Nanostructured films of amphiphilic fluorinated block copolymers for fouling release application

Effect of surface compositional heterogeneities and microphase segregation of fluorinated amphiphilic copolymers on antifouling performance

In this paper, a series of fluorinated amphiphilic copolymers composed of 2-perfluorooctylethyl methacrylate (FMA) and 2-hydroxyethyl methacrylate (HEMA) monomers were prepared, and their surface properties and antifouling performance were investigated. Bovine serum albumin (BSA) and human plasma fibrinogen (HFg) were used as model proteins to study protein adsorption onto the fluorinated amphiphilic surfaces. All the fluorinated amphiphilic surfaces exhibit excellent resistant performance of protein adsorption measured by X-ray photoelectron spectroscopy (XPS). The surface compositional heterogeneities on the molecular scale play an important role in the antifouling properties. It was found that the copolymers exhibited better antifouling properties than the corresponding homopolymers did, when the percentage of hydrophilic hydroxyl groups is from 4% to 7% and the percentage of hydrophobic fluorinated moieties is from 4% to 14% on the surface. In addition, the protein molecular size scale and the pattern of microphase segregation domains on the surface strongly affect the protein adsorption behaviors. These results demonstrate the desirable protein-resistant performance from the fluorinated amphiphilic copolymers and provide deeper insight of the effect of surface compositional heterogeneity and microphase segregation on the protein adsorption behaviors.

The performance of aminoalkyl/fluorocarbon/hydrocarbon-modified xerogel coatings against the marine alga Ectocarpus crouaniorum: relative roles of surface energy and charge

The effect of a series of xerogel coatings modified with aminoalkyl/fluorocarbon/hydrocarbon groups on the adhesion of a new test species, the filamentous brown alga Ectocarpus crouaniorum, has been explored, and compared with the green alga Ulva linza. The results showed that E. crouaniorum adhered weakly to the less polar, low wettability coatings in the series, but stronger adhesion was shown on polar, higher surface energy coatings containing aminoalkyl groups. The results from a separate series of coatings tuned to have similar surface energies and polarities after immersion in artificial seawater (ASW), but widely different surface charges, demonstrated that surface charge was more important than surface energy and polarity in determining the adhesion strength of both E. crouaniorum and U. linza on xerogel coatings. No correlation was found between adhesion and contact angle hysteresis. X-ray photoelectron spectroscopy analysis of samples after immersion in ASW confirmed the presence of charged ammonium groups on the surface of the aminoalkylated coatings.

Interfacial tension analysis of oligo(ethylene glycol)-terminated self-assembled monolayers and their resistance to bacterial attachment

The fouling resistance of oligo(ethylene glycol) (OEG)-terminated self-assembled monolayers (SAMs) of alkanethiolates on gold has been well established. Although hydration of the OEG chains seems key to OEG-SAM resistance to macromolecular adsorption and cellular attachment, the details of how hydration prevents biofouling have been inferred largely through computational methods. Because OEG-SAMs of different lengths exhibit differing degrees of fouling resistance, the interactions between water and OEG-SAMs leading to fouling resistance can be deduced by comparing the properties of fouling and nonfouling OEG-SAMs. While all OEG-SAMs had similar water contact angles, contact angles taken with glycerol were able to individuate between different OEG-SAMs and between fouling and nonfouling OEG-SAMs. Subsequent estimation of surface and interfacial tension using a colloidal model showed that nonfouling surfaces are associated with an increased negative interfacial tension between those OEG-SAMs that resisted attachment and water. Further analysis of this interfacial tension experimentally confirmed current mathematical models that cite OEG-water hydrogen-bond formation as a driving force behind short-term fouling resistance. Finally, we found a correlation between solid-water interfacial tension and packing density and molecular density of ethylene glycol.

