The unusually large film thickness at which confinement effects manifest themselves in surface fluctuations of unentangled four-arm star polymers has been defined using film thicknesses from 10R_g to 107R_g. For 15k four-arm star polystyrene (SPS), confinement appears at a thickness between 112 nm (40R_g) and 72 nm (26R_g), which is remarkably larger than the thicknesses at which confinement appears for unentangled 6k linear (<15 nm, <7R_g) and 6k and 14k cyclic (24 and 22 nm, respectively) polystyrenes. Data for 15k star films can be rationalized using a two-layer model with a 17 nm (6R_g) thick highly viscous layer at the substrate, which is significantly thicker than the 1R_g thick “irreversibly adsorbed” layer. For a 29 nm (10R_g) thick film, more striking confinement occurs due to the combined influence of both interfaces. These results underscore the extraordinary role long-chain branching plays in dictating surface fluctuations of thin films.

中文翻译：

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异常约束减缓了星形聚合物熔膜的表面波动

使用 10 R _g至 107 R _g的膜厚度定义了异常大的膜厚度，限制效应在未缠结的四臂星形聚合物的表面波动中表现出来。对于 15k 四臂星形聚苯乙烯 (SPS)，约束出现在 112 nm (40 R _g ) 和 72 nm (26 R _g ) 之间的厚度，这明显大于未纠缠的 6k 线性 (< 15 nm，<7 R _g）和 6k 和 14k 环状（分别为 24 和 22 nm）聚苯乙烯。15k 恒星薄膜的数据可以使用具有 17 nm (6 R _g) 基底上的厚高粘性层，比 1 R _g厚的“不可逆吸附”层厚得多。对于 29 nm (10 R _g ) 厚的薄膜，由于两个界面的综合影响，会出现更显着的限制。这些结果强调了长链支化在决定薄膜表面波动方面的非凡作用。