Dynamic polarisation of a charged colloid in an oscillating electric field

Abstract

The dynamical behaviour of a charged colloid in an electrolyte solution is studied using direct numerical simulations via the smoothed profile method. We calculated the complex polarisability of a single colloidal particle under an AC electric field, where the polarisation is affected by the zeta potential of the colloid, the diffusion constant of the ions, the thickness of the electric double layer, and the frequency of the AC field. Two dynamically distinct regimes were observed depending on the applied frequency, specifically, on whether it is faster or slower than the ionic diffusion rate over the colloidal size. The present results showed very good agreements with the Maxwell–Wagner–O’Konski (MWO) theory and standard electrokinetic theories for all frequency regimes provided the zeta potential is low. For highly charged particles with high zeta potential, the standard electrokinetic models agree well with the present results for all frequency regimes. In the intermediate regimes, differences are observed with the MWO theory, as it ignores the deformation of the electric double layer.