Kinetic stability and heat capacity of vapor-deposited glasses of o-terphenyl

TitleKinetic stability and heat capacity of vapor-deposited glasses of o-terphenyl
Publication TypeJournal Article
Year of Publication2015
AuthorsWhitaker, Katherine R., M. Tylinski, Mathias Ahrenberg, Christoph Schick, and M. D. Ediger
JournalJournal of Chemical Physics
Start Page084511
Date Published08/2015

The reversing heat capacity of vapor-deposited o-terphenyl glasses was determined by in situ alternating current nanocalorimetry. Glasses were deposited at substrate temperatures ranging from 0.39 Tg to Tg, where Tg is the glass transition temperature. Glasses deposited near 0.85 Texhibited very high kinetic stability; a 460 nm film required ∼104.8 times the structural relaxation time of the equilibrium supercooled liquid to transform into the liquid state. For the most stable o-terphenyl glasses, the heat capacity was lower than that of the ordinary liquid-cooled glass by 1 ± 0.4%; this decrease represents half of the difference in heat capacity between the ordinaryglass and crystal. Vapor-deposited o-terphenyl glasses exhibit greater kinetic stability than vapor-deposited glasses of indomethacin, in qualitative agreement with recent surface diffusion measurements indicating faster surface diffusion on o-terphenyl glasses. The stable glass to supercooled liquid transformation was thickness-dependent, consistent with transformation via a propagating front initiated at the free surface.