title: Influence of substrate temperature on the stability of glasses prepared by vapor deposition.
abstract: 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 (Tg=315 K), it was determined that depositions near 0.85Tg (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 0.6Tg, this mobility is diminished or absent, resulting in low stability, vapor-deposited glasses.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Kearns
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Swallen
authors.forename: M D
authors.initials: MD
authors.lastname: Ediger
authors.forename: Tian
authors.initials: T
authors.lastname: Wu
authors.forename: Lian
authors.initials: L
authors.lastname: Yu
mesh_terms: D002151:Calorimetry; D002152:Calorimetry, Differential Scanning; D002626:Chemistry, Pharmaceutical / Q000379:methods; D002627:Chemistry, Physical / Q000379:methods*; D005740:Gases; D005898:Glass; D006358:Hot Temperature; D007213:Indomethacin / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D013379:Substrate Specificity; D013499:Surface Properties; D013696:Temperature; D013816:Thermodynamics
chemical_list: D005740:Gases; D007213:Indomethacin