Characterisation of Colloids by Electric Birefringence.

Electro optic methods are becoming an extremely popular means of characterising macromolecules and colloidal particles in suspension due to the rapid nature by which measurements can be made. This study describes the construction of an apparatus capable of measuring transient electric birefringence which is induced by the application of a pulsed A.C. field. The following industrially important colloidal materials are considered in this study: Polytetrafluoroethane (PTFE), Kaolin, Montmorillonite, Vermiculite, Anatase and Rutile; the latter two materials being two polymorphs of Titanium Dioxide. From the obtained transient data values of the rotary diffusion coefficients for the dispersed particles may be obtained which are related to the major particle dimension. A description of the method used to generate a two parameter size distribution is given along with the theory required to calculate the particles’ optical and electrical parameters. The frequency dispersion of birefringence has also been measured and used to calculate values of the diffusion coefficient utilising the theory of Thurston and Bowling" Comparisons have been made with the field free data obtained from transient decay.