title: How much time is needed to form a kinetically stable glass? AC calorimetric study of vapor-deposited glasses of ethylcyclohexane.
abstract: Glasses of ethylcyclohexane produced by physical vapor deposition have been characterized by in situ alternating current chip nanocalorimetry. Consistent with previous work on other organic molecules, we observe that glasses of high kinetic stability are formed at substrate temperatures around 0.85 Tg, where Tg is the conventional glass transition temperature. Ethylcyclohexane is the least fragile organic glass-former for which stable glass formation has been established. The isothermal transformation of the vapor-deposited glasses into the supercooled liquid state was also measured. At seven substrate temperatures, the transformation time was measured for glasses prepared with deposition rates across a range of four orders of magnitude. At low substrate temperatures, the transformation time is strongly dependent upon deposition rate, while the dependence weakens as Tg is approached from below. These data provide an estimate for the surface equilibration time required to maximize kinetic stability at each substrate temperature. This surface equilibration time is much smaller than the bulk α-relaxation time and within two orders of magnitude of the β-relaxation time of the ordinary glass. Kinetically stable glasses are formed even for substrate temperatures below the Vogel and the Kauzmann temperatures. Surprisingly, glasses formed in the limit of slow deposition at the lowest substrate temperatures are not as kinetically stable as those formed near 0.85 Tg.
authors: Institute of Physics, University of Rostock, Wismarsche Str. 43-45, 18051 Rostock, Germany.
authors: Y Z
authors: YZ
authors: Chua
authors: Institute of Physics, University of Rostock, Wismarsche Str. 43-45, 18051 Rostock, Germany.
authors: M
authors: M
authors: Ahrenberg
authors: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: M
authors: M
authors: Tylinski
authors: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: M D
authors: MD
authors: Ediger
authors: Institute of Physics, University of Rostock, Wismarsche Str. 43-45, 18051 Rostock, Germany.
authors: C
authors: C
authors: Schick