Liquid crystal textures: an overview
Ingo Dierking
Abstract
After a short introduction into surface alignment, elasticity and the optics of liquid crystals, an overview is given about the textures in polarising microscopy. This covers the most common textures of calamitic thermotropic mesogens, i.e. molecules of rod-shape, which form nematic, fluid smectic, hexatic and soft crystal phases, but also those of disc-shaped, bowl-shaped, and bent-core molecules. The most characteristic textures are discussed for respective discotic, bowlic and bent-core phases. Chiral mesogens are also included to provide a broad overview of their helical structures on observed textures and to discuss frustrated phases, such as the Blue Phases and Twist Grain Boundary phases. In the second part, lyotropic phases are introduced, thus those which form in the presence of a solvent. These include the standard amphiphilic phases, but also those formed by shape-anisotropic colloids mainly in water. We cover the phases of inorganic rod-like colloids, disc-like clays, rod-shaped viruses, DNA, chiral rods such as cellulose nanocrystals, and lyotropic phases of 2D-materials, for example, graphene oxide, MoS2 and MXene. It is hoped that this overview can be used by younger researchers as a tutorial style introduction into the field of liquid crystal textures.