation technology, such as the alginate gel-encapsulated corrosion inhibitor capsules disclosed in CN120097986A, is used for the controlled release of active substances in drug delivery and corrosion protection, it is primarily designed for independent use in fluids and for releasing its contents in response to specific stimuli, such as pH or temperature. This type of technology focuses on solving the targeted delivery and release problem of corrosion inhibitors in closed fluid environments such as deep wells. Its capsule structure and coating system differ fundamentally in composition, function, and application, and cannot be directly applied to coating fields that require strong adhesion, mechanical toughness, and surface antifouling functions.

[0006] In existing technologies, there are no reports of loading natural antifouling agents into hydrogels and then composited with PDMS matrices in micronized form to simultaneously enhance the mechanical properties of PDMS coatings and achieve controlled release of environmentally friendly antifouling agents. Therefore, there is an urgent need to develop a novel composite antifouling coating that can synergistically address the two major technical bottlenecks of insufficient mechanical properties in PDMS coatings and uncontrolled release of natural antifouling agents, achieving a balance between antifouling and mechanical properties to meet the requirements of long-term, green protection for marine equipment. Summary of the Invention

[0007] Purpose of the Invention: The purpose of this invention is to address the shortcomings of existing technologies by providing a capsaicin / sodium alginate-polyacrylamide hydrogel-modified PDMS antifouling coating, its preparation method, and its application. Based on the hydrogel material's ability to encapsulate antifouling agents and enhance mechanical properties, and the effective inhibition of biological growth by capsaicin, sodium alginate-polyacrylamide is used as an antifouling reservoir to continuously release environmentally friendly antifouling agents. The hydrogel powder is incorporated into a polydimethylsiloxane prepolymer through a drying ball milling technique, followed by curing to achieve a low surface energy antifouling effect. This synergistic effect allows for multi-faceted intervention in the biofouling process, enabling the composite material to jointly address marine biofouling.

[0008] Technical solution: The present invention discloses a capsaicin / sodium alginate-polyacrylamide hydrogel modified PDMS antifouling coating. The effective components of the antifouling coating consist of a polydimethylsiloxane PDMS matrix and capsaicin / sodium alginate-polyacrylamide hydrogel dry powder dispersed therein; the mass ratio of polyacrylamide:sodium alginate:capsaicin is in the range of (35-40):(20-25):(1~2); the mass content of capsaicin in the antifouling coating is 0.5-0.7% of the total mass.

[0009] The composite coating in this invention features a typical "matrix-dispersed phase" structure. The PDMS matrix, as the continuous phase, provides the main framework of the coating. Its low surface energy makes it difficult for fouling organisms to adhere, and even if they do, they are easily washed away by water flow due to weak forces. The hydrogel dry powder dispersed phase, as the functional phase, is uniformly dispersed within the PDMS network. When the coating is immersed in seawater, water gradually penetrates into the PDMS matrix and comes into contact with the internal hydrogel particles. The hydrogel absorbs water and swells, slowly and continuously releasing the capsaicin (CAP) loaded within it to the coating surface through diffusion, forming a layer of low-concentration antifouling agent. This effectively inhibits the growth and attachment of surrounding microorganisms, algal spores, and larvae. PDMS provides physical antifouling, while capsaicin provides chemical antifouling. The two work synergistically through different mechanisms to achieve a dual antifouling effect of "active killing + passive defense." In addition, the rigid hydrogel particles dispersed in the flexible PDMS network can effectively prevent crack propagation and dissipate impact energy, thus playing a reinforcing and toughening role similar to the steel bars in reinforced concrete.

[0010] Furthermore, by mass parts, it includes the following components:

[0011] 350-370 parts of PDMS prepolymer;

[0012] 35-40 parts of polyacrylamide;

[0013] 20-25 parts sodium alginate;

[0014] 1-2 parts capsaicin;

[0015] 1-2 parts of ammonium persulfate;

[0016] 1-2 parts of N,N'-methylenebisacrylamide crosslinking agent.

