Fouling-release Coatings Research Articles

Superhydrophobic coating of silicone/β–MnO2 nanorod composite for marine antifouling

A novel superhydrophobic series of silicone/β–MnO2 nanorod composite was successfully fabricated for marine fouling release (FR) coatings. We studied how the self-cleaning and antifouling features were affected by controlling the β–MnO2 nanorod preparation and distribution in the silicone matrix. The nanorods exhibited a single crystal structure, a mean diameter of 20–30 nm and a length of 0.5–1 μm, and they had a wurtzite structure that preferentially grew in the [100] direction which has the most stable surface, high antimicrobial, and low free energy. Nanorod fillers of different concentrations were distributed in the silicone matrix for enhancing the surface roughness, water repellency and FR features. Surface characteristics were evaluated by using the contact angle of water experiments, atomic force microscope and scanning electron microscope for studying the superhydrophobicity and antifouling attributes. Well-dispersed nanorods exhibited a particular increase in the coating roughness, superhydrophobicity, and low surface energy properties. Thermal and mechanical properties, as well as stability in different pH solutions, were tested as durability parameters. For assessing the biological and fouling repellency effects of the coating systems, chosen micro-fouling organisms were used in the laboratory for one month. Also, a field experiment was carried out by immersing the coated samples in natural seawater up to 90 days and the screening method and image analysis were used to test the FR behavior. The well-dispersed nanorods (0.5 wt.%) presented the most profound superhydrophobic FR nanostructured coating; which demonstrated a 158° and 12.65 mN/m for the surface contact angle and free energy.

Superhydrophobic silicone/SiC nanowire composite as a fouling release coating material

A ceramic superhydrophobic series of polydimethylsiloxane/silicon carbide nanowire (SiC NW) composites was designed for marine fouling release (FR) coatings of the ship hull. Single-crystal SiC NWs with 50–80 nm diameters were grown in {111} crystal plane and employed as nanofillers. Ex situ silicone nanocomposites were facilely developed and cured by a mechanism of hydrosilation. The effects of incorporating different nanofiller concentrations on the surface, mechanical, and FR properties of silicone nanocomposites were extensively studied. Surface properties were studied by nonwettability and free energy and characterized via scanning electron and atomic force microscopes. Nanocomposites’ mechanical features were tested as durability factors. Selected microfoulants of fungi and bacterial progenies were used for biological assessments in the laboratory. A field test was performed on the developed coating samples in natural seawater for 3 months in a tropical area. Excellent distributed SiC NWs (0.5 wt%) showed outstanding hydrophobicity with 153° contact angle, 11.25 mN/m free energy of the surface, micro-/nanoscale roughness, and FR properties.

Hydrolyzable Additive-Based Silicone Elastomers: A New Approach for Antifouling Coatings.

Fouling Release Coatings are marine antifouling coatings based on silicone elastomers. Contrary to commonly used biocide-based antifouling coatings, they do not release biocides into the marine environment, however, they suffer from poor antifouling efficacy during idle periods. To improve their antifouling performances in static conditions, various amounts of hydrolyzable polymers were incorporated within a silicone matrix. These hydrolyzable polymers were chosen for the well-known hydrolytic degradation mechanism of their main chain, e.g. poly(ε-caprolactone) (PCL), or of their ester pending groups, e.g. poly(bis(trimethylsilyloxy)methylsilyl methacrylate) (PMATM2). The degradation kinetics of such hydrolyzable silicone coatings were assessed by mass loss measurements during immersion in deionized water. Coatings containing PMATM2 exhibited a maximum mass loss after 12 weeks, whereas PCL-based coatings showed no significant mass loss after 24 weeks. Dynamic contact angle measurements revealed the modifications of the coatings surface chemistry with an amphiphilic behavior after water exposure. The attachment of macrofoulers on these coatings were evaluated by field tests in the Mediterranean Sea, demonstrating the short or long-term antifouling effect of these hydrolyzable polymers embedded in the silicone matrix. The settlement of A. amphitrite barnacles on the different coatings indicated inhospitable behaviors towards larval barnacles for coatings with at least 15 wt % of additives.

