Liquid crystal defect patterning in various confinement geometries and their applications as opto-electronic devices

Abstract

Template assisted self-assembly technique, which use a combined bottom-up with self-organization and top-down with lithographic templates, is one of the most interesting issues in current nanotechnology and material science researchers. This method not only generates building blocks such as colloidal particles, block copolymers, supramolecules and surfactants with perfect ordering, but also creates many hierarchically complicated structures. In this thesis, we introduce well-ordered and perfect-shaped defect structures of a common smectic LC, 8CB (4’-n-octyl-4-cyano-biphenyl), using template assisted self-assembly techniques. A synthetic rod-like smectic liquid crystal containing a rigid aromatic group and semi-fluorinated chains generates well-ordered toroidal structures called toric focal conic domains (TFCDs) as self-assembling building blocks when confined within rectangular micro-channels. However, in case of readily available smectic liquid crystals, 8CB, the ordered arrangement of TFCDs is a challenging work because of their high mobility and low elasticity. Although recent efforts in control of 8CB defect structures, such as toric focal conic domains (TFCDs) have been performed by confining micron sized rectangular channel with surface polarity, TFCDs could not be aligned in the center of the channels. However, by only changing the confined geometry, we could fabricate the uniform sized and perfect shaped defect patterns of 8CB. This is attributed to the combining effects between antagonistic surface anchoring conditions and precisely directed molecular orientation onto inclined side walls of trapezoidal channel. Furthermore, size and ordering of arrays of 8CB can be simply controlled by varying the feature dimension of bottom width (l) and depth (h) in the trapezoid-shaped channel. Also, we suggest thermally responsive microlens arrays (MLAs) as a potential application based on liquid crystal defect pattern. This system focuses light using both the i...