About Aged Heterogeneous Liquid Inclusions Inside Organic Crystals in Relation to Crystal Formation, Structure, and Morphology

Crystals of three organic compounds grown several decades ago have been retrieved from a cellar of the Faculté de Pharmacie of Paris. The presence of liquid inclusions in these large particles has provided a unique opportunity to investigate the effects of aging on these macroscopic defects. Beside their evolution toward a shape of negative crystals, it appeared that all liquid inclusions contain a (sometimes large) gaseous bubble in equilibrium with the saturated solution. Hot-stage microscopy analyses revealed that bubbles disappear upon heating, and form back on cooling with hysteresis. Furthermore, it could be established from the combination of structural, crystal growth, and morphological studies with detailed physical characterizations that the formation of inclusions is probably due to a local growth inhibition during the development of faces situated at the extremities of elongated particles, possibly involving in some cases a structural disorder. Our results also suggest that adhesion and/or heteronucleation of gaseous microbubbles on fast-growing faces could constitute a key step during the formation of macroscopic liquid inclusions. Thus, the role of gaseous matter during crystal growth of organic compounds has been so far probably underestimated.