基底效应对受限聚合物薄膜分子链松弛行为影响的机理研究

With the recent advances in nanotechnology, relaxation behaviors of nanometer thick polymer films have attracted great interests of scientists in polymer physics and materials science. Although considerable evidences confirmed the presence of polymer/substrate interface as one of the main factors manipulating the dynamics of supported thin polymer films, the substrate effects on the dynamics of supported ultra-thin films is still an object of intense scientific debate, and how the substrate affect the entire film dynamics remains unclear. Based on our previous researches, we here propose that the nanostructure of the interfacial adsorbed layer is an important breakthrough to investigate the mechanism of the substrate effects, and a new concept of region--- “overlap region” was put forwarded to bridge the gaps between the structures of the adsorbed layer and thin film dynamics. The “overlap region” which is formed due to chain entanglement and interpenetration between the adsorbed layer and the upper bulk region, delivers the interfacial dynamics into the inner bulk of films. All the factors such as the substrate chemistry and film preparation method firstly influence the structure of the adsorbed layer, and the difference in nanostructures of the adsorbed layer further modify the structures and thickness of the “overlap region”, and finally determines the way and depth of the propagation of substrate effect into the bulk. By this route, the dynamics of thin polymer film with tens of nanometer thickness would be impacted by the slight change in the substrate. To validate this mechanism, we fabricated thin polymer film with various nanostructures of the adsorption layer by properly designing the polymer chains structure through incorporating functional groups (e.g. -OH, -COOH) which can interact with the SiOx substrate into the chains, and investigate the correlation between the structure of the adsorbed layer and the glass transition and viscoelasticity of thin polymer films. Also, the relationship between the thickness and structure of “overlap region” and the overall dynamics of thin polymer films will be also explored. The aim of the study is to elucidate the nature of the substrate effects and figure out how the substrate effects propagate into the polymer bulk, and obtain a parameter quantitating the substrate effects on thin film dynamics. These studies would be helpful in reconciling the controversies of results reported by various researcher groups, as well provide experimental method and theoretical basis to design and modulate the physical properties of polymer nanomaterials by controlling the interfacial effects.

纳米尺度聚合物的分子松弛行为受到了高分子物理学家与材料科学家的关注。然而，基底效应对支撑纳米聚合物薄膜分子松弛行为的影响还存在争议，其本质与传播途径还不清楚。本项目提出基底表面吸附层结构是研究基底效应的突破点，认为基底表面化学、制样条件等首先影响基底表面吸附层结构，再通过吸附层与本体层的重叠区结构达到影响薄膜整体分子松弛行为。项目提出通过设计SiO2基底表面吸附层链结构，研究吸附层PS结构与受限纳米PS薄膜分子运动能力（如玻璃化转变温度、黏度等）、薄膜分子运动能力开始偏离本体的临界厚度的关系，研究吸附层与本体层之间重叠区的厚度、结构与纳米受限薄膜分子运动能力之间的关系。阐明基底效应的本质及基底效应向本体传播的途径，获得衡量基底效应的物理参数。阐明文献报道结果之间存在差异的本质原因。研究成果将为通过控制吸附层结构来调节聚合物超薄膜物理性能的提供理论基础与实验手段。

纳米尺度聚合物的分子松弛行为受到了高分子物理学家与材料科学家的广泛关注。基底效应影响支撑纳米聚合物薄膜分子松弛行为的本质尚还不清楚。本项目以基底表面聚合物吸附层结构为突破点, 主要研究了基底效应对聚合物薄膜分子运动行为的影响及其传递的机理。制备了表面具有各种吸附层结构的基底材料，并研究以此为基底的聚合物薄膜分子运动能力的厚度依赖性。通过对吸附层结构的研究，关联吸附层结构如 hads/Rg 与基底效应传递距离、薄膜分子运动等的关系。阐明了基底表面化学是通过影响吸附层的纳米结构、进而影响基底效应在纳米薄膜内的传播。获得主要结果如下：1) 发展了一种直接测量基底效应传递深度方法。发现了聚合物与基底表面化学相互作用与基底效应传递深度、薄膜分子运动动力学的关系。2）获得了衡量界面效应影响聚合物薄膜分子运动深度的关键参数（hads/Rg，hads为吸附层厚度，Rg为聚合物的回转半径）。3）构建了结构精确的聚苯乙烯分子刷基底并研究了其结构与Tg的关系，以及基底分子链构象与聚合物薄膜玻璃化转变的关系。4）揭示了基底表面芳香基团修饰对聚苯乙烯吸附层结构的影响机理。5）通过调控界面吸附分子链构象来实现对聚合物薄膜动力学调控，证实了基底吸附层的构象在基底效应传递中的重要地位。6）阐明了侧链结晶聚合物分子刷聚集态结构形成及控制机理。7）测量了表面活性层的厚度并研究了自由表面与受限薄膜分子运动能力的直接关系。这些研究成果为阐明基底效应的本质及基底效应向本体传播的途径奠定了实验基础。为通过控制吸附层结构来调节聚合物超薄膜物理性能提供理论基础与实验手段。项目在《Physical Review Letters》等国内外重要学术刊物论文发表24篇。获浙江省自然科学三等奖1项，授权中国发明专利4项。培养博士1名，培养硕士17名。期间主办2019 嵌段共聚物自组装理论与模拟论坛。