[0017] A method for preparing a capsaicin / sodium alginate-polyacrylamide hydrogel-modified PDMS antifouling coating as described above includes the following steps:

[0018] Step 1: Preparation of capsaicin-loaded sodium alginate-polyacrylamide hydrogel powder

[0019] 1.1 Dissolve acrylamide monomer, N,N'-methylenebisacrylamide crosslinking agent and capsaicin in anhydrous ethanol, and sonicate to fully dissolve or disperse capsaicin to prepare solution 1;

[0020] 1.2 Dissolve sodium alginate in deionized water, heat and stir until completely dissolved to obtain a clear and viscous solution, and then cool to prepare solution 2;

[0021] Capsaicin is a hydrophobic molecule with good solubility in anhydrous ethanol. Ultrasonic treatment can accelerate its dissolution and dispersion, forming a homogeneous and stable solution1. Sodium alginate is a hydrophilic polymer that can be fully hydrated and dissolved in hot water with stirring, forming a viscous solution2, laying the foundation for subsequent network interpenetration.

[0022] 1.3 Mix and stir solutions 1 and 2 under light-protected conditions, add ammonium persulfate initiator, and react in a 40°C water bath to form a hydrogel block;

[0023] 1.4 After soaking and washing the obtained hydrogel block with deionized water, it was sheared and dispersed into a microgel suspension, which was then poured into a CaCl2 solution for cross-linking and strengthening.

[0024] 1.5 After the cross-linked hydrogel particles are filtered, vacuum dried, ground and sieved, capsaicin / SA-PAM hydrogel powder is obtained.

[0025] Step 2: Preparation of hydrogel-modified PDMS composite coating

[0026] 2.1 Mix the PDMS prepolymer and curing agent at a mass ratio of 10:1, stir and degas; the PDMS prepolymer (with vinyl end groups) and the curing agent containing Si-H bonds undergo a hydrosilylation reaction under the action of a platinum catalyst to form a cross-linked network. Pre-degassing removes the gas introduced by stirring and prevents defects in the coating.

[0027] 2.2 Add 10% of the total mass of the hydrogel dry powder obtained in step one to the degassed PDMS mixture, and grind and disperse it using a three-roll mill to make the hydrogel powder uniformly dispersed in the PDMS matrix. The three-roll mill can effectively break up the hydrogel powder agglomerates and uniformly disperse them in the viscous PDMS prepolymer mixture by using the huge shear force generated by the three high-speed rotating rollers with adjustable gap to form a homogeneous composite slurry.

[0028] 2.3 After degassing the uniformly dispersed PDMS / hydrogel mixture again, pour it into a mold and coat it to the predetermined thickness. Heat and cure to obtain an antifouling coating.

[0029] Further, step 1.3 specifically involves: at room temperature, slowly pouring solution 1 into solution 2, and magnetically stirring for 1 hour under light-protected conditions at a stirring speed of 300 rpm to form a homogeneous mixed precursor solution; then adding ammonium persulfate initiator to the mixed precursor solution and stirring for 10 minutes to dissolve it; then slowly adding 100 μL of TMEDA in a 40°C water bath to initiate the polymerization reaction, and continuing the reaction at 40°C for 6 hours. As the reaction proceeds, the solution gradually thickens, eventually forming a milky white, elastic hydrogel block.

[0030] TMEDA stands for N, N, N', N'-Tetramethylethylenediamine. TMEDA and APS undergo a redox reaction, which can efficiently and rapidly generate a large number of free radicals at a low temperature of 40°C. These free radicals attack acrylamide monomers, thereby initiating the entire chain polymerization reaction to form polyacrylamide hydrogel.

[0031] This step is a free radical polymerization reaction. Ammonium persulfate (APS) acts as an oxidant, forming a redox initiation system with the reducing agent TMEDA. Sulfate free radicals can be efficiently generated at a low temperature of 40°C. . SO4 - These free radicals initiate a chain polymerization reaction of acrylamide (AM) monomers, and the linear polymer chains are linked into a three-dimensional network structure by the crosslinking agent N,N'-methylenebisacrylamide (MBA), thereby embedding and fixing capsaicin molecules in the PAM network, and sodium alginate chains are also physically inserted into it.

[0032] Further, step 1.4 specifically involves: removing the hydrogel block obtained in step 1.3, soaking it in deionized water for 24 hours, changing the water every 8 hours to remove unreacted monomers, crosslinking agents, and initiators; then mixing the hydrogel block with deionized water, shearing it with a high-speed homogenizer to form a hydrogel microgel suspension, and then dropping or pouring the obtained hydrogel microparticles or suspension into a 2 wt% CaCl2 solution and stirring for 30 minutes; then washing again with deionized water, filtering, and collecting the modified hydrogel microparticles.

[0033] The G unit (guluronic acid) on the sodium alginate molecular chain and Ca 2+ Ionic cross-linking occurs, forming a denser and more stable "egg-box" structure. This step strengthens the overall network of the hydrogel, further locking in capsaicin and enhancing the gel's mechanical strength. Water immersion washing is to remove unreacted monomers, initiator fragments, and other small molecule impurities, preventing them from affecting the curing or coating performance of PDMS later.

