Order Electricity and Oblique Nematic Orientation on Rough Solid Surfaces

We study surface orientation of nematic 5 CB on obliquely SiO evaporated glass plates, at grazing incidence. For SiO thickness comparable with nematic molecular length, we observe a twofold degenerate oblique orientation, which allows a continuous transition between the well-known planar and oblique orientations. This transition and the subsequent saturation of obliquity for thick evaporation are quantitatively explained by an order electric model. The surface rugosity decreases the nematic order parameter on the surface and forces an oblique alignment at the "magic" angle.