By: Ana Fialho and Carolina Pereira
From: CFTC - Universidade de Lisboa
At: Instituto de Investigação Interdisciplinar, B2-01
In a cholesteric liquid crystal the molecules align in a local direction that varies periodically in space, describing a helix. This new length scale - the pitch - at an intermediate length (micrometers) between the microscopic correlation length (nanometers) and the macroscopic world (milimeters) is responsible for the interesting properties of these phase under confinement, either imposed by geometry or by an interface with another phase.
An interesting example of geometrical confinement is a toroidal system where the configuration is a result of the competition between elasticity and the geometrical, and topological, constraints. We present the director field textures of a cholesteric liquid crystal confined by a toroidal surface. The results show a twisted configuration on the surface which depends on the relation between the system's dimensions and the pitch of the cholesteric.
The system can also be confined by interfaces with other phases. The interface with the isotropic phase (normal liquid) is undulated with a layers of topological defects. We discuss how the surface tension and the structure of the interface varies with the parameters of the system. We also show how the pitch changes the wetting properties, compared to a nematic liquid crystal which is the limit of infinite pitch (no helix).