We report a method for producing stable low-density polymer films by using supercritical carbon dioxide (scCO 2). Two different molecular weight polystyrene films with various thicknesses were exposed to scCO 2 along the density fluctuation ridge in P-T phase diagram. The swollen structures could be then frozen by flash evaporation of CO 2 without forming additional voids. X-ray reflectivity data clearly showed that exposure to scCO 2 could be used to produce uniform low-density films of about 2R g thick or less, where R g is radius of polymer gyration.

We investigated an effect of CO2 sorption on the compatibility of immiscible polystyrene (PS) and polybutadiene (PB) bilayers by using in situ neutron reflectivity. By labeling either polymer with deuterium, we found that the excess CO2 molecules were adsorbed to both top PS and bottom PB layers when the bilayers were exposed to CO2 at the narrow T and P regime near the critical point of pure CO2. Furthermore, we clarified that this excess sorption of CO2 molecules increased the interfacial width between the layers up to 100 angstroms even near room temperature, while the interfacial width without CO2 exposure has been reported to be at most 40 A even at the highest temperature (T congruent with 175 degrees C).