Emergence and stabilization of transient twisted defect structures in confined achiral liquid crystals at a phase transition

Abstract

Spontaneous emergence of chirality is a pervasive theme in soft matter. We report a transient twist forming in achiral nematic liquid crystals confined to a capillary tube with square cross...

Escape into the third dimension in cholesteric liquid crystals

“…These materials are achiral but have a small twist elastic constant, leading to an energetic preference for twisted textures but no preference for left vs right handedness. Similar helices of disclinations have also been observed in thermotropic materials [38].…”

“…In a coreless defect the winding is an integer, generically ±1. Depending on confinement and material properties, a ±1-winding singular line in an achiral nematic may either split into a pair of ±1/2 disclination lines or else be removed by escape [1,3,4,37,38].…”

“…A radial +1 singularity may decompose into a pair of +1/2 disclination lines instead of escaping. This process is naturally associated with chiral materials [3,4], but can also arise as a result of anisotropy in the elastic constants, for example in achiral materials which have a relatively small twist elastic constant compared to the bend and splay elastic constants [38,39]. We revisit this situation in section 6 below.…”

Self-assembly of cellulose nanocrystals confined to square capillaries

“…21 Molecular LCs have displayed unexpected structures when confined inside a square capillary. For example, nematic LCs formed helical defects with four-fold symmetry 22,23 and lyotropic chromonic LCs formed metastable doubly twisted structures. 12 To date the self-assembly of lyotropic colloidal nanoparticle components, e.g., cellulose nanocrystals (CNCs), confined to containers with sharp-cornered, degenerate boundaries has not been studied.…”

Using Nanoscopic Solvent Defects for the Spatial and Temporal Manipulation of Single Assemblies of Molecules

“…Defects in nematic solvents can take the shapes of points, , lines (disclinations), ,, or walls, , with the region of disordered solvent typically being about ∼10 nm in size (e.g., diameter of a line defect). The high free-energy density of the disordered solvent in the defect core has been shown to trigger the formation of well-defined assemblies of both small-molecule amphiphiles and polymers at concentrations below which assemblies form in the bulk nematic solvent phase. ,,,, For example, dipyrro­methene­boron difluoride (BODIPY)-labeled fatty acids (BODIPY-alkanoic acids) and phospholipids (e.g., 1,2-dilauroyl- sn -glycero-3-phospho­choline (DLPC)) undergo cooperative self-assembly in nematic solvent defects with thermodynamic signatures (e.g., critical aggregation concentrations) analogous to those observed with amphiphiles in aqueous solvent systems. Super-resolution optical microscopy (STORM) and cryo-transmission electron microscopy (cryo-TEM) reveal that the phospholipid amphiphiles formed multilamellar cylindrical assemblies with mean diameters of ∼30 nm in line defects (Figure d) or nanoscopic toroidal assemblies with overall diameters of 200 nm in point defects .…”