Viscoelastic twist properties of some nematic liquid crystalline azoxybenzenes

Abstract

The static and dynamic behavior of the Frederiks transition for twist of a uniform planar nematic sample in an external magnetic field has been studied by monitoring the associated conoscopic figure. In particular, the decay of this figure after the field has been switched off is considered in detail in order to obtain results for the twist viscosity γ1. Results for the twist elastic constant K2 and for the viscosity γ1 are reported for the homologous series of p, p′-dialkylazoxybenzenes. K2 is found to be smaller than both K1 and K3, while K2 varies little along the series. The temperature dependence of γ1 can be described by a combination of an activated process and a term depending on the orientational order parameter.

Sulphur as a Structural Element in Calamitic Liquid Crystals: Terminal, Linking and Lateral Substitutions

“…It has been demonstrated that the elastic constants depend on molecular structure, intermolecular association, and temperature of nematics [271,274,275]. The ratio K 33 =K 11 was found to be less than unit for a weakly polar two-ring thioester derivative [276], which is similar in value to those of other weakly polar derivatives [3].…”

Pyrimidine as a Structural Fragment in Calamitic Liquid Crystals

“…It has been shown that the elastic constants depend on molecular structure, intermolecular association, and temperature of NLCs [276][277][278]. The elastic constant ratio K 33 =K 11 of liquid crystals is an important parameter for supertwisted nematic liquid crystal displays (STNLCDs), defining their electro-optical performance [279].…”

Ketonization in Calamitic Liquid Crystals

“…It has been shown that the elastic constants depend on molecular structure, intermolecular association, and temperature of nematic LCs [169][170][171]. The elastic constant ratio K 33 =K 11 of liquid crystals is an important parameter for supertwisted nematic liquidcrystal displays (STN-LCDs) and define their electrooptical performance [172].…”