Tailoring the dielectric properties, DC conductivity, hopping frequency and activation energy of an achiral nematic liquid crystal using CdSe/ZnS quantum dots

We demonstrate here the impact of doping of varying concentration of CdSe/ZnS quantum dots (QDs) on molecular alignment, dielectric and electrical conductivity properties of a planar aligned nematic liquid crystal (NLC), 4-(trans-4′-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). Polarized optical microscopy confirmed that macroscopic alignment of NLC matrix remained planar up to 1.0 wt% of dopant QDs. However, the quality of alignment deteriorated in higher concentrations (0.5 and 1.0 wt%) due to aggregation of QDs and accompanied by formation of large number of defects as compared to lower concentrations. Both components of dielectric permittivity ( ε ′ ⊥ and ε ′ ∥ ) show the strong concentration dependence. The dielectric anisotropy ( Δε ′ ) decreases monotonically with increase of dopant concentration. Temperature evolution of short-axis molecular relaxation shows typical Arrhenius behavior and corresponding activation energy is concentration dependent. The threshold voltage is increased monotonically with an increase of dopant concentration and attributed to enhanced ion-induced screening and reduced Δε ′ . The DC conductivity is increased monotonically with QD concentration. However, the activation energy shows non-monotonic behavior with dopant concentration A similar behavior is also observed with temperature dependent ions hopping frequency and related activation energy. These results demonstrate that CdSe/ZnS QDs could systematically tune dielectric and ionic conductivity in 6CHBT through a concentration-dependent interplay of molecular ordering, QDs aggregation, and charge transport. Our findings would pave the way forward for the optimization of CdSe/ZnS QDs-6CHBT composites to exploit the futuristic advanced displays, electrical and other photonic devices.