Time-Resolved Diagnostics of Explosive Boiling of Ibuprofen Solution in Subcritical CO2: From Microaggregates to CO2 Nanoclusters

Using an in situ method of time-resolved Mie scattering indicatrix registration, the dynamics of micro- and nanoparticle formation during the explosive boiling of a solution of ibuprofen in subcritical carbon dioxide (T0 = 302 K, P0 = 71 bar) were investigated. The process is found to exhibit multistage behavior. At the jet front, ibuprofen microaggregates with a mean radius of 1.4 ± 0.2 μm are formed, maintaining a stable size over the initial ~100 ms. Subsequent reduction in boiling intensity results in a decrease in the particle radius to 650 ± 100 nm. In the following stage, nanoscale CO2 clusters (20–50 nm) are detected by the Mie scattering technique. The findings indicate that the final size of the resulting ibuprofen particles is governed not only by the initial thermodynamic conditions but also by the boiling dynamics of the ibuprofen-saturated CO2 solution during the pulsed ejection process.