Colloidal electro-phoresis in the presence of symmetric and asymmetric electro-osmotic flow

TL;DR

This study uses advanced light scattering techniques to analyze colloidal electro-phoresis and electro-osmotic flow, providing detailed insights into particle and solvent dynamics in microfluidic environments.

Contribution

It introduces a novel measurement approach combining super-heterodyne light scattering with integral mode analysis to simultaneously determine electro-phoretic and electro-osmotic mobilities.

Findings

Successful measurement of particle velocity distribution across the cell

Demonstration of asymmetric electro-osmotic flow measurement

Potential for internal calibration in microfluidic electro-kinetic studies

Abstract

We characterize the electro-phoretic motion of charged sphere suspensions in the presence of substantial electro-osmotic flow using a recently introduced small angle super-heterodyne dynamic light scattering instrument (ISASH-LDV). Operation in integral mode gives access to the particle velocity distribution over the complete cell cross-section. Obtained Doppler spectra are evaluated for electro-phoretic mobility, wall electro-osmotic mobility and particle diffusion coefficient. Simultaneous measurements of differing electro-osmotic mobilities leading to asymmetric solvent flow are demonstrated in a custom made electro-kinetic cell fitting standard microscopy slides as exchangeable sidewalls. Scope and range of our approach are discussed demonstrating the possibility of an internal calibration standard and using the simultaneously measured electro-kinetic mobilities in the interpretation of microfluidic pumping experiment involving an inhomogeneous electric field and a complex solvent flow pattern.