Dielectrophoresis and impedance studies of dielectric particles suspended in liquids

Bahaj, Abubakr Salem (1982) Dielectrophoresis and impedance studies of dielectric particles suspended in liquids. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This thesis reports on a study of dielectrophoresis (the motion of dielectric particles due to polarization in a non-uniform electric field) and of the impedance characteristics of dielectric particles in various liquids. In order to determine the experimental approach suited to dielectrophoresis, a variety of techniques were investigated. These included Pohl's yield method, a particle velocity method, and a method involving the trapping of lone bubbles by balancing the dielectrophoretic force against buoyancy. The latter method was found to be the most amenable to dielectrophoresis. A ring-disc electrode system was initially used to establish a cusped electric field to produce the trapping effect. Conventionally, electrodes of the order of a few millimetres are used resulting in a high potential difference being required to trap the bubbles. By scaling down the electrodes it was possible to confine small particles in a position of stable equilibrium at potential differences of only a few volts. As only low voltages were required, variable frequency measurements in aqueous media were made and problems due to Joule heating and turbulence became negligible. The frequency response of lone microscopic divinyl benzene (DVB) particles and impedance characteristics of populations of these particles were determined in electrolyte solutions at various concentrations. The resultant excess polarization spectra of the lone particles was attributed to relaxation effects at the particle/liquid interface. These relaxation effects were also thought to be responsible for the dispersion in the impedance of the particle population.

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