Density-Fluctuation-Induced Swelling of Polymer Thin Films in Carbon Dioxide

Abstract

We report an anomalous swelling of polymer thin films in carbon dioxide (${\mathrm{C}\mathrm{O}}_{2}$) which is associated (in both locus and form) with the density fluctuation ridge that forms along the extension of the coexistence curve of gas and liquid in the $P\mathrm{\text{\ensuremath{-}}}T$ phase diagram. Neutron reflectivity results showed that ${\mathrm{C}\mathrm{O}}_{2}$ could be sorbed to a large extent ($\ensuremath{\sim}60%$) in thin polymer films even when the bulk miscibility of the polymer with ${\mathrm{C}\mathrm{O}}_{2}$ is very poor. The anomalous swelling is found to scale with the polymer radius of gyration (${R}_{g}$) and extends to a distance approximately $10\text{ }{R}_{g}$.