Surface modifying amphiphilic additives and their effect on the fouling-release performance of siloxane-polyurethane coatings

Investigation of Amphiphilic PDMS-Hyperbranched Polyglycerol Copolymers to Tune the Fouling-Release Properties in a Moisture Curable Coating System

Hyperbranched polyglycerol (HBPG) has been proven to be effective as a hydrophilic material when incorporated into amphiphilic copolymers, enhancing fouling-release properties. These amphiphilic polymers not only increase the effectiveness of coatings across a wide range of organisms but also impart antifouling characteristics without resorting to toxic chemicals. HBPGs exhibit high resistance to proteins and lead to the effective removal of marine organisms under low impact pressures. To enhance the effectiveness of HBPGs and facilitate polymer stratification onto the coating surface, copolymers with polydimethylsiloxane (PDMS) were synthesized through a ring-opening multibranching polymerization reaction. These amphiphilic polymers, with varying molecular weights of the PDMS block and different degrees of branching in the HBPG blocks, were incorporated into a urea-siloxane moisture-cure coating system at a concentration of 5 wt %. This study aimed to identify the optimal molecular weight of PDMS and the degree of branching in HBPG that provides the most improved fouling-release (FR) properties to the base coating. The amphiphilic copolymers underwent thorough characterization using Fourier transform infrared (FTIR), NMR, and surface tension measurements. Coatings were extensively characterized for their surface properties by using atomic force microscopy (AFM), photoinduced force microscopy (PiFM), X-ray photoelectron spectroscopy (XPS), moisture adsorption measurements, and contact angle measurements. To assess fouling-release and antifouling properties, laboratory biological assays were conducted with five common marine fouling organisms: Navicula incerta, Celluphaga lytica, Ulva linza, Chlorella vulgaris, and Amphibalanus amphitrite. Notably, 1k or 5k PDMS with a polyglycerol branching ratio of 10:1 or 15:1 emerged as the best performers across a diverse array of laboratory biological assays.

Amphiphilic Balance: Effect of the Hydrophilic-Hydrophobic Ratio on Fouling-Release Surfaces

This study demonstrated the importance of identifying the optimal balance of hydrophilic and hydrophobic moieties in amphiphilic coatings to achieve fouling-release (FR) performance that surpasses that of traditional hydrophobic marine coatings. While there have been many reports on fouling-release properties of amphiphilic surfaces, the offered understanding is often limited. Hence, this work is focused on further understanding of the amphiphilic surfaces. Poly(ethylene glycol) (PEG) and polydimethylsiloxane (PDMS) were used to create a series of noncross-linked amphiphilic additives that were then added to a hydrophobic-designed siloxane-polyurethane (SiPU) FR system. After being characterized by ATR-FTIR, XPS, contact angle analysis, and AFM, the FR performance was evaluated by using different marine organisms. The assessments showed that the closer the hydrophilic and hydrophobic moieties in a system reached a relatively equalized level, the more desirable the FR performance of the coating system became. A balanced ratio of hydrophilicity-hydrophobicity in the system at around 10-15 wt % of each component had the best FR performance and was comparable to or better than commercial FR coatings.

Evaluation of lipophosphoramidates-based amphiphilic compounds on the formation of biofilms of marine bacteria

The bacteriostatic and/or bactericidal properties of few phosphoramide-based amphiphilic compounds on human pathogenic bacteria were previously reported. In this study, the potential of two cationic (BSV36 and KLN47) and two zwitterionic (3 and 4) amphiphiles as inhibitors of marine bacterial growth and biofilm formation were investigated. Results showed that the four compounds have little impact on the growth of a panel of 18 selected marine bacteria at a concentration of 200 µM, and up to 700 µM for some bacterial strains. Interestingly, cationic lipid BSV36 and zwitterionic lipids 3 and 4 effectively disrupt biofilm formation of Paracoccus sp. 4M6 and Vibrio sp. D02 at 200 µM and to a lesser extent of seven other bacterial strains tested. Moreover, ecotoxicological assays on four species of microalgae highlighted that compounds 3 and 4 have little impact on microalgae growth with EC50 values of 51 µM for the more sensitive species and up to 200 µM for most of the others. Amphiphilic compounds, especially zwitterionic amphiphiles 3 and 4 seem to be promising candidates against biofilm formation by marine bacteria.

Marine biofouling and the role of biocidal coatings in balancing environmental impacts

Marine biofouling is a global problem affecting various industries, particularly the shipping industry due to long-distance voyages across various ecosystems. Therein fouled hulls cause increased fuel consumption, greenhouse gas emissions, and the spread of invasive aquatic species. To counteract these issues, biofouling management plans are employed using manual cleaning protocols and protective coatings. This review provides a comprehensive overview of adhesion strategies of marine organisms, and currently available mitigation methods. Further, recent developments and open challenges of antifouling (AF) and fouling release (FR) coatings are discussed with regards to the future regulatory environment. Finally, an overview of the environmental and economic impact of fouling is provided to point out why and when the use of biocidal solutions is beneficial in the overall perspective.

