Study of the Isotropic-Nematic and the Nematic-Smectic-A Phase Transitions in Carbon Nanotubes and Liquid Crystal Composites

A high-resolution ac-calorimetric study of the isotropic to nematic (\emph{I-N}) and the nematic to smectic-A (\emph{N-SmA}) phase transitions of carbon nanotubes (CNTs) and liquid crystal octyl-cyanobiphenyl (8CB) composites (8CB+CNTs) as a function of CNTs concentration is reported. Scans were performed on heating and cooling for all samples (0.5-6 wt\% of CNTs) over a wide temperature range well above and below the two transitions in pure 8CB. Both the \emph{I-N} and the \emph{N-SmA} transitions evolve in character and have their transition temperatures shift lower as the wt\% of CNTs increases. For intermediate wt\% values, new transitions features are observed, which suggest new phase ordering of the CNTs within the liquid crystal host.