41 research outputs found
Wetting of cholesteric liquid crystals
We investigate theoretically the wetting properties of cholesteric liquid
crystals at a planar substrate. If the properties of substrate and of the
interface are such that the cholesteric layers are not distorted the wetting
properties are similar to those of a nematic liquid crystal. If, on the other
hand, the anchoring conditions force the distortion of the liquid crystal
layers the wetting properties are altered, the free cholesteric-isotropic
interface is non-planar and there is a layer of topological defects close to
the substrate. These deformations can either promote or hinder the wetting of
the substrate by a cholesteric, depending on the properties of the cholesteric
liquid crystal
Pattern-induced anchoring transitions in nematic liquid crystals
In this paper we revisit the problem of a nematic liquid crystal in contact
with patterned substrates. The substrate is modelled as a periodic array of
parallel infinite grooves of well-defined cross section sculpted on a
chemically homogeneous substrate which favors local homeotropic anchoring of
the nematic. We consider three cases: a sawtooth, a crenellated and a
sinusoidal substrate. We analyse this problem within the modified Frank-Oseen
formalism. We argue that, for substrate periodicities much larger than the
extrapolation length, the existence of different nematic textures with distinct
far-field orientations, as well as the anchoring transitions between them, are
associated with the presence of topological defects either on or close to the
substrate. For the sawtooth and sinusoidal case, we observe a homeotropic to
planar anchoring transition as the substrate roughness is increased. On the
other hand, a homeotropic to oblique anchoring transition is observed for
crenellated substrates. In this case, the anchoring phase diagram shows a
complex dependence on the substrate roughness and substrate anchoring strength.Comment: 36 pages, 15 figures, revised version submitted to Journal of
Physics: Condensed Matte