The Coil–Globule Transition in Microencapsulation of TiO₂ Nanoparticles in a Supercritical CO₂ Jet

An experimental investigation was made of microencapsulation of titanium dioxide nanoparticles in PEG 8000 polyethylene glycol by pulsed expansion of a jet of a polymer solution in supercritical carbon dioxide into either a vacuum or a background gas (helium). In both cases, at a given initial temperature in the mixing reactor and a given cosolvent concentration, an electron microscopic study was carried out to determine the distance from the nozzle exit to the point in the jet axis in the vicinity of which the coil–globule transition was detected. The dependence of the position of the transition point on the initial temperature and the cosolvent (ethanol) concentration was characterized.