[0034] An application of a capsaicin / sodium alginate-polyacrylamide hydrogel-modified PDMS antifouling coating as described above in the surface protection of marine engineering equipment, used to prevent marine biofouling.

[0035] Furthermore, marine engineering equipment includes ships, vessels, underwater vehicles, port facilities, or offshore platforms.

[0036] In this invention, the sodium alginate-polyacrylamide reservoir can effectively encapsulate the antifouling agent capsaicin (CAP) while continuously releasing CAP under complex marine environments, achieving effective loading of the antifouling agent onto the hydrogel microsphere powder. Furthermore, the sodium alginate-polyacrylamide reservoir itself can be continuously hydrolyzed to release the antifouling agent, and polydimethylsiloxane reduces the surface energy of the coating, giving it self-cleaning capabilities. The hydrogel and polydimethylsiloxane have good compatibility and complement each other, providing a more practical antifouling effect. Simultaneously, by synthesizing capsaicin, a low-cost and environmentally friendly antifouling agent, the composite antifouling coating achieves antifouling performance without producing any visible or potential biological or ecological impacts. The main component of the coating, polydimethylsiloxane, plays a crucial role in the early stages of biofouling, preventing rapid initial biofilm formation. Over time, prolonged seawater impact and immersion cause a decrease in the structural strength of parts of the polydimethylsiloxane (PDMS) film. The doped sodium alginate-polyacrylamide gel network forms a cross-network, making the PMS molecular structure more compact. This improves the coating's toughness and crack-following ability, compensating for the shortcomings in the hydrophobic layer's durability and impact resistance, and enhancing the protection against biofouling on marine equipment surfaces. Furthermore, the antifouling agent capsaicin (CAP) effectively interferes with the calcium content of fungal and algal cells. 2+The hydrophobic coating achieves a balance, thereby inhibiting biofilm growth and enhancing its antifouling properties. This results in a composite hydrophobic and antibacterial surface coating to prevent further biofouling, thus reducing energy consumption during ship navigation. The hydrogel-modified self-cleaning low surface energy coating effectively reduces the adhesion of fouling organisms. The hydrogel also improves the coating's mechanical properties, achieving a balance between antifouling and mechanical properties. This synergistically addresses the problem of marine fouling organisms attaching to marine equipment, further enhancing the antifouling capabilities of marine equipment surfaces. Furthermore, the ease of production and low cost of synthetic capsaicin have made it the preferred environmentally friendly antifouling agent, enhancing the market competitiveness of hydrogel composite antifouling coatings.

[0037] In theory, both capsaicin antifouling agents and polydimethylsiloxane structures can effectively prevent fouling and isolate the marine environment. They use different physicochemical mechanisms to prevent biofouling, thereby increasing the smoothness of the surface of marine equipment, effectively saving fuel and energy, and truly protecting marine equipment.

[0038] Specifically, the prepared composite coating, while achieving chemical antifouling, works in conjunction with low surface energy coatings to resist the erosion of biofouling environments from different channels, greatly improving the antifouling protection time and effect.

[0039] In marine engineering, this invention not only solves the problem of insufficient mechanical properties of low surface energy coatings in practical applications, but also overcomes to some extent the problems of high toxicity of heavy metal antifouling agents and high extraction cost of natural antifouling agents, providing a promising solution for constructing antifouling coatings with antifouling-mechanical balance.

[0040] Furthermore, the composite antifouling coating utilizes the high structural strength of hydrogels and their ability to act as excellent carriers for slow-release antifouling agents, enabling them to release green synthetic antifouling agents into the marine biofouling environment. The main component, polydimethylsiloxane, reduces surface energy, resulting in a non-toxic antifouling effect. The continuous hydrolysis of the hydrogel's structure further enhances the antifouling effect, allowing the composite coating to maintain its antifouling performance for a longer period. This overcomes the limitations of various metal oxides as antifouling agents, which are often highly toxic and polluting, thus achieving a synergistic coating composite, environmental friendliness, and a balance between antifouling and mechanical properties.

