Visible light-induced surface grafting polymerization of perfluoropolyether brushes as marine low fouling materials

Controlled grafting of perfluoropolyether brushes from polymer substrates as low fouling marine coatings. ITX coupled to OTS-monolayers was used as dormant group and activated by visible light to induce the polymerization reaction.

Semantic segmentation for fully automated macrofouling analysis on coatings after field exposure

Biofouling is a major challenge for sustainable shipping, filter membranes, heat exchangers, and medical devices. The development of fouling-resistant coatings requires the evaluation of their effectiveness. Such an evaluation is usually based on the assessment of fouling progression after different exposure times to the target medium (e.g. salt water). The manual assessment of macrofouling requires expert knowledge about local fouling communities due to high variances in phenotypical appearance, has single-image sampling inaccuracies for certain species, and lacks spatial information. Here an approach for automatic image-based macrofouling analysis was presented. A dataset with dense labels prepared from field panel images was made and a convolutional network (adapted U-Net) for the semantic segmentation of different macrofouling classes was proposed. The establishment of macrofouling localization allows for the generation of a successional model which enables the determination of direct surface attachment and in-depth epibiotic studies.

Reduction of biofilm accumulation by constant and alternating potentials in static and dynamic field experiments

The application of electric fields to conductive coatings is an environmentally friendly way to reduce biofilm formation. In particular alternating potentials (APs) have received increasing attention in recent studies. Here, an electrochemical rotating disk setup for dynamic field exposure experiments was developed to study how APs alter the attachment of fouling organisms in a multispecies ocean environment. A specific focus of the device design was proper integration of the potentiostat in the strongly corroding saltwater environment. The effect of APs on the accumulation of fouling organisms in short term field exposures was studied. Potentials on conductive gold surfaces were periodically switched between -0.3 V and 0.3 V or between -0.8 V and 0.6 V at a frequency of 0.5 Hz. APs were capable of significantly reducing the attachment of marine fouling organisms compared with the conductive samples immersed at open circuit potentials.

Low Fouling Polysulfobetaines with Variable Hydrophobic Content

Amphiphilic polymer coatings combining hydrophilic elements, in particular zwitterionic groups, and hydrophobic elements comprise a promising strategy to decrease biofouling. However, the influence of the content of the hydrophobic component in zwitterionic coatings on the interfacial molecular reorganization dynamics and the anti-fouling performance is not well understood. Therefore, coatings of amphiphilic copolymers of sulfobetaine methacrylate 3-[N-2'-(methacryloyloxy)ethyl-N,N-dimethyl]-ammonio propane-1-sulfonate (SPE) are prepared which contain increasing amounts of hydrophobic n-butyl methacrylate (BMA). Their fouling resistance is compared to that of their homopolymers PSPE and PBMA. The photo-crosslinked coatings form hydrogel films with a hydrophilic surface. Fouling by the proteins fibrinogen and lysozyme as well as by the diatom Navicula perminuta and the green algae Ulva linza is assessed in laboratory assays. While biofouling is strongly reduced by all zwitterionic coatings, the best fouling resistance is obtained for the amphiphilic copolymers. Also in preliminary field tests, the anti-fouling performance of the amphiphilic copolymer films is superior to that of both homopolymers. When the coatings are exposed to a marine environment, the reduced susceptibility to silt incorporation, in particular compared to the most hydrophilic polyzwitterion PSPE, likely contributes to the improved fouling resistance.

Amphiphilic Zwitterionic Acrylate/Methacrylate Copolymers for Marine Fouling-Release Coatings

Methacrylate and acrylate monomers are popular building blocks for antifouling (AF) and fouling-release (FR) coatings to counteract marine biofouling. They are used in various combinations and often combined into amphiphilic materials. This study investigated the FR properties of amphiphilic ethylene glycol dicyclopentenyl ether acrylate (DCPEA) and the corresponding methacrylate (DCPEMA) blended with 5 wt % zwitterionic carboxybetaine acrylate (CBA) and the corresponding methacrylate (CBMA). A series of (co)polymers with different acrylate/methacrylate compositions were synthesized and tested against the attachment of the diatom Navicula perminuta and in short-term dynamic field exposure experiments. The more hydrophobic methacrylate DCPEMA homopolymer outperformed its acrylate counterpart DCPEA. Incorporated zwitterionic functionality of both CBMA and CBA imparted ultralow fouling capability in the amphiphilic polymers toward diatom attachment, whereas in the real ocean environment, only the employment of CBMA reduced marine biofouling. Moreover, it was observed that CBA-containing coatings showed different surface morphologies and roughnesses compared to the CBMA analogues. Particularly, a high impact was found when acrylic CBA was mixed with methacrylic DCPEMA. While the wettability of the coatings was comparable, investigated methacrylates in general exhibited superior fouling resistance compared to the acrylates.

