Development of environmentally friendly, antifouling coatings based on tethered quaternary ammonium salts in a crosslinked polydimethylsiloxane matrix

The concept of tethering quaternary ammonium salts (QASs) to a crosslinked polysiloxane matrix to produce a hybrid antifouling/fouling-release coating was investigated. A statistical experimental design was used to determine the effect of QAS concentration on biocidal activity toward a marine bacterium, Cellulophaga lytica (C. lytica). In addition to measuring biocidal activity, coating film quality as well as stability upon water immersion were evaluated. The results of the study showed that biocidal activity was strongly dependent on QAS concentration. For addition-curable coatings, the presence of 4 wt% QAS moieties resulted in approximately 50% reduction in C. lytica biofilm retention without any leachate toxicity. Attempts to increase the level of QAS moieties to increase biocidal activity resulted in coating delamination from the substrate and unacceptable film quality upon artificial seawater immersion due to excessive swelling. As a result, a moisture-curable system based on tethered QASs was investigated since moisture curing allows for higher crosslink densities to be achieved which would be expected to minimize swelling upon artificial seawater immersion. The moisture-curable coating developed showed enhanced stability upon artificial seawater immersion, greater than 80% reduction in C. lytica biofilm retention, and greater than 90% reduction in biofilm growth for the marine algae, Navicula incerta.