An evanescent wave ellipsometric technique is used to study the orientational wetting of $4^{\prime }$,4- alkylcyanobiphenyls $(n\mathrm{CB},n=5\mathrm{}–9)$ at the interface with a series of self-assembled monolayers. Brewster angle measurements are interpreted in terms of a global orientational wetting phase diagram ${(T,n,h}_1),$ where T denotes temperature, n is the alkyl chain length, and $h_1$ is the cosine of the contact angle of water with the monolayer. At temperatures below the isotropic-nematic phase transition temperature $T_{\mathrm{IN}},$ an anchoring transition from planar to homeotropic alignment occurs as the surface of the monolayer is made more hydrophobic. Homeotropic anchoring of the nematic director at $T<\mathrm{}{T}_{\mathrm{IN}}$ is associated with complete orientational wetting on approaching the isotropic-nematic phase boundary from temperatures above $T_{\mathrm{IN}}.$ The anchoring-wetting transition shifts to less hydrophobic surfaces as n increases.

• Received 8 September 1998

DOI:https://doi.org/10.1103/PhysRevE.59.3033