Wetting and dynamics of structured liquid films

The stability of a sufficiently thin, supported, homopolymer film against the development of local thickness fluctuations which can become amplified, eventually leading to structural destabilization of the film, is typically determined by long and short-range intermolecular forces. In A-B diblock copolymers, the connectivity between the blocks, the preferential attraction of one block to an external interface, combined with an incompatibility between the A-B segments, the situation is very different. Two cases, largely dictated by chiN, when chi is the Flory-Huggins interaction parameter and N is the degree of polymerization, can arise in thin copolyme films. When chiN is large, thin films exhibit comparatively stable topographical structures, where the dimensions of the topographies normal to the substrate reflect a natural length-scale associated with phase separation in the material. In the other situation, where chiN is sufficiently small, the copolymer bulk structure is homogeneous. An ordered structure can be induced into the otherwise compositionally homogeneous structure in the vicinity of a substrate. Here, depending on film thickness, a series of transient and stable topographies can develop. Wetting, early stage structural destabilization dynamics leading to the formation of droplets, and late stage coarsening of the droplets are discussed. (C) 2003 Wiley Periodicals, Inc.