Phase segregation in polymer thin films: Elucidations by X-ray and scanning force microscopy

We have used quantitative X-ray microscopy in combination with Scanning For ce Microscopy to monitor the phase separation of spun cast thin films of po lystyrene and poly(methyl methacrylate) blends upon annealing. Both techniq ues complement and enhance each other in elucidating the complicated struct ures that develop as a function of annealing time. We have determined the c omposition of the mixed phases that result from solvent spin casting. We su bsequently observe the sudden rearrangement into domains much smaller than those originally formed. Unique, intricate hydrodynamic mass flow patterns form during coarsening which are in qualitative agreement with recent simul ations of phase segregation in two-dimensional viscous fluids. Complicated polymer-polymer interfaces persist even in the later stages that are explai ned in terms of the geometric constraints of a thin film and the dependance of polymer viscosity on film thickness.