Study on the patterning of liquid crystal polymer network and MXene using electric field and its application

Abstract

Liquid crystalline materials, which are molecularly oriented in a specific direction, have different physicochemical properties depending on their arrangement. Therefore, it has recently received much attention to finely control the arrangement of liquid crystalline materials. Liquid crystal polymer networks (LCN) and MXenes, which have been actively studied due to their unique properties, are representative liquid crystalline organic and inorganic materials, respectively. This thesis deals with the study of using electric field to implement fine patterning of LCN and vertical alignment of MXene, which were challenging with previously reported methods. Stimuli-responsive deformation of LCN can be pre-programmed by controlling the mesogenic unit alignment. However, it is challenging to develop micro- or nano-scale periodic structures of liquid crystalline polymer materials using previous reports. For example, when trying to make various micro-structures using photo-alignment layer, which is the most widely used technique, it is inefficient to manufacture all the polarizing masks suitable for each structure. In this study, we designed cross-electrode cells for fine LCN micro-structures using the dielectric anisotropy of mesogenic unit and showed that more than 20 structural modifications are possible by changing the configuration of the electric field applied per a cell. Finally, the possibility of application as a next-generation tactile material was confirmed by observing the change in friction depending on the dynamic structural deformation of the fabricated LCN film. MXene is a type of transition metal carbide, nitride, and carbonitride having a two-dimensional structure. Controlling the orientation of MXene has recently been considered as an important task, because its characteristics of the high conductivity and high density of the surface terminal groups vary depending on the alignment direction. However, in particular, aligning pure MXene vertically to the substrate in a large area has not been studied so far because of its physical instability. In this study, the vertical arrangement of the MXene was achieved by applying a in-plane electric field to the aqueous solution. The arrangement of the MXene was confirmed using a polarization microscope and a scanning electron microscope. It is expected that the vertically arranged MXenes can be used as long-wavelength laser polarization tools, sensors, or high-efficiency capacitor in the future.