Designing nanostructured block copolymer surfaces to control protein adhesion

The profile and conformation of proteins that are adsorbed onto a polymeric biomaterial surface have a profound effect on its in vivo performance. Cells and tissue recognize the protein layer rather than directly interact with the surface. The chemistry and morphology of a polymer surface will govern the protein behaviour. So, by controlling the polymer surface, the biocompatibility can be regulated. Nanoscale surface features are known to affect the protein behaviour, and in this overview the nanostructure of self-assembled block copolymers will be harnessed to control protein behaviour. The nanostructure of a block copolymer can be controlled by manipulating the chemistry and arrangement of the blocks. Random, A-B and A-B-A block copolymers composed of methyl methacrylate copolymerized with either acrylic acid or 2-hydroxyethyl methacrylate will be explored. Using atomic force microscopy (AFM), the surface morphology of these block copolymers will be characterized. Further, AFM tips functionalized with proteins will measure the adhesion of that particular protein to polymer surfaces. In this manner, the influence of block copolymer morphology on protein adhesion can be measured. AFM tips functionalized with antibodies to fibronectin will determine how the surfaces will affect the conformation of fibronectin, an important parameter in evaluating surface biocompatibility.

Advances in nonfouling materials: perspectives for the food industry

Fouling of complex food components onto food-processing materials affects food quality, food safety, and operating efficiency. Developments in nonfouling and fouling-release materials for biomedical and marine applications enable the potential for adaptation to food applications; however, challenges remain. The purpose of this review is to present different strategies to prevent fouling and/or facilitate foulant removal with a critical point of view for an application of such materials on food-processing surfaces. Nonfouling, self-cleaning, and amphiphilic materials are reviewed, including an explanation of the mechanism of action, as well as inherent limitations of each technology. Perspectives on future research directions for the design of food processing surfaces with antifouling and/or fouling release properties are provided.

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.

Poly(dimethyl siloxane) (PDMS) network blends of amphiphilic acrylic copolymers with poly(ethylene glycol)-fluoroalkyl side chains for fouling-release coatings. II. Laboratory assays and field immersion trials

Amphiphilic copolymers containing different amounts of poly(ethylene glycol)-fluoroalkyl acrylate and polysiloxane methacrylate units were blended with a poly(dimethyl siloxane) (PDMS) matrix in different proportions to investigate the effect of both copolymer composition and loading on the biological performance of the coatings. Laboratory bioassays revealed optimal compositions for the release of sporelings of Ulva linza, and the settlement of cypris larvae of Balanus amphitrite. The best-performing coatings were subjected to field immersion tests. Experimental coatings containing copolymer showed significantly reduced levels of hard fouling compared to the control coatings (PDMS without copolymer), their performance being equivalent to a coating based on Intersleek 700™. XPS analysis showed that only small amounts of fluorine at the coating surface were sufficient for good antifouling/fouling-release properties. AFM analyses of coatings under immersion showed that the presence of a regular surface structure with nanosized domains correlated with biological performance.

Development and characteristics of an adhesion bioassay for ectocarpoid algae

Species of filamentous brown algae in the family Ectocarpaceae are significant members of fouling communities. However, there are few systematic studies on the influence of surface physico-chemical properties on their adhesion. In the present paper the development of a novel, laboratory-based adhesion bioassay for ectocarpoid algae, at an appropriate scale for the screening of sets of experimental samples in well-replicated and controlled experiments is described. The assays are based on the colonization of surfaces from a starting inoculum consisting of multicellular filaments obtained by blending the cultured alga Ectocarpus crouaniorum. The adhesion strength of the biomass after 14 days growth was assessed by applying a hydrodynamic shear stress. Results from adhesion tests on a set of standard surfaces showed that E. crouaniorum adhered more weakly to the amphiphilic Intersleek® 900 than to the more hydrophobic Intersleek® 700 and Silastic® T2 coatings. Adhesion to hydrophilic glass was also weak. Similar results were obtained for other cultivated species of Ectocarpus but differed from those obtained with the related ectocarpoid species Hincksia secunda. The response of the ectocarpoid algae to the surfaces was also compared to that for the green alga, Ulva.

