Polymer coatings by rapid expansion of suspensions in supercritical carbon dioxide

Suspensions of poly(2-ethylhexyl acrylate) in supercritical CO2 formed by dispersion polymerization with a poly(dimethylsiloxane)-based surfactant were sprayed to form uniform films. The viscosity reduction of the dispersed phase caused by dissolved CO2 is crucial for atomization to produce fine droplets, and for coalescence and leveling on the surface to form a uniform film. Re-suspension of the polymer after de-pressurization and re-pressurization led to modestly larger droplets in the suspension which produced a film nearly as uniform as the original one. Inferior films were produced by suspensions without surfactant. Unlike previous studies of rapid expansion of homogeneous polymer solutions and related techniques, films were produced from concentrated polymer mixtures without any organic solvent.