Electrokinetic Effect on Flow of an Aqueous Solution Through a Microchannel
In this paper, the streaming potential technique is utilized to measure the z-potential of an aqueous solution through a microchannel. A flow cell made of a parallel-plate microchannel is devised to conduct the streaming potential measurements. Particular efforts are made to characterize the well-recognized effect of surface conductance on the measured z-potential and to quantify its role in the electrokinetic phenomenon. The z-potential and the surface conductivity gs at the glass-water interface are determined simultaneously from the streaming potential equation in which the surface conductance is taken into account. A series of measured streaming potential data for the parallel-plate microchannels of different gap sizes is acquired and used to fit the streaming potential equation. This method is then applied to study the effects of surface conductance and an electrolyte on the measured z-potential at the solid-liquid interface. The detailed experimental results show that the surface conductance has a dominant effect and that neglect of this effect leads to an unacceptable underestimation of the z-potential.