The Kerr effect in aqueous dispersions of anisotropic and electrically charged latex particles

Static and dynamic electric birefringence measurements are performed on dispersions of electrically charged fluorinated latex spheres. It is shown that the Kerr constant is made up of three contributions: the first depends on the intrinsic and form anisotropy of the particle; the second arises from the presence of a slowly fluctuating electric dipole which should be originated by the statistics of the surface charge distribution, and the third is connected with the cloud of dissociated counter-ions. This latter contribution shows a non-Lorentzian frequency dispersion, and its amplitude is strongly dependent on the particle concentration and on the ionic strength.