Structure and orientation control of liquid crystal defects by physical and chemical surface treatments

Abstract

Liquid crystal (LC) materials as one of soft building blocks possessing both anisotropy and fluidity have superior advantages such as rapid formation of structures, easy deformation by change of external environments including surface treatments, electric and magnetic fields. Despite of their unique properties, it is still difficult to apply to new applications except for liquid crystal displays (LCDs). Recently, smectic LC defect structures have been proposed as a new type of bottom-up lithographic templates. Especially, well ordered hexagonal array of toric focal conic domains (TFCDs) have shown various useful applications including particle trapping, soft lithographic templates, microlens array and photomask. However, closed-packed hexagonal arrangement of TFCDs by the circular defect line is a limitation as the lithographic template and decrease availability of applications. In this thesis, we introduce simple and cost-effective surface treatment methods for controlling the structures and orientation of LC defects. Physical surface treatments by multi-directional rubbing and physical stamping methods create linear ridges that affect the LC alignment in the polymeric alignment layers. Chemical surface treatment is achieved by printing metal salts on the substrate that influence the orientation of LC molecules with the patterned stamps. We believe that simple and easy approaches facilitate the use of LC structures, one of the lithographic templates, and enable applications to new optoelectronic devices.