EFFECTS OF SURFACE MORPHOLOGY ON SUPERHYDROPHOBICITY AND BUOYANCY

1. EFFECTS OF SURFACE MORPHOLOGY ON SUPERHYDROPHOBICITY AND BUOYANCY OF THE CABBAGE LEAF AND THE VACNTS CARPET E. Lepore*, M.Giorcelli**, C. Saggese***, N. Pugno* and A. Tagliaferro* *Laboratory of Bio-inspired Nanomechanics, Department of Structural Engineering, Politecnico di Torino - **Applied Science & Technology Department - Polytecnich of Turin - *** Chemistry, Material and Chemical Engineering Department "Giulio Natta" (CMIC), Polytechnich of Milan mauro.giorcelli@polito.it In this work we have studied two types of nanostructured surfaces: the cabbage leaf and a vertical aligned carbon nanotubes carpet. These surfaces are characterized by means of contact angle, sliding angle, sliding volume and sliding speed measurements. Results are correlated with nano-morphology surface and investigated by scanning electron microscopy. Buoyancy behavior of different surfaces has been investigated through dedicated measurements which have allowed us to determine forces involved on surface. In this paper the buoyancy behavior of these surfaces is compared with one of water strider’s leg. Finally, we demonstrate that cabbage leaf and vertical aligned carbon nanotubes carpet have some common features with the water strider’s leg. 1. SURFACE CHARACTERIZATION 2. MEASUREMENTS OF WETTABILITY SV=Sliding Volume; SS=Sliding Speed; CA= Contact Angle; SA=Sliding Angle 3. MEASUREMENTS OF FLOATING Theoretically, 1 m2 of the L side of the cabbage leaf (or VACNTs carpet) could be able to support on average  3 kg. This result underline the higher bearing capacity of the natural surface (in particular, the L side of cabbage leaf), if compared to the artificial one (VACNTs carpet). Upper (adaxial) and lower (abaxial) sides of the natural cabbage leaf of Brassica oleracea. 4.CONCLUSIONS VACNTs: mechanical strength - low density. The hierarchical arrangement of structures of the surface has a strong impact on the macroscopic observable surface effects. The presence of the surface roughness on multiple scales is necessary to increase the wetting resistance and to induce a self-cleaning behavior and the water floating capacity, as water striders’ legs show. We have demonstrated that the cabbage leaf and the VACNTs carpet have some common features with the water strider’s legs. The carrying load on water is direct correlated to the superhydrophobic property and the surface structures, which range from the nanoscale to the micrometer scale, in water permit the presence of a thin layer of air at the immersed surface responsible of this behavior. Water strider’s leg (Gerris Remigis).