Acetic acid aerosol particles, formic acid aerosol particles and mixed acid/ice particles were generated in a collisional cooling cell at a temperature of 78 K and investigated using in situ rapid scan Fourier transform infrared spectroscopy. The infrared spectra reveal that the internal structure of the particles critically depends on the particle formation conditions and, especially for the mixed particles, on the composition. The acetic acid particles are likely to have only a partially crystalline structure whereas the formic acid particles are likely to have an overall crystalline structure. The existence of acid in the mixed acid/ice particles prevents the ice from crystallization even at low acid concentrations (less than 10%). Mid-infrared refractive index data were derived from the different particle spectra, which can be helpful for remote sensing of such systems.

Pure naproxen particles and mixed naproxen-polylactic acid particles were formed by pulsed rapid expansion of supercritical CO2 solutions (RESS). The characterization of the particles was carried out in the aerosol phase as a function of time after particle formation with rapid-scan infrared spectroscopy and with an aerosol particle sizer. After collection of the particles from the aerosol phase, the particles were characterized with scanning electron microscopy and powder diffraction. The present study shows clear evidence that RESS is capable of forming sub-micron naproxen particles that are coated with polylactic acid. Furthermore, it is demonstrated that coating with polylactic acid stabilizes the naproxen particles against agglomeration and coagulation.

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Free‐radical terpolymerizations of styrene, methyl methacrylate, and glycidyl methacrylate were carried out in a tubular reactor in the presence of 20 wt.% CO2 at temperatures between 120 and 180°C and pressures of 300 and 350 bar. The number average molecular weights, MN, were mostly between 2000 and 3000 g·mol−1 and polydispersity indices around 2. In part of the experiments molecular weights were controlled by n‐dodecyl mercaptan serving as the chain‐transfer agent. PREDICI modeling indicates that the targeted molecular weights of MN∼2500 g·mol−1 and polydispersities around 2 may also be reached by using an initiator cocktail, a mixture of two initiators with significantly different decomposition rate coefficients. The predictions are confirmed experimentally.