The aggregation behaviour of tetradecyldimethylaminoxide

Abstract

Static and dynamic light scattering, electrical birefringence, kinetic and rheological measurements were carried out on aqueous solutions of the zwitterionic surfactant tetradecyldimethylaminoxide (C₁₄DMAO) up to the liquid crystalline (l. c.) region. In the dilute concentration range the system forms globular micelles up to about 10 mM solutions. For higher concentrations, rodlike aggregates can be detected which increase in size with increasing concentration. At the overlap region of 100 mM solutions the forces between the micelles are repulsive up to the phase boundary and the light scattering decreases. With increasing temperature the system makes a sphere/rod transition which is indicated both by the temperature dependence of light scattering and electric birefringence. The experimental data show that the surfactant behaves like a nonionic system for low temperatures and like an ionic system for high temperatures. Also the cmc value, which is between a purely cationic and a nomonic system, shows the ambivalent nature of the surfactant. The system has no cloud point and forms a nematic phase as the first l. c. phase.