A general approach to controlling the surface composition of poly(ethylene oxide)-based block copolymers for antifouling coatings

To control the surface properties of a polystyrene-block-poly(ethylene oxide) diblock copolymer, perfluorinated chemical moieties were specifically incorporated into the block copolymer backbone. A polystyrene-block-poly[(ethylene oxide)-stat-(allyl glycidyl ether)] [PS-b-P(EO-stat-AGE)] statistical diblock terpolymer was synthesized with varying incorporations of allyl glycidyl ether (AGE) in the poly(ethylene oxide) block from 0 to 17 mol %. The pendant alkenes of the AGE repeat units were subsequently functionalized by thiol-ene chemistry with 1H,1H,2H,2H-perfluorooctanethiol, yielding fluorocarbon-functionalized AGE (fAGE) repeat units. (1)H NMR spectroscopy and size-exclusion chromatography indicated well-defined structures with complete functionalization of the pendant alkenes. The surfaces of the polymer films were characterized after spray coating by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS), showing that the P(EO-stat-fAGE) block starts to compete with polystyrene to populate the surface after only 1 mol % incorporation of fAGE. Increasing the incorporation of fAGE led to an increased amount of perfluorocarbons on the surface and a decrease in the concentration of PS. At a fAGE incorporation of 8 mol %, PS was not detected at the surface, as measured by NEXAFS spectroscopy. Water contact angles measured by the captive-air-bubble technique showed the underwater surfaces to be dynamic, with advancing and receding contact angles varying by >20°. Protein adsorption studies demonstrated that the fluorinated surfaces effectively prevent nonspecific binding of proteins relative to an unmodified PS-b-PEO diblock copolymer. In biological systems, settlement of spores of the green macroalga Ulva was significantly lower for the fAGE-incorporated polymers compared to the unmodified diblock and a polydimethylsiloxane elastomer standard. Furthermore, the attachment strength of sporelings (young plants) of Ulva was also reduced for the fAGE-containing polymers, affirming their potential as fouling-release coatings.

Amphiphilic co-networks with moisture-induced surface segregation for high-performance nonfouling coatings

Herein we report the design of a photocurable amphiphilic co-network consisting of perfluoropolyether and poly(ethylene glycol) segments that display outstanding nonfouling characteristics with respect to spores of green fouling alga Ulva when cured under high humidity conditions. The analysis of contact angle hysteresis revealed that the poly(ethylene glycol) density at the surface was enhanced when cured under high humidity. The nonfouling behavior of nonbiocidal surfaces against marine fouling is rare because such surfaces usually reduce the adhesion of organisms rather than inhibit colonization. We propose that the resultant surface segregation of these materials induced by high humidity may be a promising strategy for achieving nonfouling materials, and such an approach is more important than simply concentrating poly(ethylene glycol) moieties at an interface because the low surface energy has been maintained in our work.

Fluorine-free mixed amphiphilic polymers based on PDMS and PEG side chains for fouling release applications

Fluorine-free mixed amphiphilic block copolymers with mixtures of short side groups of polydimethyl siloxane (PDMS) and polyethylene glycol (PEG) were synthesized and studied for their ability to influence the surface properties and control the adhesion of marine organisms to coated surfaces. The settlement (attachment) and strength of adhesion of two different marine algae, the green seaweed Ulva and the diatom Navicula, were evaluated against the surfaces. It is known that hydrophobic coatings based on polydimethyl siloxane elastomers (PDMSe) are prone to protein adsorption and accumulation of strongly adherent diatom slimes, in contrast to PEG-based hydrophilic surfaces that inhibit protein adsorption and moderate only weak adhesion of diatoms. By incorporating both PDMS and PEG side chains into the polymers, the effect of incorporating both polar and non-polar groups on fouling-release could be studied. The dry surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The ability of these mixed amphiphilic polymers to reconstruct in water was examined using underwater bubble contact angle and dynamic water contact angle experiments. To understand more about surface reconstruction behavior, protein adsorption experiments were carried out with fluorescein isothiocyanate-labeled bovine serum albumin (BSA-FITC) on both dry and pre-soaked surfaces.

