Studies on dynamic behaviors of liquid crystalline defects

Abstract

Anisotropic-shaped organic molecules exhibit an intriguing behavior as a ordered fluid in liquid crystal phases. The molecules in the liquid crystal phases own electrical as well as optical anisotropic characteristics, which has led them to be most popular substances in optoelectronic devices. Until the present, it was a main aim that performance enhancement of the optoelectronic devices by minimizing defects self-assembled by liquid crystal molecules. However, control of the defects has been extensively studied to broaden the application fields of the liquid crystals, since their potential as building blocks for new applications were demonstrated. In this thesis, we mainly discuss dynamic behaviors of liquid crystalline defect structures self-assembled by external forces. Our main research activities in this thesis are the development of platforms that can give dynamic behavior to liquid crystal molecules, the analysis of the defect structures and the electro-optical characterization of optoelectronic devices built up by the defect structures. This thesis consists of four chapters. In the opening chapter (Chapter 1), we briefly introduce basic concept of liquid crystals and research objectives. In the other chapters, we demonstrate a platform to effectively provide dynamic behaviors to the defect structures. Firstly (Chapter 2), we build up the system using surface modification of substrates and an in-plane electric field. In chapter 3, we present effective way, which is a combination method of topographic patterning and applying in-plane electric field, to control smectic defect structures. In the last chapter (Chapter 4), we utilize a fluid as a substrate to observe thermal transition behavior of the defects. We believe that these platforms demonstrated in this thesis are increasingly important in materials science, because they can be directly applied to diverse soft materials as well as other liquid crystal phases. Furthermore, from the viewpoint of technology, the defect structures generated by the platforms can broaden liquid crystal based applications beyond the display applications, which is very important in this LC research field because the research field related with conventional LC phase has been more or less saturated in the industry.