Role of Chain Architecture on the Properties of Linear and Star Chain Thin Film Polymer Systems

聚合物表面与基质或外部环境之间的界面相互作用通常会导致局部聚合物结构的变化，例如单体“堆积”密度和链组织顺序。在纳米级厚度的聚合物薄膜中，物理性质的变化，包括输运性质、平均玻璃化转变温度、润湿性质和共混物的相稳定性，都与这种相互作用有关。理论和模拟表明，界面相互作用对大分子的结构很敏感。具体来说，星形大分子表现出与界面相互作用的更高倾向。当它们被吸附在界面上时，它们的构象熵惩罚比它们的线性链类似物要低。本研究的目的是了解约束（厚度和几何）和恒星的大分子功能（每个分子的臂数）在线性链/多臂恒星大分子共混物的动力学、润湿、玻璃化、相平衡和老化中的作用。该研究是通过使用模拟和辅助实验工具完成的，包括x射线光子相关光谱、介电光谱、中子散射、原子力显微镜和透射电子显微镜技术。非技术性聚合物薄膜的应用包括保护和功能涂层、有机电子器件中的活性材料成分和信息存储。聚合物薄膜的性能和可靠性受到其表面与衬底之间或与外部环境之间形成的界面的相互作用的影响。最近发现，聚合物分子的结构，无论是线性链还是星形链（即多个链连接到一个中心分支点），对界面相互作用的强度有显著影响。该项目的目标是了解聚合物分子的结构，包括连接到分支点的链的数量，如何影响聚合物薄膜的物理性质。这项研究的成功将对聚合物在润湿和粘附、保护和功能涂层以及其他活性技术中的应用产生影响。这项研究将涉及不同群体的合作者，从高中和本科生到研究生，他们将被介绍到研究中，并可能成为追求科学或技术事业的动力。

TECHNICAL Interactions at interfaces between polymer surfaces and substrates or the external environment are typically responsible for changes to the local polymer structure, such as monomer "packing" densities and chain organizational order. In polymer films of nanoscale thickness changes to physical properties, including transport properties, average glass transition temperatures, wetting properties and phase stability of blends, are associated with such interactions. Theory and simulations suggest that the interfacial interactions are sensitive to the architecture of the macromolecules. Specifically, star shaped macromolecules exhibit a higher propensity to interact with interfaces. They suffer lower conformational entropic penalties than their linear chain analogs, when adsorbed at interfaces. The goal of this research is to develop an understanding of the role of confinement (thickness and geometrical) and of the macromolecular functionality (number of arms per molecule) of stars on the dynamics, wetting, vitrification, phase equilibra and aging in linear chain/multi-arm star macromolecule blends. The research is accomplished through the use of simulations and complementary experimental tools that include X-ray photon correlation spectroscopy, dielectric spectroscopy, neutron scattering, atomic force microscopy, and transmission electron microscopy techniques.NON-TECHNICALPolymer thin films are used in applications that include protective and functional coatings, active material components in organic electronic devices, and information storage. The performance and reliability of a polymer film is influenced by interactions at interfaces formed between its surfaces and a substrate, or with the external environment. It recently became apparent that the architecture of the polymer molecule, whether it is a linear chain or star-shaped (i.e. more than one chain attached to a central branch point, has a significant impact on the strength of the interfacial interactions. The goal of this project is to understand how the architecture of the polymer molecules, including the number of chains connected to the branch point, affects the physical properties of polymer films. The success of this research will have implications on the use of polymers for wetting and adhesion, protective and functional coatings, and other active technologies. This research will involve a diverse group of collaborators, from high school and undergraduate to graduate students, who will be introduced to research and may become motivated to pursue scientific or technological careers.