Low-density polymer thin film formation in supercritical carbon dioxide

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 CO2 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. (C) 2003 American Institute of Physics