Dynamics of glass-forming liquids. XV. Dynamical features of molecular liquids that form ultra-stable glasses by vapor deposition

The dielectric relaxation behavior of ethylbenzene (EBZ) in its viscous regime is measured, and the glass transition temperature (T_g = 116 K) as well as fragility (m = 98) are determined. While the T_g of EBZ from this work is consistent with earlier results, the fragility is found much higher than what has been assumed previously. Literature data is supplemented by the present results on EBZ to compile the dynamic behavior of those glass formers that are known to form ultra-stable glasses by vapor deposition. These dynamics are contrasted with those of ethylcyclohexane, a glass former for which a comparable vapor deposition failed to produce an equally stable glassy state. In a graph that linearizes Vogel-Fulcher-Tammann behavior, i.e., the derivative of -log with respect to TT_g raised to the power of -1/2 versus TT_g, all ultra-stable glass formers fall onto one master curve in a wide temperature range, while ethylcyclohexane deviates for T ≫ T _g. This result suggests that ultra-stable glass formers share common behavior regarding the dynamics of their supercooled liquid state if scaled to their respective T_g values, and that fragility and related features are linked to the ability to form ultra-stable materials.