Wed April 1st 2015
16:00 – 17:00
ZH286
Seminar Can (polymer) glasses flow?
Thomas Salez

Details:

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 describing the experimental technique [1], we demonstrate how the theoretical tools [2] enable to directly probe the surface evolution of thin polymer films below the glass transition temperature Tg [3]. 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 localised flow over a narrow temperature region near the bulk glass transition temperature. The measurements and model presented provide a quantitative measure of surface mobility in a sample geometry where the con nement of polymer chains and substrate effects are negligible. Therefore, this study may contribute to feed further the ongoing debate around glass transition in polymer films.

[1] Physical Review Letters 109 128303 (2012)
[2] Physics of Fluids 24 102111 (2012)
[3] Science 343 994 (2014)
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The 10th Complex Motion in Fluids 2021
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