Relaxation dynamics of glasses along a wide stability and temperature range

Abstract

While lots of measurements describe the relaxation dynamics of the liquid state, experimental data of the glass dynamics at high temperatures are much scarcer. We use ultrafast scanning calorimetry to expand the timescales of the glass to much shorter values than previously achieved. Our data show that the relaxation time of glasses follows a super-Arrhenius behaviour in the high-temperature regime above the conventional devitrification temperature heating at 10 K/min. The liquid and glass states can be described by a common VFT-like expression that solely depends on temperature and limiting fictive temperature. We apply this common description to nearly-isotropic glasses of indomethacin, toluene and to recent data on metallic glasses. We also show that the dynamics of indomethacin glasses obey density scaling laws originally derived for the liquid. This work provides a strong connection between the dynamics of the equilibrium supercooled liquid and non-equilibrium glassy states.

Origin of Ultrastability in Vapor-Deposited Glasses

“…5 of all our energy measurements in liquidcooled and vapor-deposited films shows that Eqs. (1,2) collapse the numerical results very well. Moreover, the simulations indicate that the scaling functions C(x) and D(x) are nearly identical.…”

“…Additional considerations may be needed to account for the full scope of experimental observations. First, additional studies are needed to connect the surface relaxation time measured in this study with the surface mobility inferred from experiments [2,3,5,[21][22][23]26]. Second, the shape and chemical nature of vapor-deposited molecules can result in preferential orientation within the vapor-deposited film [1,13,[27][28][29][30], while such alignment bias is not expected for ordinary liquid-cooled films.…”

“…Here we use molecular dynamics simulations to model vapor deposition and an efficient Monte Carlo algorithm to determine the deposition rate needed to create ultra-stable glassy films. We obtain a scaling relation that quantitatively captures the efficiency gain of vapor deposition over bulk annealing, and demonstrates that surface relaxation plays the same role in the formation of vapor-deposited glasses as bulk relaxation does in ordinary glass formation.Compared to their liquid-cooled counterparts, vapordeposited glasses often have a higher density [1], a higher kinetic stability [2][3][4], and a lower heat capacity [5]. This makes them promising materials for a wide range of applications, such as drug delivery [6], protective coatings [7,8], and lithography [9].…”

“…Compared to their liquid-cooled counterparts, vapordeposited glasses often have a higher density [1], a higher kinetic stability [2][3][4], and a lower heat capacity [5]. This makes them promising materials for a wide range of applications, such as drug delivery [6], protective coatings [7,8], and lithography [9].…”

Why is the change of the Johari–Goldstein β-relaxation time by densification in ultrastable glass minor?

“…Glasses produced by vapor deposition on a substrate at an optimal temperature below the bulk glass transition temperature (B0.85T g , where T g is the glass transition temperature of the material) have density considerably higher than ordinary glasses even after aging for a realistically long time. [1][2][3][4][5][6][7] These glasses are more stable than the ordinary glasses (OG), and hence are called ultrastable glasses (USG). Compared with OG, some dynamic and thermodynamic properties of USG are novel and challenging to explain.…”