Don’t make the mistake of assuming all crystals dissolve the same way!

Guomin Zhu, James Dr Yoreo, and their team at the University of Washington and Pacific Northwest National Laboratory recently published an exciting study using their Hummingbird Scientific in-situ TEM liquid cell sample holder. Unlike traditional crystal dissolution, which has been predominately viewed as a process of ion-by-ion detachment into a surrounding solvent, they report a novel mechanism of dissolution by particle detachment (DPD). In the paper published in Nature Communications, the team synthesized two forms of hematite crystals—compact rhombohedra (rhHm) and spindle-shaped mesocrystals composed of smaller crystalline subunits (spHm)—to investigate their dissolution kinetics.

Using liquid phase transmission electron microscopy (LPTEM) in the Hummingbird Scientific liquid cell sample holder, the dissolution process for both crystal types was directly observed in situ. The rhHm dissolved gradually ion-by-ion, exhibiting uniform recession of the crystal edges and faces. In contrast, the mesocrystals dissolved via DPD – necks formed between the crystalline subunits, ruptured, and allowed individual particles to detach into solution. ICP-OES was used to quantify macroscopic dissolution rates, indicating spHm dissolved 7.5x faster than rhHm. The team developed an analytic model showing DPD is driven by particle misorientation and strain inherent to the mesocrystal formation during crystallization by particle attachment (CPA) and seems to mirror this growth pathway.

Figures showing dissolution of hematite. a) and b) show pre-characterization and time-lapse dissolution stages of rhHm and spHmc. c) and d) show the time-lapse TEM images of the necking process which drives dissolution in spHe. e) schematic illustrating necking process in spHe. © 2023 Springer Nature Limited

Consideration of the formation dynamics of synthetic crystals and natural minerals will help to improve predictive models for dissolution across disciplines. It reveals particle detachment as a major mechanism in dissolution of crystals formed by particle aggregation, with broad implications across subfields of materials science and geochemistry including drug delivery, nutrient release, mineral weathering, industrial settings, reactive transport, and dissolution modeling.

Reference:  Zhu, G., Legg, B.A., Sassi, M. et al. Crystal dissolution by particle detachment. Nat Commun 14, 6300 (2023). https://doi.org/10.1038/s41467-023-41443-y, Full paper © 2023 Springer Nature Limited

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