Electric Birefringence Measurements in Micellar and Colloidal Solutions

It is shown that anisometric structures in solutions of rodlike micelles, clay particles or polyelectrolytes can be oriented by electric fields. Both AC and DC fields can be used for the measurements. Results on four different systems are reported and compared. The four different systems are micellar solutions of Tetradecyldimethylaminoxide and Hexadecyloctyldimethylammoniumbromide, and polyelectrolyte solutions of Poly(sodium p-styrenesulfonate) and Saponit On the basis of the results different situations in the behaviour of the systems can be distinguished. In the dilute concentration range for all systems, information about the size, the size distribution, the induced dipole mechanism, and the optical and electrical anisotropy of the particles can be obtained. At the overlap concentration of the particles the behaviour of the charged systems differs dramatically from the uncharged systems. A second effect with opposite sign from the first one appears. This effect is referred to as the anomaly of the electric birefringence. Hence many differences between the uncharged Tetradecylaminoxide and the other three systems become apparent. It is concluded that particles orient in the anomaly region perpendicular to the electric field. At higher concentrations the behaviour is normal again and a network structure is formed, which can also be aligned in the electric field. The frequency and time dependent measurements reveal different concentration regions, which are characterized by critical concentrations, which depend on the axial ratio of the particles.