Investigation of (super)hydrophilic coatings for marine antifouling applications

Abstract

The undesirable colonization of artificial structures at sea, termed marine biofouling, has significant economic and environmental impacts. The marine antifouling (AF) market is currently dominated by biocidal coatings that release toxic heavy metals or organic biocides, limiting the attachment and growth of fouling organisms. The central aim of this thesis was to explore the potential of environmentally inert, (super)hydrophilic surfaces as next-generation AF coatings. In contrast to previous research in this area, the coatings presented here were prepared as industrially relevant copolymers and tested in the laboratory against two major fouling species; cypris larvae of the barnacle Balanus improvisus and cells of the diatom Navicula incerta, as well as a multispecies biofilm and field testing in temperate and tropical locations. The laboratory assays revealed that, in general, barnacles settled in lower numbers on bulk polymers containing ionic functionalities. The surfaces containing zwitterionic sulfobetaine methacrylate (SBMA) and anionic 3-sulfopropyl methacrylate (SPMA) were found to not only inhibit cyprid settlement but also promote high removal of juvenile barnacles, diatom cells and biofilm. The exceptional AF and fouling-release performance of these two chemistries was explained by the large degree of swelling when hydrated and presence of nonfreezable water at the interface. The surfaces presented showed limited AF efficacy when subjected to the real-world marine environment. Using behavioural analysis and imaging surface plasmon resonance (iSPR) experiments, it was shown that barnacle cyprids explored all surfaces. However, in the case of SBMA, the exploratory events were very short and the amount of retained temporary adhesive was low. In conclusion, this work demonstrates the potential of bulk hydrophilic copolymers as a starting point for the development of next-generation, green AF coatings. It is hoped that the findings of this work will encourage greater industrial participation in the development of fouling-control technologies that function via non-biocidal means.