New lyotropic nematic liquid crystals

Abstract

Studies of binary perfluorosurfactant/water systems are presented. The methods applied were 2H- and 19F-NMR spectroscopy, polarizing microscopy and viscosimetry. It is shown that several perfluorosurfactant/water systems form lyotropic nematic phases. The surfactants are rubidium, ammonium and tetramethylammonium salts of perfluorocarboxylic acids. The phase behaviour of two systems was investigated. The system C8F17COONH4/D2O forms a nematic and a lamellar phase. The micelles in the isotropic solution seem to be spherical up to high surfactant concentrations. There is evidence for a transition to disc micelles near the isotropic/nematic phase transition. The nematic phase which consists of disc micelles aligns with its director parallel to an applied magnetic field. In the system C8F17COON(CH3)4/D2O, the isotropic solution is viscoelastic what is probably due to rod-shaped micelles. With increasing concentration they at first grow, then shrink. The nematic phase is composed of disc micelles which also align parallel to an applied magnetic field. The alignment is not lost during the phase transition from the nematic phase to the second liquid crystalline phase, which is stable at lower temperatures.