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.

Perspective: Outstanding theoretical questions in polymer-nanoparticle hybrids

“…It is well-known from studies in the context of polymer thin films that interfaces perturb the glass transition temperature, T g , [197][198][199][200][201] and several simulation studies have shown that the segmental dynamics near NP surfaces are also distinct from the bulk. [202][203][204] The general trend that has emerged is that the polymer dynamics typically slows down if the NP-polymer interaction is attractive (T g increases) and speeds up if this interaction is strongly repulsive (T g decreases).…”

Is the Reduction in Tracer Diffusivity under Nanoscopic Confinement Related to a Frustrated Segmental Mobility?

“…Such proportionality justifies the use of De as a parameter to monitor adsorption; in fact, as in the case of cold crystallization, [8,9] partial or total immobilization of the chains limits the solid angle over which dipoles can reorient, yielding a reduction in the dielectric strength. [10] In fact,…”

The lifetime of the deviations from bulk behaviour in polymers confined at the nanoscale

“…The interfacial energy γ PS/Al between aluminium and PS was calculated on the basis of the Good-Girifalco-Fowkes combining rule 46 , which takes into account both polar and dispersive contributions: ] from contact angle measurements on layers thermally evaporated under similar conditions performed in a previous work by one of the authors 48 . The contribution of the surface oxide layer to influencing the wettability of the metal is reflected in the values of the contact angle and is thus taken into account in the parameters of equation (2).…”