A new formula for the dynamic mobility in a concentrated colloid

The dynamic mobility μD is the analogue of the electrophoretic mobility in an alternating electric field. It can be determined for suspensions of arbitrary concentration at MHz frequencies using electroacoustic measurements. A considerable amount of effort has been expended during the last decade in the derivation of theories for the dynamic mobility in concentrated suspensions. The objective has been to come up with a formula that can be used to calculate particle size and zeta potential from dynamic mobility measurements in concentrated suspensions. Some of these theories are based on cell models, others are based on coupled phase models and another involves the use of experimentally determined parameters. In this paper we present a new approach to this problem. We derive a formula that does not involve any ad hoc boundary conditions or adjustable parameters. The formula is compared with experimental measurements, and is used to determine size and zeta potential for a number of concentrated colloids.