  Self-cleaning surfaces often make use of superhydrophobic coatings that repel
water. Here, we report a hydrophobic Si nanospring surface, that effectively
suppresses wetting by repelling water droplets. We investigated the dynamic
response of Si nanospring arrays fabricated by glancing angle deposition. The
vertical standing nanospring arrays were approximately 250 nm tall and 60 nm
apart, which allowed the droplets to rebound within a few milliseconds after
contact. Amazingly, the morphology of the nanostructures influences the impact
dynamics. The rebound time and coefficient of restitution were also found to be
higher for Si nanosprings than vertical SI columns. It has been proposed that
the restoring force of the Si nanosprings may be responsible for the water
droplet rebound and can be explained by considering the droplet/nanospring
surface as a coupled spring system. These nanospring surfaces may find
applications in self-cleaning windows, liquid-repellent exteriors, glass panels
of solar cells, and antifouling agents for roof tiling.
