Dielectric behaviour of suspensions of non-spherical colloidal particles

Abstract

In this paper, we explore the possibility of using low-frequency dielectric dispersion (LFDD) measurements in suspensions of non-spherical particles. We present results on the LFDD of clay suspensions, with laminar, non-homogeneously charged particles, and of monodisperse spheroids of haematite (iron III oxide). The heterogeneous surface of the clay (montmorillonite) is manifested in dielectric measurements, since two relaxation times (one associated with faces and the other with edges) can be separated. Furthermore, it is found that the latter is absent at pH 7, thereby directly confirming that the edges of the clay platelets are uncharged at such pH. Experiments conducted with monodisperse haematite spheroids allow a preliminary check of existing theories for the LFDD in such geometries. Comparison of the zeta potentials deduced from dielectric and electrophoresis measurements confirm the validity of the models, and suggest that haematite could be a model spheroidal colloid, to which standard electrokinetic theories are applicable.