AUTOPHOBICITY AND LAYERING BEHAVIOR OF THIN LIQUID-CRYSTALLINE POLYMER-FILMS

The stability against breaking-up of thin spin-coated films of liquid- crystalline polymers depends on the film thickness and annealing tempe rature. This study concerns side-chain liquid-crystalline polymers, ba sed on alternating copolymers of maleic anhydride and mesogenic alkene s. The mesogenic group is a methoxybiphenyl. The as-prepared films are homogeneous and remain stable below the glass transition temperature, Upon annealing above this temperature, the films start to dewet. At t he final stage of dewetting only droplets remain on top of a rather st able bilayer, which itself does not participate in the dewetting. This indicates autophobic behavior. The bilayer is even present above the isotropization temperature. In the mesophase we have a layered film, a nd dewetting may occur over several ordered layers. In all cases the d ewetting is not linear in time and polymer slippage seems to take plac e on top of the stable bilayer. In the case of polymer slippage, a t(2 /3) dependence is expected for the growth rate. That is indeed found a bove the isotropization temperature. In the mesophase the dewetting di ffers from the ''normal'' slippage behavior and a weaker time dependen ce is observed. Around the isotropization temperature there is a stron g increase in the (initial) dewetting velocity of over more than 2 ord ers of magnitude, due to the sudden drop in viscosity.