The density evolution of polystyrene (PS) adsorbed layers on phenyl-modified SiO₂-Si substrates was investigated. The thickness and density of flattened layer on substrates with above 75% phenyl content increased over annealing time and could approach 4.7 nm and 1.37 g/cm³ at equilibrium, respectively, which were much higher than those on SiO₂-Si. The annealing time for flattened chains to reach equilibrium increased with an increasing phenyl content on the substrate. The interface sensitive sum frequency generation vibrational spectroscopy (SFG) technique revealed that both the amount and the strength of the interfacial π–π interaction between the phenyl groups of substrates and in PS chains increased with annealing time. This resulted in more stretched chains perpendicularly, leading to a denser and thicker adsorbed layer with a closest-packing structure, driven by favorable enthalpy processes. Our work provides important insight into the densification mechanism of adsorbed flattened layers.

中文翻译：

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聚苯乙烯吸附层在基材上的密度演变机制


研究了苯基改性 SiO_2-Si 衬底上聚苯乙烯 （PS） 吸附层的密度演变。苯基含量高于 75% 的衬底上平坦层的厚度和密度随着退火时间的增加而增加，平衡时可分别接近 4.7 nm 和 1.37 g/cm³，远高于 SiO_2-Si。扁平链达到平衡的退火时间随着衬底上苯基含量的增加而增加。界面敏感和频产生振动光谱 （SFG） 技术表明，衬底苯基团和 PS 链中界面 π-π 相互作用的数量和强度都随着退火时间的增加而增加。这导致垂直拉伸的链更多，在有利的焓过程的驱动下，产生更致密、更厚的吸附层，具有最紧密的堆积结构。我们的工作为吸附扁平层的致密化机制提供了重要的见解。