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

• 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
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.2789438

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.