title: Influence of a reduced mobility layer on the structural relaxation dynamics of aluminum capped ultrathin films of poly(ethylene terephthalate).
abstract: The structural dynamics of ultrathin polymer films of poly(ethylene terephthalate) capped between aluminum electrodes have been investigated by dielectric relaxation spectroscopy. A deviation from bulk behavior, appearing as an increase of the relaxation time at a fixed temperature, is observed for films of thickness below 35 nm. The slowing down acts as a constant shift factor independent from the temperature, and the fragility is constant. The interfacial energy between aluminum and poly(ethylene terephthalate) is calculated to be 3 mJ/m2, confirming a strong interaction between polymer and substrate, which leads to the presence of a layer characterized by a reduced mobility at their interfaces. We proposed a mathematical schematization of a multylayer model that allowed qualitative reproduction of the observed thickness dependences of the static and dynamic properties. In terms of such a model, the upper limit for the thickness of the reduced mobility layer was estimated as 20 nm. The conditions to extend the proposed model to different observables are finally suggested.
authors.affiliation: polyLab e Dipartimento di Fisica, Università di Pisa, Largo B. Pontecorvo 3, Pisa, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Napolitano
authors.forename: Daniele
authors.initials: D
authors.lastname: Prevosto
authors.forename: Mauro
authors.initials: M
authors.lastname: Lucchesi
authors.forename: Pasqualantonio
authors.initials: P
authors.lastname: Pingue
authors.forename: Mario
authors.initials: M
authors.lastname: D'Acunto
authors.forename: Pierangelo
authors.initials: P
authors.lastname: Rolla