Semicrystalline Polymers under Confinement as Thin Films

可结晶聚合物的薄膜几何结构将使用电学和光学方法进行研究。由薄膜几何形状引起的分子迁移率的限制将被研究，并与在大块聚合物中观察到的行为进行比较。该研究选择的材料是具有良好表征的分子量和弹性的模型体系，包括等规聚苯乙烯（i-PS）和等规聚苯乙烯与无规聚苯乙烯（a-PS）的混溶。薄膜厚度对玻璃化转变和冷结晶动力学的影响将确定均聚物i-PS和共混物的薄膜厚度和聚合物链端到端距离的均方根。在纳米尺度的薄膜中，测量取向层弛豫的光学方法，以及使用高温原子力显微镜进行表面研究，将用于证实介电实验。薄膜的非原位表征将包括通过轮廓测量法测量厚度，以及通过扫描电子显微镜分析表面结构。薄膜的结晶度将用傅里叶变换红外光谱来评估。在体尺度薄膜中，同时进行宽角和小角x射线散射，以评估结构参数，并根据散射强度的时间发展确定结晶动力学。差示扫描量热法及其温度调制变体将用于测定较厚薄膜的玻璃化转变温度和结晶度。聚合物薄膜在技术应用中得到了越来越多的应用，因此了解可结晶聚合物纳米薄膜的结构和性能具有很大的实际意义。这项工作将为聚合物薄膜中的分子运动和结晶过程提供基础信息，这些过程直接影响到薄膜的材料性质和性能特征。

Crystallizable polymers in the thin film geometry will be studied using electrical and optical methods. Constraints on molecular mobility that arise from the thin film geometry will be investigated and compared to behavior observed in the bulk polymers. Materials chosen for the study are model systems having well-characterized molecular weights and tacticity, comprising isotactic polystyrene (i-PS), and miscible blends of isotactic with atactic polystyrene (a-PS). Effects of film thickness on the glass transition and cold-crystallization kinetics film thickness and root mean square end-to-end distance of the polymer chain will be determined for homopolymer i-PS and blends. In nanometer-scale thin films, optical methods measuring alignment layer relaxation, and surface studies using elevated temperature atomic force microscopy, will be used to corroborate the dielectric experiments. Ex-situ characterization of the films will include thickness measurement by profilometry, and surface structure analysis by scanning electron microscopy. Degree of crystallinity of thin films will be assessed using Fourier Transform infrared spectroscopy. In bulk-scale films, simultaneous wide and small angle X-ray scattering will be performed to assess structural parameters and to determine crystallization kinetics from the time development of scattered intensity. Differential scanning calorimetry and its temperature-modulated variant will be used to determine the glass transition temperature and degree of crystallinity of thicker films.%%%Thin polymer films are being used more frequently in technological applications, and it is therefore of great practical interest to understand the structure and properties of crystallizable polymer nanometer-scale films. This work will provide fundamental information about the molecular motions and crystallization processes in thin polymer films, which impact directly the material properties and performance characteristics of thin films.