Induced twisted-grain-boundary phases in the binary mixtures of a cholesteric and a nematic compound

Abstract

Thermodynamical, optical-texture and dielectric studies have been performed to study the phase diagram of the binary system of 5-cholesten-3-ol-octanoate and 4-n-nonyloxybenzoic acid. It is observed that low concentrations of 5-cholesten-3-ol-octanoate (2-30 mol %) in 4-n-nonyloxybenzoic acid induce a meanfield phase diagram derived by Renn within the framework of the chiral Chen-Lubenski model. Various optical textures of the twisted-grain-boundary (TGB) phases under different conditions of molecular anchoring have been observed. Weak transitions related to the TGB phases have been detected by temperature dependent dielectric spectroscopy.

Dielectric relaxation studies in n-(4-octyloxy-2-hydroxybenzylidene)-4-carbethoxyaniline

“…with 1/T. In most of the cases, this approximation has been found experimentally true for small temperature variations (Kresse, 1983;Dhar et al, 2003). In the case of the present material, least square fits of " 0 k and " 0 ?…”

Twisted-grain-boundary (TGB) phases:nanostructured liquid-crystal analogue of Abrikosov vortex lattices

“…In another binary system of 5-cholesten-3-ol-octanoate (CHC) and 4-n-nonyloxybenzoic acid (NOBA), a similar phase diagram has been observed but excluding TGBC Ã [69]. Torogova et al [70] have reported short-range smectic ordering in the nematic phase of 4-n-alkyloxybenzoic acid, and this special property seems to play an important role among many others that are responsible for the observation of different types of TGB phases and N Ã L phase in these mixtures.…”

“…Peculiar TGB textures can be seen in recent reviews of optical textures of TGB phases by Dierking and Lagerwall [79] and Ribeiro et al [80]. Two unique textures shown in figures 15 and 16 have been recently observed for TGBC phase in ChCl-DOBA [39] and ChC-NOBA [69] binary systems respectively; however, these textures belong to the group of textures reported in Cruz et al [73] and Meier et al [74].…”

“…With the passage of time, or after a number of thermal annealing cycles, the TGB phases vanish. In these mixtures [39,69], different TGB-TGB transitions have been detected by dielectric studies as well, in addition to the usual DSC and optical-texture studies. A model has also been proposed which explains the origin of the lock-in of the smectic slabs/blocks at certain angles (Á), at least in mixed systems [39].…”

“…Figure 11 shows another type of filamentary texture, which is most commonly observed Twisted-grain-boundary (TGB) phases 187 for homeotropic aligned TGBA samples. Oily streaks are also formed if two glass plates (containing homeotropically aligned TGBA phase) are slightly sheared or pressed [38,69]. In the case of homeotropic anchoring, the helix axis of TGB phase lies parallel to the bounding surfaces (as in the case of planar aligned SmC Ã phase); hence pitch lines sometimes appear in the form of fingerprint texture [74].…”