Properties and electrokinetic behavior of non-dilute colloidal suspensions

Abstract

This paper is a critical review of how the fluid properties (e.g., density, viscosity, conductivity, and permittivity) and behaviors (e.g., electrophoretic motion, electrokinetic aggregation, chaining, and instabilities) depend on colloid volume fraction. The review focuses on electrokinetic flows in aqueous solutions with suspensions on the order of a few percent that are not considered concentrated, yet may exhibit several behaviors distinct from dilute systems such as non-linear dependence on the particle volume fraction and unexpected behavior such as chaining, aggregation, and instabilities. This non-dilute regime is applicable to a variety of emerging applications such as field induced pattern formations in colloidal dispersions, electrophoretic deposition of colloidal films, nanofluid based thermal management, micron resolution particle image velocimetry, and field induced separations in lab-on-a-chip devices. These applications are often treated as dilute when in fact they may contain considerable volume fractions of particles with significant variations in the particle mobility, fluid electrical conductivity and permittivity, as well as the fluid behavior. Original results on electric field induced particle chaining and aggregation as well as fluid instabilities that may develop due to variations in conductivity and permittivity fields are briefly presented.