The influence of MWCNTs-OH on the properties of the fouling release coatings based on polydimethylsiloxane with the incorporation of phenylmethylsilicone oil

In order to control the leaching of phenylmethylsilicone oil (PSO) reasonably from the fouling release coating based on polydimethylsiloxane, the MWCNTs-OH/Fe2O3 composite coatings was investigated, including the surface properties, the mechanical properties, especially the leaching performance of PSO and the antifouling performance of the coatings. When the content of MWCNTs-OH/Fe2O3 is controlled at 1% of the pigment volume concentration, with the increase of the volume ratio of MWCNTs-OH, the mechanical properties and the surface roughness of the coating increase. The increase in the volume ratio of MWCNTs-OH causes the transformation of the leaching behavior of PSO from the molecular network diffusion to the channel diffusion, enhancing the leaching efficiency of PSO. Moreover, the improvement of the anti-biofilm adhesion performance is confirmed by increase the leaching efficiency of PSO. The panel tests of the antifouling coatings in Yellow sea in China also indicates that coatings had the excellent antifouling effect when the volume ratio of MWCNTs-OH is more than 50% in the mixed powders.

The Role of Hydrogen Bonding in Peptoid-Based Marine Antifouling Coatings

The benefits of incorporating amphiphilic properties into antifouling and fouling-release coatings are well-established. The use of sequence-defined peptides and peptoids in these coatings allows p...

Development and Characterization of Mechanically Durable Silicone-Polythiourethane Composites Modified with Tetrapodal Shaped ZnO Particles for the Potential Application as Fouling-Release Coating in the Marine Sector.

Ecological considerations strongly necessitate the development of environmentally friendly antifouling paints. A promising alternative to biocide containing antifouling paints are fouling-release coatings, which are non-toxic and designed to prevent permanent attachment of marine organisms to the surface, due to their low surface energy. However, these coatings suffer from insufficient mechanical properties, which make them unsuitable for mechanically stressed surfaces e.g., on ship hulls. To overcome those obstacles, polydimethylsiloxane (PDMS)-polythiourethane (PTU) composites modified with tetrapodal shaped micro-nano ZnO particles (t-ZnO) were produced and characterized by evaluating the surface energy, mechanical properties, and fouling-release performance. Among all variations, PTU/1 wt.% PDMS composites with 1 wt.% t-ZnO particles possess superior properties for applications as fouling-release coatings for maritime purposes.

A new approach to testing potential leaching toxicity of fouling release coatings (FRCs)

Fouling release coatings (FRCs) are today the main environment-friendly alternative to traditional self-polishing coatings, that continuously release biocides and/or heavy metals into water. FRCs are available on the market as environmentally friendly AF paints and most of them do not contain bioactive agents, however no complete and reliable assessment of their environmental impact has yet been carried out. Only few literature data proving their AF efficacy combined with a demonstrated lack of toxicological effects are available. Ecotoxicological bioassays are commonly used to predict the potential environmental impact of traditional AF paints. Standardized methodologies to obtain leaching products from biocide-based paints are available, while few studies propose experimental methods to assess the potential effects of biocide-free FRCs leachates on non-target organisms. The aim of this work is to propose an experimental protocol to obtain leaching products from biocide-free FRCs in order to evaluate the potential release of substances having toxic effects, by means of an ecotoxicological bioassay. Two ecotoxicological end-points with different sensitivity levels were considered (multi-end-point approach). Five silicone-based commercial coatings were used: their leaching products were collected after different immersion times following the developed experimental method and then two ecotoxicological end-points were evaluated on II stage nauplii of the crustacean Amphibalanus amphitrite as model organism. Moreover, chemical analyses were performed on leachates collected after each immersion time, focusing on the presence of metals in leaching products. From the results obtained from the bioassay, even if not indicative of the real environmental impact of FRCs, a release of toxic substances was observed from tested coatings during early immersion stages, likely to affect the exposed model organism. The potential leaching toxicity of the five tested products was compared. No clear correspondence could be identified between the concentrations of metals detected in leachates and the obtained ecotoxicological data, thus suggesting that other active components might be released by FRCs responsible for the toxic effects pointed out on A. amphitrite larvae.

