Observation of a Reentrant Twist Grain Boundary Phase

Abstract

We report the occurrence of a reentrant twist grain boundary phase, which we designate as Re- TGB(A). Microscopic observations on a nonsymmetric dimer showed the phase sequence Iso- N*- TGB(A)-Sm- A-Re- TGB(A)- TGB(C*). Here N* and Sm- A stand for the chiral nematic and smectic- A phases, TGB(A) is the twist grain boundary phase with smectic- A blocks, and TGB(C*) that with smectic- C* blocks and exhibiting features of both the smectic- C* and TGB phases. The reentrance of the TGB(A) phase is unambiguously demonstrated using x-ray diffraction, selective reflection, and optical rotation data.

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

“…Later it was observed in pure systems as well [21,59]. In 1997, Pramod et al discovered a phase having two-dimensional undulation of the SmC Ã -like blocks in the form of a square lattice in binary mixtures of the chiral compound 4-(2 0 -methyl butyl phenyl 4 0 -n-octyl biphenyl-4-carboxylate (CE8) and 2-cyano-4-heptyl-phenyl-4 0 -pentyl-4-biphenyl carboxylate (7CN5) [60].…”

“…Shankar Rao et al (2001) have reported a re-entrant TGBA phase in a cholesterol based non-symmetrical dimer, namely cholesteryl 6-[4-(4-hexyloxyphenylethynyl) phenoxy] hexanoate [21]. Pressure-induced TGBA phase between N Ã and SmA phases has also been reported [22].…”

“…The TGBC phase also shows textures almost similar to the TGBA phase, but sometimes different textures are also observed. The TGBC Ã phase shows square grid pattern ( figure 13) in planar alignment [32,33,76], and filamentary texture (figure 14) in homeotropic alignment [21]. The filaments observed in the TGBC Ã phase are different from those in the TGBA and TGBC phases.…”

“…The filaments observed in the TGBC Ã phase are different from those in the TGBA and TGBC phases. The TGBC Ã filaments are undulatory in nature, the period of undulation being about the same as that of the square grid pattern obtained in the planar geometry [21,78]. According to the model of Pramod et al [60], appearance of the square grid structure in TGBC Ã phase is a consequence of the undulation of the smectic slabs.…”

Crystal structure of a liquid crystal non‐symmetric dimer: cholesteryl 4‐[4‐(4‐n‐butylphenylethynyl)phenoxy]butanoate

“…Furthermore we prepared a nonsymmetric dimer by joining a cholesteryl ester moiety to a 4-n-hexyloxytolane group (diphenylacetylene having an n-hexyloxy tail) through an n-pentyl (C 5 ) spacer. Interestingly this dimer showed a reentrant twist grain boundary phase (with smectic A blocks; TGB A ) and a newly discovered twist grain boundary phase (with smectic C* blocks; TGB C* ) [6]. More recently Jin et al…”