Anchoring strength of a nematic liquid crystal on 2D materials

The anchoring strength of a nematic liquid crystal, 4-cyano-4'-pentylbiphenyl, is estimated on two-dimensional materials such as graphene, MoS2, and hBN. The changes in brightness attributed to the director rotation at the outer boundary or at the boundary of the orientation domains in the two-dimensional materials are optically observed. Anchoring energy coefficients in the polar and azimuthal directions are estimated by comparing the brightness profile between the experimental observations and numerical calculations. The azimuthal anchoring coefficient is larger than that of polar anchoring for all cases. The polar anchoring of graphite increases with the layer number within 10 layers. The anchoring of graphite is larger than that of MoS2 and hBN flakes. Although restricted results were obtained due to the limitations of the measurement, these results may give hints for understanding the interaction between liquid crystals and two-dimensional materials and can be used for applications.