Influence of substrate temperature on the stability of glasses prepared by vapor deposition

Physical vapor deposition of indomethacin (IMC) was used to prepare glasses with unusual thermodynamic and kinetic stability. By varying the substrate temperature during the deposition from 190 K to the glass transition temperature ( T g = 315 K ) , it was determined that depositions near 0.85 T g (...

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Bibliographic Details
Published in:The Journal of chemical physics 2007-10, Vol.127 (15), p.154702-154702-9
Main Authors: Kearns, Kenneth L., Swallen, Stephen F., Ediger, M. D., Wu, Tian, Yu, Lian
Format: Article
Language:English
Subjects:
CALORIMETRY
Calorimetry, Differential Scanning
Chemistry, Pharmaceutical - methods
Chemistry, Physical - methods
ENTHALPY
Gases
GLASS
Hot Temperature
Indomethacin - chemistry
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
Kinetics
Models, Chemical
PHYSICAL VAPOR DEPOSITION
STABILITY
Substrate Specificity
SUBSTRATES
Surface Properties
Temperature
TEMPERATURE RANGE 0065-0273 K
TEMPERATURE RANGE 0273-0400 K
Thermodynamics
TRANSITION TEMPERATURE
VAPOR DEPOSITED COATINGS
VAPORS
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Summary:Physical vapor deposition of indomethacin (IMC) was used to prepare glasses with unusual thermodynamic and kinetic stability. By varying the substrate temperature during the deposition from 190 K to the glass transition temperature ( T g = 315 K ) , it was determined that depositions near 0.85 T g ( 265 K ) resulted in the most stable IMC glasses regardless of substrate. Differential scanning calorimetry of samples deposited at 265 K indicated that the enthalpy was 8 J ∕ g less than the ordinary glass prepared by cooling the liquid, corresponding to a 20 K reduction in the fictive temperature. Deposition at 265 K also resulted in the greatest kinetic stability, as indicated by the highest onset temperature. The most stable vapor-deposited IMC glasses had thermodynamic stabilities equivalent to ordinary glasses aged at 295 K for 7 months . We attribute the creation of stable IMC glasses via vapor deposition to enhanced surface mobility. At substrate temperatures near 0.6 T g , this mobility is diminished or absent, resulting in low stability, vapor-deposited glasses.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.2789438