Surface Self-Diffusion of Organic Glasses

Surface self-diffusion coefficients have been determined for the organic glass Nifedipine using the method of surface grating decay. The flattening of 1000 nm surface gratings occurs by viscous flow at 12 K or more above the glass transition temperature and by surface diffusion at lower temperatures...

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Bibliographic Details
Published in:The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2013-12, Vol.117 (50), p.13303-13309
Main Authors: Brian, Caleb W, Yu, Lian
Format: Article
Language:English
Subjects:
Condensed matter: structure, mechanical and thermal properties
Diffraction gratings
Diffusion
Diffusion in solids
Diffusion rate
Exact sciences and technology
Glass
Glass - chemistry
Gratings (spectra)
Kinetics
Low energy
Mathematical models
Nifedipine - chemistry
Physics
Relaxation time
Self-diffusion and ionic conduction in nonmetals
Surface diffusion
Surface Properties
Transport properties of condensed matter (nonelectronic)
Volatilization
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Summary:Surface self-diffusion coefficients have been determined for the organic glass Nifedipine using the method of surface grating decay. The flattening of 1000 nm surface gratings occurs by viscous flow at 12 K or more above the glass transition temperature and by surface diffusion at lower temperatures. Surface diffusion is at least 107 times faster than bulk diffusion, indicating a highly mobile surface. Nifedipine glasses have faster surface diffusion than the previously studied Indomethacin glasses, despite their similar bulk relaxation times. Both glasses exhibit fast surface crystal growth, and its rate scales with surface diffusivity. The observed rate of surface diffusion implies substantial surface rearrangement during the preparation of low-energy glasses by vapor deposition. The Random First Order Transition Theory and the Coupling Model successfully predict the large surface-enhancement of mobility and its increase on cooling, but disagree with the experimental observation of the faster surface diffusion of Nifedipine.
ISSN:1089-5639
1520-5215
DOI:10.1021/jp404944s