Zeta-potential measurement using the Smoluchowski equation and the slope of the current–time relationship in electroosmotic flow

Abstract

The ζ-potential of a solid–liquid interface is an important surface characterization quantity for applications ranging from the development of biomedical polymers to the design of microfluidic devices. This study presents a novel experimental technique to measure the ζ-potentials of flat surfaces. This method combines the Smoluchowski equation with the measured slope of current–time relationship in electroosmotic flow. This method is simple and accurate in comparison with the traditional streaming potential and electrophoresis techniques. Using this method the ζ-potentials of glass and poly(dimethylsiloxane) (PDMS) coated surfaces in KCl and LaCl 3 aqueous solutions were measured using several flow channels ranging from 200 to 300 μm in height. The ζ-potential was found to vary from −88 to −66 mV for glass surface and −110 to −68 mV for PDMS surfaces depending on the electrolyte and the ionic concentration. The measured values of the ζ-potential are found to be independent of the channel size and the applied driving voltage and generally are repeatable within ±6%.