[0041] Meanwhile, the good compatibility between the hydrogel and PDMS after the hydrogel-modified PDMS coating was obtained compensated for the poor mechanical properties of PDMS. By forming an interpenetrating network in the polydimethylsiloxane network through hydrogel, the structure of the two materials was changed. The fully flexible material gained a significant increase in toughness, while the unmodified PDMS surface maintained a low surface energy and could not maintain good mechanical properties for a long time. Therefore, the hydrogel-modified coating has great technical significance in improving the mechanical properties of the coating.

[0042] The prepared composite hydrogel-modified PDMS antifouling coating integrates a series of effective antifouling methods. In marine fouling environments, the combination of sodium alginate polyacrylamide gel particles (SA-PAM), synthetic capsaicin (CAP), and polydimethylsiloxane coating (PDMS) releases antifouling agents from the reservoir while maintaining good mechanical properties and low surface energy hydrophobicity, providing promising application prospects in marine fouling environments and achieving a multi-faceted synergistic self-cleaning and antifouling effect.

[0043] Beneficial effects: Compared with the prior art, the advantages of the present invention are as follows:

[0044] 1. Green and non-toxic. The hydrogel-modified PDMS antifouling coating of this invention is made entirely of natural and environmentally friendly components, including the hydrogel, polydimethylsiloxane, and antifouling agent. It does not contain any heavy metals such as mercury, arsenic, lead, zinc, or tin, and will not cause any visible or potential impact or hazard to the marine ecological environment, thus meeting environmental protection requirements.

[0045] 2. Simple process. The composite antifouling coating of this invention can be applied quickly without subsequent maintenance. The preparation process can be industrialized for mass production. The synthetic capsaicin is inexpensive and easy to apply, and the hydrogel material is simple to synthesize. The final product is a single-component polydimethylsiloxane coating, which is convenient to apply and effectively reduces material and construction costs.

[0046] 3. Optimized Mechanical Properties. The mechanical properties of the hydrogel-modified polydimethylsiloxane coating of this invention are optimized. This is attributed to the fact that the dense network structure and excellent elasticity and toughness of the hydrogel alter the physicochemical properties and spatial structure of the polydimethylsiloxane material. The incorporation of hydrogel significantly enhances the structural strength of polydimethylsiloxane, enabling the hydrogel-modified composite coating to acquire a variety of excellent mechanical properties and dual antifouling capabilities. The operation is simple, time-saving, and significantly improves application efficiency.

[0047] 4. Enhanced Antifouling Performance. The hydrogel-modified polydimethylsiloxane coating of this invention, while providing self-cleaning antifouling through PMDS, also expands under the influence of seawater, increasing pore size and releasing environmentally friendly antifouling agents. The surface hydrophobic layer is also washed away by ocean currents, carrying away attached organisms. This composite antifouling coating effectively participates in multiple stages of preventing marine fouling, providing long-term release of the stored antifouling agent CAP, thus jointly resisting marine fouling. This not only improves the mechanical durability of the antifouling coating and its practical performance but also overcomes the ecological problem of marine bioaccumulation caused by the use of biotoxic antifouling agents.

[0048] 5. Achieving Gradual Antifouling Throughout the Life Cycle. The hydrogel-modified polydimethylsiloxane coating of this invention possesses multi-mechanism synergistic characteristics, enabling it to protect marine equipment from marine biofouling in a gradient and degree-specific manner. Therefore, it provides protection based on the damage to the surface coating caused by different stages of fouling. In the early stages of marine fouling, the hydrophobic effect of the PDMS coating effectively prevents the formation of marine biofilms. In the medium to long term, in complex marine environments, the PDMS layer's wear and crack resistance is enhanced by the incorporation of hydrogel, providing continuous protection. During long-term seawater immersion, fouling organisms, seawater corrosion, and stress cause localized mechanical failure of the antifouling coating. However, this structural failure actually promotes the release of synthetic antifouling agents from the gel structure, thus achieving full-cycle antifouling capability.

[0049] 6. Three-in-one synergistic antifouling. In the hydrogel-modified polydimethylsiloxane coating of this invention, the synthetic capsaicin (CAP) loaded on the hydrogel is an environmentally friendly antifouling agent that can interfere with the Ca2+ of marine microbial cells. 2+ This balance inhibits the growth of fouling biofilms. Simultaneously, the hydrogel carrier, through long-term immersion, continuously swells and opens its internal pores, providing a slow-release antifouling effect and enhancing long-term antifouling performance. The main component, polydimethylsiloxane resin, has low surface energy and, through its hydrophobic and easily sliding properties, effectively prevents fouling and hinders the adhesion of fouling organisms. These three antifouling materials work in tandem, addressing biofilm formation by reducing bioactivity, killing biofilms, and providing hydrophobic and easily sliding properties. This integrated design also improves the various mechanical properties of the coating, resulting in a long-lasting composite antifouling coating.

