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纳米组装体的基础材料受到了广泛的关注。本研究项目的目的是从高分子科学的角度揭示二维高分子体系（如聚合物单层和超薄聚合物膜）的基本性质。本课题的主要研究内容如下：1）二维单层体系中高分子链的扩张利用能量传递法，成功地计算了单层体系中高分子链的均方根距离。从二维链的能量传递效率的实验值与模拟值的比较，结果表明，聚合物链在单层中采取收缩形式，以使自由面积最小化，而在表面没有链缠结。2）二维系统中的链构象和缠结空气/水剪切粘度的分子量依赖性。研究了水界面单层以阐明二维平面中的链形态。粘度与分子量的单位幂成正比，表明二维体系中聚合物链间几乎没有缠结，且各链处于分离状态。3）单分子膜中的结构弛豫机制与动力学采用时间分辨荧光退偏振方法研究了单分子膜中聚合物链的微观运动，并在纳秒尺度下计算了旋转弛豫时间。首次揭示了聚合物链段在单分子膜中的动态行为，并指出其运动主要受疏水链的内聚力控制。

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.