Antibiofouling hybrid dendritic Boltorn/star PEG thiol-ene cross-linked networks

A series of thiol-ene generated amphiphilic cross-linked networks was prepared by reaction of alkene-modified Boltorn polyesters (Boltorn-ene) with varying weight percent of 4-armed poly(ethylene glycol) (PEG) tetrathiol (0-25 wt%) and varying equivalents of pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) (0-64 wt%). These materials were designed to present complex surface topographies and morphologies, with heterogeneity of surface composition and properties and robust mechanical properties, to serve as nontoxic antibiofouling coatings that are amenable to large-scale production for application in the marine environment. Therefore, a two-dimensional matrix of materials compositions was prepared to study the physical and mechanical properties, over which the compositions spanned from 0 to 25 wt% PEG tetrathiol and 0-64 wt% PETMP (the overall thiol/alkene (SH/ene) ratios ranged from 0.00 to 1.00 equiv), with both cross-linker weight percentages calculated with respect to the weight of Boltorn-ene. The Boltorn-ene components were prepared through the esterification of commercially available Boltorn H30 with 3-butenoic acid. The subsequent cross-linking of the Boltorn-PEG-PETMP films was monitored using IR spectroscopy, where it was found that near-complete consumption of both thiol and alkene groups occurred when the stoichiometry was ca. 48 wt% PETMP (0.75 equiv SH/ene, independent of PEG amount). The thermal properties of the films showed an increase in T(g) with an increase in 4-armed PEG-tetrathiol wt%, regardless of the PETMP concentration. Investigation of the bulk mechanical properties in dry and wet states found that the Young's modulus was the greatest at 48 wt% PETMP (0.75 equiv of SH/ene). The ultimate tensile strength increased when PETMP was constant and the PEG concentration was increased. The Young's modulus was slightly lower for wet films at constant PEG or constant PETMP amounts, than for the dry samples. The nanoscopic surface features were probed using atomic force microscopy (AFM), where it was observed that the surface of the amphiphilic films became increasingly rough with increasing PEG wt%. On the basis of the physicochemical data from the diverse sample matrix, a focused compositional profile was then investigated further to determine the antifouling performance of the cross-linked Boltorn-PEG-PETMP networks. For these studies, a low, constant PETMP concentration of 16 wt% was maintained with variation in the PEG wt% (0-35 wt%). Antifouling and fouling-release activities were tested against the marine alga Ulva. Spore settlement densities were low on these films, compared to that on standards of polydimethylsiloxane and glass.

Amphiphilic block copolymer/poly(dimethylsiloxane) (PDMS) blends and nanocomposites for improved fouling-release

Amphiphilic diblock copolymers, Sz6 and Sz12, consisting of a poly(dimethylsiloxane) block (average degree of polymerisation = 132) and a PEGylated-fluoroalkyl modified polystyrene block (Sz, average degree of polymerisation = 6, 12) were prepared by atom transfer radical polymerization (ATRP). Coatings were obtained from blends of either block copolymer (1-10 wt%) with a poly(dimethylsiloxane) (PDMS) matrix. The coating surface presented a simultaneous hydrophobic and lipophobic character, owing to the strong surface segregation of the lowest surface energy fluoroalkyl chains of the block copolymer. Surface chemical composition and wettability of the films were affected by exposure to water. Block copolymer Sz6 was also blended with PDMS and a 0.1 wt% amount of multiwall carbon nanotubes (CNT). The excellent fouling-release (FR) properties of these new coatings against the macroalga Ulva linza essentially resulted from the inclusion of the amphiphilic block copolymer, while the addition of CNT did not appear to improve the FR properties.

