Effect of quantum dots on the isotropic to nematic and nematic to smectic-A phase transitions in nano composites

Modulated Differential Scanning Calorimetry (MDSC) is used to investigate the weakly first-order isotropic to nematic ($I$-$N$) and the continuous nemat to smectic-$A$ ($N$-Sm$A$) phase transitions of the liquid crystal octylcyanobiphenyl (8CB) doped with well-dispersed quantum dots (QdS) as a function of Qd concentrations. Thermal scans were performed for all samples having Qd (CdS) weight percent from $\phi_{w}$ = 0.3 to 3 wt$\% $ first on cooling and then heating under near-equilibrium conditions. The I-N transitions heat capacity peak first glows then decreases in magnitude with increasing $\phi_{w}$ leaving a maximum at $\phi_{w}$ = 0.3$\% $. The N-SmA heat capacity peak remains bulk-like for all samples. Both transitions temperatures shift lower monotonically by 3 K for $\phi_{w}$ = 0.3$\% $. The enthalpy of both transitions evolve in a nontrival way, generally decreasing with increasing $\phi_{w}$. These results are discussed in terms of the predominate disordering effects of the Qds.