Chiral Structures from Achiral Micellar Lyotropic Liquid Crystals under Capillary Confinement

Abstract

Recently, the emergence of spontaneous reflection-symmetry-broken configurations in achiral chromonic liquid crystals confined in cylindrical capillaries with homeotropic anchoring at the cylinder walls was reported, namely, the so-called twisted-escaped radial (TER) and twisted planar polar (TPP) configurations. This new example of spontaneous reflection symmetry breaking in liquid crystals was attributed to the twist elastic modulus, which is known to be unusually small in comparison to the splay and bend moduli in the case of chromonic liquid crystals. We now report the experimental observation of reflection symmetry breaking in cylindrical capillaries in the case of a classical, achiral, and nonchromonic lyotropic liquid crystal forming a nematic phase of disklike micelles orienting homeotropically at the capillary walls. We observed the same chiral TER configuration, as well as a nonplanar twisted polar (TP) configuration. The TP configuration is characterized by two half-unit so-called twist disclinations, where the director twist around the line defects drives the formation of a double helix of the disclinations along the axis of the capillary. Additionally, there is a transverse twist between the two disclination lines with the same handedness as the axial twist. Similarities with and differences from the case of chromonic liquid crystals are discussed; in particular, we examine the conditions under which spontaneous reflection symmetry breaking occurs in the nonchromonic system. It seems that the chiral TER configuration can be stabilized by the presence of point defects.

Mirror symmetry breaking in liquids and liquid crystals

“…As the resulting macroscopic helix acts as a polarising wave guide a conglomerate of macroscopic domains with opposite twist sense can be observed after cooling from the isotropic liquid. Though the exact 90°condition is very special and unlikely to be observed by chance, there are numerous other confinement induced reflections symmetry breaking conditions, especially if flow is involved, as for example observed for lyotropic nematic phases (Figure 13(c,d)) [17,141,142]. Similar to these nematic phases, director alignment, topological defects or vortex flow can provide sources of chirality in the SmC s (P R ) [*] phases.…”

“…as discussed above for the SmC phases. Reflection symmetry breaking is (Colour online) (a,b) Spontaneous reflection-symmetry breaking between two twisted surfaces (Mauguin effect) and (c,d) broken configurations as observed in lyotropic nematic LCs confined in cylindrical capillaries under homeotropic anchoring conditions between crossed polarisers with λ-retarder plate[142]; (a, b) were used under CC BY 4.0 from ref [140]. and (c,d) were reprinted with permission from ref [142],.…”

Defects and defect engineering in Soft Matter

“…The results show that inducing chirality on achiral liquid crystals using geometrical frustration is a general phenomenon in nematic liquid crystals. 111 Nikoubashman, Milchev, and coworkers observed novel nematic defect patterns when confining densely packed stiff polymers to spherical cavities of comparable size. 112 The authors demonstrated that at intermediate polymer densities, the ordering of polymer chains is the nematic type with bipolar defects.…”

“…Giesselmann and coworkers investigated this idea experimentally by using dislike micelles as achiral lytropic nematic liquid crystal, confined in a glass capillary. 111 The liquid crystal orients normal to the capillary walls (homeotropically alignment). After cooling from the isotropic phase, the authors observed a TER configuration.…”

Textures of Nematic Liquid Crystal Cylindric-Section Droplets Confined by Chemically Patterned Surfaces

“…This has a defect line strength s = +1 running along its centre. However, except for the very narrowest of capillaries [32], this proves to be unstable relative to the "escaped radial" director field (Figures 2c and 3) [27,[33][34][35][36][37][38][39][40][41] or to a situation in which the +1 defect line splits into a pair of +1/2 defect lines, giving the "planar polar" director field ( Figure 2b) [5,6,32]. When the anchoring of the nematic at the air to LC surface is planar, the main possible director fields are those in Figure 2d-g.…”