Facile fabrication of superhydrophobic sub-millimetric cone-shape pillars based on a single UV exposure to control drop impact dynamics

When a water drop is impinged upon a superhydrophobic surface with submillimetric surface structures, unconventional impact dynamics such as pancake-like bouncing and asymmetric drop spreading can occur. However, the fabrication of such surface structures often requires an unconventional fabrication approach, which is either time-consuming or costly. In this study, we propose a simple lithography-based approach to manufacture submillimetric cone-shaped pillars over a large area by taking advantage of a unique optical property of hydrogels: a change of refractive index after UV-curing. With an additional hydrophobic nanoparticle coating, we demonstrate that such structures can be used to reduce the contact time during drop impact and induce a drop rotation during rebound. Moreover, the flexibility of hydrogels enables the transfer of surface structures to non-planar substrates.