An analogy between biaxial crystal and biaxial nematic lyotropic phase

The biaxial nematic phase (N-B), the intermediate phase between the discotic nematic (N-D) and calamitic (N-C) nematic phases, is investigated from refractive index data in a potassium laurate-decanol-D2O mixture. Temperature dependence of the angle (2V) between two optic axes of this N-B phase is obtained with the use of a procedure which is analogous to that used in a biaxial crystal. In this context, biaxial positive (N-B(+)) and biaxial negative (N-B(-)) nematic phases are optically characterized. A transition from a N-B(+) to a N-B(-) configuration is found at this point where the corresponding angle reaches the maximum value. In this case, the micelle looses its predominant discotic shape to acquire a predominant calamitic shape. (C) 2010 Elsevier B.V. All rights reserved.