Chiral Induction and Defect Structures in Liquid Crystal Systems

Due to their high anisotropy (physical, electromagnetic, optical, mechanical), liquid crystals (LCs) serve as an ideal testing ground to study analogues of a large variety of physical phenomena at accessible size and energy scales. In this work, I focus in particular on two particular aspects of LC systems. The first is chiral induction, in which a localized breaking of a mirror symmetry propagates from a surface or interface out into the bulk. The second is the study of several manner of topological defect (TD) systems.I begin by using two independent techniques to verify the presence of chiral induction due to a novel chiral nanoparticle prepared by collaborating chemists: an electroclinic effect (ECE) and a Raynes’ Geometry experiment. I then introduce chirality into a thin, linear array of topological defects known as “oily streaks” and demonstrate that a surface ECE produces a twisting of the molecular sublayers of the nanostructure that is incommensurate with the symmetry of the system and report the relaxation mechanisms by which this twisting is ameliorated.I then use atomic force microscopy (AFM) nanolithography to design a particular pair of surface TDs that produce bulk disclination lines that are topologically equivalent in 3D. When an applied electric field projects the director into a quasi-2D space, the topological equivalence is broken and the two disclinations undergo different transformations: one remains undisturbed, while the other splits in two.By applying this AFM nanopatterning technique to the substrate of thin films of the kind in the second experiment, I report an unexpected surface topography at the LC-air interface above the patterning and explore the mechanisms behind this topography.