Polysulfone and polyacrylate-based zwitterionic coatings for the prevention and easy removal of marine biofouling

A series of polysulfone and polyacrylate-based zwitterionic coatings were prepared on epoxy-primed aluminum substrata and characterized for their antifouling (AF) and fouling-release (FR) properties towards marine bacteria, microalgae and barnacles. The zwitterionic polymer coatings provided minimal resistance against bacterial biofilm retention and microalgal cell attachment, but facilitated good removal of attached microbial biomass by exposure to water-jet apparatus generated hydrodynamic shearing forces. Increasing the ion content of the coatings improved the AF properties, but required a stronger adhesive bond to the epoxy-primed aluminum substratum to prevent coating swelling and dissolution. Grafted poly(sulfobetaine) (gpSBMA), the most promising zwitterionic coating identified from microfouling evaluations, enabled the removal of four out of five barnacles reattached to its surface without incurring damage to their baseplates. This significant result indicated that gpSBMA relied predominately on its surface chemistry for its FR properties since it was very thin (~1–2 µm) relative to commercial coating standards (>200 µm).     

Release characteristics of reattached barnacles to non-toxic silicone coatings

Release mechanisms of barnacles (Amphibalanus amphitrite or Balanus amphitrite) reattached to platinum-cured silicone coatings were studied as a function of coating thickness (210-770 microm), elastic modulus (0.08-1.3 MPa), and shear rate (2-22 microm s(-1)). It was found that the shear stress of the reattached, live barnacles necessary to remove from the silicone coatings was controlled by the combined term (E/t)(0.5) of the elastic modulus (E) and thickness (t). As the ratio of the elastic modulus to coating thickness decreased, the barnacles were more readily removed from the silicone coatings, showing a similar release behavior to pseudobarnacles (epoxy glue). The barnacle mean shear stress ranged from 0.017 to 0.055 MPa whereas the pseudobarnacle mean shear stress ranged from 0.022 to 0.095 MPa.     

Spontaneous multiscale phase separation within fluorinated xerogel coatings for fouling-release surfaces

Four-component xerogel films consisting of 1 mole-% n-octadecyltrimethoxysilane (C18) and 50 mole-% tetraethoxysilane (TEOS) in combination with 1-24 mole-% tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane (TDF) and 25-48 mole-% n-octyltriethoxysilane (C8) and a 1:49:50 mole-% C18/TDF/TEOS were prepared. Settlement of barnacle cyprids and removal of juvenile barnacles, settlement of zoospores of the alga Ulva linza, and strength of attachment of 7-day sporelings (young plants) of Ulva were compared amongst the xerogel formulations. Several of the xerogel formulations were comparable to poly(dimethylsiloxane) elastomer with respect to removal of juvenile barnacles and removal of sporeling biomass. The 1:4:45:50 and 1:14:35:50 C18/TDF/C8/TEOS xerogels displayed some phase segregation by atomic force microscopy (AFM) pre- and post-immersion in water. Imaging reflectance infrared microscopy showed the formation of islands of alkane-rich and perfluoroalkane-rich regions in these same xerogels both pre- and post-immersion in water. Surface energies were unchanged upon immersion in water for 48?h amongst the TDF-containing xerogel coatings. AFM measurements demonstrated that surface roughness on the 1:4:45:50 and 1:14:35:50 C18/TDF/C8/TEOS xerogel coatings decreased upon immersion in water.     

