|Title||Hiking down the energy landscape: Progress toward the Kauzmann temperature via vapor deposition|
|Publication Type||Journal Article|
|Year of Publication||2008|
|Authors||Kearns, K. L., S. F. Swallen, M. D. Ediger, T. Wu, Y. Sun, and L. Yu|
|Journal||Journal of Physical Chemistry B|
|Keywords||AROMATIC HYDROCARBONS, BOND LATTICE, FREE-VOLUME, GLASS-FORMING LIQUIDS, INDOMETHACIN POLYMORPHS, ORGANIC MATERIALS, PHYSICAL PROPERTIES, STRUCTURAL RELAXATION, SUPERCOOLED LIQUIDS, TRANSITION|
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.
|Alternate Journal||J. Phys. Chem. B|