Field-induced periodic chiral pattern in the Nx phase of achiral bimesogens

Abstract

Some hydrocarbon-linked mesogenic dimers are known to exhibit an additional nematic phase (Nx) in the temperature range below the conventional nematic (Nu) phase. One of the features of this phase is the presence of optical response typically found in chiral systems, while the involved molecules are non-chiral. We demonstrate that the two domains of opposite handedness found in planar cells can be controlled/induced by the external electric field and these form periodic striped patterns. The effect of frequency and amplitude of the electric field on the periodicity and formation of the domain pattern is investigated.

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the NTB–N phase transition

“…One of the early studies of a liquid crystal dimer, with an odd spacer, showing a nematic-nematic transition was reported by Sepelj et al 1 although the nature of the low-temperature nematic phase was not identified and so was labelled N x . Similar dimers with odd spacers having a N x -N transition were reported by Panov et al 2 and the behaviour of such dimers has also been studied [3][4][5] but again without the low-temperature nematic being properly identified. Cestari et al 6 have examined an odd liquid crystal dimer and observed a nematic-nematic transition but, as the result of an extensive investigation based on numerous techniques, were able to identify the low-temperature nematic as we shall see shortly.…”

Twist-bend heliconical chiral nematic liquid crystal phase of an achiral rigid bent-core mesogen

“…Under an applied electric field, domains with two different molecular tilts are apparent, with distinct boundaries (Figure 3c), that are visible even at zero field (Figure 3e), similar to the domain boundaries seen in bent molecular dimers (Figure 3f), as first reported by Panov et. al [9]. When the E field is reversed, the molecular tilts in the two sets of domains are reversed and their colors interchange (Figure 3d).…”

“…Recently, the twist-bend nematic (N TB ) phase, a fundamentally new type of nematic ground state of achiral molecules, exhibiting layer-free, helical liquid crystal ordering of nanoscale pitch, has been structurally identified and characterized [1,2]. The twist-bend nematic phase was initially suggested as a theoretical possibility by Meyer over 40 years ago [3] and discussed in 2000 by Dozov [4] and Memmer [5], who suggested that the tendency for local bend curvature in the director field of bent molecules (for example, Figure 1a [6,7] having nematic characteristics, spontaneous chirality [8,9], and smectic textural features [10,11] but no smectic-like lamellar x-ray diffraction peaks [12] have been interpreted in terms of the N TB structure [4]. The N TB phase is in general polar and structurally chiral despite being formed from achiral molecules.…”

Hierarchical elasticity of bimesogenic liquid crystals with twist-bend nematic phase

“…10 In planar cells, the N tb phase also exhibited spontaneous periodic stripe patterns in micrometer-scale. 7,11 Although the latter is reminiscent of the smectic phase, X-ray scattering patterns and nuclear magnetic resonance spectroscopy indicated that the N tb phase is nematic-like rather than of the lamellar type. 2,[12][13][14] The twist-bend nematic phase was predicted by Meyer in 1973 in chiral molecules, 15 and Dozov predicted spontaneous symmetry-breaking in an achiral banana-shaped mesogen.…”

“…1(a-ii) and 1(c-ii)). 11,18 In a 3.2-lmthick planar cell, micro-scale stripe patterns grew along the rubbing direction ( Fig. 1(a-iii)) and gradually spread across the entire cell area on cooling ( Fig.…”