Iridescent colours in surfactant solutions

Abstract

We report on a surfactant system which is in the liquid crystalline lamellar state and where the spacings between the lamellar layers can be expanded to several thousand Å. As a consequence the solutions show bright iridescent colours when they are illuminated with w hite light against a dark background. The system consists of the zwitterionic surfactant tetradecyldimethylaminoxide in the presence of some cosurfactant and small amounts of hydrocarbon.

The system can be swollen with water up to a volume fraction of 0.99 without loss of the liquid crystallinity. The systems are thermodynamically stable and the iridescent colours reappear after the order has been destroyed by shaking the solutions. It is believed that the large spacings are due to electrostatic forces between the surfactant layers. The charges on the layers are due to protonation of the aminoxide groups by water. The existence region of the iridescent phase as a function of surfactant, hydrocarbon and cosurfactant is reported. The spacings for the phases were determined from light transmission and light scattering measurements.