Graphene-oxide-doped oriented nickel oxide film achieved through brush coating for liquid crystal system

Hybrid films containing nickel oxide and graphene oxide are introduced in this work. The hybrid films are fabricated through a one-step brush-coating process, and the weight ratios of graphene oxide are controlled to 0, 5, and 15 %. The fabricated hybrid films show oriented nano/microgroove structures on their surfaces by directional shear stress, which originates from the brush hair movements during the solution-processed brushcoating process. The hybrid film formation is confirmed using X-ray photoelectron spectroscopy. The films also demonstrate high optical transmittance with amorphous structures. The hybrid films are then used to form liquid crystal (LC) alignment layers, and uniform as well as homogeneous LC alignment is confirmed via polarized optical microscopy and pretilt angle analyses. Compared to the pure nickel-oxide film, the hybrid film with graphene oxide enhances LC alignment stability by increasing the polar anchoring energy of the surface LC molecules. From these observations, the hybrid film containing metal oxide and graphene oxide is expected to be a promising alternative for functional LC systems.