In situ surface analysis of novel marine foul-release coatings

Exposure of artificial surfaces such as ship hulls to a marine environment leads to the attachment of assorted biomolecules, single celled organisms and marine invertebrates such as barnacles or mussels. Together, they form a structure known as a biofilm. These films lead to higher fuel consumption and add considerable expense to the operation of ships used by industrial and naval organisations. The work presented in this thesis describes the surface analysis of a novel poly(dimethylsiloxane) (PDMS) based foul-release coating. The coating also contains poly(ethylene glycol) groups (PEG). The differing chemical properties between these two domains led to an observed surface modification effect in water, whereby contact angle measurements decreased from ~110o to ~65 o over a period of five minutes. This effect was rapidly reversible on drying. Time of Flight-Secondary Ion Mass Spectrometry cryogenic depth profiling experiments confirmed this change in surface chemistry where the frozen surface of the coating was shown to have a higher intensity of ions associated with PEG groups at the surface compared to that in the bulk. Water immersion also led to a swelling of the surface seen by a change in the surface topography by Atomic Force Microscopy investigations. When applied to glass surfaces the coatings were flat and generally defect free regardless of the application method used. On exposure to Pseudomonas aeruginosa the coatings were found to be ten times more effective at preventing bacterial adhesion in the first instance than a PDMS standard. The mechanism of action was shown to be non-toxic by live/dead staining and did not appear to affect the way in which bacteria move on a surface. A flow adhesion assay demonstrated that a flow rate of almost two orders of magnitude lower was required to remove fifty percent of bacteria from a coated surface than on a glass standard, demonstrating the foul-release ability of the switching coating. Sea trials in a French coastal region highlighted the importance of exposing candidate coatings to a true marine environment for a suitable duration in order to determine their potential for use. Ultimately we show that the coating presented is a candidate for use as an effective coating for preventing marine biofouling and surface analysis was deemed to be an appropriate methodology to analyse coatings that have changing properties on exposure to water