High-Resolution Calorimetric Study of the Nematic—Smectic-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi></mml:math>Transition in Octyloxycyanobiphenyl (80CB)

Abstract

An ac technique has been used to measure the heat capacity of 8OCB at 1 atm along several high-pressure isobars. The ${C}_{p}$ data near the essentially second-order nematic-smectic-$A$ (N-$\mathrm{Sm}A$) transition are inconsistent with the logarithmic singularity expected from the $d=3$, $n=2$ model of de Gennes but agree with a power-law divergence with $\ensuremath{\alpha}={\ensuremath{\alpha}}^{\ensuremath{'}}$ in the range 0.2-0.3. This behavior and an unexpected exponential decrease in the magnitude of the critical N-$\mathrm{Sm}A$ heat capacity with increasing pressure are also confirmed in octylcyanobiphenyl (8CB).