Ordering and dewetting in spin-coated films of a liquid crystalline main chain polymer

The ordering of spin-coated films of a main-chain smectic liquid crystalline polymer with an azobenzene group connected by flexible spacers to a phenyl malonate unit has been studied as a function of film thickness using scanning force microscopy and UV/Vis spectroscopy. Already the as-prepared films are characterized by a significant out-of-plane orientation of the azobenzene groups. Annealing of films thicker than 7 nm results in aggregation and homeotropical alignment of azobenzene groups forming smectic layers parallel to the substrate. An optically isotropic mesophase was found upon annealing in the temperature range of smectic mesophase.Films thinner than the bilayer thickness of 7 nm exhibit a completely different behavior, whereby spin-coating results in a spontaneously homeotropic alignment of the azobenzene units. A subsequent annealing generates a structure of holes and rims. Within the holes a polymer monolayer remains, planarly aligned to substrate.