Effect of CNTs and Induced Chirality on Smectic- Smectic Liquid Crystal Phase Transitions

High-resolution calorimetry results are presented of carbon nanotubes (CNTs) and the liquid crystal (LC) 9OO4 nano-colloidal dispersions as a function of temperature, scan rate, and CNT concentration ($0$, $0.025$, $0.05$, $0.20$ wt/$\%$). The CNT used have an enantiomeric excess that has been shown to induce chirality into this LC. The pure LC exhibits the phase sequence $I$-$N$-Sm$A$-Sm$C$-Sm$B$-$Cr$ on cooling with the expected heat capacity $C_p$ signatures, except for the Sm$A$-Sm$C$ transition, manifesting a double-$C_p$ peak $\sim 2$~K apart at low effective scan rates ($< 0.5$~K~min$^{-1}$). The introduction of CNTs results in the $I$-$N$, $N$-Sm$A$, and Sm$A$-Sm$C$ double $C_p$ features shifting to higher temperatures by $\sim 1$~K and remain sharp. However, the Sm$C$-Sm$B$ and Sm$B$-$Cr$ transitions shift to lower temperatures by $\sim 3-4$~K and broaden dramatically with increasing CNT content. We interpret these observations as a consequence of the $\pi$-$\pi$ interactions between the phenyl rings of 9OO4 and the graphene surfaces that induces bulk chirality, and the pinning of the director parallel to the CNT long-axis far from the surface. The balance of these two mechanisms may stabilize phases that lack any in-smectic-plane ordering.