Anchoring and orientational wetting of nematic liquid crystals on self-assembled monolayer substrates: An evanescent wave ellipsometric study

An evanescent wave ellipsometric technique is used to study the orientational wetting of 4',4-alkylcyanobiphenyls (nCB,n = 5-9) 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-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 < T-IN is associated with complete orientational wetting on approaching the isotropic-nematic phase boundary from temperatures above T-IN. The anchoring-wetting transition shifts to less hydrophobic surfaces as n increases. [S1063-651X(99)12002-6].