Why we need to look beyond the glass transition temperature to characterize the dynamics of thin supported polymer films

Proceedings of the National Academy of Sciences of the United States of America
Wengang ZhangFrancis W Starr

Abstract

There is significant variation in the reported magnitude and even the sign of [Formula: see text] shifts in thin polymer films with nominally the same chemistry, film thickness, and supporting substrate. The implicit assumption is that methods used to estimate [Formula: see text] in bulk materials are relevant for inferring dynamic changes in thin films. To test the validity of this assumption, we perform molecular simulations of a coarse-grained polymer melt supported on an attractive substrate. As observed in many experiments, we find that [Formula: see text] based on thermodynamic criteria (temperature dependence of film height or enthalpy) decreases with decreasing film thickness, regardless of the polymer-substrate interaction strength ε. In contrast, we find that [Formula: see text] based on a dynamic criterion (relaxation of the dynamic structure factor) also decreases with decreasing thickness when ε is relatively weak, but [Formula: see text] increases when ε exceeds the polymer-polymer interaction strength. We show that these qualitatively different trends in [Formula: see text] reflect differing sensitivities to the mobility gradient across the film. Apparently, the slowly relaxing polymer segments in the substrate r...Continue Reading

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Jun 3, 2017·The Journal of Chemical Physics·Wengang ZhangFrancis W Starr
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Aug 3, 2017·The Journal of Chemical Physics·Wengang ZhangFrancis W Starr

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Citations

Oct 13, 2018·Physical Review Letters·Xavier Monnier, Daniele Cangialosi
Jun 5, 2020·Science Advances·Xavier MonnierIsabella Gallino
Aug 9, 2021·The Journal of Chemical Physics·Xiang-Meng JiaZhong-Yuan Lu
Jan 15, 2020·Langmuir : the ACS Journal of Surfaces and Colloids·Anne-Sophie VaillardSophie Cantin
Jun 14, 2019·The Journal of Physical Chemistry. B·Wengang ZhangJack F Douglas

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