A new approach for directional homogeneous alignment of liquid crystals using electric field-guided orientation of nonionic amphiphiles

Abstract

Conventional homogeneous alignment of liquid crystals (LCs) utilizes rubbed or photo-aligned polyimide surfaces that determine the molecular orientation of LCs along in-plane direction. However, this alignment method based on polymeric layer requires complicated layer forming processes and considerable synthetic effort for special functional polyimides. In this study, a simple and unprecedented directional alignment approach has been developed to horizontally align nematic LCs using electric field-guided orientation of nonionic amphiphiles, spontaneously forming nanoscale supramolecular thin layer on the indium tin oxide substrate via hydrogen bonding. The in-plane electric field between simple slit electrodes induced the horizontal orientation of the anchored amphiphilic molecules parallel with electric field. Furthermore, the subsequent immobilization of inclined amphiphiles along a directional electric field through photopolymerization of common mesogenic diacrylates within LC medium resulted in a new type of homogenous alignment layer with a well-defined orientation direction for LCs. The proposed facile alignment methodology using small quantities of nonionic amphiphiles and mesogenic diacrylates afforded uniform and stable planar alignment of LC molecules with the controlled director. This novel alignment approach is expected to find a wide range of potential applications involving LC displays, optically patterned retarders, biosensors, and electronic lenses.