Comparing refractive index and density changes with decreasing film thickness in thin supported films across different polymers
Comparing refractive index and density changes with decreasing film thickness in thin supported films across different polymers
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DOI：
10.1063/5.0012423
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发表时间：
2020-07-28
影响因子：
4.4
通讯作者：
Roth, Connie B.
中科院分区：
文献类型：
--
作者：
Han, Yixuan;Huang, Xinru;Roth, Connie B.
长期以来，聚合物薄膜的密度变化一直被认为是这种纳米受限系统中厚度相关的玻璃化转变温度 T-g(h) 变化的可能解释，因为玻璃化转变从根本上与冷却时材料致密化过程中的堆积挫败有关。我们使用椭圆光度法来比较聚（2-乙烯基吡啶）（P2VP）、聚（甲基丙烯酸甲酯）（PMMA）和聚苯乙烯（PS）支撑薄膜的温度依赖性折射率随厚度n（h）的减小，因为这些聚合物具有不同的二氧化硅基底相互作用。我们观察到所有三种聚合物的 n(h) 趋势相似，P2VP 和 PS 几乎相等，其特征是 h 的折射率明显增加
Density changes in thin polymer films have long been considered as a possible explanation for shifts in the thickness-dependent glass transition temperature T-g(h) in such nanoconfined systems, given that the glass transition is fundamentally associated with packing frustration during material densification on cooling. We use ellipsometry to compare the temperature-dependent refractive index with decreasing thickness n(h) for supported films of poly(2-vinyl pyridine) (P2VP), poly(methyl methacrylate) (PMMA), and polystyrene (PS), as these polymers have different silica substrate interactions. We observe similar n(h) trends for all three polymers, with near equivalence of P2VP and PS, characterized by a large apparent increase in refractive index for h