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

We report an anomalous swelling of polymer thin films in carbon dioxide ([Formula presented]) 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 [Formula presented] phase diagram. Neutron reflectivity results showed that [Formula presented] could be sorbed to a large extent ([Formula presented]) in thin polymer films even when the bulk miscibility of the polymer with [Formula presented] is very poor. The anomalous swelling is found to scale with the polymer radius of gyration ([Formula presented]) and extends to a distance approximately [Formula presented].