Fig. 3.

Writing and erasing patterns. (A) A jet of water has been used to create letter-shaped regions of Wenzel and nano-Cassie state in the plastrons of single-level (1-tier) and two-level (2-tier) topography surfaces, respectively. The escaping air pushed aside by the jet has formed into macroscopic bubbles that act as gas reservoirs (indicated by arrows in the figure). (B) Water has been drained from the container. The sample with single-level topography has small droplets where the letters have been, whereas the sample with hierarchical topography has emerged from the water completely dry. (C) Demonstrating the reverse transition: a small region of micro-Cassie state is created by suction inside a larger region of nano-Cassie state (created by a jet of water). The inset is a photograph taken with a camera. Scale bar is 40 μm. (D) The middle one of the 5 nano-Cassie dots is repeatedly erased (returned to micro-Cassie state) and rewritten. Scale bar is 4 mm.