Induced-charge electro-osmosis around metal and Janus spheres in water: Patterns of flow and breaking symmetries

TL;DR

This study experimentally characterizes the flow patterns of induced-charge electro-osmosis around metallic and Janus spheres in water, revealing symmetry breaking, flow irregularities at high fields, and specific decay behaviors.

Contribution

It provides new experimental insights into ICEO flow patterns around different sphere types and under varying electric field conditions.

Findings

Quadrupolar flows with asymmetric velocities observed around metallic spheres.

Flow irregularities and vortices appear at high electric fields.

Far-field flow decay follows an r-3 power law.

Abstract

We establish experimentally the flow patterns of induced-charge electro-osmosis (ICEO) around immobilized metallic spheres in aqueous electrolyte. The AC field modifies local electrolyte concentration and causes quadrupolar flows with inward velocities being smaller than the outward ones. At high fields, the flow becomes irregular, with vortices smaller than the size of the sphere. Janus metallo-dielectric spheres create dipolar flows and pump the fluid from the dielectric toward the metallic part. The experimentally determined far-field flows decay with the distance as r-3.