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Controlling the crystal polymorph by exploiting the time dependence of nucleation rates

Little, Laurie, King, Alice A. K., Sear, Richard and Keddie, Joseph (2017) Controlling the crystal polymorph by exploiting the time dependence of nucleation rates Journal of Chemical Physics, 147 (14).

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Abstract

Most substances can crystallise into two or more different crystal lattices, called polymorphs. Despite this, there are no systems in which we can quantitatively predict the probability of one competing polymorph forming, instead of the other. We address this problem using large scale (hundreds of events) studies of the competing nucleation of the alpha and gamma polymorphs of glycine. In situ Raman spectroscopy is used to identify the polymorph of each crystal. We find that the nucleation kinetics of the two polymorphs is very different. Nucleation of the alpha polymorph starts off slowly but accelerates, while nucleation of the gamma polymorph starts off fast but then slows. We exploit this difference to increase the purity with which we obtain the gamma polymorph by a factor of ten. The statistics of the nucleation of crystals is analogous to that human mortality, and using a result from medical statistics we show that conventional nucleation data can say nothing about what, if any, are the correlations between competing nucleation processes. Thus we can show that it is impossible to disentangle the competing nucleation processes. We also find that the growth rate and the shape of a crystal depends on when it nucleated. This is new evidence that nucleation and growth are linked.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
NameEmailORCID
Little, Lauriel.little@surrey.ac.uk
King, Alice A. K.
Sear, RichardR.Sear@surrey.ac.uk
Keddie, JosephJ.Keddie@surrey.ac.uk
Date : 13 October 2017
Identification Number : 10.1063/1.4993566
Copyright Disclaimer : Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. This article appeared in Journal of Chemical Physics, 2017, 147 (14), Laurie J. Little and Alice A. K. King and Richard P. Sear and Joseph L. Keddie; 'Controlling the crystal polymorph by exploiting the time dependence of nucleation rates' DOI: 10.1063/1.4993566.
Uncontrolled Keywords : Polymorphism; Crystallography; Biomolecules; Raman spectroscopy; Raman spectra
Depositing User : Clive Harris
Date Deposited : 28 Sep 2017 08:36
Last Modified : 27 Sep 2018 02:08
URI: http://epubs.surrey.ac.uk/id/eprint/842418

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