Disclination lines in nematic liquid crystal between a structured photoalignment layer and a homeotropic alignment layer

Abstract

Topological defects in nematic liquid crystals (NLCs) are an interesting material system to study both from a theoretical point of view and for applications in photonics, soft-robotics and colloidal assembly. By using a photo-aligned template at one or both confining substrates, different disclination interconnections in the bulk can be readily stabilized. We imposed a periodic defect grid of 1/2 and −1/2 defects at the surface with the help of photoalignment and combined this with a uniform homeotropic counter substrate. This alignment configuration was used to study the optical properties and the relative stability of different types of disclinations in detail. The arrays of disclination lines are investigated by polarizing optical microscopy for different orientations of the polarizers and for different applied voltages. A theoretical analysis is performed to understand the relative frequency of occurrence for distinct types of disclinations and numerical simulations are used to verify the difference in optical appearance. The unequal elastic constants for splay, twist and bend strongly influence both properties and make it possible to identify different types of disclination lines form their optical appearance.