Volume 122, 2003
From the journal:

Faraday Discussions

Are metastable, precrystallisation, density-fluctuations a universal phenomena?

Ellen L. Heeley,a   C. Kit Poh,b   Wu Li,a   Anna Maidens,c   Wim Bras,d   Igor P. Dolbnya,d   Anthony J. Gleeson,e   Nicolas J. Terrill,e   J. Patrick A. Fairclough,a   Peter D. Olmsted,c   Rile I. Ristic,b   Micheal J. Hounslowb  and  Anthony J. Ryana  

a Department of Chemistry, University of Sheffield, Sheffield, UK

b Department of Chemical and Process Engineering, University of Sheffield, Sheffield, UK

c Department of Physics, The University of Leeds, Leeds, UK

d DUBBLE CRG, ESRF, Grenoble, France

e CCLRC Daresbury Laboratory, Warrington, UK

Abstract

In-situ observations of crystallisation in minerals and organic polymers have been made by simultaneous, time-resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) techniques. In isotactic polypropylene slow quiescent crystallisation shows the onset of large scale ordering prior to crystal growth. Rapid crystallisations studied by melt extrusion indicate the development of well resolved oriented SAXS patterns associated with long range order before the development of crystalline peaks in the WAXS region. Block copolymers self-assemble into mesophases in polymer melts above a critical chain length (or above a critical temperature) and this self-assembly process is shown to be susceptible to an incipient crystallisation. Mesophase formation is observed at anomalously high temperatures in ethylene-oxide containing block copolymers below the normal melting point of the polyoxy ethylene chains. Formation of calcium carbonate from aqueous solutions of sodium carbonate and calcium nitrate is observed to be a two-stage process and precipitation proceeds by the production of an amorphous metastable phase. This phase grows until it is volume filling and leads to the formation of the two polymorphs Calcite and Vaterite. These three sets of results suggest pre-nucleation density fluctuations, leading to a metastable phase, play an integral role in all three classes of crystallisation. In due course, this phase undergoes transformation to “normal” crystals.

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Article information

DOI
https://doi.org/10.1039/B202680E
Article type
Paper
Submitted
18 Mar 2002
Accepted
29 Apr 2002
First published
16 Aug 2002

Faraday Discuss., 2003,122, 343-361

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Are metastable, precrystallisation, density-fluctuations a universal phenomena?

E. L. Heeley, C. K. Poh, W. Li, A. Maidens, W. Bras, I. P. Dolbnya, A. J. Gleeson, N. J. Terrill, J. P. A. Fairclough, P. D. Olmsted, R. I. Ristic, M. J. Hounslow and A. J. Ryan, Faraday Discuss., 2003, 122, 343 DOI: 10.1039/B202680E

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