Rf/ac-calorimetry on 8CB+aerosil dispersions

Using a new high-resolution AC calorimetric technique employing RF (dielectric) heating, both the heat capacity and permittivity of a sample may be simultaneously probed. Relative resolutions of better than 0.06\% in the ratio of heat capacity to applied heating power, and 0.03\% in the phase shift measurements are easily obtained. This new and powerful technique has been applied to aerosil dispersions in the liquid crystal octylcyanobiphenyl (8CB) through the \textit{I}-\textit{N} and \textit{N}-Sm\textit {A} phase transitions. The temperature dependence of the applied heating power, proportional to the permittivity and hence the orientational order, shows no change through the \textit{N}- Sm\textit{A} for $\rho_S = 0.1$~g/cc. This indicates that at the point where sharp $C_p$ features are lost, the Sm\textit{A} and \textit{N} phases are effectively decoupled, consistent with recent NMR studies.