Difference in the annealing behaviour of thin films of PS/PMMA blends and copolymers as revealed by ToF-SIMS and AFM

Surface characterization of thin films of polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends and diblock copolymers was done using time-of-flight secondary ion mass spectrometry (ToF-SIMS) and atomic force microscopy (AFM) in order to compare their annealing behaviour. The spin-cast films, of 12 nm thickness, were annealed at 160 degreesC for different time periods ranging from 2 hours to 1 week. ToF-SIMS spectra of annealed blends showed a decrease in the concentration of PS and an increase in the concentration of PMMA on the surface as compared to the as-cast sample. The spectra of copolymers showed an increase in concentration of PS on the surface on annealing, with PMMA concentration decreasing. AFM images with the help of SIMS information allowed us to conclude that in the case of blends, PS formed droplet-like domains on a PMMA matrix and, in copolymers, PS with its lower surface free energy segregated to the surface without complete phase separation, which is not possible for copolymers. Copyright (C) 2004 John Wiley Sons, Ltd.