Simulating Local Tg Reporting Layers in Glassy Thin Films

详细信息    查看全文

• 作者：Jeffrey DeFelice ; Scott T. Milner ; Jane E. G. Lipson
• 刊名：Macromolecules
• 出版年：2016
• 出版时间：March 8, 2016
• 年：2016
• 卷：49
• 期：5
• 页码：1822-1833
• 全文大小：467K
• ISSN：1520-5835

文摘

One of the most notable deviations from bulk fluid properties is the onset of a thickness-dependent glass transition temperature (T_g) for nanometrically thin polymer films. Experimental and theoretical observations suggest that this behavior is a response to the interfaces, which perturb the local properties of a film and play an increasingly important role in influencing the global properties of a film as its thickness decreases. In this work, we probe the global and local properties of free-standing films using our limited mobility (LM) model, which is a simple kinetic lattice model that simulates free volume and mobility in a fluid. We provide insight about the role of mobility in affecting the thickness-dependent film-average T_g of free-standing polymer films by characterizing the depth to which mobility propagates from a free surface, i.e., the “mobile layer depth”. We also consider the effect of “stacking” free-standing polymer films, where confinement by interfaces composed of the same material yields T_g suppression intermediate to that of substrate supported and free-standing films. In order to characterize the local properties of a film, we utilize “reporting layers” located near the free surface and film interior, from which we compute local glass transition temperatures and make connections with experimental results reported for real polymer films.