structural Effects of Hydrophobic coatings on barnacle adhesion

One of the components in designing antifouling (AF) coatings is controlling the wettability of the surface by modifying the nanostructure of the surface. While hydrophobic coatings can reduce the surface energy they do not necessarily prevent proteins from adsorbing. Air pockets embedded in self-assembled monolayers (SAMs) can decrease wettability and possibly reduce attachment of larval and adult barnacles. In this study, hydrophobic surfaces with different morphological structures were studied to determine their effect on adhesion of adult barnacles and adsorption of barnacle glue.

Microscope glass slides were treated with alkyl silane self-assembled monolayers to produce hydrophobic and superhydrophobic surfaces. Contact angles were determined as a measure of wetting (A). Adult barnacles Amphibalanus amphitrite were allowed to reattach to the substrates for two weeks. Barnacles were removed from the substrate by shear force following the ASTM standard methods. Adhesion strength was recorded for each sample along with area of the base plate. Residual glue remaining on the substrates after barnacle removal was stained with a Coomassie G250 protein stain. The pixel density of the stain was quantified through image analysis and then compared to the non-treated control slides (B).

The average contact angles for the hydrophobic surfaces were between 100^o and 120^o, while superhydrophobic were between 145^o to 155^o. The applied pressure necessary to remove the barnacles was higher for both hydrophobic surfaces compared to the control slides. The remaining glue density was consistent with the pressure results demonstrating that more glue remained attached to the hydrophobic surfaces compared to the control slides (C). This agrees with the literature that the surface quality of hydrophobicity is not sufficient to reduce biofouling and that the physical structure can have a greater impact.

We are continuing to study the effect of nanostructures on the adsorption of barnacle glue. We have fabricated substrates containing hydrophobic SAMs conjugated to silver nanoparticles. The density of nanoparticles can be tuned in order to adjust the hydrophobicity of the surface.