The relationship between dynamic and pseudo-thermodynamic measures of the glass transition temperature in nanostructured materials.

Despite decades of research on the effects of nanoconfinement on the glass transition temperature T, apparent discrepancies between pseudothermodynamic and dynamic measurements of these effects have raised questions regarding the presence of long-ranged interfacial dynamic gradients in glass-forming liquids. Here we show that these differences can be accounted for based on disparities in these methods' weightings over local T's within an interfacial gradient. This finding suggests that a majority of experimental data are consistent with a broad interfacial dynamic interphase in glass-forming liquids.

Does fragility of glass formation determine the strength of T-nanoconfinement effects?

Nanoscale confinement has been shown to alter the glass transition and associated mechanical and transport properties of glass-forming materials. Inspired by expected interrelations between nanoconfinement effects, cooperative dynamics in supercooled liquids, and the "fragility" (or temperature-abruptness) of the glass transition, it is commonly expected that nanoconfinement effects on T should be more pronounced for more fragile glass formers. Here we employ molecular dynamics simulations of glass formation in the bulk and under nanoconfinement of model polymers in which we systematically tune fragility by several routes.

Three-Layer Model for the Emergence of Ultrastable Glasses from the Surfaces of Supercooled Liquids.

Ultrastable glasses produced by vapor deposition exhibit properties consistent with glasses that have been aged for thousands of years or more. These materials' properties are believed to emerge from the presence of a mobile layer at the surface of supercooled liquids that allows access to lower-energy states. However, the precise mechanism by which this enhanced mobility is translated into ultrastable glass behavior remains incompletely understood.