Diverging electrophoretic and dynamic mobility of model silica colloids at low ionic strength in ethanol

Abstract

Electroacoustics and laser Doppler electrophoresis were employed to measure the mobility of surface-modified silica colloids in ethanol as a function of the ionic strength. Sufficiently low volume fractions were chosen to exclude effects of interparticle interactions. At high ionic strength, the electrophoretic mobility μe is equal to the (electroacoustic) dynamic mobility μd at 3.3MHz. However, the ratio μd / μe increases significantly to ~5 at low ionic strength. This increase may be related to the porous outer layer of the surface-modified silica spheres.