We show that the thickness, h₀, dependence of the effective viscosity, η_eff(h₀), of unentangled random copolymer films of styrene (St) and 4-methoxystyrene (MeOS) supported by silica (SiOx) can be easily tuned by tuning the MeOS concentration, X_MeOS, in the copolymer. When X_MeOS is increased from 0% to 100%, η_eff(h₀) changes steadily from suppressed to enhanced with decreasing film thickness. At X_MeOS = 10%, η_eff(h₀) displays a nonmonotonic variation. Results obtained by fitting a three-layer model to the η_eff(h₀) data show that η_eff(h₀) of the X_MeOS = 0% film was dominated by the mobility-enhancing effect of the free surface, but as X_MeOS increases, the mobility-slowing effect of the substrate surface increases and dominates. The results also show that the propagation distance, l_t, of the substrate effect increases with increasing X_MeOS and is ∼2.6 to 6 times the radius of gyration of the polymer. We tentatively suggest the long propagation distances to be caused by the long-range van der Waals interactions. Analysis of the van der Waals interfacial potentials of the films supports this interpretation.

中文翻译：

---

不同共聚物组成的苯乙烯和4-甲氧基苯乙烯无缠结无规共聚物薄膜的有效粘度

我们表明，可以很容易地调节由二氧化硅（SiO x）支撑的苯乙烯（St）和4-甲氧基苯乙烯（MeOS）的无缠结无规共聚物膜的厚度h ₀，有效粘度_ηeff（h ₀）的依赖性。通过调节共聚物中的MeOS浓度X _MeOS。当X _MEOS从0％提高到100％，η _EFF（ħ ₀）从抑制到随膜厚增强稳步变化。在X _MEOS = 10％，η _EFF（ħ ₀）显示非单调变化。结果通过三层模型拟合到所获得的η _EFF（ħ ₀）的数据显示，η _EFF（ħ ₀的的）X _MEOS = 0％膜通过自由表面的流动性增强效果占主导地位，但作为X _MeOS增加，衬底表面的迁移率降低效果增加并占主导地位。结果还表明，底物效应的传播距离l _t随着X _MeOS的增加而增加约为聚合物回转半径的2.6至6倍。我们初步建议，长距离范德华相互作用会引起长传播距离。对薄膜的范德华界面势的分析支持了这种解释。