Comparison of laboratory and field testing performance evaluations of siloxane-polyurethane fouling-release marine coatings

A series of eight novel siloxane-polyurethane fouling-release (FR) coatings were assessed for their FR performance in both the laboratory and in the field. Laboratory analysis included adhesion assessments of bacteria, microalgae, macroalgal spores, adult barnacles and pseudobarnacles using high-throughput screening techniques, while field evaluations were conducted in accordance with standardized testing methods at three different ocean testing sites over the course of six-months exposure. The data collected were subjected to statistical analysis in order to identify potential correlations. In general, there was good agreement between the laboratory screening assays and the field assessments, with both regimes clearly distinguishing the siloxane-polyurethane compositions comprising monofunctional poly(dimethyl siloxane) (PDMS) (m-PDMS) as possessing superior, broad-spectrum FR properties compared to those prepared with difunctional PDMS (d-PDMS). Of the seven laboratory screening techniques, the Cellulophaga lytica biofilm retraction and reattached barnacle (Amphibalanus amphitrite) adhesion assays were shown to be the most predictive of broad-spectrum field performance.     

Spontaneous multiscale phase separation within fluorinated xerogel coatings for fouling-release surfaces

Four-component xerogel films consisting of 1 mole-% n-octadecyltrimethoxysilane (C18) and 50 mole-% tetraethoxysilane (TEOS) in combination with 1–24 mole-% tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane (TDF) and 25–48 mole-% n-octyltriethoxysilane (C8) and a 1:49:50 mole-% C18/TDF/TEOS were prepared. Settlement of barnacle cyprids and removal of juvenile barnacles, settlement of zoospores of the alga Ulva linza, and strength of attachment of 7-day sporelings (young plants) of Ulva were compared amongst the xerogel formulations. Several of the xerogel formulations were comparable to poly(dimethylsiloxane) elastomer with respect to removal of juvenile barnacles and removal of sporeling biomass. The 1:4:45:50 and 1:14:35:50 C18/TDF/C8/TEOS xerogels displayed some phase segregation by atomic force microscopy (AFM) pre- and post-immersion in water. Imaging reflectance infrared microscopy showed the formation of islands of alkane-rich and perfluoroalkane-rich regions in these same xerogels both pre- and post-immersion in water. Surface energies were unchanged upon immersion in water for 48 h amongst the TDF-containing xerogel coatings. AFM measurements demonstrated that surface roughness on the 1:4:45:50 and 1:14:35:50 C18/TDF/C8/TEOS xerogel coatings decreased upon immersion in water.     

Combinatorial materials research applied to the development of new surface coatings XVI: fouling-release properties of amphiphilic polysiloxane coatings

High-throughput methods were used to prepare and characterize the fouling-release (FR) properties of an array of amphiphilic polysiloxane-based coatings possessing systematic variations in composition. The coatings were derived from a silanol-terminated polydimethylsiloxane, a silanol-terminated polytrifluorpropylmethylsiloxane (CF₃-PDMS), 2-[methoxy(polyethyleneoxy)propyl]-trimethoxysilane (TMS-PEG), methyltriacetoxysilane and hexamethyldisilazane-treated fumed silica. The variables investigated were the concentration of TMS-PEG and the concentration of CF₃-PDMS. In general, it was found that the TMS-PEG and the CF₃-PDMS had a synergist effect on FR properties with these properties being enhanced by combining both compounds into the coating formulations. In addition, reattached adult barnacles removed from coatings possessing both TMS-PEG and relatively high levels of CF₃-PDMS displayed atypical base-plate morphologies. The majority of the barnacles removed from these coatings exhibited a cupped or domed base-plate as compared to the flat base-plate observed for the control coating that did not contain TMS-PEG or CF₃-PDMS. Coating surface analysis using water contact angle measurements indicated that the presence of CF₃-PDMS facilitated migration of TMS-PEG to the coating/air interface during the film formation/curing process. In general, coatings containing both TMS-PEG and relatively high levels of CF₃-PDMS possessed excellent FR properties.     