[0050] 7. Achieving a balance between mechanical properties, antifouling performance, and environmental friendliness through multi-mechanical synergy. In the composite coating of this invention, capsaicin (CAP) and sodium alginate-polyacrylamide hydrogel have been reported to have good compatibility, enabling them to jointly cope with various harsh biofouling environments. By incorporating the hydrogel loaded with the antifouling agent into the polydimethylsiloxane prepolymer, a responsive effect against large fouling organisms (mussels, oysters) is achieved. The synergistic effect of the three materials results in a composite coating with superior long-term antifouling performance, various mechanical properties, and environmental reliability compared to coatings using only one material. The hydrogel controls the slow release of CAP while significantly enhancing the mechanical properties of the polydimethylsiloxane material. This synergistic effect of the three materials ultimately achieves a balance between the mechanical properties, high-efficiency antifouling, and environmental friendliness of the composite antifouling coating. Attached Figure Description

[0051] Figure 1 The synthesis route and application principle of the SAPAM@CAP-PDMS composite coating provided in this embodiment of the invention;

[0052] Figure 2Fourier transform infrared spectrum of SAPAM@CAP-PDMS composite coating provided in an embodiment of the present invention. Detailed Implementation

[0053] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings. However, the scope of protection of the present invention is not limited to the embodiments described. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are all conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, the reagents and materials used in the following embodiments are all commercially available.

[0054] Example 1: Preparation of capsaicin-loaded sodium alginate-polyacrylamide hydrogel microparticles

[0055] Step 1: Preparation of a gel liquid containing polyacrylamide-capsaicin and sodium alginate

[0056] (1) Weigh 2.0g of acrylamide monomer, 0.04g of MBA crosslinking agent (accounting for 2% of AM mass) and 0.05g of capsaicin into another 50mL beaker. Add 10mL of anhydrous ethanol and sonicate for 10 minutes to fully dissolve or disperse the capsaicin, thus preparing solution 1;

[0057] (2) Weigh 1.0 g of sodium alginate into a 100 mL beaker, add 40 mL of deionized water, and stir continuously (500 rpm) in a 60 ℃ water bath for at least 4 hours until completely dissolved to obtain a clear and viscous 2.5 wt% SA solution. Cool to room temperature to prepare solution 2;

[0058] To prepare a capsaicin-free blank sample, after removing the capsaicin component from solution 1, the rest of the preparation process is the same as the steps above.

[0059] Step 2: Preparation of capsaicin-loaded sodium alginate-polyacrylamide hydrogel microparticles

[0060] (1) At room temperature, slowly pour solution 1 into solution 2 and stir magnetically (300 rpm) for 1 hour under light-protected conditions (capsaicin is easily decomposed by light) to form a homogeneous mixed precursor solution. Ensure that capsaicin is evenly dispersed.

[0061] (2) Add 0.02 g of ammonium persulfate (APS) to the above mixed solution and stir for 10 minutes to dissolve it. Transfer the beaker to a 40 ℃ water bath and slowly add 100 μL of TMEDA to initiate the polymerization reaction. Continue the reaction at 40 ℃ for 6 hours. As the reaction proceeds, the solution will gradually thicken and eventually form a milky white hydrogel block with a certain degree of elasticity.

[0062] (3) The obtained hydrogel block was removed and soaked in deionized water for 24 hours, with the water changed every 8 hours to remove unreacted monomers, crosslinking agents, and initiators. It was then mixed with deionized water and sheared using a high-speed homogenizer to form a hydrogel microgel suspension. The obtained hydrogel microparticles or suspension were added dropwise or poured into a 2 wt% CaCl2 solution and stirred for 30 minutes. Afterward, it was washed again with deionized water, filtered, and the modified hydrogel microparticles were collected. The final product was placed in a vacuum drying oven and dried at 40 ℃ to constant weight to obtain capsaicin / SA-PAM hydrogel powder. It was ground and sieved (200 mesh) to obtain uniformly sized microparticles for later use.

