Regulating the aggregation of colloidal particles in an electro-osmotic micropump.

Zhu Zhang,Sanli Faez,Joost De Graaf

doi:10.1039/d0sm01084g

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 via video microscopy the electro-osmotic aggregation of colloidal particles at the opening of a micrometer-sized silica channel in the 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.

Highlights

Micropores and microporous structures are omnipresent building blocks of applied fluid mechanics and systems for industrial fluid processing.[1]
We study via video microscopy the electro-osmotic aggregation of colloidal particles at the opening of a micrometer-sized silica channel in the presence of a salt gradient
Under the application of a DC electric field, the aggregation of colloidal particles (CPs) at the pore opening occurred, which led to the clogging of the channel

Summary

Introduction

Micropores and microporous structures are omnipresent building blocks of applied fluid mechanics and systems for industrial fluid processing.[1]. We have investigated the underlying physical processes to this phenomenon numerically by solving for the fluid flow, electric field, and salt concentration profiles in a representative geometry, as specified by the Stokes–Poisson–Nernst–Planck (SPNP) equations. Our model shows that aggregation results from a balance between fluid advection and particle electro-phoresis, both of which are modulated strongly by the presence of a salt gradient. This balance leads to fluid vortices forming at the channel opening, which are representative of the flow patterns observed in the experiment and which initiate the accumulation of CPs

Methods

Results

Discussion

Conclusion