Surface-anchored alkylated graphene oxide as a two-dimensional homeotropic alignment layer for nematic liquid crystals

Abstract

Graphene oxide (GO) is one of the thinnest two-dimensional (2D) organic materials and has been investigated for application in various fields due to its excellent mechanical and optical properties. The unique planar structure and hydrophilic functional groups allow GO to spontaneously form various nanoarchitectures. Herein, we report an unprecedented methodology to achieve the homeotropic alignment of nematic liquid crystals (NLCs) using surface-anchored alkylated graphene oxide (AGO). The GO is functionalized by amino reactions with dodecylamine to impart amphiphilic characteristics. This AGO spontaneously forms a 2D-alignment layer on indium tin oxide surface via polar affinity, and the hydrophobic alkyl chains of AGO guide the constant direction of the NLCs. Furthermore, a study on the effect of the alkylation ratio of AGO on the NLC orientation was conducted, and the achievement of a 2D-alignment layer based on the optimal AGO successfully resulted in the initial homeotropic orientation of the NLCs without any defects. Compared to a conventional polymer alignment layer, it showed a comparable alignment ability, and exhibited an improved optical transmittance due to the ultrathin nature of the AGO alignment layer. This new modus of NLC vertical alignment based on the use of AGO can expand the utility of functionalized GO.