[0063] Example 2: Preparation of SAPAM@CAP-PDMS composite coating

[0064] (1) Weigh the PDMS prepolymer and curing agent (platinum-divinyltetramethyldisiloxane complex) into a beaker at a mass ratio of 10:1. Stir manually with a glass rod for 2 minutes, then place it in a centrifuge to remove bubbles (or place it in a vacuum drying oven to remove vacuum) for about 10-15 minutes until the bubbles are completely eliminated;

[0065] (2) Weigh a certain mass (10% of the total mass of PDMS) of capsaicin / SA-PAM hydrogel powder and slowly add it to the degassed PDMS prepolymer mixture. Grind and disperse the mixture using a three-roll mill. By adjusting the roller gap and roller speed, the hydrogel powder is evenly dispersed in the PDMS matrix under high shear force. Repeat grinding 3-5 times until the mixture is uniform and free of particles. After dispersion, place the mixture in a vacuum drying oven again and evacuate for 15 minutes to remove air bubbles introduced during stirring and grinding.

[0066] (3) Pour the uniform SAPAM@CAP-PDMS composite onto an aluminum alloy 5000 plate treated with a release agent. Control the coating thickness (≤500 μm) using a doctor blade or automatic coater. Place the coating in an 80℃ forced-air drying oven and heat-cur for 2-4 hours to obtain the SAPAM@CAP-PDMS coating test sample. The PDMS and SAPAM-PDMS coating samples do not contain SAPAM@CAP or CAP components, respectively, and the remaining preparation process is the same as the above process.

[0067] To prepare a capsaicin-free blank sample, use the capsaicin-free blank solution sample from step one. The other preparation procedures are the same as those above.

[0068] The loading method of the antifouling agent CAP is as described in step 1 of Example 1. Fourier transform infrared spectra of sodium alginate gel, sodium alginate-polyacrylamide hydrogel microparticles loaded with synthetic capsaicin, and the antifouling coating surfaces SA (a), SAPAM@CAP (b), and SAPAM@CAP-PDMS (c) obtained in Example 2 are shown below. Figure 2 As shown.

[0069] Test Example 1: Water contact angle of PDMS, SAPAM-PDMS, and SAPAM@CAP-PDMS coatings

[0070] This embodiment demonstrates a standardized procedure for measuring the static water contact angle (WCA) of four types of samples: 5000 blank aluminum alloy samples, PDMS coating, SAPAM-PDMS coating, and SAPAM@CAP-PDMS coating.

[0071] 5000 blank aluminum alloy samples, PDMS, SAPAM-PDMS, and SAPAM@CAP-PDMS prepared in Examples 1 and 2 were immersed in natural seawater for 7 days. Water contact angle tests were performed on the surface after 1, 3, and 7 days. The hydrophobic and antifouling properties of the coatings were tested using the water contact angle. The test and analysis methods are referenced in: General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China, Standardization Administration of China. GB / T 30693-2014. Measurement of Water Contact Angle of Plastic Films [S]. Beijing: China Standards Press, 2014.

[0072] The testing method is as follows: Using ultrapure water as the test liquid, first ensure the surface of each coated sample is clean and fix it on the test stage, adjusting it to the center of the camera's field of view. In the static contact angle test, a droplet volume of 5.0 μL was used, and measurements were taken three times at different positions on each sample. The final result was the arithmetic mean. In the roll-off angle test, the droplet volume was increased to 15.0 μL, and measurements were taken three times at different positions, with the average value taken.

[0073] The test results are as follows: the blank aluminum alloy 5000 sample had a low water contact angle, indicating that its surface is hydrophilic; water droplets quickly wet and spread, unable to maintain a stable bead-like morphology. This contrasts sharply with the PDMS coating. PDMS, SAPAM-PDMS, and SAPAM@CAP-PDMS coatings all exhibited water contact angles close to 110° (Table 1). These water contact angle data fully demonstrate the surface's hydrophobic properties: excellent anti-wetting resistance to water. Simultaneously, the test showed that droplets could freely slide off the surface without leaving any residue. This phenomenon further confirms that using PDMS as the main component of the coating can impart excellent and stable antifouling performance. Furthermore, the test showed that the contact angle decrease of SAPAM-PDMS and SAPAM@CAP-PDMS coatings after immersion for more than 7 days was less than that of PDMS alone, indicating that the addition of the hydrogel component SAPAM endows PDMS with long-lasting mechanical properties, improving the mechanical and antifouling durability of the PDMS coating.