Investigation of the role of hydrophilic chain length in amphiphilic perfluoropolyether/poly(ethylene glycol) networks: towards high-performance antifouling coatings

The facile preparation of amphiphilic network coatings having a hydrophobic dimethacryloxy-functionalized perfluoropolyether (PFPE-DMA; M(w) = 1500 g mol(-1)) crosslinked with hydrophilic monomethacryloxy functionalized poly(ethylene glycol) macromonomers (PEG-MA; M(w) = 300, 475, 1100 g mol(-1)), intended as non-toxic high-performance marine coatings exhibiting antifouling characteristics is demonstrated. The PFPE-DMA was found to be miscible with the PEG-MA. Photo-cured blends of these materials containing 10 wt% of PEG-MA oligomers did not swell significantly in water. PFPE-DMA crosslinked with the highest molecular weight PEG oligomer (ie PEG1100) deterred settlement (attachment) of algal cells and cypris larvae of barnacles compared to a PFPE control coating. Dynamic mechanical analysis of these networks revealed a flexible material. Preferential segregation of the PEG segments at the polymer/air interface resulted in enhanced antifouling performance. The cured amphiphilic PFPE/PEG films showed decreased advancing and receding contact angles with increasing PEG chain length. In particular, the PFPE/PEG1100 network had a much lower advancing contact angle than static contact angle, suggesting that the PEG1100 segments diffuse to the polymer/water interface quickly. The preferential interfacial aggregation of the larger PEG segments enables the coating surface to have a substantially enhanced resistance to settlement of spores of the green seaweed Ulva, cells of the diatom Navicula and cypris larvae of the barnacle Balanus amphitrite as well as low adhesion of sporelings (young plants) of Ulva, adhesion being lower than to a polydimethyl elastomer, Silastic T2.

Micelle formation and gelation of (PEG-P(MA-POSS)) amphiphilic block copolymers via associative hydrophobic effects

A series of well-defined amphiphilic di- and triblock copolymers have been synthesized, using atom transfer radical polymerization, with poly(ethylene glycol) (PEG) and poly(methacrylisobutyl polyhedral oligomeric silsesquioxane) P(MA-POSS) as the hydrophilic and hydrophobic blocks, respectively. The detailed self-assembly behavior of the amphiphilic macromolecules in aqueous media was studied using both static and dynamic light scattering (SLS and DLS) techniques. The evolution of block copolymer micelle formation in THF/water mixture (20/80 v/v) was monitored as the THF evaporated from the solvent mixture. Initially the block copolymer chains existed as unimers in solution, followed by the formation of smaller aggregates (R(h) < 2 nm) after 30 min, eventually growing in size to reach an equilibrium size when all the THF evaporated within 24 h. The micelles formed by the block copolymers were found to be kinetically unstable (not frozen); i.e., they tended to revert to individual copolymer chains on dilution. The hydrodynamic radii, R(h), of the micelles varied with the degree of polymerization (DP) of the hydrophobic P(MA-POSS); for example, for PEG(5K)-b-P(MA-POSS), an increase from R(h) approximately 13.3 +/- 1.1 nm to R(h) approximately 17.5 +/- 1.4 nm was observed with a nominal change in the DP of P(MA-POSS) from 4 to 6. The micelles formed by the triblock copolymers (P(MA-POSS)-b-PEG(10K)-b-P(MA-POSS)) were comparable in size to the diblock copolymer micelles; e.g., R(h) approximately 14.0 +/- 1.3 nm was found for P(MA-POSS)(4)-b-PEG(10K)-b-P(MA-POSS)(4). The micellar structures created by the triblocks in aqueous media were "flowerlike", where the PEG middle block adopted a loop conformation in the micelle corona. In addition to micelles, larger aggregates formed by P(MA-POSS)-b-PEG(10K)-b-P(MA-POSS) were also detected in solution. The larger aggregates may suggest a contribution from some PEG blocks adopting an extended conformation with one end dangling in solution, causing gelation at higher copolymer concentrations via intermicellar interactions. The P(MA-POSS)(4)-b-PEG(10K)-b- P(MA-POSS)(4) formed a gel in water at approximately 8.8 wt % copolymer concentration. No gel formation by diblock copolymers was observed; however, the addition of a small amount of triblock copolymer to an aqueous solution of diblock copolymer results in gel formation. Finally, rheological behavior of the obtained gels was also investigated.

