FREQUENCY-DEPENDENCE OF THE DIELECTRIC AND ELECTROOPTIC RESPONSE IN SUSPENSIONS OF CHARGED ROD-LIKE COLLOIDAL PARTICLES

We have performed an experimental investigation on the electrokinetic properties of charged rod-like fluorinated latex colloids. Systematic measurements of electrophoretic mobility, dielectric constant and elec tric birefringence have been performed as a function of the concentrat ion of added nonionic surfactant and salt. In the investigated range o f parameters, the zeta potential is a strongly decreasing function of the concentration of nonionic surfactant, while it is basically indepe ndent from ionic strength. We have obtained the frequency dependence o f dielectric constant and Kerr constant as a function of zeta-potentia l and ionic strength. We observe the transition from a low frequency b ehavior, where both the dielectric constant and the Kerr constant are enhanced by the presence of the double layer, to a high frequency beha vior, where both quantities take the value expected for unchanged part icles in an insulating medium. The shape of the frequency dispersion o f the Kerr constant coincides with that of the dielectric constant, bu t the cut-off frequencies are the same only when the zeta-potential of the particles is low. (C) 1998 Elsevier Science B.V. All rights reser ved.