Exploring Quantum Dots Size Impact at Phase Diagram and Electrooptical Properties in 8CB Liquid Crystal Soft-Nanocomposites

Abstract

We explore the influence of functionalized core–shell CdSe/ZnS quantum dots on the properties of the host liquid crystal compound 4-cyano-4′-octylbiphenyl (8CB) through electrooptical measurements. Two different diameters of quantum dots are used to investigate the size effects. We assess both the dispersion quality of the nanoparticles within the mixtures and the phase stability of the resulting anisotropic soft nanocomposites using polarizing optical microscopy. The temperature-mass fraction phase diagrams of the nanocomposites reveal deviations from the linear behavior in the phase stability lines. We measure the birefringence, the threshold voltage of the Fréedericksz transition, and the electrooptic switching times of the nanocomposite systems in planar cell geometry as functions of temperature, mass fraction, and diameter of the quantum dots. Beyond a critical mass fraction of the dopant nanoparticles, the nematic order is strongly reduced. Furthermore, we investigate the impact of the nanoparticle size and mass fraction on the viscoelastic coefficient. The anchoring energy at the interfaces of the liquid crystal with the cell and the quantum dots is estimated.

Keywords

• anchoring energy
• birefringence
• Fréedericksz transition
• liquid crystals
• quantum dots
• soft-nanocomposites