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Crystal nucleation and growth in a polymorphic system: Ostwald's rule, p-aminobenzoic acid and nucleation transition states

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Abstract

Ostwald's rule remains a long standing guide to crystallisation in polymorphic systems. It is often assumed that this rule has its origins in nucleation processes that favour metastable phases. Here a mathematical formalism is developed which shows that in fact the validity of this rule depends on both the relative nucleation and growth rates of the available forms. The implication of this result for previous nucleation studies is discussed. Surprisingly there is no existing comprehensive data set for both nucleation and growth kinetics of a polymorphic material. Accordingly new data for the α and β forms of p-aminobenzoic acid are reported here. These demonstrate the important contribution of growth to the polymorphic outcome and also suggest molecular scale mechanisms that dominate nucleation. In particular the uniquely rapid crystallisation behaviour observed in aqueous solutions is interpreted in both kinetic and structural terms.

Graphical abstract: Crystal nucleation and growth in a polymorphic system: Ostwald's rule, p-aminobenzoic acid and nucleation transition states

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Publication details

The article was received on 10 Nov 2017, accepted on 08 Jan 2018 and first published on 10 Jan 2018


Article type: Paper
DOI: 10.1039/C7CE01960B
Citation: CrystEngComm, 2018, Advance Article
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    Crystal nucleation and growth in a polymorphic system: Ostwald's rule, p-aminobenzoic acid and nucleation transition states

    J. F. B. Black, P. T. Cardew, A. J. Cruz-Cabeza, R. J. Davey, S. E. Gilks and R. A. Sullivan, CrystEngComm, 2018, Advance Article , DOI: 10.1039/C7CE01960B

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