Low-frequency dielectric response of charged oblate spheroidal particles immersed in an electrolyte

We studied the low-frequency polarization response of an oblate spheroidal particle with surface charge immersed in an electrolyte. Because the charged spheroid attracts counterions which form an electric double layer around the particle, the dielectric response involves an interplay between the motion of these counterions and the spheroidal shape of the particle. For two different counterion distributions in the thin electric double-layer limit, we obtained analytic expressions for the polarization coefficients to the first nontrivial order in frequency. We find that the polarization response normal to the symmetry axis depends on the total amount of charge carried by the oblate spheroid, while that parallel to the symmetry axis is suppressed when there is less charge on the edge of the spheroid. We then show that a dilute suspension of charged particles has an enhancement in the low-frequency dielectric response which is suppressed by high ion concentrations in the electrolyte. Both higher aspect ratios and smaller sizes of the spheroids lead to a stronger dielectric enhancement. The characteristic frequency associated with the dielectric enhancement scales inversely with the particle size, and it has a weak dependence on the shape of spheroid.