Molecular orientational correlations in isotropic phases of nematogenic and smectogenic compounds

We report on the pretransitional behaviour in isotropic phases of compounds belonging to chemical series such that the transition temperatures T N1 and TNA (I = isotropic, N = nematic, A = smectic A) may be brought close together, sometimes even to give a single T 1A transition. The departure from mean-field behaviour is interpreted in terms of a coupling between the fluctuations of the translational and orientational order.