1. Schematic of liquid droplet residing on solid surface in different situations.

A: Wetting phenomenon on a flat solid surface with contact angle θ. B: Droplet in contact with a rough surface in Wenzel state. C: Droplet in contact with a rough surface in Cassie state. Both states can result in a high apparent contact angle, but the droplet rolls off more easily under Cassie state (indicated by black arrow). For water strider legs, pillars sketched in (B) and (C) represent protruding leg bristles.