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The addition of block copolymers (i.e. oils) is a common technique to enhance the biofouling-resistance properties of poly(dimethylsiloxane) (PDMS)-based fouling-release coatings. These copolymers diffuse from the bulk to the surface of the coating, thus modifying the properties of the surface and providing fouling-resistance properties. Upon release, dissolution or degradation of copolymer molecules at the surface, new molecules can diffuse from the bulk of the coating and cover the surface. Therefore, the long-term performance of these coatings is dependent on the stability and release rate of copolymer molecules from the surface. A method was developed to quantify the concentration of PDMS-based block copolymers from fouling-release coatings. About 300 experimental coatings exposed to seawater for up to 5.2 years were included in the analysis. The results showed that the loss of copolymer (in % on a weight basis) is significantly higher in warm waters, while the initial copolymer concentration in the coating does not have any effect for copolymer concentrations between 1 and 7 wt%. In short-term exposure, it was found that loss of copolymer was much higher in coatings containing small amounts of an organic biocide (copper pyrithione). Conversely, biocide-containing coatings displayed larger copolymer retention values in long-term experiments. Opposite results were obtained for biocide-free coatings, suggesting that the addition of the organic biocide alters the release profile of copolymers from fouling-release coatings. Finally, the potential of long-term field-studies is discussed, as compared to short-term laboratory experiments usually performed within fouling-release coatings studies. [ABSTRACT FROM AUTHOR]

Amphiphiles (i.e. amphiphilic molecules such as surfactants, block copolymers and similar compounds) are used in small amounts to modify the surface properties of polymeric materials. In silicone fouling-release coatings, PEG-based amphiphiles are added to provide biofouling-resistance. The success of this approach relies on the ability of the amphiphiles to diffuse through the coating film and cover the surface of the coating. A novel method for the measurement of diffusion coefficients of PEG-based amphiphiles of different chemistries in PDMS-based coatings is presented here. The diffusion coefficient of the amphiphiles shows a weak dependency on their molecular weight, although this dependency is much less pronounced than for other rubbery polymeric materials. The biofouling-resistance properties in fouling-release coatings were also studied for these amphiphiles. It was found that the diffusion coefficient does not have any influence on the biofouling-resistance results for the studied compounds. Instead, the chemistry of the hydrophobic block of the amphiphiles is much more significant, with PEG-PDMS block copolymers showing the best properties among the studied compounds. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen peroxide (H2O2) may be considered an environmentally friendly antifouling alternative to common biocides such as Cu2O and various organic compounds. In this work, the efficiency of antifouling coatings releasing hydrogen peroxide via enzyme-mediated conversion of starch, under Mediterranean and equatorial climatic conditions, is investigated. During seawater exposure of the coatings, starch is first converted to glucose by glucoamylase (rate-controlling step) and subsequently glucose is rapidly oxidised by hexose oxidase in a reaction producing hydrogen peroxide. The coatings formulated have been characterised in terms of common coating characteristics and immersed on rafts in seawater outside Singapore and Spain to monitor antifouling efficiency. The results have been compared to results previously reported from temperate waters in the North Sea outside The Netherlands. Using laboratory assays, the transient hydrogen peroxide release rate from the coatings at different temperatures has been measured. The investigations are used to evaluate the ocean performance of the antifouling coatings. Coatings can be formulated with starch/enzyme ‘pigments’ in considerable amounts and yet retain the mechanical properties required of an antifouling coating. However, the antifouling effect of the coatings immersed in seawater near Singapore and Spain, when inspected after 8 and 14 weeks, respectively, is insufficient. In comparison, previous studies under colder conditions showed an effect exceeding that of two commercial references over 67 days. The release rate of hydrogen peroxide from the coatings is shown to be greatly influenced by temperature, and therefore the results provided here suggest an antifouling effect that is highly dependent on the environment of the coating. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]