Delamination of a rigid punch from an elastic substrate under normal and shear forces

Delamination of rigid objects from an elastic substrate with finite thickness is a fundamental problem underlying applications such as marine fouling release coatings or anti-icing coatings. Most existing theoretical studies assume that delamination is driven by forces normal to the substrate surface, while in practice the delamination force may also include shear components that are parallel to the substrate surface. In this work, we consider a model system where a rigid cylindrical punch is detached from an elastic substrate under normal force, shear force or both. Our focus is to determine the pull-off force and to reveal the delamination mechanics under various geometrical and loading conditions, specifically the substrate thickness and the position and angle of the delamination force. To gain theoretical insights, we first study a plane strain model where a long rigid strip is adhered to an elastic half-space, and obtain an analytical solution revealing how the pull-off force depends on the loading position and angle. Moreover, we develop a three-dimensional finite element model to simulate the delamination of a rigid cylindrical punch from an elastic substrate with finite thickness. Three delamination modes are identified from finite element results: Mode-I crack propagation, Mode-II crack propagation, and interface cavitation. For the first two modes, we obtain empirical formulas to calculate the pull-off force using adhesion energy, substrate modulus, contact radius and substrate thickness. We also find that the analytical solution derived from the plan strain model can serve as a qualitative guide to estimate the effect of loading position and angle on the pull-off force.

Parallelized microfluidic diatom accumulation assay to test fouling-release coatings.

Assessing the efficiency of the next generation of protective marine coatings is highly relevant for their optimization. In this paper, a parallelized microfluidic testing device is presented to quantify the accumulation of a model organism (Navicula perminuta) under constant laminar flow. Using automated microscopy in conjunction with image analysis, the adhesion densities on the tested surfaces could be determined after exposure to a flow of suspended algae for 90 min. The optimized protocol for the assay is presented, and the reproducibility of the densities of attached diatoms was verified on four identical surfaces (self-assembled dodecanethiol monolayers). A set of well-characterized self-assembled monolayers with different chemical terminations was used to validate the performance of the assay and its capability to discriminate diatom accumulation on different surface chemistries under dynamic conditions. The observed trends are in good agreement with previously published results obtained in single channel accumulation and detachment assays. To demonstrate the practical relevance of the dynamic experiment, diatom attachment on four technically relevant silicone coatings with different fouling-release properties could clearly be distinguished.

Sol-gel polysiloxane films containing different surface-active trialkoxysilanes for the release of the marine foulant Ficopomatus enigmaticus

Sol-gel polysiloxane films containing varied amounts of different trialkoxyorganosilanes, carrying hydrophobic perfluoroalkyl (F) and/or hydrophilic polyoxyethylene (P) side chains, were prepared. The effect of the surface-active agents F and P on the film surface properties were investigated by contact angle measurements and angle-resolved X-ray photoelectron spectroscopy (AR-XPS) analysis. In particular, AR-XPS proved that the fluorinated side chains migrated to the film surface depending on both the nominal amount of F and the presence of P in the formulation. Moreover, the films underwent surface chemical modification upon contact with water, as a result of an increase in P chains and a concomitant decrease in F chains at the film surface. The biological performance of the films was evaluated against the serpulid Ficopomatus enigmaticus, a widespread and invasive marine biofoulant, and demonstrated the potential of the amphiphilic films containing P chains as fouling-release coatings in the marine environment.

Synthesis of Polydimethylsiloxane-Modified Polyurethane and the Structure and Properties of Its Antifouling Coatings

Polydimethylsiloxane (PDMS) could be used to improve the antifouling properties of the fouling release coatings based on polyurethane (PU). A series of polydimethylsiloxane-modified polyurethane coatings were synthesized with various PDMS contents, using the solvent-free method. The effects of PDMS content and seawater immersion on the chain structure and surface morphology were investigated by confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and X-ray diffraction (XRD). Based on the measurements of contact angles of deionized water and diiodomethane, surface free energies of the coatings were estimated according to the Owens two-liquid method. The PDMS-modified polyurethane exhibited lower surface free energy and a lower glass transition temperature than polyurethane. The presence of PDMS increased the degree of microphase separation, and enhanced the water resistance of the coatings. The optimum amount of PDMS reduced the elastic modulus and increased the ductility of the coating. The presence of PDMS benefited the removal of weakly attached organisms. Panel tests in the Yellow Sea demonstrated the antifouling activity of the PDMS-modified polyurethane.

Fouling Release Coatings Based on Polydimethylsiloxane with the Incorporation of Phenylmethylsilicone Oil

In this study, phenylmethylsilicone oil (PSO) with different viscosity was used for research in fouling release coatings based on polydimethylsiloxane (PDMS). The surface properties and mechanical properties of the coatings were investigated, while the leaching behavior of PSO from the coatings was studied. Subsequently, the antifouling performance of the coatings was investigated by the benthic diatom adhesion test. The results showed that the coatings with high-viscosity PSO exhibited high levels of hydrophobicity and PSO leaching, while the high PSO content significantly decreased the elastic modulus of the coatings and prolonged the release time of PSO. The antifouling results indicated that the incorporation of PSO into coatings enhanced the antifouling performance of the coating by improving the coating hydrophobicity and decreasing the coating elastic modulus, while the leaching of PSO from the coatings improved the fouling removal rate of the coating. This suggests a double enhancement effect on the antifouling performance of fouling release coatings based on PDMS with PSO incorporated.