Synthesis and Characterization of Dendritic and Linear Glycol Methacrylates and Their Performance as Marine Antifouling Coatings

Dendritic polyglycerol (PG) was covalently coupled to 2-hydroxyethyl methacrylate (HEMA) by an anionically catalyzed ring-opening polymerization generating a dendritic PG-HEMA with four PG repetition units (PG₄MA). Coatings of the methacrylate monomer were prepared by grafting-through and compared against commercially available hydrophilic monomers of HEMA, poly(ethylene) glycol methacrylate (PEGMA), and poly(propylene) glycol methacrylate (PPGMA). The obtained coatings were characterized by modern surface analytical techniques, including water contact angle goniometry (sessile and captive bubble), attenuated total internal reflection Fourier transform infrared spectroscopy, and atomic force microscopy. The antifouling (AF) and fouling-release (FR) properties of the coatings were tested against the model organisms Cobetia marina and Navicula perminuta in laboratory-scale dynamic accumulation assays as well as in a dynamic short-term field exposure (DSFE) in the marine environment. In addition, the hydration of the coatings and their susceptibility toward silt uptake were evaluated, revealing a strong correlation between water uptake, silt incorporation, and field assay performance. While all glycol derivatives showed good resistance in laboratory settlement experiments, PPGMA turned out to be less susceptible to silt incorporation and outperformed PEGMA and PG₄MA in the DSFE assay.

Sol-Gel-Based Hybrid Materials as Antifouling and Fouling-Release Coatings for Marine Applications

Hybrid materials (HMs) offer unique properties as they combine inorganic and organic components into a single material. Here, we developed HM coatings for marine antifouling applications using sol-gel chemistry and naturally occurring polysaccharides. The coatings were characterized by spectroscopic ellipsometry, contact angle goniometry, AFM, and ATR-FTIR, and their stability was tested in saline media. Marine antifouling and fouling-release properties were tested in laboratory assays against the settlement of larvae of the barnacle Balanus improvisus and against the settlement and removal of the diatom Navicula incerta. Furthermore, laboratory data were confirmed in short-term dynamic field assays in Florida, USA. All hybrid coatings revealed a superior performance in the assays compared to a hydrophobic reference. Within the hybrids, those with the highest degree of hydrophilicity and negative net charge across the surface performed best. Alginate and heparin showed good performance, making these hybrid materials promising building blocks for fouling-resistant coatings.

Amphiphilic Dicyclopentenyl/Carboxybetaine-Containing Copolymers for Marine Fouling-Release Applications

Zwitterionic materials received great attention in recent studies due to their high antifouling potential, though their application in practical coatings is still challenging. Amphiphilic polymers have been proven to be an effective method to combat fouling in the marine environment. This study reports the incorporation of small amounts of zwitterionic carboxybetaine methacrylate (CBMA) into hydrophobic ethylene glycol dicyclopentenyl ether acrylate (DCPEA). A new set of copolymers with varying amphiphilicities was synthesized and coated on chemically modified glass substrates. The antifouling capabilities were assessed against the diatom Navicula perminuta and multiple species in the field. Unsurprisingly, high diatom densities were observed on the hydrophobic control coatings. The integration of small zwitterionic contents of only ∼5 wt % was already sufficient to rapidly form a hydrophilic interface that led to a strong reduction of fouling. Ultralow fouling was also observed for the pure zwitterionic coatings in laboratory experiments, but it failed when tested in the real ocean environment. We noticed that the ability to absorb large amounts of water and the diffuse nature of the interphase correlate with the adsorption of silt, which can mask the hydrophilic chemistries and facilitate the settlement of organisms. The amphiphilic coatings showed low fouling in dynamic short-term field exposures, which could be explained by the reduced tendency of the coatings for sediment adsorption.