The control of marine biofouling on xerogel surfaces with nanometer-scale topography

Mixtures of n-octadecyltrimethoxysilane (C18, 1-5 mole-%), n-octyltriethoxysilane (C8) and tetraethoxysilane (TEOS) gave xerogel surfaces of varying topography. The 1:49:50 C18/C8/TEOS xerogel formed 100-400-nm-wide, 2-7-nm deep pores by AFM while coatings with?≥3% C18 were free of such features. Segregation of the coating into alkane-rich and alkane-deficient regions in the 1:49:50 C18/C8/TEOS xerogel was observed by IR microscopy. Immersion in ASW for 48?h gave no statistical difference in surface energy for the 1:49:50 C18/C8/TEOS xerogel and a significant increase for the 50:50 C8/TEOS xerogel. Settlement of barnacle cyprids and removal of juvenile barnacles, settlement of zoospores of the alga Ulva linza, and strength of attachment of 7-day sporelings were compared amongst the xerogel formulations. Settlement of barnacle cyprids was significantly lower in comparison to glass and polystyrene standards. The 1:49:50 and 3:47:50 C18/C8/TEOS xerogels were comparable to PDMSE with respect to removal of juvenile barnacles and sporeling biomass, respectively.     

A preliminary study on the properties and fouling-release performance of siloxane-polyurethane coatings prepared from poly(dimethylsiloxane) (PDMS) macromers

Siloxane-polyurethane fouling-release (FR) coatings based on aminopropyl terminated poly(dimethylsiloxane) (PDMS) macromers were prepared and characterized for FR performance via laboratory biological assays. These systems rely on self-stratification, resulting in a coating with a siloxane-rich surface and polyurethane bulk. Previously, these coating systems have used PDMS with multiple functional groups which react into the polyurethane bulk. Here, aminopropyl terminated PDMS macromers were prepared, where a single amine group anchors the PDMS in the coating. Coatings were prepared with four molecular weights (1000, 5000, 10,000, and 15,000 g mol?1) and two levels of PDMS (5% and 10%). High water contact angles and low surface energies were observed for the coatings before and after water immersion, along with low pseudobarnacle removal forces. Laboratory bioassays showed reduced biofilm retention of marine bacteria, good removal of diatoms from coatings with low molecular weight PDMS, high removal of algal sporelings (young plants), and low removal forces of live barnacles.     

Factors that influence elastomeric coating performance: the effect of coating thickness on basal plate morphology, growth and critical removal stress of the barnacle Balanus amphitrite

Silicone coatings are currently the most effective non-toxic fouling release surfaces. Understanding the mechanisms that contribute to the performance of silicone coatings is necessary to further improve their design. The objective of this study was to examine the effect of coating thickness on basal plate morphology, growth, and critical removal stress of the barnacle Balanus amphitrite. Barnacles were grown on silicone coatings of three thicknesses (0.2, 0.5 and 2 mm). Atypical ("cupped") basal plate morphology was observed on all surfaces, although there was no relationship between coating thickness and i) the proportion of individuals with the atypical morphology, or ii) the growth rate of individuals. Critical removal stress was inversely proportional to coating thickness. Furthermore, individuals with atypical basal plate morphology had a significantly lower critical removal stress than individuals with the typical ("flat") morphology. The data demonstrate that coating thickness is a fundamental factor governing removal of barnacles from silicone coatings.     

Combinatorial materials research applied to the development of new surface coatings IX: An investigation of novel antifouling/fouling-release coatings containing quaternary ammonium salt groups

