Conductivity of a concentrated colloidal suspension of spherical particles in an alternating electric field

In this paper the complex (ac) conductivity of a concentrated suspension of spherical colloidal particles is considered in the light of a cell model. Previous works have dealt with the study of the conductivity of a concentrated colloidal suspension for general conditions, including arbitrary zeta potential, particle volume fraction, double-layer thickness, and ionic properties of the solution, but only the static case (dc electric fields) was addressed. In this contribution, the complex conductivity of a concentrated suspension is studied for the same general conditions as in the static case. The numerical data presented in this paper cover a wide range of typical situations including the special case of overlap of double layers of adjacent particles. Like in the static case, the treatment is based on the use of a cell model to account for hydrodynamic and electrical interactions between particles. The two relaxation processes occurring in the frequency range of interest (alpha and Maxwell-Wagner- O’Konski) are analyzed for different values of the ionic strength, particle radius, zeta potential and particle concentration. Roughly speaking, these two relaxations tend to overlap in frequency as the volume fraction of solids increases for otherwise general conditions; in such cases, no clear distinction can be established between them. On the other hand, considerable attention has also been devoted to the numerical analysis of the complex conductivity for those special situations where overlapping between double layers is nonnegligible. Finally, a comparison between theoretical predictions and some experimental results is shown, revealing a general good agreement.Financial support for this work by MCyT, Spain (Project MAT 2004-00866), and FEDER funds is gratefully acknowledged