A high-pressure polar light microscopy to study the melt crystallization of myristic acid and ibuprofen in CO2

A high-pressure polar light microscopy approach was proposed and developed to study the melt crystallization behaviors of myristic acid and ibuprofen respectively in CO₂ at different pressures and crystallization temperatures. The crystallization kinetics was analyzed by the Avrami equation. Results revealed that the crystallization rates of both myristic acid and ibuprofen increased with the CO₂ pressure, while the crystallization activation energy of ibuprofen decreased (more negative) with the increase of CO₂ pressure. On the other hand, the crystallization rate of ibuprofen decreased with the increase of the crystallization temperature at fixed pressure. However, the presence of CO₂ did not change the nucleation or growth patterns of myristic acid and ibuprofen, as indicated by the analyzed results of the Avrami equation. The X-ray diffraction (XRD) analysis further confirmed that CO₂ had no influence on the crystal form of myristic acid or ibuprofen. This study revealed that the crystallization behaviors of myristic acid and ibuprofen were evidently different from those of polymers in CO₂ reported in the literature.