Origin of two modes of non-isothermal crystallization of glasses produced by milling

Sayantan Chattoraj, Chandan Bhugra, Chitra Telang, Li Zhong, Zeren Wang, Changquan Calvin Sun

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

Purpose: To mechanistically explain the origin of two distinct non-isothermal crystallization modes, single-peak (unimodal) and two-peak (bimodal), of organic glasses. Methods: Glasses of ten organic molecules were prepared by melt-quenching and cryogenic milling of crystals. Non-isothermal crystallization of glasses was monitored using differential scanning calorimetry and powder X-ray diffractometry. Results: The non-isothermal crystallization of glass, generated by milling, is either unimodal or bimodal, while that of melt-quenched glass without being milled is always unimodal. The mode of crystallization of amorphous phase depends on the relative position of the crystallization onset (T c) with respect to glass transition temperature (T g), and can be explained by a surface crystallization model. Bimodal crystallization event is observed when T c is below or near T g, due to the fast crystallization onset at milled glass surfaces. Unimodal crystallization is observed when T c is well above T g. We have verified this model by intentionally inducing flip between the two crystallization modes for several compounds through manipulating glass surface area and T c. Conclusions: The two modes of crystallization of organic glasses is a result of the combined effects of faster surface crystallization and variation in specific surface area by milling.

Original languageEnglish (US)
Pages (from-to)1020-1032
Number of pages13
JournalPharmaceutical research
Volume29
Issue number4
DOIs
StatePublished - Apr 1 2012

Keywords

  • Amorphous
  • Bimodal
  • Crystallization onset
  • Glass transition
  • Kinetic flip
  • Surface crystallization
  • Unimodal

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