Studying the Role of Surface Topography in Marine Anti-Fouling Coatings

This Ph.D. Thesis focuses on understanding the effects of topography in surface coatings to reduce or inhibit marine biofouling. We benefited from prior work in the Genzer group that revealed the robustness of hierarchical periodic surface topographies at reducing marine fouling. We aimed to break these hierarchical structures down into individual periodicities to attain fundamental understanding of their interplay with fouling organisms. To accomplish this, we utilize both computer simulations and experiments. We employ computer simulation to build our theoretical understanding of the interplay between size and shape of periodic surface features with fouling particles of spherical shape. We first developed a model for single particle adhesion, in which we demonstrated that the feature width (lambda) had a large effect on the adhesion energy and position of the adsorbing particle. The minimum adsorption regime was lambda/D ~ 0.5 where D is the diameter of the adsorbing particle. We expanded this model to examine multiple particles adsorbing on the same substrate to discover substrates with minimum number of adsorbing particles and minimum total adhesion. The minimum adhesion energy was found again at lambda/D ~ 0.5; furthermore, this was also the region of fewest adsorbed particles. In the next stage of simulations, we further expanded the model to examine settlement of spherical particles with predefined size-polydispersity and studied their settlement on flat and periodically-corrugated substrates. We used normal distributions of varying standard deviation to generate assemblies of polydisperse particles. We found lambda/Dmean ~ 0.5 as the minimum adhesion condition for the periodic substrates, where Dmean is the average value of the normal distribution. Additionally, at lambda/D mean ~ 0.5 these surfaces managed to reduce adhesion energy by > 10% when compared to flat substrates even at large polydispersity (Dmean = 20 STD = 8). In experiments we utilized photolithography of negative photoresists to build periodic surface structures of varying feature width (10 -- 200 mum) and feature height (10 -- 400 mum). We combined soft lithography and hot embossing to create the dozens of surfaces needed to test our surfaces against the barnacle species Balanus Amphitrite in their cyprid form. Settlement testing, by collaborators in the UK, revealed dramatic effects of surface topography on these barnacle cyprids. At 200 mum, feature width, our surface prevented any cyprids from attaching. Beyond this we developed low-fouling/foul-release chemical coatings based on polymer network gels, which allowed only ~15% of barnacle cyprids to settle and released ~45% of adsorbed juvenile barnacles. Finally, we developed a spraycoating method to conformally coat our microstructures with these low-fouling/foul-release polymers to improve our microtextures further. The contribution of this body of work contributes significantly in furthering our understanding on the role of surface topographies to reduce marine fouling.