Transient behaviour of streaming potential development in microfluidic channels

Abstract

Electrokinetic (EK) flow is a flow of an electrolyte in narrow capillaries driven by the combined influence of electric field and pressure, is of significant interest in microfluidic devices. Pressure-driven-flow in a microchannel with charged solid surfaces induces streaming current, streaming potential and is a sub-group of EK flow. In this paper a transient numerical simulation of ion transport leading to the development of a streaming potential across a finite length cylindrical microchannel is considered. The problem is analyzed through the coupling of fluid dynamics, electrical field and free charge density (ion concentration) distribution. The solution based on finite element analysis shows the transient development of ionic fluxes, currents, and the streaming potential across the channel. The simulation results show that the streaming potential across the channel is predominantly set up at the timescale of the developing convective transport, while the equilibrium ion concentrations are developed over a considerably longer duration, typically conforming to the diffusional time scale.