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 Force Microscopy to monitor the phase separation of spun cast thin films of polystyrene and poly(methyl methacrylate) blends upon annealing. Both techniques complement and enhance each other in elucidating the complicated structures that develop as a function of annealing time. We have determined the composition of the mixed phases that result from solvent spin casting. We subsequently 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 simulations of phase segregation in two-dimensional viscous fluids. Complicated polymer-polymer interfaces persist even in the later stages that are explained in terms of the geometric constraints of a thin film and the dependance of polymer viscosity on film thickness. Thin film polymer blends have considerable technological importance and are used in numerous applications ranging from multi-color photographic printing to paints, adhesives and protective coatings. Compared to the bulk properties, less is known about the properties of blends when they are processed into thin films. Numerous studies [1-10] have shown that for binary polymer blends the spinodal decomposition and coarsening process can be more complex in thin films where various boundary conditions are imposed. Most of the recent studies of phase separation in thin films relied on various scanning force and optical microscopy methods. These methods can only probe features that vary in topography, mechanical properties or have large differences in reflectivity, and hence these studies have mostly concentrated on () E-mail: Harald [email protected]