Amphiphilic surface active triblock copolymers with mixed hydrophobic and hydrophilic side chains for tuned marine fouling-release properties

Two series of amphiphilic triblock surface active block copolymers (SABCs) were prepared through chemical modification of two polystyrene-block-poly(ethylene-ran-butylene)-block-polyisoprene ABC triblock copolymer precursors. The methyl ether of poly(ethylene glycol) [M(n) approximately 550 g/mol (PEG550)] and a semifluorinated alcohol (CF(3)(CF(2))(9)(CH(2))(10)OH) [F10H10] were attached at different molar ratios to impart both hydrophobic and hydrophilic groups to the isoprene segment. Coatings on glass slides consisting of a thin layer of the amphiphilic SABC deposited on a thicker layer of an ABA polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene thermoplastic elastomer were prepared for biofouling assays with algae. Dynamic water contact angle analysis, X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) measurements were utilized to characterize the surfaces. Clear differences in surface structure were realized as the composition of attached side chains was varied. In biofouling assays, the settlement (attachment) of zoospores of the green alga Ulva was higher for surfaces incorporating a large proportion of the hydrophobic F10H10 side chains, while surfaces with a large proportion of the PEG550 side chains inhibited settlement. The trend in attachment strength of sporelings (young plants) of Ulva did not show such an obvious pattern. However, amphiphilic SABCs incorporating a mixture of PEG550 and F10H10 side chains performed the best. The number of cells of the diatom Navicula attached after exposure to flow decreased as the content of PEG550 to F10H10 side chains increased.

The surface-segregated nanostructure of fluorinated copolymer-poly(dimethylsiloxane) blend films

Two fluorinated/siloxane copolymers, O5/19 and D5/3, carrying 6 and 8 CF(2) groups in the fluoroalkyl tail, respectively, were used as the surface-active components of cured poly(dimethylsiloxane) (PDMS) blends at different loadings (0.3-5.0 wt % with respect to PDMS). The surface chemical composition was determined by angle-resolved X-ray photoelectron spectroscopy at the takeoff angles theta of 0 degrees, 60 degrees, and 75 degrees. It was found that the fluorinated copolymer was surface-segregated, and in-depth segregation (approximately 5 nm) depended upon the chemical structure of the copolymer. The surface fluorine atomic percentage of the blends with D5/3 was up to 3 orders of magnitude higher than the theoretical value expected for ideal homogeneous samples. Moreover, small amounts of the copolymer in the blends were sufficient to saturate the outermost surface in fluorine content. The chemical composition of the surface-segregated nanostructure of the films was also proven to be affected by external environment, namely, exposure to water.

Synthesis and self-assembly of brush-type poly[poly(ethylene glycol)methyl ether methacrylate]-block-poly(pentafluorostyrene) amphiphilic diblock copolymers in aqueous solution

Well-defined fluorinated brush-like amphiphilic diblock copolymers of poly[poly(ethylene glycol)methyl ether methacrylate] (P(PEGMA)) and poly(pentafluorostyrene) (PPFS) have been successfully synthesized via atom transfer radical polymerization (ATRP). The self-assembly behavior of these polymers in aqueous solutions was studied using (1)H NMR, fluorescence spectrometry, static and dynamic light scattering and transmission electron microscopy techniques. The micellar structure comprised of PPFS as the core and brush-like (hydrophobic main chain and hydrophilic branches) polymers as the coronas. The hydrodynamic radius (R(h)) of the micelles in aqueous solution was in the nanometer range, independent of the polymer concentration, consistent with a closed association model. Diblock copolymers with a longer P(PEGMA) block formed micelles with smaller R(h) and lower aggregation numbers consistent with an improved solubilization of the core. The micelles possessed a thick hydration layer as verified by the ratio of the radius of gyration, R(g) to the hydrodynamic radius, R(h). The aggregation number and ratio of R(g) to R(h) were observed to increase with temperature (20-50 degrees C), while the R(h) of the micelle decreased slightly over the same temperature range. An increase in temperature induced the brush-like PEG segments in the corona to dehydrate and shrink while forming micelles with larger aggregation numbers.