Polysiloxane coatings containing chemically-bound (“tethered”) quaternary ammonium salt (QAS) moieties were investigated for potential application as environmental-friendly coatings to control marine biofouling. A combinatorial/high-throughput approach was applied to the investigation to enable multiple variables to be probed simultaneously and efficiently. The variables investigated for the moisture-curable coatings included QAS composition, ie alkyl chain length, and concentration as well as silanol-terminated polysiloxane molecular weight. A total of 75 compositionally unique coatings were prepared and characterized using surface characterization techniques and biological assays. Biological assays were based on two different marine microorganisms, a bacterium, Cellulophaga lytica and a diatom, Navicula incerta, as well as a macrofouling alga, Ulva. The results of the study showed that all three variables influenced coating surface properties as well as antifouling (AF) and fouling-release (FR) characteristics. The incorporation of QAS moieties into a polysiloxane matrix generally resulted in an increase in coating surface hydrophobicity. Characterization of coating surface morphology revealed a heterogeneous, two-phase morphology for many of the coatings investigated. A correlation was found between water contact angle and coating surface roughness, with the contact angle increasing with increasing surface roughness. Coatings based on the QAS moiety containing the longest alkyl chain (18 carbons) displayed the highest micro-roughness and, thus, the most hydrophobic surfaces. With regard to AF and FR properties, coatings based on the 18 carbon QAS moieties were very effective at inhibiting C. lytica biofilm formation and enabling easy removal of Ulva sporelings (young plants) while coatings based on the 14 carbon QAS moities were very effective at inhibiting biofilm growth of N. incerta.     

A preliminary study on the properties and fouling-release performance of siloxane–polyurethane coatings prepared from poly(dimethylsiloxane) (PDMS) macromers

Siloxane–polyurethane fouling-release (FR) coatings based on aminopropyl terminated poly(dimethylsiloxane) (PDMS) macromers were prepared and characterized for FR performance via laboratory biological assays. These systems rely on self-stratification, resulting in a coating with a siloxane-rich surface and polyurethane bulk. Previously, these coating systems have used PDMS with multiple functional groups which react into the polyurethane bulk. Here, aminopropyl terminated PDMS macromers were prepared, where a single amine group anchors the PDMS in the coating. Coatings were prepared with four molecular weights (1000, 5000, 10,000, and 15,000 g mol^?1) and two levels of PDMS (5% and 10%). High water contact angles and low surface energies were observed for the coatings before and after water immersion, along with low pseudobarnacle removal forces. Laboratory bioassays showed reduced biofilm retention of marine bacteria, good removal of diatoms from coatings with low molecular weight PDMS, high removal of algal sporelings (young plants), and low removal forces of live barnacles.     

Combinatorial materials research applied to the development of new surface coatings IX: an investigation of novel antifouling/fouling-release coatings containing quaternary ammonium salt groups

Polysiloxane coatings containing chemically-bound ("tethered") quaternary ammonium salt (QAS) moieties were investigated for potential application as environmental-friendly coatings to control marine biofouling. A combinatorial/high-throughput approach was applied to the investigation to enable multiple variables to be probed simultaneously and efficiently. The variables investigated for the moisture-curable coatings included QAS composition, ie alkyl chain length, and concentration as well as silanol-terminated polysiloxane molecular weight. A total of 75 compositionally unique coatings were prepared and characterized using surface characterization techniques and biological assays. Biological assays were based on two different marine microorganisms, a bacterium, Cellulophaga lytica and a diatom, Navicula incerta, as well as a macrofouling alga, Ulva. The results of the study showed that all three variables influenced coating surface properties as well as antifouling (AF) and fouling-release (FR) characteristics. The incorporation of QAS moieties into a polysiloxane matrix generally resulted in an increase in coating surface hydrophobicity. Characterization of coating surface morphology revealed a heterogeneous, two-phase morphology for many of the coatings investigated. A correlation was found between water contact angle and coating surface roughness, with the contact angle increasing with increasing surface roughness. Coatings based on the QAS moiety containing the longest alkyl chain (18 carbons) displayed the highest micro-roughness and, thus, the most hydrophobic surfaces. With regard to AF and FR properties, coatings based on the 18 carbon QAS moieties were very effective at inhibiting C. lytica biofilm formation and enabling easy removal of Ulva sporelings (young plants) while coatings based on the 14 carbon QAS moities were very effective at inhibiting biofilm growth of N. incerta.     

