Influence of bivalent ions on the low frequency electro-optic response of charged colloids in low electrolyte suspensions

Two low frequency dielectric relaxations are related to the process of surface polarization of charged particles: one, detected in the kHz/MHz frequency domain (αp) and a second one, detected in the domain of particle rotation (αn). The paper presents results concerning the second low frequency relaxation. A parameter is defined (the ratio of the two effects αn/αp), which is representative for the relation of this relaxation to particle surface electric state. The ratio αn/αp remains constant (or varying in narrow limits) with field intensity. The influence of mono- and bivalent (counter) ions on this parameter is followed as a first step to the analysis of the mechanism of the second relaxation. The results show that the only electro-optic parameter which distinguishes the adsorption of bivalent ions on particle surface is the ratio αn/αp. The analysis of the second low frequency relaxation is important for elucidating of various problems: the difference in the electro-optic saturation curves taken at ac and dc pulses; the mobility of condensed ions; the significant discrepancy between the variation of particle polarizability and electrophoretic mobility in numerous cases, etc.