A microstructural study of polystyrene—polyether sulphone polymer blends

Polystyrene (PS)‐polyether sulphone (PES) polymer blend thin films were prepared for investigation in a scanning transmission electron microscope. The microstructures of PS‐PES films (prepared by drawing from solutions at temperatures above ambient) of three different compositions were characterized: (1) 75 wt% PS‐25 wt% PES, (2) 50 wt% PS‐50 wt% PES, and (3) 25 wt% PS‐75 wt% PES. For films prepared at ∼ 40°C all three compositions exhibited microstructures consisting of spherical inclusions, ranging from ∼0.2μm to ∼ 1.2μm in diameter. The microscope used here was equipped with an energy‐dispersive X‐ray spectrometer, and this was employed to determine the chemical content of the inclusions and the matrix material. From X‐ray analysis, it was found that films (1) and (2) consisted entirely of PES‐rich inclusions, while film (3) contained both PS‐rich and PES‐rich inclusions. In addition, these analyses revealed that films (2) and (3) possessed a ‘mixed’ PS‐PES matrix phase. At the other temperatures for film preparation some significant differences in morphology were observed, reflecting the different rates of solvent evaporation.