Janus-like asymmetrically oxidized graphene: Facile synthesis and distinct liquid crystal alignment at the oil/water interface

Janus graphene oxide (GO) usually refers to a unique two-dimensional material with asymmetric surface chemistries on opposite faces of the sheets. Herein, we propose a facile and efficient method to fabricate Janus-like GO (JGO) with a novel asymmetric structure along the faces of the sheets. Unlike the traditional post-synthesis of double-faced Janus GO based on pre-prepared GO, the novel JGO with a randomly distributed asymmetric oxidation structure along the sheet face can be achieved by a simple ultrasonic treatment on partially oxidized graphene. The asymmetric oxidation structure along the sheet face of our Janus GO was confirmed by confocal micro-Raman imaging and analysis of height profiles by atomic force microscopy. Due to the asymmetric oxidation structure, the as-prepared JGO has amphiphilic characteristics, with hydrophilicity on one side of the sheet and hydrophobicity on the other side, leading to an eyelash-like liquid crystal alignment at the oil/water interface. The perpendicular alignment rather than the parallel orientation behavior of GO liquid crystals at the oil/water interface further confirms the asymmetric structure of our JGO along the face graphene sheets. The simple approach and a new class of JGO proposed herein provide a new insight into understanding the asymmetric chemistry of graphene.