Small angle x-ray scattering study on the conformation of polystyrene in toluene during adding anti-solvent CO₂

The conformation of polystyrene in the anti-solvent process of supercritical fluids (compressed CO₂ + polystyrene + toluene) has been studied by small angle x-ray scattering with synchrotron radiation as an x-ray source. Coil-to-globule transformation of the polystyrene chain was observed with the increase of the anti-solvent CO₂ pressure; i.e. polystyrene coiled at a pressure lower than the cloud point pressure (P_c) and turned into a globule with a uniform density at pressures higher than P_c. Fractal behaviour was also found in the chain contraction, and the mass fractal dimension increased with increasing CO₂ pressure.