posted on 2018-05-08, 00:00authored byY. P. Li, X. Y. Li, X. P. Zhu, M. K. Lei, A. Lakhtakia
Water drops impacting windshields
of high-speed trains and aircraft as well as blades in steam turbine
power generators obliquely and at high speeds are difficult to repel.
Impacting drops penetrate the void regions of nanotextured and microtextured
superhydrophobic coatings, with this pinning resulting in the loss
of drop mobility. In order to repel high-speed water drops, we nanotextured
polymer surfaces with nanowire bundles separated from their neighbors
by microscale void regions, with the nanowires in a bundle separated
from their neighbors by nanoscale void regions. Water drops with speeds
below a critical speed rebound completely. Water drops with speeds
exceeding a critical speed rebound partially, but residual droplets
that begin to be pinned undergo a spontaneous dewetting process and
slide off. The natural oscillations of residual droplets drive this
dewetting process in the interbundle void regions, resulting in a
transition from the sticky Wenzel state to the slippery Cassie state
without external stimuli.