Defects in the twist-bend nematic phase: Stabilities and instabilities of focal conic domains and related topics

Abstract

This article provides an explanation for the instability of toric focal conic domains and the stability of parabolic focal conic domains in the twist-bend nematic (N TB ) phase, by reason of the presence (the first case) or absence (the second case) of defect densities attached to the conics, which are disclinations. This result is obtained after a reminder of the theory of attached defects (the extended Volterra process) and is followed by its usage in other cases (dislocations, disclinations, dispirations, double helices) in the N TB phase. The notion of spin disclination is introduced.

Pretransitional behavior of viscoelastic parameters at the nematic to twist-bend nematic phase transition in flexiblen-mers

“…The twist-bend nematic (N TB ) phase is the most recently discovered, as well as one of the most intriguing, manifestations of molecular orientational order in soft matter. Meyer 1 originally conjectured the existence of a stable combination of twist and bend distortions in the nematic state of achiral mesogens with velopment [15][16][17][18][19] , and the combination of efforts have elucidated several remarkable properties of the N TB phase:…”

“…On cooling below the N-N TB transition (T = T NT B ), shrinkage in the pseudo-layer spacing (decreasing p 0 ) causes the pseudo-layer planes (planes of constant heliconical phase) to buckle, producing a striped optical texture and the appearance, at lower temperature or near the surfaces of untreated sample cells, of smectic-A-like focal conic defects. 7,19,29,30 As T → T NT B from above, the bend elastic constant decreases; if the "bare" splay to twist elastic constant ratio exceeds 2, a twist-bend modulation is favored at lower temperature 2 .…”

Polymerisation of twist-bend nematic textures for electro-optical applications

“…Another advantage of the N TB phase is its wide variety of textures. Indeed, FCD defects, 23 stripe patterns 25 and double helices 26 have already been reported for this phase. In smectics, the structure of double helices has been explained in terms of screw dislocations of giant Burgers vector.…”

Geometry of Bend: Singular Lines and Defects in Twist-Bend Nematics

“…The singularities in the smectic phase field then all induce β lines in the director. In the Supplemental Material [25], we provide examples for twist-grain-boundaries [38][39][40] and parabolic focal conics [41,42]. A separate set of examples of β lines is provided by the vortex structures familiar from cholesterics and Skyrmions.…”