The effects of nitric oxide in settlement and adhesion of zoospores of the green alga Ulva

Previous studies have shown that elevated nitric oxide (NO) reduces adhesion in diatom, bacterial and animal cells. This article reports experiments designed to investigate whether elevated NO reduces the adhesion of zoospores of the green alga Ulva, an important fouling species. Surface-normalised values of NO were measured using the fluorescent indicator DAF-FM DA and parallel hydrodynamic measurements of adhesion strength were made. Elevated levels of NO caused by the addition of the exogenous NO donor SNAP reduced spore settlement by 20% and resulted in lower adhesion strength. Addition of the NO scavenger cPTIO abolished the effects of SNAP on adhesion. The strength of attachment and NO production by spores in response to four coatings (Silastic T2; Intersleek 700; Intersleek 900 and polyurethane) shows that reduced adhesion is correlated with an increase in NO production. It is proposed that in spores of Ulva, NO is used as an intracellular signalling molecule to detect how conducive a surface is for settlement and adhesion. The effect of NO on the adhesion of a range of organisms suggests that NO-releasing coatings could have the potential to control fouling.

The role of surface energy and water wettability in aminoalkyl/fluorocarbon/hydrocarbon-modified xerogel surfaces in the control of marine biofouling

Xerogel films with uniform surface topogrophy, as determined by scanning electron microscopy, atomic force microscopy (AFM), and time-of-flight secondary ion mass spectrometry, were prepared from aminopropylsilyl-, fluorocarbonsilyl-, and hydrocarbonsilyl- containing precursors. Young's modulus was determined from AFM indentation measurements. The xerogel coatings gave reduced settlement of zoospores of the marine fouling alga Ulva compared to a poly(dimethylsiloxane) elastomer (PDMSE) standard. Increased settlement correlated with decreased water wettability as measured by the static water contact angle, theta(Ws), or with decreased polar contribution (gamma(P)) to the surface free energy (gamma(S)) as measured by comprehensive contact angle analysis. The strength of attachment of 7-day sporelings (young plants) of Ulva on several of the xerogels was similar to that on PDMSE although no overall correlation was observed with either theta(Ws) or gamma(S). For sporelings attached to the fluorocarbon/hydrocarbon-modified xerogels, the strength of attachment increased with increased water wettability. The aminopropyl-modified xerogels did not follow this trend.

ABC triblock surface active block copolymer with grafted ethoxylated fluoroalkyl amphiphilic side chains for marine antifouling/fouling-release applications

An amphiphilic triblock surface-active block copolymer (SABC) possessing ethoxylated fluoroalkyl side chains was synthesized through the chemical modification of a polystyrene-block-poly(ethylene-ran-butylene)-block-polyisoprene polymer precursor. Bilayer coatings on glass slides consisting of a thin layer of the amphiphilic SABC spray coated on a thick layer of a polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) thermoplastic elastomer were prepared for biofouling assays with the green alga Ulva and the diatom Navicula. Dynamic water contact angle analysis and X-ray photoelectron spectroscopy (XPS) were used to characterize the surfaces. Additionally, the effect of the Young's modulus of the coating on the release properties of sporelings (young plants) of the green alga Ulva was examined through the use of two different SEBS thermoplastic elastomers possessing modulus values of an order of magnitude in difference. The amphiphilic SABC was found to reduce the settlement density of zoospores of Ulva as well as the strength of attachment of sporelings. The attachment strength of the sporelings was further reduced for the amphiphilic SABC on the "low"-modulus SEBS base layer. The weaker adhesion of diatoms, relative to a PDMS standard, further highlights the antifouling potential of this amphiphilic triblock hybrid copolymer.