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We investigate the physical foaming process of glassy poly(ether imide) and poly(ether sulfone) using carbon dioxide and report temperature−concentration diagrams (“foam diagrams”) marking out the foaming envelope in which dense CO2-saturated films expand and microvoids are introduced. Two types of porosities are observed. Closed microcellular structures occur at carbon dioxide saturation levels below 50 cm3 (STP)/cm3 (polymer); nanoporous bicontinuous (open) structures with pore sizes as small as 40 nm occur above this CO2 concentration threshold, which is identical for both polymers. The cellular-to-bicontinuous transition is characterized in detail on the basis of gas permeation measurements and is represented as a separate window inside the foaming diagram. In this paper, the transition to bicontinuous structures is reported for the first time, and its generic physical basis is critically reviewed.

This paper presents an analysis of the sorption kinetics of water vapor and liquid water in the glassy polymer sulfonated poly(ether ether ketone) (S-PEEK). Sorption isotherms are determined experimentally using a gravimetric sorption balance, and the relative contributions of Fickian diffusion and relaxational phenomena are quantified as a function of the water concentration in the polymer using the model of Hopfenberg and Berens.Analysis of the sorption isotherms and determination of the sorption kinetics prove the occurrence of both Fickian sorption behavior and relaxational phenomena already at very low water concentrations in the polymer. With increasing water concentration, the relative importance of relaxation phenomena increases, whereas the relative contribution of Fickian diffusion decreases.Based on the water vapor sorption kinetics only, the Fickian diffusion coefficient increases over two orders of magnitude with increasing water vapor concentration. Taking also the diffusion kinetics from liquid water sorption experiments into account reveals a change of even three orders of magnitude of the Fickian diffusion coefficient when the water concentration in the polymer increases.