Surface effects on orientation of liquid crystals

Optical second harmonic generation (SHG) is now being used to measure the orientations of mesogens adsorbed at a variety of polar organic surfaces (e.g. rubbed films of polyimides). For some surfaces, at least, these measurements can be used to predict the anchoring of bulk liquid crystals. Few rules exist, however, to guide the design of surfaces for manipulation of the orientations of adsorbed mesogens (and thus bulk anchoring). These rules are difficult to establish on surfaces as complicated as those of rubbed polymers. Self-assembled monolayers formed from functionalized alkanethiols on semi-transparent films of gold and silver do permit the synthesis of well defined surfaces, and these surfaces are now being used in studies of the anchoring of liquid crystals. Orientations of liquid crystals on these surfaces differ substantially from orientations observed in the past on surfaces formed from organosilanes.