Abstract
The phase diagram of the sodium dodecylsulphate/decanol/water system is studied by2H NMR spectroscopy in the range between the calamitic nematic (N+ C) and discotic nematic (N− D) phases. In this narrow range a nematic biaxial phase (NBX) is observed. The phase transitions between the nematic phases are all of first order. The shape of the surfactant aggregates in the nematic phases varies with composition and temperature.