title: Entropy Drives Calcium Carbonate Ion Association.
abstract: The understanding of the molecular mechanisms underlying the early stages of crystallisation is still incomplete. In the case of calcium carbonate, experimental and computational evidence suggests that phase separation relies on so-called pre-nucleation clusters (PNCs). A thorough thermodynamic analysis of the enthalpic and entropic contributions to the overall free energy of PNC formation derived from three independent methods demonstrates that solute clustering is driven by entropy. This can be quantitatively rationalised by the release of water molecules from ion hydration layers, explaining why ion association is not limited to simple ion pairing. The key role of water release in this process suggests that PNC formation should be a common phenomenon in aqueous solutions.
authors.affiliation: Material Physics, BASF SE, D-67056, Ludwigshafen, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Kellermeier
authors.affiliation: Department of Chemistry, Curtin Institute for Computation and Institute for Geoscience Research, Curtin University, PO Box U1987, Perth, WA, 6845, Australia.
authors.forename: Paolo
authors.identifier: http://orcid.org/0000-0003-0692-0505
authors.initials: P
authors.lastname: Raiteri
authors.affiliation: Department of Chemistry, Physical Chemistry, University of Konstanz, Universitätsstraße 10, D-78464, Konstanz, Germany.
authors.forename: John K
authors.initials: JK
authors.lastname: Berg
authors.affiliation: Reactive Systems and Inorganic Nanomaterials Research, BASF SE, D-67056, Ludwigshafen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kempter
authors.affiliation: Department of Chemistry, Curtin Institute for Computation and Institute for Geoscience Research, Curtin University, PO Box U1987, Perth, WA, 6845, Australia.
authors.forename: Julian D
authors.initials: JD
authors.lastname: Gale
authors.affiliation: Department of Chemistry, Physical Chemistry, University of Konstanz, Universitätsstraße 10, D-78464, Konstanz, Germany.
authors.forename: Denis
authors.identifier: http://orcid.org/0000-0003-1612-051X
authors.initials: D
authors.lastname: Gebauer
keywords: calcium carbonate; entropy; ion association; ion pairing; pre-nucleation clusters