Comparative study of biofilm formation on biocidal antifouling and fouling-release coatings using next-generation DNA sequencing

The bacterial and eukaryotic communities forming biofilms on six different antifouling coatings, three biocidal and three fouling-release, on boards statically submerged in a marine environment were studied using next-generation sequencing. Sequenced amplicons of bacterial 16S ribosomal DNA and eukaryotic ribosomal DNA internal transcribed spacer were assigned taxonomy by comparison to reference databases and relative abundances were calculated. Differences in species composition, bacterial and eukaryotic, and relative abundance were observed between the biofilms on the various coatings; the main difference was between coating type, biocidal compared to fouling-release. Species composition and relative abundance also changed through time. Thus, it was possible to group replicate samples by coating and time point, indicating that there are fundamental and reproducible differences in biofilms assemblages. The routine use of next-generation sequencing to assess biofilm formation will allow evaluation of the efficacy of various commercial coatings and the identification of targets for novel formulations.

Dynamic field testing of coating chemistry candidates by a rotating disk system

Quick and reliable testing is crucial for the development of new fouling release (FR) coatings. Exposure of these coatings to natural multispecies communities is essential in evaluating their efficacy. To this end, we present a rotating disk setup for dynamic field exposure. To achieve a well-defined flow on the surface of the disk, an easy to use sample mounting system was developed that provides a smooth and even surface. We related the angular velocity of the disk to the wall shear stress on the surface with a hydrodynamic model. The wall shear stress was adjusted to values previously found to be suitable to discriminate dynamic diatom attachment on different coating chemistries in the lab. The effect of the dynamic conditions was shown by comparing polystyrene slides under static and dynamic exposure. Using a set of self-assembled monolayers, the discrimination potential of the assay in a multispecies environment was demonstrated.

Sharply Reduced Biofilm Formation from Cobetia marina and in Black Sea Water on Modified Siloxane Coatings

Siloxane fouling release coatings are currently the only viable non-toxic commercial alternative to toxic biocide antifouling paints. However, they only partially inhibit biofouling since biofilms remain a major issue. With the aim to improve the bacterial resistance of siloxane coatings modified with non-ionic surfactant (NIS), antioxidant (AO) or both NIS/AO, the ability of PEG-silane co-cross-linker was investigated to reduce Cobetia marina adhesion and multispecies biofilm formation from natural seawater. Surface physical-chemical and physical-mechanical parameters relevant to bio-adhesion were estimated before the testing of the biofilm formation. Slightly reduced biofilm from C. marina and sharply reduced multispecies biofilm, formed in natural sea water, were found on the PEG-silane co-cross-linked coatings without modifying additives. However, both C. marina growth and biofilm formation from natural sea water were sharply reduced on the PEG-silane co-cross-linked coatings containing NIS or AO, even more, no C. marina adhesion was seen on the coating containing NIS and AO simultaneously. Possible explanations of the observed effects are presented in this article. It was concluded that the PEG-silane co-cross-linker, toghether with NIS and AO, can be used as an efficient tool to additionally reduce the bioadhesion of Gram-negative marine bacteria and multispecies biofilm formation on siloxane antifouling coatings.

Visualization of the distribution of surface-active block copolymers in PDMS-based coatings

Poly(dimethylsiloxane) (PDMS) has been widely employed in the area of fouling-release coatings and other fields due to its unique combination of properties including low elastic modulus and low glass transition temperature. The drawback of PDMS in some applications is its hydrophobic surface, which results in non-specific protein adsorption and wettability issues. Poly(ethylene glycol)-based surface-active block copolymers and surfactants have been added to PDMS coatings and films to impart biofouling resistance and hydrophilicity to the PDMS surface with successful results. Information regarding the distribution and release of these block copolymers from PDMS-based coatings has been previously reported. However, the distribution and behaviour of these compounds in the bulk of the PDMS coating are not fully understood.A novel fluorescent-labelled triblock PEG-b-PDMS-b-PEG copolymer was synthesized and added to a PDMS coating for visualization purposes. The surface-activity and biofouling resistance of the synthesized copolymer was confirmed by water contact angle measurements and seawater immersion experiments. Confocal laser scanning microscopy (CLSM) images showed that the triblock copolymer aggregates in spherical domains within the PDMS coating film. The size of these domains vary between 1 and 7 μm, with larger domains being present on the bulk of the film and smaller closer to the surface. The diffusion of the copolymer could be observed over time, with copolymer molecules diffusing from the bulk to the surfaces of the PDMS film. Finally, an overview of the possibilities provided by the presented methodology in the field of fouling-release coatings is discussed.