Effects of crosslink density in zwitterionic hydrogel coatings on their antifouling performance and susceptibility to silt uptake

Hydrogel coatings effectively reduce the attachment of proteins and organisms in laboratory assays, in particular when made from zwitterionic monomers. In field experiments with multiple species and non-living material, such coatings suffer from adsorption of particulate matter. In this study, the zwitterionic monomer 3-[N-(2-methacryloyloxyethyl)-N,N-dimethylammonio] propanesulfonate (SPE) was copolymerized with increasing amounts of the photo-crosslinker benzophenon-4-yloxyethyl methacrylate (BPEMA) to systematically alter the density of crosslinks between the polymer chains. The effect of increasing crosslink density on the antifouling (AF) performance of the coatings was investigated in laboratory assays and fields tests. In both cases, the AF performance was improved by increasing the crosslinker content. The coatings reduced protein, diatom, and barnacle accumulation, and showed better resistance to biomass accumulation. The findings underline that the marine AF performance of hydrogel coatings does not only depend on the specific chemical structure of the polymers, but also on their physico-chemical properties such as rigidity and swelling.

Sediment challenge to promising ultra-low fouling hydrophilic surfaces in the marine environment

Hydrophilic coatings exhibit ultra-low fouling properties in numerous laboratory experiments. In stark contrast, the antifouling effect of such coatings in vitro failed when performing field tests in the marine environment. The fouling release performance of nonionic and zwitterionic hydrophilic polymers was substantially reduced compared to the controlled laboratory environment. Microscopy and spectroscopy revealed that a large proportion of the accumulated material in field tests contains inorganic compounds and diatomaceous soil. Diatoms adhered to the accumulated material on the coating, but not to the pristine polymer. Simulating field tests in the laboratory using sediment samples collected from the test sites showed that incorporated sand and diatomaceous earth impairs the fouling release characteristics of the coatings. When exposed to marine sediment from multiple locations, particulate matter accumulated on these coatings and served as attachment points for diatom adhesion and enhanced fouling. Future developments of hydrophilic coatings should consider accumulated sediment and its potential impact on the antifouling performance.

Fouling-Release Properties of Dendritic Polyglycerols against Marine Diatoms

Dendritic polyglycerols (PGs) were grafted onto surfaces using a ring-opening polymerization reaction, and the fouling-release properties against marine organisms were determined. The coatings were characterized by spectroscopic ellipsometry, contact angle goniometry, ATR-FTIR, and stability tests in different aqueous media. A high resistance toward the attachment of different proteins was found. The PG coatings with three different thicknesses were tested in a laboratory assay against the diatom Navicula incerta and in a field assay using a rotating disk. Under static conditions, the PG coatings did not inhibit the initial attachment of diatoms, but up to 94% of attached diatoms could be removed from the coatings after exposure to a shear stress of 19 Pa. Fouling release was found to be enhanced if the coatings were sufficiently thick. The excellent fouling-release properties were supported in dynamic field-immersion experiments in which the samples were continually exposed to a shear stress of 0.18 Pa.

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.

Transported biofilms and their influence on subsequent macrofouling colonization

Biofilm organisms such as diatoms are potential regulators of global macrofouling dispersal because they ubiquitously colonize submerged surfaces, resist antifouling efforts and frequently alter larval recruitment. Although ships continually deliver biofilms to foreign ports, it is unclear how transport shapes biofilm microbial structure and subsequent macrofouling colonization. This study demonstrates that different ship hull coatings and transport methods change diatom assemblage composition in transported coastal marine biofilms. Assemblages carried on the hull experienced significant cell losses and changes in composition through hydrodynamic stress, whereas those that underwent sheltered transport, even through freshwater, were largely unaltered. Coatings and their associated biofilms shaped distinct macrofouling communities and affected recruitment for one third of all species, while biofilms from different transport treatments had little effect on macrofouling colonization. These results demonstrate that transport conditions can shape diatom assemblages in biofilms carried by ships, but the properties of the underlying coatings are mainly responsible for subsequent macrofouling. The methods by which organisms colonize and are transferred by ships have implications for their distribution, establishment and invasion success.

Conditioning of self-assembled monolayers at two static immersion test sites along the east coast of Florida and its effect on early fouling development

Among the first events after immersion of surfaces in the ocean is surface 'conditioning'. Here, the accumulation and composition of the conditioning films formed after immersion in the ocean are analyzed. In order to account for different surface chemistries, five self-assembled monolayers that differ in resistance to microfouling and wettability were used. Water samples from two static immersion test sites along the east coast of Florida were collected at two different times of the year and used for experiments. Spectral ellipsometry revealed that conditioning films were formed within the first 24 h and contact angle goniometry showed that these films changed the wettability and rendered hydrophobic surfaces more hydrophilic and vice versa. Infrared reflection adsorption spectroscopy showed that the composition of the conditioning film depended on both the wettability and immersion site. Laboratory and field assays showed that the presence of a conditioning film did not markedly influence settlement of microorganisms.

