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

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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.