Substrate vs. free surface: Competing effects on the glass transition of polymer thin films
Substrate vs. free surface: Competing effects on the glass transition of polymer thin films
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DOI：
10.1016/j.polymer.2013.08.013
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发表时间：
2013-10
期刊：
影响因子：
4.6
通讯作者：
W. Xia;Shawn Mishra;S. Keten
中科院分区：
文献类型：
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作者：
W. Xia;Shawn Mishra;S. Keten
聚合物薄膜的玻璃化转变温度（Tg）可以强烈地受到支撑固体基底和自由表面的组合效应的影响。这两种效应的相对重要性取决于基底-膜相互作用的强度，这两种效应经常相互竞争。利用一个原子通知粗粒模型的聚（甲基丙烯酸甲酯）（PMMA），在这里，我们发现之间的关系的基板-薄膜界面能和空间分布ofTg跨薄膜。我们发现，在临界界面能以上，薄膜T对界面能的线性依赖关系被打破，薄膜T达到一个渐近值。分析的空间变化ofTg跨越薄膜显示，短程界面附近的粘性表面产生一个长程界面，导致空间均匀升值ofTg整个膜，不像弱粘性表面，显示沿沿着膜的深度急剧梯度。这些发现解释了最近的实验，并揭示了一个通用的方法来调整filmTgvia工程基板膜相互作用。
The glass-transition temperature (Tg) of polymer thin films can be strongly influenced by the combined effects of the supporting solid substrate and the free surface. The relative importance of these two effects, which often compete with each other, depends on the strength of the substrate–film interactions. Utilizing an atomistically informed coarse-grained model for poly(methyl methacrylate) (PMMA), here we uncover the relationship between the substrate–film interfacial energy and the spatial distribution ofTgacross thin films. We find that above acritical interfacial energy, the linear dependence of filmTgon the interfacial energy breaks down and filmTgattains an asymptotic value. Analyses on the spatial variation ofTgacross the thin film reveal that the short-range interface near the cohesive surface generates a long-range interphase that leads a spatially uniform appreciation ofTgthroughout the film, unlike weakly cohesive surfaces that show sharp gradients along the depth of film. These findings explain recent experiments and reveal a versatile approach for tuning filmTgvia engineered substrate-film interactions.