Electric birefringence study of the dielectric properties of anisotropic and electrically charged latex particles

Static and dynamic electric birefringence measurements are performed on aqueous dispersions of electrically charged fluorinated latex particles having an almost spherical shape. The Kerr constant is nonzero because of the intrinsic and form anisotropy of the particles, and is considerably enhanced at low frequencies by a contribution due to the cloud of dissociated counterions. We discuss in detail this effect which shows a non-Lorentzian frequency dispersion, and an amplitude strongly dependent on the particle concentration and on the ionic strength. The data are interpreted by making a connection with the theory of the dielectric constant of polyelectrolyte solutions