Tetrahydrofuran, a water-soluble cyclic ether molecule, is well known for its ability to form clathrate hydrates (cubic structure II, melting point 277.5 K). An aqueous solution of THF (17:1 molecular ratio) was hyperquenched (cooled at a rate of ) to 77 K to give recoverable samples of ∼1 g of metastable amorphous material. The crystallization process was studied on three complementary length scales by x-ray powder diffraction, quadrupole echo double resonance (QEDOR) NMR spectroscopy, and Raman spectroscopy as the amorphous material was annealed at temperatures between 80 and 190 K. Results show that phase separation of the two components occurred predominantly during the annealing process, resulting in clusters of crystalline THF and ice Ic before clathrate hydrate crystallization was initiated. During the hyperquenching process, the decreasing molecular mobility of water molecules between room temperature and the fictive temperature (the temperature below which the solution becomes structurally immobilized upon hyperquenching) inhibits growth of the crystal nuclei that normally would result in crystalline clathrate hydrate formation. Annealing the samples between 110–140 K showed that the local hydrogen bonded O–H--O structure of the water molecules changed toward the arrangement characteristic of crystalline ice Ic. We propose that this process forces the THF out of the glassy solution, thus increasing the THF cluster size in the deposit so that these become visible to diffraction. Further annealing, above 150–160 K caused large-scale growth of crystalline clathrate hydrate material, which then could be associated with a reduction in the THF cluster size, and ice Ic.
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1 April 1999
Research Article|
April 01 1999
Evidence for phase separation during the crystallization of hyperquenched glassy clathrate hydrate forming solutions
C. A. Tulk;
C. A. Tulk
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada
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Y. Ba;
Y. Ba
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada
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D. D. Klug;
D. D. Klug
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada
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G. McLaurin;
G. McLaurin
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada
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J. A. Ripmeester
J. A. Ripmeester
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada
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J. Chem. Phys. 110, 6475–6483 (1999)
Article history
Received:
October 27 1998
Accepted:
December 30 1998
Citation
C. A. Tulk, Y. Ba, D. D. Klug, G. McLaurin, J. A. Ripmeester; Evidence for phase separation during the crystallization of hyperquenched glassy clathrate hydrate forming solutions. J. Chem. Phys. 1 April 1999; 110 (13): 6475–6483. https://doi.org/10.1063/1.478550
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