Graphene Oxide Liquid Crystals Aligned in a Confined Configuration: Implications for Optical Materials

Orientation control of two-dimensional (2D) colloidal liquid crystals in both microscopic and macroscopic scales holds massive promise for improved multifield applications. In this respect, graphene oxide (GO) is used as a platform substance for 2D carbon-based lyotropic liquid crystal (LC) materials. Here, we design the directed alignment of aqueous GO -LC dispersion confined in a rectangular capillary tube. The isotropic GO dispersion is loaded into a horizontal capillary and subsequently concentrated to the LC phase by slow water evaporation at open ends of the tube. An obtained surprising result, GO layers organize normal to the inner surfaces of the capillary with a highly ordered orientation of the optic axis over tens of millimeters. Such transverse orientation of GO layers originates from the meniscus region and then moves toward the center, caused by the interfacial effect and the sequential isotropic-to-nematic transition. This aligned mesomorphic system is characterized via optical retardation, nematic order parameter, absorption, and modified Cauchy's transmission equation about the dependency of both birefringence and wavelength with concentration. Finally, the aligned GO-LC layers are preserved in a polymer composite matrix by photopolymerizing the evaporation-aligned GO/acrylamide-LC dispersion confined in a capillary. This composite shows higher thermal stability than polyacrylamide until 500 C of about 6.1%. Our experimental findings provide efficient advantages for controlling the orientation of GO-LC and 2D materials, beneficial for diverse optical applications due to their directional ordering.