High-pressure volumetric measurements near a smectic-nematic-isotropic triple point.

Abstract

High-pressure volumetric measurements were used to investigate the importance of short-range smectic fluctuations in the nematic-isotropic transition. Three members of the homologous series of di-alkylazoxybenzenes were chosen as samples, since the nematic range varies considerably in these compounds. The investigation was aided by the discovery of a smectic-A--nematic--isotropic triple point at elevated pressure in the ninth member of the series. Theoretical work on pretransitional effects in the isotropic phase is not very useful in describing the effect of large smectic fluctuations on the nematic-isotropic transition itself. However, one recent theoretical proposal argues that the volume change at this transition should increase due to the presence of short-range smectic order, and our experimental results confirm this prediction.