The Slow Molecular Mobility in Amorphous Ketoprofen and Ibuprofen

The slow molecular dynamics in two active pharmaceutical drugs, ketoprofen and ibuprofen, have been studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). This study allowed finding the main kinetic features of the fast secondary (γ) relaxation, of the Johari-Goldstein relaxation, and of the main (glass transition) relaxation, in particular their distribution of relaxation times. The fragility index of the two glass formers was determined based on data from DSC and from TSDC. The obtained results were compared with those obtained by other experimental techniques, namely, dielectric relaxation spectroscopy.