Effect of quantum dots on the phase behavior and order of 8CB liquid crystal

Abstract

We experimentally investigate the impact of surface functionalized hydrophobic core-shell CdSe/ZnS quantum dots on the phase behavior and order of the host liquid crystal compound 4-cyano-4'-octylbiphenyl (8CB) by means of polarized optical microscopy, polarized micro-Raman spectroscopy and X-ray diffraction. The orientational order of the nanocomposite system is probed by means of birefringence measurements as a function of temperature and mass fraction of the quantum dots. The dispersion quality of the dopant in the samples, partial-aggregation phenomena and/or nanoparticle organization give rise to non-monotonic variation of the probed thermodynamic quantities. A critical dopant mass fraction above which the nematic phase becomes paranematic is evidenced. A phenomenological model accounts for phase separation effects and a qualitative interpretation of the experimental results. The impact of nanoparticles on the macroscopic nematic order is discussed in the frame of a random anisotropy Lebwohl-Lasher model.