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    Influence of a Reduced Mobility Layer on the Structural Relaxation Dynamics of Aluminum Capped Ultrathin Films of Poly(ethylene terephthalate)

    Year: 2007

    Journal: Langmuir, 2007, 23 (4), pp 2103–2109, 20111221

    Authors: Simone Napolitano, Daniele Prevosto, Mauro Lucchesi, Pasqualantonio Pingue, Mario D'Acunto, and Pierangelo Rolla

    Organizations: polyLab e Dipartimento di Fisica, Università di Pisa, Largo B. Pontecorvo 3, Pisa, Italy, NEST CNR-INFM and Scuola Normale Superiore, I-56100, Pisa, Italy, Dipartimento Ingegneria Chimica e Scienze dei Materiali, Università di Pisa, via Diotisalvi 2, Pisa, Italy, and Laboratory for Acoustics and Thermal Physics, Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D B-3001 Heverlee, Belgium

    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.