Influence of surface characteristics on biofouling formed on polymers exposed to coastal sea waters of India.

Biofouling on six different (silicone rubber, polydimethylsiloxane, polypropylene, high density polyethylene, polyvinylchloride, and polycarbonate) substrata with varying surface energy (18-40 mN/m) and surface roughness (R(a) 45-175 μm) was studied in the Eastern coastal waters of India over a short period of time (3 days). The results showed that the substrata surface energy (SE) followed by the surface roughness (R(a)) had profound effect on attachment of fouling organisms. After one day of immersion, viable count of bacteria in the biofilm was positively correlated with surface energy (r=0.69, p<0.05) and not with surface roughness (r=-0.02) of the substratum. Whereas, Pseudomonas count was inversely correlated with surface energy (r=-0.66, p<0.05) and surface roughness (r=-0.52, p<0.05). The attachment of macrofouler and the surface characteristics were also well correlated with SE 0.48 and with roughness 0.62, p<0.05. A positive correlation was observed amongst the various biofouling constituents such as bacteria, ATP, carbohydrates and organic matter on almost all the substrata. However after the first day, the surface characteristics of the substratum became less important and the conditioning film that was formed on the substrata appeared to directly influence further fouling on the surfaces, as evidenced by poor correlation between surface energy and macrofouler attachment (r=-0.11). The observation of high numbers of Hydroides elegans on PVC could be solely due to the influence of surface roughness (r=0.62). Though there is no marked difference in the 'primary film', and the composition of the biofilm, the amount of attached macrofouler is minimal on silicone rubber and polydimethylsiloxane on subsequent days of immersion, which reveals the foul release quality of these substrata probably due to their flexible nature.