The influence of suspended nanoparticles on the Frederiks threshold of the nematic host

Abstract

In recent years, several papers reported an enhanced dielectric anisotropy when ferroelectric particles were suspended in a liquid crystal. These results seem to be sensitive to the liquid crystal used and the preparation method of the ferroelectric particles. In this paper, we compare different preparation methods of suspended barium titanate in two different liquid crystal hosts. As a control experiment, we followed similar preparation steps with non-ferroelectric silica particles. In all cases, we found a broadening of the optical Frederiks transition but no change in the dielectric anisotropy. Raman spectroscopy has been used to investigate the loss of tetragonal structure in the barium titanate as a function of milling time and particle size. As reported in the earlier literature, barium titanate does not exhibit a welldefined tetragonal crystal structure below a certain particle size and loses its ferroelectric features. This provides a simple rationalization for the absence of any dielectric enhancement.

Elastic constants, viscosity and response time in nematic liquid crystals doped with ferroelectric nanoparticles

“…However, the data available 24,35,36 indicate some interesting similarities. All those liquid crystals are based on cyclohexane, they are uorinated and, as expected, in the undoped version have relatively modest dielectric anisotropy.…”

A comparison between size dependent paraelectric and ferroelectric BaTiO3 nanoparticle doped nematic and ferroelectric liquid crystals

“…The electro-optic and dielectric properties were investigated in detail, also as a function of loading concentration. We use commercial liquid crystal materials 5CB and a ferroelectric Felix mixture, due to their known neat properties and wide use 4,8,19,33,34 in research and applications. Polyimide Kapton tape was used as a protective layer for the central area prior to the immersion of the substrates in hydrochloric acid (30%) for 7min to dissolve the ITO.…”

“…anisotropic properties such as dielectric, refractive indices and elastic constants [1][2][3] to exploit the possibilities of a switchable matrix. The main objectives behind investigating NP-LC hybrid systems are to tune the properties of the liquid crystal, [4][5][6][7][8] to modify the properties of NPs through transfer of self-organisation in the liquid crystal medium, 9 and/or to obtain additional functionalities not available by either materials in their intrinsic form.…”

Electrically charged dispersions of ferroelectric nanoparticles

“…[1][2][3] One example of such nanodispersions is colloidal suspensions of ferroelectric NPs in liquid crystals. 4 Such suspensions demonstrated a significant increase in the dielectric anisotropy, birefringence, clearing temperature as well as the reduction in the Freedericksz transition [5][6][7][8][9][10][11][12] as compared with the undoped samples. Ferroelectric NPs doped LCs also have decreased voltage of the electrically driven texture transitions and the Bragg reflection in cholesteric LCs, 13 as well as changing the spontaneous polarization of the ferroelectric smectic LCs.…”