Electro-osmosis on anisotropic super-hydrophobic surfaces

TL;DR

This paper presents a theoretical framework for electro-osmotic flow on striped super-hydrophobic surfaces, revealing how slip length and surface charge influence flow behavior and enabling design strategies for microfluidic devices.

Contribution

It introduces a general theoretical description linking electro-osmotic mobility to slip-length tensors on anisotropic super-hydrophobic surfaces, highlighting novel flow control mechanisms.

Findings

Flow can be amplified by charged slip regions.

Flow reversal occurs with opposite charges on gas and solid regions.

Strategies for microfluidic mixing are proposed.

Abstract

We give a general theoretical description of electro-osmotic flow at striped super-hydrophobic surfaces in a thin double layer limit, and derive a relation between the electro-osmotic mobility and hydrodynamic slip-length tensors. Our analysis demonstrates that electro-osmotic flow shows a very rich behavior controlled by slip length and charge at the gas sectors. In case of uncharged liquid-gas interface, the flow is the same or inhibited relative to flow in homogeneous channel with zero interfacial slip. By contrast, it can be amplified by several orders of magnitude provided slip regions are uniformly charged. When gas and solid regions are oppositely charged, we predict a flow reversal, which suggests a possibility of huge electro-osmotic slip even for electro-neutral surfaces. On the basis of these observations we suggest strategies for practical microfluidic mixing devices. These results provide a framework for the rational design of super-hydrophobic surfaces.