Topography and surface composition of thin films of blends of poly(methyl methacrylate) and poly(ethylene oxide)

Thin films of PMMA-PEO blends have been formed by spin casting. The AFM images of PEG-rich films have an angular character associated with the crystallinity of the polyether. Addition of PMMA produces more rounded submicron features with height of the order of nanometers, which annealing studies suggest are PMMA-rich regions. Heating for an hour above the T-g of PMMA leaves a smooth surface. The topographical features are postulated to arise from metastable phases formed during the solvent evaporation. For a series of blends of constant composition with varying molecular weights of PMMA, a linear relationship is obtained for the average height of the features versus the radius of gyration of PMMA, with the step height corresponding to four PMMA molecules. The surface compositions of the films were determined by XPS and SIMS. Segregation of PMMA, observed for unannealed, low PMMA content blends, is ascribed to the partial crystallinity of the films, while higher PMMA content blends have similar surface and bulk compositions.