Fluctuation modes of a twist-bend nematic liquid crystal

Abstract

We report a dynamic light scattering study of the fluctuation modes in a thermotropic liquid crystalline mixture of monomer and dimer compounds that exhibits the twist-bend nematic (${\mathrm{N}}_{\mathrm{TB}}$) phase. The results reveal a spectrum of overdamped fluctuations that includes two nonhydrodynamic and one hydrodynamic mode in the ${\mathrm{N}}_{\mathrm{TB}}$ phase, and a single nonhydrodynamic plus two hydrodynamic modes (the usual nematic optic axis or director fluctuations) in the higher temperature, uniaxial nematic phase. The properties of these fluctuations and the conditions for their observation are comprehensively explained by a Landau-deGennes expansion of the free energy density in terms of heliconical director and helical polarization fields that characterize the ${\mathrm{N}}_{\mathrm{TB}}$ structure, with the latter serving as the primary order parameter. A "coarse-graining" approximation simplifies the theoretical analysis, and enables us to demonstrate quantitative agreement between the calculated and experimentally determined temperature dependence of the mode relaxation rates.

14 pages and 8 figures

References in corpus (7)

• Nematic twist-bend phase with nanoscale modulation of molecular orientation
• A Twist-Bend Chiral Helix of 8nm Pitch in a Nematic Liquid Crystal of Achiral Molecular Dimers
• Statistical mechanics of bend flexoelectricity and the twist-bend phase in bent-core liquid crystals
• Twist-bend nematic liquid crystals in high magnetic fields
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• Landau theory for helical nematic phases
• Second harmonic light scattering induced by defects in the twist-bend nematic phase of liquid crystal dimers

Cited by in corpus (8)

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• Electric field distortions in structures of the twist bend nematic (NTB) phase of a bent-core liquid crystal
• Comparative analysis of anisotropic material properties of uniaxial nematics formed by flexible dimers and rod-like monomers
• Geometry of Bend: Singular Lines and Defects in Twist-Bend Nematics
• Smectic-like rheology and pseudo-layer compression elastic constant of a twist-bend nematic liquid crystal
• Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helical structure, macroscopic polarization and fast switching speeds
• Non-Newtonian rheology in twist-bend nematic liquid crystals