mz8b00695_si_001.pdf (1.26 MB)
Temperature-Independent Rescaling of the Local Activation Barrier Drives Free Surface Nanoconfinement Effects on Segmental-Scale Translational Dynamics near Tg
journal contribution
posted on 2018-10-11, 13:48 authored by Daniel Diaz-Vela, Jui-Hsiang Hung, David S. SimmonsNear-interface
alterations in dynamics and glass formation behavior
have been the subject of extensive study for the past two decades,
both because of their practical importance and in the hope of revealing
underlying correlation lengths underpinning glass transition more
generally. Here we employ molecular dynamics simulations of thick
films to demonstrate that these effects emerge, for segmental-scale
translational dynamics at low temperature, from a temperature-independent
rescaling of the local activation barrier. This rescaling manifests
as a fractional power law decoupling relationship of local dynamics
relative to the bulk, with a transition from a regime of weak decoupling
at high temperatures to a regime of strong decoupling at low temperatures.
The range of this effect saturates at low temperatures, with 90% of
the surface perturbation in the barrier lost over a range of 12 segmental
diameters. These findings reduce the phenomenology of Tg nanoconfinement effects to two propertiesa position-dependent,
temperature independent, barrier rescaling factor and an onset time
scalewhile substantially constraining the predictions required
from any theoretical explanation of this phenomenon.
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Temperature-Independent Rescalingsurface perturbationT g nanoconfinement effectseffect saturatesglass formation behaviorSegmental-Scale Translational DynamicsLocal Activation Barrier Drives Free Surface Nanoconfinement Effectssegmental-scale translational dynamicsbarrier rescaling factoractivation barrierrescaling manifestsT g Near-interface alterationscorrelation lengths underpinning glass transitionregimepower law decoupling relationshiptemperature-independent rescalingdynamics simulations
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