The ghost of fouling communities past: the effect of original community on subsequent recruitment

Biofouling on ships has been linked to the spread of invasive species, which has been identified as one of the current primary threats to the environment. Previous research on antifouling coatings suggested that the quantity of fouling, as well as community composition, on biocidal coatings was modified by prior fouling settlement. The experiment reported in this paper was designed to determine how preconditioning affected the rate and composition of subsequent fouling on transplanted silicone coatings. A series of 10 × 20 cm panels coated with Intersleek 700 or DC3140 were placed at three locations in Florida (Ponce Inlet, Sebastian Inlet, and Port of Miami), which were characterized by distinct fouling communities. Panels were immersed for four months, cleaned, and reciprocally transplanted among the three sites. Fouling community composition and coverage were characterized at bimonthly intervals both before and after transplantation. The original fouling community affected the subsequent fouling composition and recolonization by tunicates, sea anemones, barnacles, sponges, hydroids, and arborescent bryozoans. The community-level effects were short-term, lasting 2-4 months, but specific responses lasted up to 14 months post-transplant.

Static vs dynamic settlement and adhesion of diatoms to ship hull coatings

Many experiments utilize static immersion tests to evaluate the performance of ship hull coatings. These provide valuable data; however, they do not accurately represent the conditions both the hull and fouling organisms encounter while a ship is underway. This study investigated the effect of static and dynamic immersion on the adhesion and settlement of diatoms to one antifouling coating (BRA 640), four fouling-release coatings (Intersleek(®) 700, Intersleek(®) 900, Hempasil X3, and Dow Corning 3140) and one standard surface (Intergard(®) 240 Epoxy). Differences in community composition were observed between the static and dynamic treatments. Achnanthes longipes was present on all coatings under static immersion, but was not present under dynamic immersion. This was also found for diatoms in the genera Bacillaria and Gyrosigma. Melosira moniformis was the only diatom present under dynamic conditions, but not static conditions. Several common fouling diatom genera were present on panels regardless of treatment: Amphora, Cocconeis, Entomoneis Cylindrotheca, Licmophora, Navicula, Nitzschia, Plagiotropis, and Synedra. Biofilm adhesion, diatom abundance and diatom diversity were found to be significantly different between static and dynamic treatments; however, the difference was dependent on coating and sampling date. Several coatings (Epoxy, DC 3140 and IS 700) had significantly higher biofilm adhesion on dynamically treated panels on at least one of the four sampling dates, while all coatings had significantly higher diatom abundance on at least one sampling date. Diversity was significantly greater on static panels than dynamic panels for Epoxy, IS 700 and HX3 at least once during the sampling period. The results demonstrate how hydrodynamic stress will significantly influence the microfouling community. Dynamic immersion testing is required to fully understand how antifouling surfaces will respond to biofilm formation when subjected to the stresses experienced by a ship underway.

Diatom community structure on commercially available ship hull coatings

Diatoms are primary colonizers of both antifouling and fouling-release ship hull coatings. There are few published studies which report on diatom community development on modern ship hull coatings. This study reports diatom communities on eight commercial marine ship hull coatings exposed at three static immersion sites along the east coast of Florida, viz. Daytona, Sebastian, and Miami. The coatings tested were three ablative copper systems (Ameron ABC-3, International BRA-640, and Hempel Olympic 76600), two copper-free biocidal systems (E-Paint SN-1, Sherwin Williams HMF), and three fouling-release (FR) systems (International Intersleek 700, International Intersleek 900, and Hempel Hempasil). One hundred and twenty-seven species comprising 44 genera were identified, including some of the more commonly known foulers, viz. Achnanthes, Amphora, Cocconeis, Entomoneis, Licmophora, Melosira, Navicula, Nitzschia, Synedra, and Toxarium. A significant difference was seen among sites, with the more estuarine site, Sebastian, having lower overall diatom abundance and higher diversity than Daytona and Miami. Copper coatings were primarily fouled by Amphora delicatissima and Entomoneis pseudoduplex. Copper-free coatings were fouled by Cyclophora tenuis, A. delicatissima, Achnanthes manifera, and Amphora bigibba. FR surfaces were typified by C. tenuis, and several species of Amphora. The presence of C. tenuis is new to the biofouling literature, but as new coatings are developed, this diatom may be one of many that prove to be problematic for static immersion. Results show coatings can be significantly influenced by geographical area, highlighting the need to test ship hull coatings in locations similar to where they will be utilized.

