Temperature Dependence of the Deviations from Bulk Behavior in Ultrathin Polymer Films

The temperature dependence of the deviations from bulk behavior in ultrathin polymer films is demonstrated. The validity of a model aiming to rationalize the influence of interfacial interactions on the structural relaxation of polymers has been experimentally verified. The polymer layers at the very interface with the metal have a high number of contacts with the wall, because of specific hydrogen bond interactions. The resulting changes in the chain conformation allow only restricted segmental mobility. The influence of an absorbing substrate has been treated as a small perturbation in the activation energy, without affecting the energy landscape scenario. The deviations from bulk behavior are derived from the balance of such a perturbation and the energy of the thermal bath. The model results, supported by experimental evidence, show how these effects are related to the time scale of the experiment and increase upon cooling.