The dielectric α-relaxation in polymer films: A comparison between experiments and atomistic simulations
The dielectric α-relaxation in polymer films: A comparison between experiments and atomistic simulations
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聚合物薄膜中的介电 α 弛豫：实验与原子模拟之间的比较
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
Wolfgang Paul
中科院分区：
文献类型：
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作者：
M. Solar;E. Mapesa;Friedrich Kremer;Kurt Binder;Wolfgang Paul
聚合物薄膜的玻璃化转变温度是否取决于薄膜厚度的问题已经引起了近二十年的激烈争论。最令人困惑的发现之一是，在支撑膜中观察到的介电α弛豫似乎与厚度无关。这是令人困惑的，不仅在其他技术或其他几何形状有时显示出显着的转变作为膜厚度的函数，但更重要的是，因为所有类型的聚合物膜模型的计算机模拟揭示了结构和动力学的变化接近硬表面或自由表面。我们的研究结果表明，解释这一明显的矛盾的事实，只有在1-2 nm的壁的密度变化是足够大，改变动力学。此外，壁解吸动力学，它引入了一个新的能量尺度（至少对于简单的货车范德华吸引力），是受制于低温下的α-松弛。
The question of whether the glass transition temperature in thin polymer films depends on the film thickness or not has given rise to heated debate for almost two decades now. One of the most puzzling findings is the seemingly universal thickness independence of the dielectric α-relaxation observed for supported films. It is puzzling not only in view of the fact that other techniques or other geometries sometimes showed a significant shift of as a function of film thickness, but more so, because computer simulations for all types of polymer film models revealed changes in the structure and dynamics close to a hard surface or a free surface. Our results suggest to explain this apparent contradiction by the fact that only within 1–2 nm from the wall the density changes are sufficiently large to alter the dynamics. Additionally, the wall desorption kinetics, which introduces a new energy scale (at least for simple van der Waals attraction), is enslaved to the α-relaxation at low temperatures.