# Perspectives in Liquid-Crystal-Aided Nanotechnology and Nanoscience
## 2 Modification of Physical Properties of LC Materials by Nanodopants
Figure 4: (**a**) A Schlieren texture (**left**) of 0.5 vol % BaTiO\({}_{3}\) + 5 CB observed by polarizing optical microscopy, POM. Observation between parallel polarizers (**right**) provides evidence that the dispersed particles are collected in the topological defects. (**b,c**) Permittivity components \(\varepsilon_{\perp}\)\({}^{\prime}\) and \(\varepsilon_{\parallel}\)\({}^{\prime}\), respectively. (**d**) The relationship between the electro-optic response time and the concentration of BaTiO\({}_{3}\) with (**d**) the field on-time and (**e**) the off-time for larger (ferroelectric) and smaller (non-ferroelectric) particles. (**f**) The relationship between the concentration of BaTiO\({}_{3}\) and threshold voltage V\({}_{\text{th}}\), and (**g**) splay elastic constant K\({}_{11}\). Reproduced with permission from [173]. Copyright (2017) AIP. Apart from that, the presence of gold nanoparticles also promoted the reorientational motion of LC molecules by applying an electric field. Furthermore, an increase of dielectric permittivity and ionic conductivity was found in the gold nanoparticle-columnar discotic LC (HAT4) suspensions [183]. Silver nanoparticles are also quite popular among the metal nanoparticles and have been widely used as nanodopants for the modification of LC physical properties [179] due to their high electric and thermal conductivity, nano-scale calorimetric effect, excellent chemical stability, and various medical and catalysts applications [184; 185; 186]. The thermodynamic, dielectric and electro-optic characteristics of a nematic LC (6 CHBT) mixed with silver nanoparticles with different sizes have been studied by [PERSON] et al. They found that the first-order phase transition temperature of the mixture was marginally increased, while the dielectric permittivity, and elastic constants decreased compared to the pure LC [187]. QDs are semiconductor nanoparticles in the range from two to 10 nanometres in diameter. They are usually composed of thousands of atoms of group II and VI elements (e.g., CdSe, CdTe, ZnO), group III and V elements (e.g., InP, InAs), and group IV-VI elements (e.g., PbS) [188]. As a semiconductor material, the electrons of QDs will be promoted from the valence band to the conduction band by the irradiation of photons with energies larger than the band gap. Since these electrons are not stable in the conduction band, they will transit back to the valence band and recombine with the holes. As a result, the extra energy will be emitted as photons with a wavelength related to the bandgap. According to the developed bulk Wannier-Hamiltonian model of [PERSON] [189; 190], this bandgap is dependent on the size of the employed QDs. Their unique size- and shape-dependent electro-optic characteristics made QDs the focal point of research in various fields including photonics, sensors, medicine, information storage, etc. The special physical properties have made QDs a promising nanodopant for modifying physical properties and improving the electro-optic responses of LC materials [191; 192; 193; 194]. [PERSON] et al. recently found that the inclusion of QDs (CdSe-QDs) would effectively influence phase transition temperatures and enhance the dielectric anisotropy of nematic LCs (4 PP4 OB). Moreover, it increased the transition voltage for switching LC molecules from homogeneous alignment to homeotropic alignment, decreased the splay elastic constant, and increased the relaxation frequency of the LC matrix [195]. [PERSON] et al. reported that nematic LC 1832A dispersed with QDs (InP/ZnS) exhibited a promoted molecule alignment, leading to an enhanced non-linear optical anisotropy. They also found that the physical characteristics of the composite, including elastic constants, switching time, and viscosity, were distinctly decreased, while faster electro-optical response, enhanced birefringence and larger dielectric anisotropy were observed [196].