A multi-step approach for testing non-toxic amphiphilic antifouling coatings against marine microfouling at different levels of biological complexity

Marine biofouling on artificial surfaces such as ship hulls or fish farming nets causes enormous economic damage. The time for the developmental process of antifouling coatings can be shortened by reliable laboratory assays. For designing such test systems, it is important that toxic effects can be excluded, that multiple parameters can be addressed simultaneously and that mechanistic aspects can be included. In this study, a multi-step approach for testing antifouling coatings was established employing photoautotrophic biofilm formation of marine microorganisms in micro- and mesoscoms. Degree and pattern of biofilm formation was determined by quantification of chlorophyll fluorescence. For the microcosms, co-cultures of diatoms and a heterotrophic bacterium were exposed to fouling-release coatings. For the mesocosms, a novel device was developed that permits parallel quantification of a multitude of coatings under defined conditions with varying degrees of shear stress. Additionally, the antifouling coatings were tested for leaching of potential compounds and finally tested in sea trials. This multistep-approach revealed that the individual steps led to consistent results regarding antifouling activity of the coatings. Furthermore, the novel mesocosm system can be employed for advanced antifouling analysis including metagenomic approaches for determination of microbial diversity attaching to different coatings under changing shear forces.

Amphiphilic Alginates for Marine Antifouling Applications.

Amphiphilic polymers are promising candidates for novel fouling-release coatings for marine applications. We grafted amphiphilic alginates with fluorinated side chains to glass and silicon substrates and characterized the obtained films by contact angle goniometry, spectroscopic ellipsometry, XPS, and ATR-FTIR. The potential to inhibit protein attachment was tested against four different proteins, and intermediate fluorine loadings showed the strongest reduction with respect to hydrophobic, aliphatic controls. A similar trend was observed in dynamic attachment experiments using Navicula perminuta diatoms and settlement experiments with zoospores of the green algae Ulva linza. The results indicate that amphiphilic alginates are promising natural and renewable biomacromolecules that could be included in future protective coating technologies.

Silicone/Ag@SiO2 core-shell nanocomposite as a self-cleaning antifouling coating material.

The effects of Ag@SiO2 core–shell nanofiller dispersion and micro-nano binary structure on the self-cleaning and fouling release (FR) in the modelled silicone nano-paints were studied. An ultrahydrophobic polydimethylsiloxane/Ag@SiO2 core–shell nanocomposite was prepared as an antifouling coating material. Ag@SiO2 core–shell nanospheres with 60 nm average size and a preferential {111} growth direction were prepared via a facile solvothermal and a modified Stöber methods with a controlled shell thickness. Ag@SiO2 core–shell nanofillers were inserted in the silicone composite surface via solution casting technique. A simple hydrosilation curing mechanism was used to cure the surface coating. Different concentrations of nanofillers were incorporated in the PDMS matrix for studying the structure–property relationship. Water contact angle (WCA) and surface free energy determinations as well as atomic force microscopy and scanning electron microscope were used to investigate the surface self-cleaning properties of the nanocomposites. Mechanical and physical properties were assessed as durability parameters. A comparable study was carried out between silicone/spherical Ag@SiO2 core–shell nanocomposites and other commercial FR coatings. Selected micro-foulants were used for biological and antifouling assessments up to 28 days. Well-distributed Ag@SiO2 core–shell (0.5 wt%) exhibited the preferable self-cleaning with WCA of 156° and surface free energy of 11.15 mN m−1.

Antifouling and Photocatalytic Antibacterial Activity of the AquaSun Coating in Seawater and Related Media.

Prolonged testing of the new xerogel photocatalytic coating AquaSun applied to a surface probe immersed in ocean water irradiated with simulated solar radiation shows excellent action against biofouling. Activated by moderate solar radiation, the organosilica film has also good antimicrobial properties. Considering the high stability, the environmental footprint, and the low cost of this sol–gel marine coating, the technology has significant potential toward replacing conventional antifouling and foul-release coatings with a single product of broad applicability.