Uniaxial to biaxial nematic phase transition in a bent-core thermotropic liquid crystal by polarising microscopy

Polarising optical microscopy (POM) shows evidence for a reversible uniaxial nematic (N-U) to biaxial nematic (N-B) phase transition in a quiescent melt of bent-core mesogens (BCM). A second superimposed Schlieren texture, attributed to a second director field, grows into the NU phase on lowering the temperature and disappears again on heating, indicating a fully reversible N-B to NU phase transition. This POM result together with recent X-ray data provides a new signature for the N-B phase in this class of BCMs, and offers a new method for assessment of new biaxial nematic phases.