Role of molecular bend angle and biaxiality in the stabilization of the twist-bend nematic phase

Abstract

Within mean-field theory for V-shaped molecules, we have investigated how the alteration of a molecule's structural features influence the stabilization of modulated and non-modulated nematic phases.

The Beauty of Twist-Bend Nematic Phase: Fast Switching Domains, First Order Fréedericksz Transition and a Hierarchy of Structures

“…As the electric field is applied across the parallel-rubbed planar-aligned cell, the N TB phase is converted to a splay-bend for fields larger than a few V/µm depending on the ∆ε and optical biaxiality. This was observed for the first time in [30] especially for a bent-core LC, and was theoretically predicted by Longa et al [31,32] soon after. This has recently been verified by Meyer et al [33] through birefringence measurements, which suggest that molecular biaxiality plays a key role in not only stabilising the N TB phase but also in producing a field-induced splay-bend phase.…”

Biaxiality-driven twist-bend to splay-bend nematic phase transition induced by an electric field

“…During the review process of our manuscript, Tomczyk and Longa ( 48 ) published a theoretical model that considers the role of the biaxiality of the order parameter tensor in modulated nematic phases. Using a generalized mean-field model, they predicted two distinct N TB nematic phases, N TB (macroscopically uniaxial) and N TB,B (macroscopically biaxial), for bent-core molecules.…”

“…Using a generalized mean-field model, they predicted two distinct N TB nematic phases, N TB (macroscopically uniaxial) and N TB,B (macroscopically biaxial), for bent-core molecules. Further development of the model of ( 48 ) to describe the phase behavior under applied fields may clarify further the complex phase behavior of the modulated nematic phases and their broken uniaxial symmetry.…”

Molecular biaxiality determines the helical structure – infrared measurements of the molecular order in the nematic twist-bend phase of difluoro terphenyl dimer

“…That was the reason to consider the nematic phase as uniaxial and also to simplify the structure analysis. Such an exception, however, can indicate the possibility that the biaxial nematic phase might appear in between the nematic uniaxial (N U ) and the twist-bend (N TB ) phase [5,10]. A small sample biaxiality, which was found in N TB phase by comparing corresponding perpendicular absorbance components (in both alignment), A Y ≠A h , are likely to be induced by anchoring effect [39][40][41].…”

“…An important leitmotif in the science of soft and liquid crystal materials is the understanding of the mutual relations between the shape of a molecule and macroscopic selforganization and the search for new possibilities of ordering based on the study of various molecules shapes [1][2][3][4][5][6][7][8][9][10]. A fairly recent, and quite remarkable, manifestation of spontaneous chirality in the fluid of achiral molecules is the nematic twist-bend (N TB ) liquid crystal phase, which is formed by long-range 1D ordered molecules following the heliconical precession of the director [4,5,[11][12][13][14][15][16][17]. The structure is based mainly on the twist of the biaxial molecular order around the molecular long axes, quantitatively related to the curvature of the bend of the molecule.…”