Dynamic Electrophoresis in Low Dielectric Fluids

Matt Preston (Advisor: Lee R. White)

It is possible to apply an oscillating electric field in the megahertz frequency range to a colloidal suspension and to measure the phase and magnitude of the dynamic electrophoretic mobility of the particles.  By comparing measurements made on a system with the predictions made by models, it is possible to find the particle size and the zeta potential z of the system.

Approximate analytic solutions have been derived in the cases of thin double layers, thick double layers, and low z.  The primary feature of these solutions is that they allow the size to be determined independently of the zeta potential by measurements on mobility phase, and then allow a determination of zeta potential from mobility magnitude.  Even the most sophisticated of these solutions is not always capable of describing measured data.  The figure below shows mobility phase measurements made at the Lubrizol Corporation on a dilute suspension of carbon black particles in dodecane with a PIBS dispersant, along with a thick double layer and low zeta potential curves.

An exact numerical solution of the governing equations shows that at high zeta potentials, there is a dramatic effect of this value on the mobility phase, but due to the rapid decay of relevant length scales in the frequency regime on interest, the current numerical scheme cannot obtain accurate solutions at high frequencies and for thick double layers.

Our current goal in this area is to create a robust numerical technique that is capable of accurately describing the electrophoretic mobility of suspensions of highly charged particles in low dielectric fluids.