Characterization of the rapid expansion of supercritical solutions by Fourier transform infrared spectroscopy in situ

A new apparatus for the in situ characterization of the rapid expansion of supercritical solutions (RESS) by Fourier transform infrared spectroscopy is presented. The infrared characterization is complemented by particle sizing with a scanning mobility particle sizer, by three-wavelengths-extinction measurements, and by scanning electron microscopy. Several examples show that a wide range of information about particle properties can be obtained with this setup. One new aspect is the possibility to expand into the vacuum which also allows us to investigate the conditions in the collision-free region before the Mach disk. These investigations elucidate that in the free jet region the solvent CO2 condenses to particles with mean radii >50 nm for pre-expansion pressures between 100-400 bar and temperatures between 298-398 K