Conoscopic image of a biaxial negative nematic phase in a potassium laurate-decanol-D2O mixture

The discotic nematic (ND)-biaxial nematic (NB)-calamitic nematic (NC) phase transitions are studied in a potassium laurate-decanol-D2O mixture by optical conoscopy. The ND+ (NC−) phase is uniaxial positive (negative) as expected. Nevertheless, inside the biaxial range, beyond the known biaxial positive (NB+) nematic phase we have also found a biaxial negative (NB−) nematic phase optically characterized through conoscopic images. A transition point from a NB+ to a NB− configuration is determined and discussed in this work.