Transient Wetting and 2D Spinodal Decomposition in a Binary Polymer Blend

We have used ion beam analysis and scanning near-field optical microscopy to characterize the three-dimensional domain structure of a thin film of a phase-separating polymer mixture. In the initially mixed film, there first occurs coverage of one of its surfaces by an unbroken layer of one phase; between this "wet" surface and the substrate, layers of domains form. Eventually, the layered domain structure becomes unstable, and a transformation occurs to the equilibrium wetting state where both phases are in contact with both surfaces, causing a phase separation to be purely two-dimensional at later times. During this "transient wetting" process, lateral and vertical domain sizes grow with time as t 1/3 independent of the dimensionality of the domains.