New Frontiers for Liquid-repellent Surfaces: Assessment of their Drag Resistance and Vibration Reduction Properties

In the last decades, liquid-repellent surfaces have drawn huge interest from both the scientific community and the industry. In fact, a wide range of industrially relevant properties - namely self-cleaning, anti-icing, antifouling, anti-friction and many more - derives from the liquid-repellent attitude of materials and components. In the last years, the Smart Surfaces Group at CNR-ISTEC has developed an expertise in the design, fabrication and characterization of inorganic or hybrid coatings able to strongly reduce the surface wetting of industrial materials: metals and alloys, glasses, ceramics, natural fibers, polymeric films, etc. Through the choice of suitable deposition methods (dip coating, spray coating, roller printing) and process parameters, the coatings surface chemistry and morphology can be tuned in order to broaden the range of liquids which can be repelled. Being the know-how of materials and processing criteria to superhydrophobic, oleophobic and amphiphobic surfaces rather strengthened, our current work is now eager to explore the further potential of these surfaces, aiming to extend their application range at industrial level in the sectors of i.e aerospace, maritime and naval applications. This approach requires very often to address different scientific competences, equipment and facilities. The already established collaboration with CNR-INSEAN is allowing to study the underwater behavior of superhydrophobic surfaces. More specifically, ISTEC CNR fabricated large water-repellent surfaces (45 x 30 cm) on aluminum slabs as per two biomimetic approaches, namely the SuperHydrophobic Surface (SHS) and the Slippery, Liquid-Infused Porous Surface approach (SLIPS). CNR-INSEAN, together with Centro per Esperienze Idrodinamiche della Marina Militare (CEIMM) custom-made an experimental setup to assess the materials surface behavior in terms of skin-friction drag resistance and acceleration response. Results showed that SLIPSs provide a remarkable decrease in drag resistance (10-16% reduction in friction coefficient) and in acceleration amplitude at mid-high frequencies (2.5 dB reduction in noise radiation). These findings, although preliminary, could have huge positive fallout on naval transportation, as they would lead to higher speed, lower emission and increased mission range for underwater vehicles, more reliable operation of sensors, diminished fatigue of pipes and launchers, increased on-board comfort for ship crews and passengers.