Electric birefringence studies on concentrated aqueous polyoxyethylene surfactant systems

Abstract

Pulsed-electric-field birefringence measurements (Kerr constant, B, and relaxation time, τ) have been made on polyoxyethylene surfactant solutions in the concentration region just prior to the formation of liquid-crystal phases. For solutions in the pre-hexagonal region both B and τ initially increase with temperature and then decrease as the hexagonal phase melts. This is consistent with the presence of interacting rod micelles. For the pre-lamellar region the behaviour is more complex; at high concentration B increases with temperature and concentration, while τ increases with concentration and decreases with temperature. At lower concentrations B changes sign while τ exhibits a maximum and becomes very short. Tentative explanations based on changes in the nature of micellar interactions and a rod/disc shape transition are proposed.