Studies on helical nanostructures of bent-core liquid crystals using template-assisted self-assembly

Abstract

There has been growing interests in the bent-core liquid crystal (BCLC) materials as functional nanobuilding blocks, because of its spontaneous polar and chiral properties from the bent-shaped molecular structures. Such an appearance of macroscopic polar-chirality is originated from the unique molecular assembling process, in forming of stacked layers of achiral molecules with a broken symmetry that exhibits macroscopic chirality, which is generally refered as a helical nanofilament (HNF) LC phase. In this research, we focus on the control of HNFs by introducing the concept of template-assisted hierarchical self-assembly (TASA) of BCLCs. This system is based on the coupling of two main concepts: (i) the use of confined geometries that linearly arranged rectangular microchannels and the films of Al2O3 populated with arrays of nm-scale pores by the anodic oxidation of aluminum (AAO), and (ii) the helical crystalline nanofilament (HNFs) formation from the bent-shaped mesogens. By using the relevant surface conditions with the well-designed geometries in micro- or nanoscale, we can achieve the controlled molecular assemblies that determine the final morphologies of the chiral superstructures. When expanded to the nanoscale confinement, we could achieve the controlled single HNFs with the tunable physical dimensions (length, width and helicity). For morphological modification of HNFs, we used two different experimental approaches: modifying the molecular structure at the synthesizing step and introducing another guest LC materials with bent-core LCs as binary mixtures into the nanoconfinement system. Under nano-scale confinement, the specific mutual interactions between two different LC materials could be maximized that finally modified the resulting HNF morphologies in three different shapes. From these few trials, we could successfully achieve a various shape of vertical HNFs with the controlled physical dimensions, and also find great potentials of our system to be expanded to the 3D-nanopatterning applications. We expect that our system will contribute to the fundamental understanding of the mesophase behavior of liquid crystals under limited spatial condition, and also will expand the field of future applications using LC materials.