Evidence for Triclinic Symmetry in Smectic Liquid Crystals of Bent-Shape Molecules

Abstract

The first experimental evidence for triclinic symmetry of bulk smectic liquid-crystal samples of achiral banana-shaped molecules is presented. This phase corresponds to the so-called Sm-CG phase consisting of biaxial molecules and characterized by two tilt directions with respect to the layer normal: tilt of the molecular plane (clinic) and tilt of the molecular kink direction (leaning). Each smectic layer has a polarization component normal to the smectic layers (C1 symmetry). The observations suggest that the phase tentatively labeled as B7 is identical with the Sm-CG phase.

Organization of the polarization splay modulated smectic liquid crystal phase by topographic confinement

“…As for many smectics appearing upon cooling directly from the isotropic phase via a first order transition, i.e., having no intervening nematic phase, the B7s are not easily aligned into macroscopically oriented domains of any sort with the anisotropic surface treatment methods such as optical-or mechanical-rubbed polymer surfaces or obliquely deposited silicon monoxide (SiOx) (7)(8)(9)(10)(11) that are typically useful for aligning LCs. Topographic patterning has been demonstrated to align LCs (12)(13)(14) and has recently emerged as an effective alignment technique for both nematic and smectic LCs, and in particular for layered LC phases growing directly from the isotropic (15)(16)(17)(18).…”

Liquid crystal nanocomposites produced by mixtures of hydrogen bonded achiral liquid crystals and functionalized carbon nanotubes

“…A close similarity was suggested between the smectic X phase found in these substances and the C G phase or its analogue B 7 phase in the bent-core LC [11]. These phases are examples of the typical smectic states where left-and right-handed helices are induced in an LC system whose constituent molecules are achiral.…”

“…The closed dimers can also be viewed as flexible bent-core-like molecules, showing similarities with phases found in large-size banana-like system [11], but exhibiting a more complex structure. A close similarity was suggested between the smectic X phase found in these substances and the C G phase or its analogue B 7 phase in the bent-core LC [11].…”

“…On the other hand, its dimeric structure allows an induced chirality although it is an achiral LC system, i.e. it is a hopeful candidate for the realization of the long sought-after C 1 symmetry in LC systems like the bent-core molecules [11].…”

The unique physical properties of the hydrogen bonded in dimers liquid crystals

“…The direction of this s IR vibration is collinear with the stacking Raman vibration modulating the electronic π-π interaction between the LC benzenes and the carbon hexagons of the SWCNTs causing the LC dimer ring to bend and further to promote a multitude of sterically grazed bent dimers. As a result of this nanoscale process, a macroscopic electrical polarization P arises, which is characteristic of ferroelectric LC states [16,17]. We depict the two mechanisms and corresponding models for symmetric and non-symmetric supramolecular complexes in figure 3 and figure 4.…”