Advances in phase-sensitive acoustic microscopy studies of polymer blend films: annealing effects and micro-elastic characterization of PS/PMMA blends.

The unique phase-sensitive acoustic microscope is used for the structural and mechanical characterization of thin films of polystyrene/polymethylmethacrylate blends. The effect of annealing on blends of polystyrene/polymethylmethacrylate spin coated from different solvents unto a substrate is studied. Varying the solvents according to vapour pressure and spin coating at different speeds (for thickness variation) led to changes in phase domain distributions and overall structural properties before annealing. Annealing in vacuum at 190 degrees C for 48 h resulted in the elimination of solvent effects with all samples reverting to a similar morphology irrespective of common solvent and thickness. The Young's moduli at specific points on the film (E(polystyrene)= 3.4 +/- 0.3 GPa, E(polymethylmethacrylate)= 4.2 +/- 0.4 GPa) and over a given area (E(polystyrene/polymethylmethacrylate)= 3.9 +/- 0.4 GPa) were determined by combinatory use of the atomic force microscope and phase-sensitive acoustic microscope. These results demonstrate a minimally invasive method for the quantitative characterization of polymer blend films.