High-pressure measurements in a homologous series of liquid crystals

Pressure-volume-temperature measurements throughout the nematic phase for the first six members of the homologous series of di-alkoxyazoxybenzenes are reported. These data represent the first investigation of thermodynamic parameters in an homologous series, thus demonstrating the role of the end chains in a specific molecular geometry. Measurements at constant volume permit the conversion of previous orientational order studies at atmospheric pressure to constant-volume conditions. Measurements at constant temperature at the nematic-isotropic phase transition reveal the behavior of the specific volume, volume discontinuity, and volume dependence of the mean-field potential in this series. Finally, the implication of these data on several liquid-crystal theories is explored.