Recent studies suggest the presence of a previously unknown region of metastable liquid immiscibility in the CaCO3-H2O system1–3. Unfortunately, because these liquid-like states are short lived our understanding of their physical properties is limited. Moreover, the low solubility of CaCO3 in water poses significant challenges to both experimental and theoretical investigations that might provide new insights into this behavior. However, similar behavior is observed in the MgSO4-H2O system4 where the liquid-liquid coexistence curve is perched metastabily above the Kieserite solubility curve. While the presence of liquid CaCO3 is yet to be confirmed absolutely, it is notable that both systems exhibit retrograde solubility behavior, suggesting an underlying parity in the physical and chemical driving forces that govern phase separation. Additionally, theoretical investigations indicate that ions in these systems assemble into polymeric aggregates, which may explain the origin of the lower solution critical temperature that is typically observed in synthetic polymer systems. Herein we discuss the evidence for liquid phase coexistence in the CaCO3- and MgSO4-H2O systems and report initial results from molecular dynamics simulations of supersaturated magnesium sulfate solutions. (1) Nielsen, M. H.; Aloni, S.; Yoreo, J. J. De. In situ TEM imaging of CaCO3 nucleation reveals coexistence of direct and indirect pathways. Science. 2014, 345 (6201), 1158–1162. (2) Wallace, A. F.; Hedges, L. O.; Fernandez-Martinez, A.; Raiteri, P.; Gale, J. D.; Waychunas, G. A.; Whitelam, S.; Banfield, J. F.; De Yoreo, J. J. Microscopic Evidence for Liquid-Liquid Separation in Supersaturated CaCO3 Solutions. Science. 2013, 341 (6148), 885–889. (3) Bewernitz, M. A.; Gebauer, D.; Long, J.; Colfen, H.; Gower, L. B. A metastable liquid precursor phase of calcium carbonate and its interactions with polyaspartate. Faraday Discuss. 2012, 159, 291–312. (4) Wang, X.; Chou, I.-M.; Hu, W.; Burruss, R. C. In situ observations of liquid–liquid phase separation in aqueous MgSO4 solutions: Geological and geochemical implications. Geochim. Cosmochim. Acta 2013, 103, 1–10.

Molecular dynamics based investigations of liquid-liquid phase separation in the CaCO3- and MgSO4-H2O systems

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.