Regular Article - Soft Matter
On the bridge hypothesis in the glass transition of freestanding polymer films
Gulliver, CNRS UMR 7083, ESPCI Paris, Univ. PSL, 75005, Paris, France
2 School of Chemistry, Center for the Physics and Chemistry of Living Systems, Ratner Institute for Single Molecule Chemistry, and the Sackler Center for Computational Molecular and Materials Science, Tel Aviv University, 6997801, Tel Aviv, Israel
3 Department of Physics and Astronomy, University of Waterloo, N2L 3G1, Waterloo, ON, Canada
4 Univ. Bordeaux, CNRS, LOMA, UMR 5798, F-33400, Talence, France
Accepted: 15 February 2023
Published online: 1 March 2023
Freestanding thin polymer films with high molecular weights exhibit an anomalous decrease in the glass-transition temperature with film thickness. Specifically, in such materials, the measured glass-transition temperature evolves in an affine way with the film thickness, with a slope that weakly depends on the molecular weight. De Gennes proposed a sliding mechanism as the hypothetical dominant relaxation process in these systems, where stress kinks could propagate in a reptation-like fashion through so-called bridges, i.e. from one free interface to the other along the backbones of polymer macromolecules. Here, by considering the exact statistics of finite-sized random walks within a confined box, we investigate in details the bridge hypothesis. We show that the sliding mechanism cannot reproduce the basic features appearing in the experiments, and we exhibit the fundamental reasons behind such a fact.
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