Invited Paper MB+BI-MoA1
Engineered Polymer Coatings for Foul-Release Applications

Monday, October 15, 2007, 2:00 pm, Room 609

Marine biofouling is a serious and complex problem resulting in losses of operating efficiency of ships.  Current coating technologies derived from copper- and tin-based compounds are being banned because of detrimental effects on marine environment.  Hence there is need for developing efficient marine coatings that would possess no ecological concern.  In addition to various chemical approaches, surface topography has also been shown to be important for mechanical defense against biofouling.  For instance, Hoipkemeirer-Wilson and coworkers reported that topographically corrugated surfaces are capable of reducing biofouling.  The degree to which fouling was reduced was found to depend on the dimensions of the geometrical protrusions as well as the chemistry of the surfaces.  Because biofouling includes a very diverse range of various species, whose sizes span several orders of magnitude, one single topographical pattern will not likely perform as an effective antifouling surface.  Rather, surface corrugations having multiple length scales acting in parallel should be used in designing effective antifouling surfaces. We have developed a method leading to substrate comprising hierarchically wrinkled (H-wrinkled) topographies.  These specimens were prepared by first uniaxially stretching poly(dimethylsiloxane) films, exposing them to ultraviolet/ozone (UVO) radiation for extended periods of time (30-60 minutes), and releasing the strain.  After the strain was removed from the specimens the surface skin buckled perpendicularly to the direction of the strain.  A detailed analysis of the buckled surface uncovered the presence of hierarchical buckling patterns; buckles with smaller wavelengths (and amplitude) rested parallel to and within larger buckles, forming a nested structure.  At least 5 distinct buckle generations (G) were detected with their wavelengths ranging from tens of nanometers to a fraction of a millimeter.  The method for producing coatings with H-wrinkled topographies may represent a convenient platform for designing foul-release surfaces.  Our recent sea water immersion experiments involving testing over an extended time period indicated that these coating are far superior to flat coatings.  We will discuss how the H-wrinkle topographies can be applied to make coatings from just about any type of material and offer methodologies for preparing amphiphilic foul-release coatings from commercially available materials.  While more work still needs to be done, the initial observations suggest that the H-wrinkled coatings may represent a new and promising platform for fabricating efficient foul-release marine coatings.