Ion size effects on the electrokinetics of salt-free concentrated suspensions in ac fields

TL;DR

This paper investigates how finite ion size influences the electrokinetic behavior of salt-free colloidal suspensions under oscillating electric fields, revealing significant effects on mobility and dielectric response.

Contribution

It introduces the importance of ion size effects in electrokinetic models, especially for high particle charges, enhancing understanding of salt-free suspension dynamics.

Findings

Ion size increases the mobility increment at certain frequencies.

Enhanced Maxwell-Wagner-O'Konski process with higher particle charges.

Ion size effects are crucial for accurate electrokinetic modeling.

Abstract

We analyze the influence of finite ion size effects in the response of a salt-free concentrated suspension of spherical particles to an oscillating electric field. Salt-free suspensions are just composed of charged colloidal particles and the added counterions released by the particles to the solution, that counterbalance their surface charge. In the frequency domain, we study the dynamic electrophoretic mobility of the particles and the dielectric response of the suspension. We find that the Maxwell-Wagner-O'Konski process associated with the counterions condensation layer, is enhanced for moderate to high particle charges, yielding an increment of the mobility for such frequencies. We also find that the increment of the mobility grows with ion size and particle charge. All these facts show the importance of including ion size effects in any extension attempting to improve standard electrokinetic models.