Sliding of Water Droplets on Smooth Hydrophobic Silane
Coatings with Regular Triangle Hydrophilic Regions
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Abstract
The
effect of the triangular pinning region on the sliding of water
droplets on the smooth hydrophobic surface was investigated. Smooth
hydrophobic silane coatings with various regular triangle hydrophilic
regions were prepared using photolithography and octadecyltrimethoxysilane
(ODS). The hydrophilic area in the surfaces was aligned hexagonally
with a constant area fraction. Thereby water contact angles of the
coatings were almost equivalent. The water droplet sliding velocity
increased continuously
with increasing pattern size. Anisotropic sliding velocity was observed
on the surface, suggesting different pinning effects. The sliding
motion of water droplets on the gradient surface with changing hydrophilic
region size deflects against the downward direction. The deflection
length depends on the direction of triangle hydrophilic regions and
the initial sliding position. These results demonstrate that control
of the sliding velocity while sustaining the static contact angle
is feasible by designing the shape and alignment of chemical heterogeneity