Observations of triply reentrant behaviour and a multicritical point in a single component liquid crystal system at high pressure

Abstract

We report here the observation of pressure induced triply reentrant behavior in a single component liquid crystal system, viz., 4-n-decyloxy phenyl-4’-(4’’-nitrobenzoyloxy benzoate. At atmospheric pressure, this compound exhibits the following sequence of transitions on cooling from the isotropic phaie, I-N-Ad-C-C2 but over a relatively narrow pressure range of 1.2-1.38 kbar it exhibits five additional phases in the following sequence, I-N-Ad-Nre-Ad(re)-Nre-A1-C-A2-C2. Here Ad, Al and A2 refer to the different polymorphic forms of the A phase. This remarkable behavior is in agreement with the predictions of the frustrated spin-gas theory. Another interesting' observation was the occurrence of an A1-Nre-Ad multicritical point in the same compound at high pressure. The nature of this multicritical point has been studied in detail. The results lead us to postulate a novel alternative for the predicted A1-Nre-Ad bicritical point in the framework of the mean field theory.