Regulating Aggregation of Colloidal Particles in an Electro-Osmotic Micropump

TL;DR

This study investigates electro-osmotic aggregation of colloidal particles in microchannels, combining experimental video microscopy and numerical modeling to understand and control clogging and flow reversal in microfluidic systems.

Contribution

It introduces a combined experimental and numerical approach to analyze particle aggregation and flow control in electro-osmotic microchannels, advancing microfluidic pump design.

Findings

Electro-osmotic aggregation causes channel clogging.

Reversal of electric potential can unclog channels.

Square-wave electric potentials enable controlled particle flow.

Abstract

Unrestricted particle transport through microfluidic channels is of paramount importance to a wide range of applications, including lab-on-a-chip devices. In this article, we study using video microscopy the electro-osmotic aggregation of colloidal particles at the opening of a micrometer-sized silica channel in presence of a salt gradient. Particle aggregation eventually leads to clogging of the channel, which may be undone by a time-adjusted reversal of the applied electric potential. We numerically model our system via the Stokes-Poisson-Nernst-Planck equations in a geometry that approximates the real sample. This allows us to identify the transport processes induced by the electric field and salt gradient and to provide evidence that a balance thereof leads to aggregation. We further demonstrate experimentally that a net flow of colloids through the channel may be achieved by applying a square-waveform electric potential with an appropriately tuned duty cycle. Our results serve to guide the design of microfluidic and nanofluidic pumps that allow for controlled particle transport and provide new insights for anti-fouling in ultra-filtration.