Measurements of streaming potential for mica covered by colloid particles

The zeta potentials of natural mica, bare and covered by positively charged latex particles of micrometer size range, were determined by the streaming potential method. Measurements were carried out using the parallel-plate channel formed by clamping together two mica sheets separated by a Teflon spacer. The dependence of streaming potential on surface coverage (Theta) of adsorbed particles was determined for various ionic strengths and particle sizes. The coverage was determined directly by optical and electron microscope counting procedures. It was found that the negative streaming potential for bare mica E-s was significantly increased by the presence of adsorbed particles. The dependence of the reduced streaming potential E-sp/E-s (where E-sp is the zeta potential in the presence of particles) on Theta exhibited an universal behavior being independent of particle size and ionic strength. These experimental data were interpreted in terms of a theoretical model postulating that the streaming potential change was due to flow damping over the interface and by charge transport from the double-layer surrounding adsorbed particles. In contrast with previous approaches no assumption of the slip (shear) plane shift upon particle adsorption was made. By exploiting the experimental results it was suggested that colloid and bioparticle adsorption kinetics can be studied in situ using the streaming potential method.