Uniaxial and Biaxial Nematic Phases in Sodium Dodecyl Sulphate - Decanol - D2O Mixtures. An Optical Conoscopy Study

Abstract

The system SDS/decanol/water is investigated by polarized optical microscopy. A reported biaxial island is here confirmed by conoscopy, in the temperature interval 20°C to 26°C. Coexistence regions of the two uniaxial nematic phases (discotic ND + cylindrical NC) are also confirmed, in different temperature intervals. While the biaxial phase is stable for at least 10 hours, in a reproducible way, along the same time the coexistence region evolves with time, and drops of the discotic phase grow immersed in a NC matrix. Results are explained in terms of recent theories dealing with stabilization of mixtures of cylinders and discs.