Slow Relaxation, Spatial Mobility Gradients and Vitrification in Confined Films
arXiv:1410.4138 · doi:10.1063/1.4900507
Abstract
Two decades of experimental research indicates that spatial confinement of glass-forming molecular and polymeric liquids results in major changes of their slow dynamics beginning at large confinement distances. A fundamental understanding remains elusive given the generic complexity of activated relaxation in supercooled liquids and the major complications of geometric confinement, interfacial effects and spatial inhomogeneity. We construct a predictive, quantitative, force-level theory of relaxation in free-standing films for the central question of the nature of the spatial mobility gradient. The key new idea is that vapor interfaces speed up barrier hopping in two distinct, but coupled, ways by reducing near surface local caging constraints and spatially long range collective elastic distortion. Effective vitrification temperatures, dynamic length scales, and mobile layer thicknesses naturally follow. Our results provide a unified basis for central observations of dynamic and pseudo-thermodynamic measurements.
arXiv comment11 pages, 4 figures
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- Theory of the Spatial Transfer of Interface-Nucleated Changes of Dynamical Constraints and Its Consequences in Glass-Forming Films
- Theory of Activated Glassy Dynamics in Randomly Pinned Fluids
- Front propagation versus bulk relaxation in the annealing dynamics of a kinetically constrained model of ultrastable glasses
- Connection between fragility, mean-squared displacement and shear modulus in two van der Waals bonded glass-forming liquids
- Non-monotonic effect of confinement on the glass transition
- Enhanced diffusion in finite-size simulations of a fragile diatomic glass former
- Energy barriers and cooperative motion at the surface of freestanding glassy polystyrene films
- Screening and collective effects in randomly pinned fluids: A new theoretical framework