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Thermodynamic vs. kinetic basis for polymorph selection
Hodnett, Benjamin K.; Verma, Vivek
Ratios of equilibrium solubilities rarely exceed two-fold for polymorph pairs. A model has been developed based on two intrinsic properties of polymorph pairs, namely the ratio of equilibrium solubilities of the individual pairs (C*me/C*st) and the ratio of interfacial energies (st/me) and one applied experimental condition, namely the supersaturation identifies which one of a pair of polymorphs nucleates first. A domain diagram has been developed, which identifies the point where the critical free energy of nucleation for the polymorph pair are identical. Essentially, for a system supersaturated with respect to both polymorphs, the model identifies that low supersaturation with respect to the stable polymorph (Sst) leads to an extremely small supersaturation with respect to the metastable polymorph (Sme), radically driving up the critical free energy with respect to the metastable polymorph. Generally, high supersaturations sometimes much higher than the upper limit of the metastable zone, are required to kinetically favour the metastable polymorph
Keyword(s): classical nucleation theory; polymorphs; interfacial energy; solubility; supersaturation; metastable zone width
Publication Date:
2019
Type: Journal article
Peer-Reviewed: Yes
Language(s): English
Institution: University of Limerick
Funder(s): Science Foundation Ireland
Citation(s): 12RC2275
Processes 7, 272
12/RC/2275
Publisher(s): MDPI
First Indexed: 2019-05-19 06:25:20 Last Updated: 2019-06-29 06:47:47