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

• Published in: Materials today communications 2021-09, Vol.28, p.102539, Article 102539
• Main Authors: Son, Seung-Rak, An, Jongil, Choi, Jin-Wook, Kim, Soyern, Park, Jisung, Lee, Jun Hyup
• Format: Article
• Language: English
• Subjects: Graphene oxide; Nematic liquid crystals; Self-assembly; Surface functionalization; Vertical alignment layer
• ISSN: 2352-4928; 2352-4928
• DOI: 10.1016/j.mtcomm.2021.102539

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. [Display omitted] •The amphiphilic AGO spontaneously formed an ultrathin 2D molecular layer on ITO surface.•The 2D AGO alignment layer induced stable vertical alignment of the NLCs.•The AGO with a high grafting density afforded a uniform and straight NLC orientation.•A high transmittance and comparable electro-optical properties of the device were achieved.