Field-induced clearing in sphere-sphere and rod-sphere binary mixtures of charged colloidal particles

Binary mixtures of larger and smaller colloids having charges of equal sign display unusual response to low-frequency electric fields. We show here that the previously reported negative torque acting on rodlike particles when in presence of a sea of smaller particles is accompanied by a field-induced clearing of the suspension. Measurements of transmitted intensity performed on mixtures of large (dilute) and small (semidilute) spherical particles indicate that such a clearing effect is universal and due to an anisotropic E2 -dependent redistribution of the small spheres around the large ones. We interpret this behavior as resulting from O(E2) electro-osmotic flows whose magnitude is greatly enhanced by the presence of the small particles.