Surface modification of polymeric nanocomposite thin films using supercritical carbon dioxide

We report on an efficient and environmentally friendly means to modify surface properties of polymer films supported for nanoparticles. Ultrathin polystyrene (PS) films (<300 Å), in which inorganic nanoparticles were embedded, were exposed to supercritical carbon dioxide (scCO2). The swollen structure was then preserved by quickly evaporating CO2. X-ray reflectivity (XR) results showed that this procedure produced polymeric nanocomposite films with a low-density region of about 150 Å at the polymer/air interface. The formation of the low-density layer was independent of the nature of the particles, indicating that the surface modification through exposure to scCO2 may be a universal phenomenon regardless of a choice of nanoparticles.