Managing the use of copper-based antifouling paints

Copper is the biocide of choice for present-day antifouling (AF) paints. It is also a major source of copper loading in to the marine environment and, as such, might cause local copper levels to exceed water quality criteria. The present study is multifaceted and looks into the overall impact of copper-based AF paints on copper concentrations along a 64-km stretch of the Indian River Lagoon and at Port Canaveral, Florida. This preliminary study is one of the first to outline issues and present background evidence on the current status of copper and copper-based AF usage in Florida and to address the need for management. Previous measurements of copper levels in these waters show a history of copper contamination close to marinas, boatyards, and at Port Canaveral that often exceed state and federal water quality standards. Further, we estimate that the total annual copper input into the Indian River Lagoon is between 1.7 tons/year (sailboats) and 2.1 tons/year (powerboats) from boats in 14 marinas. We estimate the copper input into Port Canaveral to be about 1.4 tons/year from seven cruise ships. A brief survey of marina operators and boat owners revealed attitudes and practices associated with AF paint usage that ranged from excellent to inferior. Management recommendations are made for a proactive approach to improving AF paint selection and application, assessing the environmental status of copper, and redefining existing management practices for sustainable AF paint usage and environmental health.

Surface elastic modulus of barnacle adhesive and release characteristics from silicone surfaces

The properties of barnacle adhesive on silicone surfaces were studied by AFM indentation, imaging, and other tests and compared to the barnacle shear adhesion strength. A multilayered structure of barnacle adhesive plaque is proposed based on layered modulus regions measured by AFM indentation. The fracture of barnacles from PDMS surfaces was found to include both interfacial and cohesive failure of barnacle adhesive plaque, as determined by protein staining of the substratum after forced barnacle release from the substrate. Data for freshly released barnacles showed that there was a strong correlation between the mean Young's modulus of the outermost (softest) adhesive layer (E<0.3 MPa) and the shear strength of adhesion, but no correlation for other higher modulus regions. Linear, quadratic, and Griffith's failure criterion (based on rough estimate of crack length) regressions were used in the fit, and showed significance.

The effects of silicone fluid additives and silicone elastomer matrices on barnacle adhesion strength

Barnacle adhesion strength was used to screen seventy-seven polydimethylsiloxane elastomeric coatings for fouling-release properties. The test coatings were designed to investigate the effect on barnacle adhesion strength of silicone fluid additive type, additive location, additive molecular weight, additive loading level, mixtures of additives, coating matrix type and coating fillers. The type of silicone fluid additive was the primary controlling factor in barnacle fouling-release. The type of silicone matrix in which the fluid resided was found to alter the effect on fouling-release. Two PDMS fluids, DMSC15 and DBE224, significantly reduced the adhesion strength of barnacles compared to unmodified elastomers. Optimum fouling-release performance was dependent on the interaction of fluid type and elastomeric matrix.

The influence of biofilms on skin friction drag

The contribution of biofilms to skin friction drag is not clearly defined, and as regulations continue to restrict the use of biocides in antifouling paints, they are likely to form a greater presence on ship hulls. This paper reviews the flow regime around a ship's hull, the basics of boundary layer structure, and the effects of rigid surface roughness on drag. A review of experimental studies of biofilms in turbulent shear flows at laboratory and ship-scale is made. The consensus of these studies shows that biofilms increase skin friction drag. Some measurements carried out in turbulent boundary layer flow using a two-component, laser Doppler velocimeter (LDV) are also presented. These results indicate an increase in skin friction for biofilms that is dependent on composition as well as thickness.

The testing and evaluation of non-toxic antifouling coatings

Field testing of non-toxic antifouling coatings has required the development of test protocols that can quantify their performance. This includes the evaluation of the biofouling communities, the measurement of biofouling adhesion using a calibrated water jet and the measurement of barnacle adhesion in shear. Data are presented for several test surfaces, and the results are discussed with respect to the coating characteristics.