Comparison of the properties of nematic liquid crystals doped with TiO2 and CdSe/ZnS nanoparticles

We have compared optical and electrical properties as well as the electro-optical characteristics of the pure and doped LC with 0.1 wt% of TiO2 nanoparticles and the CdSe/ZnS quantum dots (QDs) with core sizes of about 5 nm and different core shells. A significant difference in the IR absorption spectra and the low-frequency dielectric spectra of LC composites was not observed. The addition of 0.1 wt% nanoparticles caused no significant change in the order parameter or dielectric anisotropy of the LC. The addition of QDs increased the ion density by an order of magnitude compared to the pure LC and LC doped TiO2 due to the shell disruption of nanoparticles. The rotational viscosity evaluated by the test of electrical response of LC cells was twice bigger in case of LC doped with QDs. It has been shown the change in the rotational viscosity correlated with the ion density in the LC. An increase in the electrical conductivity was observed for the LC doped QDs. TiO2 nanoparticles significantly reduced the conductivity in high electric fields. Optical response time of LC cell with QDs was about twice less than with the pure LC and equal to 0.76 ms for the variation of phase retardation on 2π. It is connected with an increase in the pretilt angle of LC director in the cell with QDs and decrease in the anchoring energy. Increasing the dynamic viscosity and reducing the anchoring energy contributed to slowing the switching of the LC cell with the QDs during the relaxation process. TiO2 nanoparticles had smaller effect on electro optical characteristics of the LC cell and quench the photoluminescence of LC less effectively than QDs due to insignificant changes in the LCs properties.