Pressure Studies on 7 <i>S</i>5, 8 <i>S</i>5 and Their Mixtures

Abstract

Abstract Pressure studies have been taken up on heptyloxy-p'-pentylphenylthiobenzoate ( S5), octyloxy-p'-pentylphenyl thiobenzoate ( S5) and their mixtures. It is observed that the range of the smectic A phase increases with increasing pressure with an accompanying decrease in the smectic C range. Thus, although two kinds of triple points, viz., crystal-smectic C nematic and smectic (mosaic)–smectic C–smectic A have been observed in the P–T diagrams of S5 and S5, the NAC point observed in the temperature-concentration diagram of binary mixtures of S5 and S5 at the 42.5% concentration of S5 could not be observed in the P–T diagram of either the pure compounds or the mixtures, whose concentrations were chosen on either side of the critical 42.5% concentration. These studies also show that pressure has the effect of increasing the stability of the monolayer smectic A in contrast to the case of the bilayer smectic A wherein pressure destabilizes the layer causing the nematic phase to reenter.