ζ potential measurement by means of the plane interface technique

Abstract

The ζ potential of quartz and sapphire plates in contact with aqueous solutions was measured by means of the plane interface technique, which involves establishing the liquid flow velocity—depth profile using reference (polystyrene latex) particles. The electroosmotic velocity obtained by extrapolation of the velocity profile to the cell wall permits calculation of the ζ potential of the cell wall—solution interface. The plane interface technique was also used to obtain the ζ potential at aqueous sodium dodecyl sulfate (SDS) solution surfaces with an open cell in which the upper boundary consists of an air—solution interface and the lower boundary, a quartz—solution interface. It was essential to eliminate the meniscus in the open cell to obtain normal velocity profiles. The ζ potential of the aqueous SDS solution surface paralleled the Stern potential, calculated from the surface tension—SDS concentration data by use of Gibbs adsorption equation and Gouy-Chapman theory, though the former was larger in magnitude than the latter.