Hiking down the Energy Landscape:  Progress Toward the Kauzmann Temperature via Vapor Deposition

• Published in: The journal of physical chemistry. B Vol. 112; no. 16; pp. 4934 - 4942
• Main Authors: Kearns, Kenneth L, Swallen, Stephen F, Ediger, M. D, Wu, Tian, Sun, Ye, Yu, Lian
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.04.2008
• Subjects: Kinetics; Molecular Structure; Temperature; Thermodynamics; Volatilization; Water - chemistry
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp7113384

Physical vapor deposition was employed to prepare amorphous samples of indomethacin and 1,3,5-(tris)naphthylbenzene. By depositing onto substrates held somewhat below the glass transition temperature and varying the deposition rate from 15 to 0.2 nm/s, glasses with low enthalpies and exceptional kinetic stability were prepared. Glasses with fictive temperatures that are as much as 40 K lower than those prepared by cooling the liquid can be made by vapor deposition. As compared to an ordinary glass, the most stable vapor-deposited samples moved about 40% toward the bottom of the potential energy landscape for amorphous materials. These results support the hypothesis that enhanced surface mobility allows stable glass formation by vapor deposition. A comparison of the enthalpy content of vapor-deposited glasses with aged glasses was used to evaluate the difference between bulk and surface dynamics for indomethacin; the dynamics in the top few nanometers of the glass are about 7 orders of magnitude faster than those in the bulk at T g − 20 K.