Multimodal particle size measurement using truncated pulsed electro-optic birefringence

Abstract

A pulsed electric field induces transient birefringence in a suspension of anisotropic particles. The rate of decay of the birefringence depends strongly on the particle size via the rotary diffusion coefficient, D, of the particles. A more analytical method has been developed in which values of D, obtained from the initial slope of the post-field decay for a range of applied pulses of the same low electric field strength, but for continuously decreasing pulse durations Theta , are analysed to yield size distributions for the dispersed particles. By adopting a least-squares fitting and smoothing procedure, this electro-optical method is shown to handle arbitrarily multimodal distributions. The method is appraised via regenerated theoretical data for a mixture of submicrometre spheres and for experimental data on suspensions of lozenges of polytetrafluoroethylene and iron oxide spheroids. The method is suitable for submicrometre-sized particles.