1D-Confinement Inhibits the Anomaly in Secondary Relaxation of a Fluorinated Polymer.

We present an experimental study of the dynamics of a well-pronounced secondary relaxation observed in bulk and ultrathin films of the fluorinated copolymer poly(vinylidene fluoride--hexafluoropropylene) (PVdF-HFP). In proximity to the glass transition, an anomalous phenomenon is observed: the β-relaxation slows down upon heating. Measurements as a function of the film thickness show that this exceptional behavior gradually vanishes upon confinement at the nanoscale level. Regardless of sample size, the relaxation dynamics could be described in terms of the Minimal Model via an asymmetric double well potential. Supported by a structural investigation of surfaces and interfaces, our results reveal that the presence of adsorbing walls induces an increase in glass transition temperature, which counterbalances the asymmetry in the double well potential responsible for molecular motion.