Bipolar configuration with twisted loop defect in chiral nematic droplets under homeotropic surface anchoring

Abstract

Optical textures and appropriate orientational structures have been studied within droplets of chiral nematic dispersed in polymer assigning the homeotropic anchoring. The helix axis of the chiral structure inside droplets forms the bipolar configuration. The optical droplet textures were analysed in the unpolarised light, analyser switching-off scheme and in crossed polarisers. The twisted loop defect reveals itself convincingly in all schemes. Its appearance at the optical patterns of the chiral nematic droplets has been examined depending on their size and the aspect direction. The existence of the defect has been verified by the structural and optical calculations. The effect of an electric field on both the defect line shape and the orientational structure of chiral nematic has been studied.

Optical Textures and Orientational Structures in Cholesteric Droplets with Conical Boundary Conditions

“…The layer-like structure is formed in the cholesteric droplets under both tangential and homeotropic boundary conditions at sufficiently high N 0 [38,39]. In CLC droplets under conical boundary conditions the layer-like structure is observed at N 0 ≥ 3.95 (Figure 4).…”

“…Thus, structures with point defect (hedgehog) in the bulk or near the droplet surface are observed at small N 0 < 2.5 [36,37]. The layer-like structure with the double twisted defect loop [33,35,[38][39][40] or structures with several points defects [36,37] are formed at large N 0 > 2.5. When 2.9 < N 0 < 5.8, the axisymmetric structure with the surface circular defect at the droplet's equator is formed [41,42].…”

“…In the cholesteric droplets with homeotropic boundary conditions (the director n is oriented perpendicular to the interface), the helical ordering of the director is frustrated, which leads to the formation of various orientational structures [33,[35][36][37][38][39][40]. Thus, structures with point defect (hedgehog) in the bulk or near the droplet surface are observed at small N 0 < 2.5 [36,37].…”

Toroidal Configuration of a Cholesteric Liquid Crystal in Droplets with Homeotropic Anchoring

“…1) e-mail: kmn@iph.krasn.ru В случае гомеотропного сцепления на поверхности капли должно происходить нарушение геликоидального упорядочения или/и граничных условий. В результате в каплях могут сформироваться структуры с различной комбинацией точечных и линейных дефектов в объеме и вблизи поверхности [19,20], структура с линейным поверхностным дефектом в виде двойной закрученной спирали [15,21,22], структура вложенных чаш [15] и другие слоеподобные структуры [23,24]. Формирование структур с точечными дефектами в объеме позволяет, с одной стороны сохранить гомеотропную ориентацию на всей поверхности капли, с другой стороны реализовать закрутку директора в объеме.…”

“…Так, в структуре с биполярным распределением оси геликоида при / 0 > 5 формирующийся в каплях шаг спирали близок к собственному шагу спирали 0 [25]. В этом случае на поверхности капли возникает закрученный кольцевой дефект [22], позволяющий одновременно и сохранять гомеотропную ориентацию директора практически на всей поверхности капли, и реализовать закрученную структуру в объеме.…”