CO2 sorption induced dilation in polysulfone:: Comparative analysis of experimental and molecular modeling results

Experimental sorption and dilation data of the polysulfone/CO2 system at 308 K and pressures up to 50 bar were measured utilizing a gravimetric sorption balance and a dilatometer based on a capacitive distance sensor. The data of this glassy polymer/gas system were subjected to a thorough kinetic analysis on the basis of a viscoelastic model, which allows the separation of the diffusive/elastic fraction of the sorption/dilation process from the slower relaxational part. The results were interpreted in terms of the common dual mode sorption model and the site distribution model of Kirchheim. Detailed atomistic packing models of the same polymer/gas system were created for two reference states with regard to concentration and swelling. The CO2 sorption isotherms of the packing models corresponding to these two swelling states, calculated using GCMC simulations, could be combined in order to interpolate the gas uptake over the intermediate pressure range with good agreement to the experimental data. The elastic part of the gas induced dilation is successfully described by MD simulations and derived partial molar volumes are in satisfying agreement with experimental findings. Finally, the free volume of the packing models is probed and the obtained size distribution of the free volume elements is compared to the results of the analysis of experimental data according to the site distribution model.