Coupling between Orientational and Translational Order in a Liquid Crystal

A high-resolution measurement of the optical birefringence has been made in 4-cyano-4{'}-octyloxybiphenyl to study in detail the orientational order parameter near the nematicsmectic-A transition. There is no measureable discontinuity in the birefringence, but there is an abrupt change in its temperature coefficient at the transition. Contrary to the general impression obtained from published results, the behavior of the orientational order parameter does not follow the predictions of mean-field molecular and phenomenological theories, with or without fluctuations.