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Open AccessArticle

Critical Size of Secondary Nuclei Determined via Nucleation Theorem Reveals Selective Nucleation in Three-Component Co-Crystals

Department of Chemical Engineering, Advanced Materials Laboratory of Ministry of Education (MOE), Tsinghua University, Beijing 100084, China
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Entropy 2019, 21(11), 1032; https://doi.org/10.3390/e21111032
Received: 7 September 2019 / Revised: 20 October 2019 / Accepted: 21 October 2019 / Published: 24 October 2019
(This article belongs to the Special Issue Crystallization Thermodynamics)
The critical size of the secondary nuclei plays an important role in determining the crystal growth rate. In the past, the Nucleation Theorem has been applied to determine the number of molecules in the critical nuclei of a single-component crystal via variation of the crystal growth rate with dilution by the non-crystallizable component. In this work, we extend the method to the three-component co-crystal poly (ethylene oxide)/urea/thiourea inclusion compound. The theoretical crystal growth kinetics were deduced and the dependence of the radial growth rate of the inclusion compound spherulites on the mass fraction of urea in urea/thiourea was measured. The results reveal that the secondary nuclei of the poly (ethylene oxide)/urea/thiourea inclusion compound consist mainly of ethylene oxide repeating units and urea molecules. We propose that only urea molecules and ethylene oxide repeating units are selected to form the secondary nuclei while co-crystallization of the three components happens at the lateral spreading stage. As a result, the composition of the critical secondary nuclei is different from that of the bulk inclusion compound crystals. The work is expected to deepen our understanding of the nucleation of multi-component co-crystals. View Full-Text
Keywords: critical size of nuclei; secondary nuclei; co-crystal; inclusion compound; selective nucleation critical size of nuclei; secondary nuclei; co-crystal; inclusion compound; selective nucleation
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Gao, Y.; Guo, B.; Xu, J. Critical Size of Secondary Nuclei Determined via Nucleation Theorem Reveals Selective Nucleation in Three-Component Co-Crystals. Entropy 2019, 21, 1032.

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