On-line monitoring of antifouling and fouling-release surfaces using bioluminescence and fluorescence measurements during laminar flow

A laminar flow biofilm-monitoring system was used to determine the efficacies of three antifouling (AF) coatings and five fouling-release (FR) coatings againstVibrio harveyi attachment. On-line measurements of tryptophan fluorescence and bioluminescence from each coating, normalized to an upstream stainless steel coupon, were used to determine the effects of AF and FR surfaces on biofilm formation. The AF coatings consisted of 5, 10, and 35 wt% Sea Nine 211 (C9211) incorporated into a vinyl copolymer. Both the 10 and 35 wt% coatings significantly inhibited biofilm biomass development measured by tryptophan fluorescence compared to the stainless steel control.V. harveyi bioluminescence was significantly greater than tryptophan fluorescence in cells attached to these coatings, suggesting that bioluminescence expression may be a marker for cellular stress or toxicity in biofilms. Five different polydimethylsiloxane (PDMS) FR coatings did not inhibit biofilm formation under low flow conditions. However, four PDMS coatings demonstrated decreased biomass levels compared to stainless steel after exposure to a shear stress of 330 dynes cm^–2. There was no toxic additive in these coatings; bioluminescence and tryptophan fluorescence were proportional.     

Microfluidic detachment assay to probe the adhesion strength of diatoms

Fouling release (FR) coatings are increasingly applied as an environmentally benign alternative for controlling marine biofouling. As the technology relies on removing fouling by water currents created by the motion of ships, weakening of adhesion of adherent organisms is the key design goal for improved coatings. In this paper, a microfluidic shear force assay is used to quantify how easily diatoms can be removed from surfaces. The experimental setup and the optimization of the experimental parameters to study the adhesion of the diatom Navicula perminuta are described. As examples of how varying the physico-chemical surface properties affects the ability of diatoms to bind to surfaces, a range of hydrophilic and hydrophobic self-assembled monolayers was compared. While the number of cells that attached (adhered) was barely affected by the coatings, the critical shear stress required for their removal from the surface varied significantly.     

A new flow-through bioassay for testing low-emission antifouling coatings

Current antifouling (AF) technologies are based on the continuous release of biocides into the water, and consequently discharge into the environment. Major efforts to develop more environmentally friendly coatings require efficient testing in laboratory assays, followed by field studies. Barnacles are important fouling organisms worldwide, increasing hydrodynamic drag on ships and damaging coatings on underwater surfaces, and thus are extensively used as models in AF research, mostly in static, laboratory-based systems. Reliable flow-through test assays for the screening of biocide-containing AF paints, however, are rare. Herein, a flow-through bioassay was developed to screen for diverse low-release biocide paints, and to evaluate their effects on pre- and post-settlement traits in barnacles. The assay distinguishes between the effects from direct surface contact and bulk-water effects, which are crucial when developing low-emission AF coatings. This flow-through bioassay adds a new tool for rapid laboratory-based first-stage screening of candidate compounds and novel AF formulations.     

Colonisation and succession of marine biofilm-dwelling ciliate assemblages on biocidal antifouling and fouling-release coatings in temperate Australia

Ciliate assemblages are often overlooked, but ubiquitous components of microbial biofilms which require a better understanding. Ciliate, diatom and bacterial colonisation were evaluated on two fouling-release (FR) coatings, viz. Intersleek 970 and Hempasil X3, and two biocidal antifouling (AF) coatings, viz. Intersmooth 360 and Interspeed 5640, in Port Phillip Bay, Australia. A total of 15 genera were identified during the 10 week deployment. Intersleek 970 displayed the most rapid fouling by ciliates, reaching 63.3(± 5.9) cells cm^?2. After 10 weeks, all four coatings were extensively fouled. However, the toxicity of the AF coatings still significantly inhibited microbial fouling compared to the FR coatings. On all treatments, colonies of sessile peritrichs dominated the ciliate assemblage in the early stage of succession, but as the biofilm matured, vagile ciliates exerted more influence on the assemblage structure. The AF coatings showed selective toxic effects, causing significant differences in the ciliate species assemblages among the treatments.     

