M. Raimondo, M. Caruso, A. Corozzi, H. Akkaya, E. Ciappi, B. Jacob
CNR ISSMC,
Italy
Keywords: biomimetic, hybrid coatings, superhydrophobicity, anti-fouling, drag reduction
Summary:
Bio-fouling phenomena, consisting of undesirable settlement and accumulation of microorganisms on submerged surfaces – vehicles and infrastructures – have severe adverse influence on sustainability in marine areas due to efficiency reduction, increasing of fuel consumption and gas emission, other than detrimental effects on corrosion resistance and wearing of materials and components over the time. Additionally, the formation of biofouling, including different steps of microorganism accumulation, increases the weight and roughness of ship hulls, which, in turn, raises the wall frictional resistance. According to the literature, the design of non-sticking superhydrophobic surfaces through biomimetic approaches represents one of the most effective strategies to prevent, or at least to control, biofilm accumulation. In this work, Lotus leaf-like coatings (LF) with air mediated solid interface and lubricant mediated interface (SLIPS, Slippery Liquid Infused Porous Surfaces) stood up for their ability to prevent the attachment of marine microorganisms and to reduce the wall friction in underwater conditions. Depending on two different approaches, hybrid coatings were obtained by deposition of ceramic oxides (Al2O3 or SiO2) as inner component followed by dipping of a fluorosilane (LF) or infusion of a lubricant (SLIPS) giving rise, respectively, to a solid and liquid working interface. LF hybrid coatings reached static contact angle as high as 160-170° while SLIPS contact angle hysteresis values were lower than 5°. Both coating typologies were subjected to a larvae settlement lab test (no droplet choice), which allowed to demonstrate their good antifouling attitude. Moreover, summertime tests in open sea confirmed these results even for long time exposure. Drag reduction analyses, conducted at the Hydrodynamic Experimental Facility Cavitation Tunnel (CEIMM) of the Italian Navy in Rome, proved that SLIPS coatings were the best performing in reducing the hydrodynamic force of a 15% if compared to the uncoated samples. Based on these results, we can underline that both biomimetic approaches adopted in this work were able to provide antifouling behavior or hydrodynamic friction reduction abilities, but that the performance effectiveness and their combination depend on the relative ratio of static and dynamic repellence against water.