Energy barriers and cooperative motion at the surface of freestanding glassy polystyrene films

D Fujimoto and WA MacFarlane and J Rottler, JOURNAL OF CHEMICAL PHYSICS, 153, 154901 (2020).

DOI: 10.1063/5.0022958

We investigate the near-surface relaxation of freestanding atactic polystyrene films with molecular dynamics simulations. As in previous coarse-grained simulations, relaxation times for backbone segments and phenyl rings are linked to their bulk relaxation times via a power-law coupling relation. Variation of the coupling exponent with distance from the surface is consistent with depth-dependent activation barriers. We also quantify a reduction in dynamical heterogeneity at the interface, which can be interpreted in the framework of cooperative models for glassy dynamics.

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