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Commending topological defects of liquid crystals (LCs) facilitates many configurational simulations and experimental manipulations of active soft matter for electro-optical (EO), optical and photonic applications. In this dissertation, investigation of topological defects in cholesteric liquid crystals (CLCs) enables better visualizing and control unique self-assembly, dielectric and optical properties of CLCs and leads to the development of a fast switching active retarder film based on a CLC with uniform lying helix (ULH) texture, a bistable light diffractive CLC films based on metastable bubble domain (BD) texture, and an in-plane-switching (IPS) LC device based on two-dimensional graphene electrode.We first demonstrate a giant flexoelectro-optic effect (FOE) in a CLC with ULH texture. The electric-field-induced helical axis (HA) rotation of a ULH structure due to flexoelectric coupling is accomplished by the surface-localized polymer network stabilization. A 40 times enhancement in flexoelastic coefficient compared to a conventional CLC materials is achieved by using the CLC based on CB7CB bimesogen. The giant FOE of a polymer-stabilized ULH (PS-ULH) enables the development of an active retarder having high optical contrast and sub-millisecond response time.The second part of dissertation is to investigate topology-mediated optical and electro-optical properties of CLCs with BD texture (CLC-BD) providing unique bistability between the light transmission and light scattering states. The CLC-BD device requires electric field only during switching between transparent and opaque states creating great potential applications as active diffusers and smart windows. An opto-mechanical modulation is demonstrated with a light-sensitive chiral azo-benzene dye doping in a CLC-BD device. To close, the augmentation of EO behavior in a nematic IPS device with graphene transparent electrode is demonstrated. We command the EO switching on photo-lithographically-patterned graphene electrode with a highly-effective non-contact LC photoalignment method to maximize the field-driven optical contrast of a prototyped device. Our experiments provide a solution for technical challenges related to processing and handling of two-dimensional graphene on rigid and flexible substrates and facilitate the applications of graphene for devices with complex and high-definition electrode patterns. |
