Dynamic Wettability Modulation of Textured, Soft and LIS Interfaces Using Electrowetting

TL;DR

This study uncovers a counterintuitive electrowetting phenomenon where droplets are ejected laterally on textured, lubricant-infused surfaces due to unbalanced electrocapillary forces, enabling new droplet control methods.

Contribution

It reveals the dependence of droplet dynamics on surface topology and wetting state, demonstrating rapid lateral ejection on specific microtextured, lubricant-infused surfaces, which contrasts with traditional spreading behavior.

Findings

Droplets experience lateral motion and detachment on densely textured, lubricant-infused surfaces.

Unbalanced electrocapillary forces cause lateral ejection, not spreading.

Surface topology and wetting state critically influence droplet behavior.

Abstract

Electrowetting on textured and lubricant infused surfaces is conventionally expected to promote enhanced droplet spreading by reducing apparent contact angles. Contrary to this intuition, we report rapid tangential droplet ejection at applied DC voltages on specific microtextured, lubricant infused surfaces. Using high speed imaging and a precisely controlled electrowetting setup, we reveal the dependence of droplet dynamics on surface topology, wetting state, and the presence of a lubricant. On densely textured thick PDMS substrates of post spacing 5 to 10 um in a low hysteresis non-wetting Cassie state, and on all lubricant infused textured surfaces, droplets experience sudden lateral motion and eventual detachment. We attribute this counterintuitive phenomenon to unbalanced electrocapillary forces at the contact line combined with minimal pinning, which allows asymmetries in electric stresses to translate directly into net lateral motion. In contrast, Wenzel state droplets or surfaces with larger texture spacing exhibit conventional spreading with strong adhesion. By capturing the fundamental interplay among electrostatic driving forces, contact line pinning, and interfacial mobility, our results provide a new paradigm for controlled droplet transport and ejection in electrowetting systems mediated by dense micro posts and lubricant induced interfaces.