High-Throughput Ellipsometric Characterization of Vapor-Deposited Indomethacin Glasses

A method for the high-throughput preparation and characterization of vapor-deposited organic glasses is presented. Depositing directly onto a substrate with a large temperature gradient allows many different glasses to be prepared simultaneously. Ellipsometry is used to characterize these glasses, a...

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Bibliographic Details
Published in:The journal of physical chemistry. B 2013-12, Vol.117 (49), p.15415-15425
Main Authors: Dalal, Shakeel S, Fakhraai, Zahra, Ediger, M. D
Format: Article
Language:English
Subjects:
Birefringence
Density
Deposition
Ellipsometry
Glass
Liquids
Mathematical models
Vapor deposition
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Summary:A method for the high-throughput preparation and characterization of vapor-deposited organic glasses is presented. Depositing directly onto a substrate with a large temperature gradient allows many different glasses to be prepared simultaneously. Ellipsometry is used to characterize these glasses, allowing the determination of density, birefringence, and kinetic stability as a function of substrate temperature. For indomethacin, a model glass former, materials up to 1.4% more dense than the liquid-cooled glass can be formed with a continuously tunable range of molecular orientations as determined by the birefringence. By comparing measurements of many properties, we observe three phenomenological temperature regimes. For substrate temperatures from T g + 11 K to T g – 8 K, equilibrium states are produced. Between T g – 8 K and T g – 31 K, the vapor-deposited materials have the macroscopic properties expected for the equilibrium supercooled liquid while showing local structural anisotropy. At lower substrate temperatures, the properties of the vapor-deposited glasses are strongly influenced by kinetic factors. Different macroscopic properties are no longer correlated with each other in this regime, allowing unusual combinations of properties.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp405005n