[0074] Table 1. Water contact angles of blank sample, PDMS, SAPAM-PDMS, and SAPAM@CAP-PDMS

[0075]

[0076] Experimental Example 2: Algal Resistance Testing with Blank Samples, PDMS, SAPAM-PDMS, and SAPAM@CAP-PDMS

[0077] Algal attachment is a key step in the second stage of marine biofouling. This study used *Chlorella sp.* as the experimental organism to evaluate the anti-algal performance of a composite self-polishing low surface energy polyacrylic acid antifouling coating. Before the experiment, all equipment, including culture media and pipettes, required for co-culture were sterilized with UV light for 30 minutes. The *Chlorella* strain was cultured in F / 2 medium at 20°C under a visible light LED light source (2000 lux) for 8 days. Algal culture in the logarithmic growth phase was then diluted with the culture medium to a concentration of 10. 5 cells / mL, used for subsequent immersion experiments.

[0078] The three coated samples (PDMS, SAPAM-PDMS, and SAPAM@CAP-PDMS) prepared in Example 1, along with 5000 untreated aluminum alloy blank samples, were immersed in the aforementioned algae suspension for 7 days, with alternating day / dark light cycles during the experiment. Afterward, the sample surfaces were thoroughly rinsed with sterile PBS buffer (pH = 7.3) to remove any unattached algal cells. The algal biomass on the coating surface was quantified by measuring the absorbance at 440 nm, thereby evaluating its anti-algae performance.

[0079] The results are shown in Table 2. Significant differences in algae adhesion were observed on the surfaces of different samples. Comparison based on characteristic absorption signals indicated that the SAPAM@CAP-PDMS hydrogel-modified PDMS antifouling coating exhibited a lower algae coverage level. Its anti-algae mechanism is mainly attributed to the continuous release of the antifouling agent capsaicin (CAP) and the physical barrier effect provided by the PDMS layer. The coating's resistance to algae adhesion was calculated to be 76.71%. The resistance calculation formula is as follows:

[0080] Algal resistance rate = (Absorbance of blank group - Absorbance of experimental group) / Absorbance of blank group × 100%

[0081] Table 2 Absorbance of blank sample, PDMS, SAPAM-PDMS, and SAPAM@CAP-PDMS

[0082]

[0083] Experimental Example 3: Tensile strength and impact resistance tests under different hydrogel addition conditions

[0084] By changing the hydrogel addition ratio, the ratio of polydimethylsiloxane prepolymer to hydrogel powder was set to 8:1, 9:1, and 10:1, respectively, and the ratio of polydimethylsiloxane prepolymer to curing agent was set to 8:1, 9:1, and 10:1, respectively. The resulting SAPAM@CAP-PDMS coatings were subjected to tensile strength tests and impact resistance tests according to GB / T 16777-2008 and GB / T 1732-2020.

[0085]

[0086] Experimental examples show that when the ratio of polydimethylsiloxane prepolymer to hydrogel powder is set to 10:1, and the ratio of polydimethylsiloxane prepolymer to curing agent is also set to 10:1, PMMA-CAP@MSDS achieves the highest tensile strength and impact strength. When the curing agent ratio is too high, the composite coating exhibits a significant decrease in impact resistance and insufficient curing. When the hydrogel addition ratio is too high, the PDMS coating has a loose internal structure and low strength, resulting in a significant decrease in tensile strength compared to sample 9.

[0087] Experiment 4: Comparison of the overall effects of PDMS, SAPAM-PDMS, and SAPAM@CAP-PDMS coatings

[0088]

[0089] The preparation process of the SAPAM@CAP-PDMS coating is as follows: the ratio of polydimethylsiloxane prepolymer to hydrogel powder is set to 10:1, and the ratio of polydimethylsiloxane prepolymer to curing agent is also set to 10:1. The mixture is stirred until homogeneous, and then poured onto an aluminum alloy 5000 plate treated with a release agent. The coating thickness (≤500 μm) is controlled using a doctor blade or automatic coater. The coating is then placed in an 80℃ forced-air drying oven and cured for 2-4 hours to obtain the SAPAM@CAP-PDMS coating test sample.

[0090] The results above show that the SAPAM@CAP-PDMS coating prepared by this process has the best overall effect.

[0091] This invention relates to a capsaicin / sodium alginate-polyacrylamide hydrogel-modified PDMS antifouling coating, its preparation method, and its application. By utilizing environmentally friendly capsaicin as an antifouling agent and sodium alginate-polyacrylamide as a gel carrier to load the antifouling agent and enhance the coating's various mechanical properties, and polydimethylsiloxane to provide high-efficiency antifouling performance, the overall mechanical and antifouling properties are synergistically enhanced, achieving a multi-faceted integration of environmental friendliness, high-efficiency antifouling, and mechanical durability in marine engineering materials. Furthermore, the mechanical properties of the material can be modified by controlling the ratio of hydrogel and curing agent. The SAPAM@CAP-PDMS coating improves both mechanical and environmentally friendly antifouling performance through gel-loaded antifouling agents and gel powder incorporation. Integrating two popular polymer material processes to prepare the antifouling coating combines their application advantages, making its efficient and stable antifouling application in the marine engineering field possible.

