Influence of material transition and interfacial area changes on flow and concentration in electro-osmotic flows

[Display omitted] ► Combined material and geometrical transition in electrokinetic flows was studied. ► Material and geometrical transition resulted in dispersion and reduced flow rates. ► Effect of only geometrical transition on species was less compared to material transition. ► Sample dispersion was quantified with standard metrics. ► Correlations were developed to estimate the reduction in flow rates. This paper presents a numerical study to investigate the effect of geometrical and material transition on the flow and progression of a sample plug in electrokinetic flows. Three cases were investigated: (a) effect of sudden cross-sectional area change (geometrical transition or mismatch) at the interface, (b) effect of only material transition (i.e. varying ζ-potential), and (c) effect of combined material transition and cross-sectional area change at the interface. The geometric transition was quantified based on the ratio of reduced flow area A2 at the mismatch plane to the original cross-sectional area A1. Multiple simulations were performed for varying degrees of area reduction i.e. 0–75% reduction in the available flow area, and the effect of dispersion on the sample plug was quantified by standard metrics. Simulations showed that a 13% combined material and geometrical transition can be tolerated without significant loss of sample resolution. A 6.54% reduction in the flow rates was found between 0% and 75% combined material and geometrical transition.