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Updated: Apr 11, 2026

Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films
Published on: January 26, 2016
Molecular Weight Effects on the Glass Transition and Confinement Behavior of Polymer Thin Films
Wenjie Xia1, David D Hsu1, Sinan Keten1
1Department of Civil & Environmental Engineering and Department of Mechanical Engineering, Northwestern University, Evanston, IL, 60208, USA.
Abstract:
Nanoscale polymer thin films exhibit strong confinement effects on Tg arising from free surfaces. However, the coupled influence of molecular weight (MW) and surface effects on Tg is not well understood for low MW film systems below the entanglement length. Utilizing atomistically informed coarse-grained molecular dynamics simulations for poly(methyl methacrylate) (PMMA), it is demonstrated that the decrease in free-standing film Tg with respect to bulk is more significant for low MW compared to high MW systems. Investigation of the local interfacial properties reveals that the increase in the local free volume near the free surface is greater for low MW, explaining the MW dependence of Tg -confinement behaviors. These findings corroborate recent experiments on low MW films, and highlight the relationship between nanoconfinement phenomena and local free volume effects arising from free surfaces.
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