[0092] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for preparing a capsaicin / sodium alginate-polyacrylamide hydrogel-modified PDMS antifouling coating, characterized by comprising the following steps: Step 1: Preparation of capsaicin-loaded sodium alginate-polyacrylamide hydrogel powder 1.1 Dissolve acrylamide monomer, N,N'-methylenebisacrylamide crosslinking agent and capsaicin in anhydrous ethanol, and sonicate to fully dissolve or disperse capsaicin to prepare solution 1; 1.2 Dissolve sodium alginate in deionized water, heat and stir until completely dissolved to obtain a clear and viscous solution, and then cool to prepare solution 2; 1.3 Mix and stir solutions 1 and 2 under light-protected conditions, add ammonium persulfate initiator, and react in a 40°C water bath to form a hydrogel block; 1.4 After soaking and washing the obtained hydrogel block with deionized water, it was sheared and dispersed into a microgel suspension, which was then poured into a CaCl2 solution for cross-linking and strengthening. 1.5 After the cross-linked hydrogel particles are filtered, vacuum dried, ground and sieved, capsaicin / SA-PAM hydrogel powder is obtained. Step 2: Preparation of hydrogel-modified PDMS composite coating 2.1 Mix the PDMS prepolymer and curing agent at a mass ratio of 10:1, stir and degas; 2.2 Add 10% of the total mass of the hydrogel powder obtained in step 1 to the degassed PDMS mixture, and grind and disperse it using a three-roll mill to make the hydrogel powder uniformly dispersed in the PDMS matrix; 2.3 After degassing the uniformly dispersed PDMS / hydrogel mixture again, pour it into a mold and coat it to a predetermined thickness, then heat and cure it to obtain the antifouling coating. Step 1.3 specifically involves: at room temperature, slowly pouring solution 1 into solution 2, and magnetically stirring for 1 hour under light-protected conditions at a stirring speed of 300 rpm to form a homogeneous mixed precursor solution; then adding ammonium persulfate initiator to the mixed precursor solution and stirring for 10 minutes to dissolve it; then slowly adding 100 μL of TMEDA in a 40°C water bath to initiate the polymerization reaction, and continuing the reaction at 40°C for 6 hours. As the reaction proceeds, the solution gradually thickens, eventually forming a milky white, elastic hydrogel block. Step 1.4 specifically involves: taking out the hydrogel block obtained in step 1.3 and soaking it in deionized water for 24 hours, changing the water every 8 hours to remove unreacted monomers, crosslinking agents, and initiators; then mixing the hydrogel block with deionized water and shearing it using a high-speed homogenizer to form hydrogel microparticles or microgel suspensions; then adding or pouring the obtained hydrogel microparticles or microgel suspensions into a 2 wt% CaCl2 solution and stirring for 30 minutes; then washing again with deionized water, filtering, and collecting the modified hydrogel microparticles.

2. A capsaicin / sodium alginate-polyacrylamide hydrogel modified PDMS antifouling coating, characterized in that: The antifouling coating is prepared by the preparation method described in claim 1; the effective component of the antifouling coating is composed of polydimethylsiloxane PDMS matrix and capsaicin / sodium alginate-polyacrylamide hydrogel dry powder dispersed therein; the mass ratio of polyacrylamide:sodium alginate:capsaicin is in the range of (35-40):(20-25):(1~2).

3. The capsaicin / sodium alginate-polyacrylamide hydrogel modified PDMS antifouling coating according to claim 2, characterized in that: By mass parts, it includes the following components: 350-370 parts of PDMS prepolymer; 35-40 parts of polyacrylamide; 20-25 parts sodium alginate; 1-2 parts capsaicin; 1-2 parts of ammonium persulfate; 1-2 parts of N,N'-methylenebisacrylamide crosslinking agent.

4. The application of the capsaicin / sodium alginate-polyacrylamide hydrogel modified PDMS antifouling coating as described in claim 2 or 3 in the surface protection of marine engineering equipment, for preventing marine biofouling.

5. The application according to claim 4, characterized in that: The marine engineering equipment includes ships, submarines, port facilities, or offshore platforms.

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