We review the effects of solvent density inhomogeneties in CO₂ on the swelling and dynamics of the polymer thin films. Using neutron reflectivity (NR) we found that CO₂ could be sorbed to a large extent in polymer thin films even when the bulk miscibility of the polymers with CO₂ was very poor. The swelling was reversible and reached a maximum at pressures and temperatures along the density fluctuation ridge which forms along the extension of the coexistence curve of gas and liquid in the pressure- temperature phase diagram for CO₂. The functional form of the dilation amplitude followed that of the density fluctuations as a function of temperature and pressure. In addition, the NR measurements showed that uniform density films were formed with a maximum roughness less than 25 Å. Hence we concluded that the swelling did not seem to be associated with phase separation which ultimately leads to a void formation when CO₂ is rapidly evaporated as previously reported for the bulk films. We have also studied the dynamics of polymer thin films in CO₂ by means of NR and dynamic secondary ion mass spectrometry (DSIMS) measurements. The results show that the large degree of anomalous swelling observed is associated with a decrease in glass transition temperature that occurs only within a narrow region associated with the density fluctuation ridge. Within the ridge the diffusion coefficients scale as M^-2 and can be approximated by an effective William- Landel-Ferry (WLF) equation.