EPR study of molecular ordering in liquid crystal: NOBA

The molecular ordering in the nematic and smectic-C phases of the liquid crystal p-n-nonyloxy benzoic acid (NOBA) is investigated. The phase transition from isotropic to nematic phase is of first order. In the nematic phase over a wide range of temperatures the order parameter remained constant. In the low temperature nematic phase a possible mechanism namely polymerisation involving hydrogen bonds is suggested. The apparent fall in the order parameter at nematic to smectic-C tramition is attributed to the tilt angle in the smectic-C phase.