Napolitano Simone, Prevosto Daniele, Lucchesi Mauro, Pingue Pasqualantonio, D'Acunto Mario, Rolla Pierangelo
polyLab e Dipartimento di Fisica, Università di Pisa, Largo B. Pontecorvo 3, Pisa, Italy.
Langmuir. 2007 Feb 13;23(4):2103-9. doi: 10.1021/la062229j. Epub 2007 Jan 12.
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.
通过介电弛豫光谱研究了夹在铝电极之间的聚对苯二甲酸乙二酯超薄聚合物薄膜的结构动力学。对于厚度低于35nm的薄膜，观察到与本体行为的偏差，表现为在固定温度下弛豫时间增加。这种减慢作用作为一个与温度无关的恒定位移因子，并且脆性是恒定的。计算得出铝与聚对苯二甲酸乙二酯之间的界面能为3mJ/m²，证实了聚合物与基底之间存在强相互作用，这导致在它们的界面处存在一层具有降低迁移率的层。我们提出了一个多层模型的数学示意图，该示意图能够定性再现所观察到的静态和动态性质的厚度依赖性。根据这样一个模型，迁移率降低层的厚度上限估计为20nm。最后提出了将所提出的模型扩展到不同可观测值的条件。
