Molecular mechanisms of interphase evolution in the liquid polystyrene-glassy poly(phenylene oxide) system

Abstract

We report a diffusion study on a series of interphases formed between a polystyrene-rich (PS) liquid layer and a poly(phenylene oxide) (PPO) glassy matrix. Diffusion was promoted by annealing the polymer pair at several temperatures below the glass transition temperature of the PPO matrix, in experiments where the liquid component was supplied from an unlimited source. Depth PS concentration profiles were obtained via optical sectioning through the glassy layer with confocal Raman microspectroscopy. The PS profiles measured in all the samples had sharp diffusion fronts followed by a region with relatively uniform PS concentration. From the time evolution of the PS front advance, we directly obtained the time-scaling laws for interphase kinetics which are interpreted in the context of the Fickean and case II diffusion theories. Despite some recent studies reporting the occurrence of case II in this particular system, our results and analysis show conclusively that interphase kinetics are, on the contrary, markedly Fickean. Results previously published by other authors on this polymer pair are also analyzed with the aim of offering a unified view about the mechanism that controls interphase evolution at the molecular level. © 2009 American Chemical Society.