Light scattering study of polydimethyl siloxane in liquid and supercritical carbon dioxide

In this paper, we report the results of static and dynamic light scattering investigations of polydimethyl siloxane (PDMS) solutions in both liquid and supercritical carbon dioxide (CO2). This study was performed below the theta point and provides quantitative information on the CO2 solvent quality over a large range of temperature (25-54 degreesC) and density (0.97-1.01 g/mL). The solvent quality of the CO2 can be adjusted by independently varying temperature or density, as demonstrated by the dependence of the second virial coefficient on these two parameters. The theta temperature was observed to be a strong function of CO2 density and may be a weak function of the PDMS molecular weight. The strength of the excluded volume interactions in the PDMS-CO2 solution was determined to be weaker than predicted, and no universal behavior was observed.