Comparative study of the impact and sliding behavior of water droplets on two different hydrophobic silane coatings

Abstract Smooth hydrophobic silane coatings were prepared on a Si substrate using ODS (CH 3 (CH 2 ) 17 Si(OCH 3 ) 3 ) and FAS17 (CF 3 (CF 2 ) 7 (CH 2 ) 2 Si(OCH 3 ) 3 ). Results obtained using ellipsometry and Kelvin force microscopy suggest that ODS molecules in the coating are tilting or inflected, whereas those of FAS17 are more normal to the substrate. Impact and sliding behaviors of water droplets on the respective surfaces were investigated using a 15 μL water droplet by varying the droplet release height. Droplets on ODS slid down faster than on FAS17 when released from 0 mm height (i.e. traditional dynamic hydrophobicity measurement). The order was reversed when providing the impact velocity. Comparison of energy dissipation during the impact process revealed that the droplet on ODS, because of its large deformation, loses more energy than that on FAS17. These results demonstrate that the order of droplet removal performance depends on the presence or absence of some initial velocity.