基底界面效应对聚苯乙烯薄膜分子运动行为的影响

本文研究了Si／Si02、Si／Si—H基底与聚苯乙烯（Ps）之间的界面相互作用对Ps薄膜的玻璃化转变及相关力学性能的影响．结果显示，无论何种基底，Ps薄膜的玻璃化转变温度（L）都随其厚度降低而降低．但相同厚度（〈110nm）下，以Si／Si-H为基底时Ps薄膜的瓦比以Si／Si02为基底的PS薄膜高．Si／Si02表面Ps薄膜疋开始下降的临界厚度为110nm，远高于以Si／Si—H为基底时的40nm．对Ps薄膜的膨胀系数和弹性模量进行研究，也得到相似的临界厚度．另外，与Si／Si02基底相比，在Si／Si-H上的Ps薄膜具有更低的膨胀系数以及较高弹性模量．可能原因是Si／Si-H与Ps具有较强的相互作用，限制了该界面分子的运动能力，导致基底／PS界面效应对薄膜分子运动的影响力增强，造成该薄膜瓦的厚度依赖性下降，并呈现出相对较硬的力学特征．

Effects of substrate/polymer interfacial interactions on dynamics of thin polystyrene films

The glass transition temperature （Tg） and viscoelasticity of thin polystyrene （PS） films supported on Si/Si-H and Si/SiO2 substrates were investigated using an ellipsometry and force-distance （F-D） measurements of atom force microscopy. It was found that Tg of thin PS films deposited on either Si/Si-H or Si/SiO2 decrease with decreasing of film thickness. However, Tg of PS film on Si/SiO2 substrate depressed more dramatically than that on Si/Si-H. The threshold thickness for Tg reduction of thin PS film on Si/SiO2 （110 nm） is higher than that of film on Si/Si-H （40 nm）. Meanwhile, thin PS film supported by Si/SiO2 exhibits the higher thermal expansivity compared with that on Si/Si-H substrate. Surface F-D measurements reveal the film on Si/Si-H substrate is stiffened, showing a higher elastic modulus. In order to understand the mechanism of the substrate effect, the interfacial energy and long-range van der Waals potential （Фvdw） were investigated and a strong attractive interaction between PS and Si/Si-H substrate was found. Thus, the packing density was enhanced and the molecular mobility of PS chains at Si/Si-H/PS interface was suppressed. This strong interaction resulted in higher Tg and elastic modulus of thin PS film compared with that on Si/SiO2 substrate.