Coupling between nematic and smectic ordering in reentrant nematic systems

Abstract

We present here experimental evidence of the coupling between smectic and nematic ordering in systems exhibiting the reentrant nematic phase. Pressure-temperature diagrams of a large number of systems have been studied. In every case the major axis of the elliptically shaped smectic A-nematic phase boundary is found to be nearly parallel to the nematic-isotropic phase boundary although the slopes vary widely from system to system. Similar correlations are also shown to exist in the temperature-concentration diagram of binary systems. A few representative phase diagrams are presented which illustrate this point.