Thermoplastic,rubber-like marine antifouling coatings with micro-structures via mechanical embossing

Abstract

New processing routes and materials for non-biocidal, antifouling (AF) coatings with an improved performance are currently much sought after for a range of marine applications. Here, the processing, physical properties and marine AF performance of a fluorinated coating based on a thermoplastic (non-crosslinked) fluorinated polymer are reported. It was found that the addition of lubricating oil and hydrodynamic drag reducing microstructures improved the AF properties substantially, i.e. the settlement of a marine biofilm, containing mixed microalgae including diatoms, was reduced to low levels. More importantly, the remaining fouling was removed from the coatings at low hydrodynamic shear rates and promising AF properties were obtained. Moreover, additional potential benefits were revealed originating from the thermoplastic nature of the coating material which might result in significant cost reductions.     

Mechanical aspects of silicone coatings for hard foulant control

Barnacle release mechanisms and the durability of silicone coatings have been studied. Release studies were performed on both transparent, single‐layer silicone coatings and duplex silicone coatings. The release forces of pseudobarnacles (epoxied studs) and Chesapeake Bay barnacles (Balanus improvisus) were measured with a pull‐off (tension) tester; modes of release were revealed in video recordings of the separation process from transparent coatings on glass. Scratch tests with 0.8 mm spherically‐tipped diamond provided a measure of durability (tear resistance). Release forces from both coatings decreased as coating thickness increased. Both pseudobarnacles and barnacles separated by a peeling process, although differences in peeling modes were seen. The durability of coatings increased with increasing coating thickness. Release behavior is discussed in terms of a fracture mechanic's model for pull‐off separation, and the differences in adhesion between barnacles and pseudobarnacles are described.     

Microfluidic accumulation assay probes attachment of biofilm forming diatom cells

Testing of fouling release (FR) technologies is of great relevance for discovery of the next generation of protective marine coatings. In this paper, an accumulation assay to test diatom interaction under laminar flow with the model organism Navicula perminuta is introduced. Using time lapse microscopy with large area sampling allows determination of the accumulation kinetics of the diatom on three model surfaces with different surface properties at different wall shear stresses. The hydrodynamic conditions within the flow cell are described and a suitable shear stress range to perform accumulation experiments is identified at which statistically significant discrimination of surfaces is possible. The observed trends compare well to published adhesion preferences of N. perminuta. Also, previously determined trends of critical wall shear stresses required for cell removal from the same set of functionalized interfaces shows consistent trends. Initial attachment mediated by extracellular polymeric substances (EPS) present outside the diatoms leads to the conclusion that the FR potential of the tested coating candidates can be deducted from dynamic accumulation experiments under well-defined hydrodynamic conditions. As well as testing new coating candidates for their FR properties, monitoring of the adhesion process under flow provides additional information on the mechanism and geometry of attachment and the population kinetics.     

Ship hull in-water cleaning and its effects on fouling-control coatings

Abstract

Today, ship hull fouling is managed through fouling-control coatings, complemented with in-water cleaning. During cleaning, coating damage and wear must be avoided, for maximum coating lifetime and reduced antifoulant release. When possible, cleaning should target early stages of fouling, using minimal forces. However, such forces, and their effects on coatings, have not yet been fully quantified. In this one-year study, minimal cleaning forces were determined using a newly-designed immersed waterjet. The results show that bi-monthly/monthly cleaning, with maximum wall shear stress up to ～1.3?kPa and jet stagnation pressure ～0.17?MPa, did not appear to cause damage or wear on either the biocidal antifouling (AF) or the biocide-free foul-release (FR) coatings. The AF coating required bi-monthly cleanings to keep fouling to incipient slime (time-averaged results), while the FR coating had a similar fouling level even without cleaning. The reported forces may be used in matching cleaning parameters to the adhesion strength of the early stages of fouling.