Formation of a colloidal band via pH‐dependent electrokinetics

Abstract

Electroosmosis on nonuniformly charged surfaces often gives rise to intriguing flow behaviors, which can be utilized in applications such as mixing processes and designing micromotors. Here, we demonstrate nonuniform electroosmosis induced by electrochemical reactions. Water electrolysis creates pH gradients near the electrodes that cause a spatiotemporal change in the wall zeta potential, leading to nonuniform electroosmosis. Such nonuniform EOFs induce multiple vortices, which promote the continuous accumulation of particles that subsequently form a colloidal band. The band develops vertically into a “wall” of particles that spans from the bottom to the top surface of the chamber. Such a flow‐driven colloidal band can be potentially used in colloidal self‐assembly and separation processes irrespective of the particle surface properties. For instance, we demonstrate these vortices can promote rapid segregation of soft colloids such as oil droplets and fat globules.

Long-range transport and directed assembly of charged colloids under aperiodic electrodiffusiophoresis

“…Recent experimental observations highlight the potential of coupling electric fields with induced gradients of electroactive species to control the assembly and transport of charged particles. 31,[37][38][39] In a recent work, we confirmed that electrodiffusiophoresis (EDP)-phoretic motion under diffusiophoresis and electrophoresis-was the mechanism responsible for the focusing and levitation of charged particles under uniform dc fields. 40 With the aid of confocal microscopy and ratiometric analysis, we observed that the passage of current through water induces significant pH gradients.…”