Berlin 2008 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 20: POSTERS Driven Soft Matter
CPP 20.6: Poster
Wednesday, February 27, 2008, 16:00–18:30, Poster A
Salt concentration and particle density dependence of electrophoretic mobilities of spherical colloids in aqueous suspension — •Tetyana Köller1, Holger Reiber1, Thomas Palberg1, and Felix Carrique2 — 1Institut für Physik, Johannes Gutenberg Universitaet, 55099 Mainz, Germany — 2Departamento de Fisica Aplicada 1, Universidad de Málage, Campus de Teatinos, 29071 Málaga, Spain
Using Laser Doppler Velocimetry in the super-heterodyne mode, we conducted a systematic study of the electrophoretic mobility of dispersions of small silica spheres (a=18nm) suspended in water at different salinity and particle concentration. The concentration of NaCl was varied from 40μM up to 16mM, while the particle concentrations were varied between 4,2x10^18 m^-3 and 2,1x10^20 m^-3. We find a decrease of mobility with increasing salt concentrations and an increase with increased particle number densities. The latter observation is not backed by the standard cell model of electrophoresis with Shilov-Zharkikh boundary conditions. Rather, if the experimental data are interpreted within that model an unexpected change of the zeta potential at constant added salt concentration results. Interestingly, all experimental data collapse on a single master curve, if plotted versus the ratio C* of particle counter ions to added salt ions. We obtain a logarithmic increase of mobility for C*<1 and a plateau for C*>1. This may indicate a change of the Stern layer structure not yet included in the theoretical model.