Dresden 2014 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 38: Glasses and Glass Transition - Part II (joint session CPP/ DY/DF)
DY 38.4: Talk
Thursday, April 3, 2014, 16:30–16:45, ZEU 114
A direct quantitative measure of surface mobility in a glassy polymer — Yu Chai1, •Thomas Salez2, Joshua D. McGraw3, Michael Benzaquen2, Kari Dalnoki-Veress4, Elie Raphaël2, and James A. Forrest1 — 1University of Waterloo, Canada — 2ESPCI, Paris, France — 3Saarland University, Saarbrücken, Germany — 4McMaster University, Hamilton, Canada
The simple geometry of a polymer film on a substrate with a step at the free surface is unfavourable due to the excess interface induced by the step, thus allowing for a new nanoprobe of the melt state rheology. After recalling the experimental technique, we demonstrate how the same theoretical tools enable to understand the surface evolution of thin polymer films below the glass transition temperature Tg. While above Tg the entire volume between the substrate and the free surface participates to the flow, below Tg only a near surface region responds to the excess interfacial energy. In the latter case, the developed thin film theory for flow limited to the free surface region is in excellent agreement with experimental data. Strikingly, the system transitions from whole film flow to surface localized flow over a narrow temperature region near the bulk glass transition temperature. The measurements and model presented provide a quantitative measure of the surface mobility in a sample geometry where the confinement of polymer chains and substrate effects are negligible. Therefore, this study may help to solve further the ongoing controversy around glass transition in polymer films.