Kinetics of flowing dispersions. Part 11.—Dielectric constants of streaming suspensions of spheroids

Abstract

The variations in dielectric constant of a dilute suspension of rigid spheroids in a dielectric fluid in a combined uniform shear and electric field have been examined. Electrical polarization of the particles perturbs the local electric field thus causing additional electrical displacements which, when compared with the electrical displacement of the pure medium, makes it possible to calculate the dielectric constant of the suspension as a function of particle orientation.

By combining the dielectric theory with that for the distribution of particle orientations, dielectric constants in both the transient and steady states are evaluated. Since the particle rotations, and hence the orientation distributions, depend on the relative magnitudes of electrical to hydrodynamic torques acting on the particles, the dielectric constant depends on the intensity of electric field, i.e., the suspensions show non-linear dielectric and anisotropic behaviour. It is shown that the dielectric constant oscillates when shear is applied, but that for various reasons which are considered the oscillations are damped in practical suspensions and eventually a steady state value is attained.

Preliminary measurements with metal coated fibres confirm this general pattern of behaviour.