Polymer coatings by rapid expansion of suspensions in supercritical carbondioxide

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