(542d) Concentration Gradients in Polymer Films Swollen with Supercritical CO2

The swelling of thin polymer films by supercritical carbon dioxide has been shown to exhibit an anomalous maximum in the sorption isotherms. This swelling maximum occurs when the activity of the fluid phase approaches unity and increases as the critical temperature is approached. Using an in-situ selective reactive templating approach based upon silica condensation within hydrophilic domains of an amphiphilic polymer film, the CO2 distribution within the film can be elucidated from size of the pores generated by the hydrophobic domains as examined using transmission electron microscopy of film cross sections. The origin of the maximum in the swelling of the thin films is demonstrated to be concentration gradients that extend from both interfaces of the film; as the temperature approaches the critical temperature, progressively larger local swelling at both interfaces is found. The impact of both temperature and finite film thickness on the concentration gradients will be discussed.