Engineering Nematic Liquid Crystal 5CB Alignment Using Graphene Oxide Coatings

Liquid crystal (LC) devices traditionally employ polyimide-coated substrates with unidirectional rubbing to establish a stable nematic director orientation. However, graphene-based surfaces offer an alternative alignment strategy due to their unique molecular interactions with nematic liquid crystals (NLCs). The honeycomb lattice of graphene, with a C–C bond length of 1.42 Å, closely matches the 1.40 Å bond length of benzene rings in typical NLC molecules, enabling epitaxial-like interactions. These interactions are dominated by π–π electron stacking between the aromatic cores of the LC molecules and the graphene lattice, producing uniform planar alignment over large areas. The resulting binding energy, estimated between 0.74 and 0.88 eV per molecule, is associated with partial charge transfer and delocalized π-orbital overlap, further stabilizing the LC orientation.

In this study, we investigated the anchoring properties of nematic 5CB liquid crystal on graphene oxide (GO) thin films using the saturation voltage method (SVM). This approach applies a potential difference to reorient the director from planar to homeotropic, enabling quantitative assessment of anchoring strength. Measurements were performed on sandwich cells with indium–tin oxide electrodes coated with GO and compared with reference cells exhibiting strong (polyimide) and weak (formvar) anchoring. Our results demonstrate that GO substrates significantly influence nematic alignment, highlighting their potential in advanced liquid crystal technologies, including GHz–THz transducers.