Polymer Science in Quasi-Two-Dimensional Systems-Analysis of Internal Structures of Polymer Ultra-thin Films with Molecular Dimensions

聚合物薄膜作为制备有机组装纳米结构的基础材料，已经引起了人们的广泛关注。本研究旨在从聚合物科学的角度揭示聚合物单层和超薄聚合物薄膜等二维聚合物体系的基本性质。1)二维单层体系中聚合物的扩链利用能量传递方法，成功地求出了单层体系中单链的均方根距离。通过对二维链的能量传递效率实验值和模拟值的比较，发现聚合物链在单分子层中以收缩的形式存在，从而使表面没有链缠结的自由面积最小。2)二维体系中的链构象和纠缠行为研究了空气/水界面单分子层剪切粘度对分子质量的依赖关系，以阐明二维平面内的链形态。粘度与分子质量的单位次方成正比，表明聚合物链之间几乎不存在纠缠，且在二维体系中各链是分离的。3)单分子膜的结构松弛机理和动力学用时间分辨荧光退偏方法研究了聚合物链在单层膜中的微观运动，并在纳秒尺度上估算了其转动弛豫时间。首次揭示了聚合物链段在单分子膜中的动态行为，表明疏水链的内聚力决定了聚合物链段的迁移率。

Polymer thin films has attracted much attention as a basic material for fabricating nanometric structures of organic assemblies. This research project has been performed in order to reveal fundamental properties of two-dimensional polymer systems such as polymer monolayer and ultra-thin polymer films from a view of polymer science. The issues focused in this project were listed as follows.1) Chain expansion of a single polymer in two-dimensional monolayer systems By using the energy transfer method, the root square mean distance of a single polymer chain was successfully evaluated in a monolayer system. From the comparison of the experimental value of energy transfer efficiency and the simulated value for two-dimensional chains, it was revealed that the polymer chains took contracted forms in the monolayer in order to minimize free area without chain entanglement at the surface.2) Chain conformation and entanglement in two-dimensional systems Molecular weight dependence of the shear viscosity for the air/water interfacial monolayers was investigated to elucidate chain morphology in the two-dimensional plane. The viscosity was proportional to the unit power of the molecular weight, indicating that there exists little entanglement of the polymer chains and each chain is segregated in the two-dimensional system.3) Structural relaxation mechanism and dynamics in monolayersThe microscopic motion of polymer chain in a monolayer was examined by time-resolved fluorescence depolarization method, and the rotational relaxation times were evaluated in a nanosecond scale. The dynamic behavior of polymer segment in the monolayer was revealed for the first time and indicated that the mobility is predominantly governed by the cohesive force of hydrophobic chains.