Studies on liquid crystal phases under nanoconfinement and their optical applications

Abstract

Manipulation of micro- and nano-structures based on soft matter over a large area has been of interest in the material sciences and industrial applications because this is believed to be an alternative tool for the lithographic applications that have been achieved by top-down photolithography. Indeed, these soft matter based approaches have been further extended to other advanced applications, such as organic semiconductor based devices, soft templates for nano-objects trapping and nature-inspired biomedical applications. All these achievements could be attained by the ordering and orientation control of soft matter at micro and nanometre-scales. Among the various kinds of soft matter, liquid crystal (LC) material is particularly susceptible to external environments in which its orientation can be easily controlled using various methods. This simple alignment method is very useful to control the orientation of LC structures, but sometimes this is not sufficient to obtain a uniformly aligned large domain without defects. To maximise the surface anchoring effect, topographical confinement can be used, and the resultant large surface-to-volume ratio gives rise to much stronger LC/surface interaction. This effort can also yield exceptional physical property changes that are not presented in a bulk state, such as the suppression of thermal phase transitions and unusual mechanical behavior. In this Ph.D. thesis, control of liquid crystal phases using confined geometries is discussed. The controlled LC in the nano-confined geometry exhibits the particular physical property, whereas it can be varied during the phase transition. As combining this aspect into optical structures such as photonic crystals and plasmonic structures, the light can be modulated in the nanoconfined LC medium, which can be a basis for demonstrating switchable optical structures.