Pressure studies on 7S5, 8S5 and their mixtures

Abstract

Pressure studies have been taken up on heptyloxy-p'-pentylphenylthiobenzoate , octyloxy-p'-pentylphenyl thiobenzoate 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 and the NAC point observed in the temperature-concentration diagram of binary mixtures of and at the 42.5% concentration of 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.