The role of nano-roughness in antifouling

Nano-engineered superhydrophobic surfaces have been investigated for potential fouling resistance properties. Integrating hydrophobic materials with nanoscale roughness generates surfaces with superhydrophobicity that have water contact angles (theta) > 150 degrees and concomitant low hysteresis (< 10 degrees). Three superhydrophobic coatings (SHCs) differing in their chemical composition and architecture were tested against major fouling species (Amphora sp., Ulva rigida, Polysiphonia sphaerocarpa, Bugula neritina, Amphibalanus amphitrite) in settlement assays. The SHC which had nanoscale roughness alone (SHC 3) deterred the settlement of all the tested fouling organisms, compared to selective settlement on the SHCs with nano-and micro-scale architectures. The presence of air incursions or nanobubbles at the interface of the SHCs when immersed was characterized using small angle X-ray scattering, a technique sensitive to local changes in electron density contrast resulting from partial or complete wetting of a rough interface. The coating with broad spectrum antifouling properties (SHC 3) had a noticeably larger amount of unwetted interface when immersed, likely due to the comparatively high work of adhesion (60.77 mJ m(-2) for SHC 3 compared to 5.78 mJ m(-2) for the other two SHCs) required for creating solid/liquid interface from the solid/vapour interface. This is the first example of a non-toxic, fouling resistant surface against a broad spectrum of fouling organisms ranging from plant cells and non-motile spores, to complex invertebrate larvae with highly selective sensory mechanisms. The only physical property differentiating the immersed surfaces is the nano-architectured roughness which supports longer standing air incursions providing a novel non-toxic broad spectrum mechanism for the prevention of biofouling.