Reversible switching between superhydrophobic states on a hierarchically structured surface

TLDR

Superhydrophobicity, exemplified by self‑cleaning plant leaves and underwater‑breathing insect surfaces, relies on the Cassie wetting state where trapped air prevents wetting, but pressure can irreversibly transition to the Wenzel state, compromising non‑wetting functionality. The study introduces a reversible, localized, instantaneous transition between two Cassie states on a dual‑scale superhydrophobic surface to enable writing, erasing, rewriting, and storing optically displayed information. This transition is achieved by a two‑level (dual‑scale) topography that traps air at different length scales, allowing controlled switching between Cassie states. The dual‑scale surface successfully demonstrates reversible switching, enabling rapid, localized manipulation of optical information stored in plastrons.

Abstract

Nature offers exciting examples for functional wetting properties based on superhydrophobicity, such as the self-cleaning surfaces on plant leaves and trapped air on immersed insect surfaces allowing underwater breathing. They inspire biomimetic approaches in science and technology. Superhydrophobicity relies on the Cassie wetting state where air is trapped within the surface topography. Pressure can trigger an irreversible transition from the Cassie state to the Wenzel state with no trapped air--this transition is usually detrimental for nonwetting functionality and is to be avoided. Here we present a new type of reversible, localized and instantaneous transition between two Cassie wetting states, enabled by two-level (dual-scale) topography of a superhydrophobic surface, that allows writing, erasing, rewriting and storing of optically displayed information in plastrons related to different length scales.