Enhanced Tensile Properties, Biostability, and Biocompatibility of Siloxane-Cross-Linked Polyurethane Containing Ordered Hard Segments for Durable Implant Application

This work developed a series of siloxane-modified polyurethane (PU-Si) containing ordered hard segments by a facile method. The polyaddition between poly(ε-caprolactone) and excess diurethane diisocyanate was carried out to synthesize a polyurethane prepolymer with terminal isocyanate groups, which was then end-capped by 3-aminopropyl triethoxysilane to produce alkoxysilane-terminated polyurethane; the target products of PU-Si were obtained with hydrolysis and the condensation of alkoxysilane groups. The chemical structures were confirmed by FT-IR and XPS, and the effect of the siloxane content or cross-linked degree on the physicochemical properties of the PU-Si films was investigated in detail. The formation of the network structure linked by Si-O-Si bonds and interchain denser hydrogen bonds endowed PU-Si films with fine phase compatibility, low crystallinity, high thermal stability, and excellent tensile properties. Due to the high cross-linked degree and low interfacial energy, the films displayed a high surface water contact angle and low equilibrium water absorption, which resulted in slow hydrolytic degradation rates. Furthermore, the evaluation of protein adsorption and platelet adhesion on the PU-Si film surface presented high resistance to biofouling, indicating superior surface biocompatibility. Consequently, the siloxane-cross-linked polyurethane, which possessed excellent tensile properties, high biostability, and superior biocompatibility, showed great potential to be explored as biomaterials for durable implants.

Studying the Effect of Pre-Polymer Composition and Incorporation of Surface-Modifying Amphiphilic Additives on the Fouling-Release Performance of Amphiphilic Siloxane-Polyurethane Coatings

Combining amphiphilic fouling-release (FR) coatings with the surface-active nature of amphiphilic additives can improve the antifouling/fouling-release (AF/FR) properties needed to offer broad-spectrum resistance to marine biofoulants. This work is focused on further tuning the amphiphilic character of a previously developed amphiphilic siloxane-polyurethane (SiPU) coating by varying the amount of PDMS and PEG in the base system. Furthermore, surface-modifying amphiphilic additives (SMAAs) were incorporated into these amphiphilic FR SiPU coatings in varying amounts. ATR-FTIR, contact angle and surface energy measurements, and AFM were performed to assess changes in surface composition, wettability, and morphology. AF/FR properties were evaluated using laboratory biological assays involving Cellulophaga lytica, Navicula incerta, Ulva linza, Amphibalanus amphitrite, and Geukensia demissa. The surfaces of these coatings varied significantly upon changes in PDMS and PEG content in the coating matrix, as well as with changes in SMAA incorporation. AF/FR properties were also significantly changed, with formulations containing the highest amounts of SMAA showing very high removal properties compared to other experimental formulations, in some cases better than that of commercial standard FR coatings.

Hybrid Tri-Cure Organo-Silicon Coatings for Monument Preservation

A coating system integrating three distinct chemistries was developed to protect materials used in monuments and construction. Initial curing is achieved using a UV-initiated thiol-ene reaction to form a non-impressionable/non-sticky surface. Second, amine/epoxy reactions form a firm surface adhesion and give mechanical strength through consolidation. Third, alkoxysilane sol-gel curing integrates the siloxane network while adding thermal stability, hydrophobicity, and a hardened surface. The final design utilizes a photoacid generator to increase the reaction speed of the second and third curing steps. The coating can be applied by spray, dip, or wipe on methods and exhibits a rapid non-impressionable surface (as fast as 10 min) that resists graffiti and environmental conditions, and is used and stored as a single-component system with a pot life exceeding six months. A series of experiments were used to determine the coating properties and durability, including field testing and accelerated weathering.

Durable Liquid- and Solid-Repellent Elastomeric Coatings Infused with Partially Crosslinked Lubricants

Surfaces that are resistant to both liquid fouling and solid fouling are critical for many industrial and biomedical applications. However, surfaces developed to address these challenges thus far have been generally susceptible to mechanical damage. Herein, we report the design and fabrication of robust solid- and liquid-repellent elastomeric coatings that incorporate partially crosslinked lubricating chains within a durable polymer matrix. In particular, we fabricated partially crosslinked omniphobic polyurethane (omni-PU) coatings that can repel a broad range of liquid and solid foulants. The fabricated coatings are an order of magnitude more resistant to cyclic abrasion than current state-of-the-art slippery surfaces. Further through the integration of classic wetting and tribology models, we introduce a new material design parameter (K_AR) for abrasion-resistant polymeric coatings. This combination of mechanical durability and broad antifouling properties enables the implication of such coatings to a wide variety of industrial and medical settings, including biocompatible implants, underwater vehicles, and antifouling robotics.

Grooming of fouling-release coatings to control marine fouling and determining how grooming affects the surface

Grooming may be an effective technique to control marine biofouling without damaging the coating or discharging active ingredients into the environment. This study assessed the grooming performance of three experimental biocide-free siloxane polyurethane (SiPU) fouling-release coatings. Coatings were statically immersed in Port Canaveral, Florida, and groomed every two weeks for five months using three different brush types. The ungroomed panels became heavily fouled with biofilm, tubeworms, barnacles, and bryozoans. Two of the brushes were able to control the fouling with a coverage of <5%. The commercial silicone elastomer coating was damaged from grooming procedures, while the SiPU coatings were not. Laboratory biological assays were carried out and mirrored the grooming results. Through surface characterization techniques, it was concluded that the coatings were unaffected by the grooming procedures. This study shows that marine fouling on durable SiPU fouling-release coatings can be controlled via grooming without damage or changing the surface properties.