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

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TECHNICAL SUMMARY: While during the last decade significant progress has been made toward understanding and controlling the structure and properties of polymers at the nanoscale, major challenges and opportunities, both scientific and technological, remain. Research has largely been devoted to the properties of linear-chain polymer systems; the influence of polymer chain architecture on the properties of thin films has largely remained unexplored. The goal of this proposal is to understand the effect of chain architecture on the miscibility, dynamics, glass transition and aging phenomena in thin film linear/star molecule and star/star molecule mixtures. There are several reasons for studying star polymers. Star molecules suffer a smaller loss in entropy than linear chains upon adsorption at interfaces. In additional to their interfacial properties, the dynamics of star shaped molecules, specifically the longest relaxation time, ?ä, and the viscosity, ?Ø, are slow; ?ä and ?Ø scale exponentially with the degree of polymerization, N, of the chain arm length. Perhaps the most fascinating aspect of star shaped molecules is that for low functionalities, f, and for sufficiently large N, they exhibit properties similar to linear chains. However, for very large f, they exhibit behavior akin to colloids. Guided by theoretical predictions, an experimental program, which exploits tools that include neutrons, electrons, X-rays, dielectric spectroscopy, ellipsometry and mechanical instruments, has been designed to develop an understanding of the influence of confinement and interfacial interactions on miscibility, microstructure, structural instabilities, aging phenomena and dynamics in star shaped molecule based systems (linear/star molecule and star/star molecule mixtures). The properties of these systems promise to be truly fascinating and present intriguing possibilities for new science and applications.NON-TECHNICAL SUMMARY: Diverse technologies, from coatings to functional materials for organic electronic devices and sensors, rely on the properties and performance of polymer thin films. Research on thin polymer films has primarily been devoted to linear chain polymers; little is understood about the properties of chains of different architectures, such as star shaped polymers. Star shaped molecules, by virtue of their architecture offer a number of potential, and unique, advantages over linear chain systems for certain applications. For example, they show promise for adhesive applications, and potentially for certain battery and sensor applications, as it is possible to take advantage of the multi-arm architecture for attachment of molecules/nanoparticles of varying functionalities. The goal of this proposal is to develop an understanding of the role of chain architecture on properties (miscibility, aging phenomena, glass transition and dynamics) of linear chain/star shaped molecule and of star/star molecule mixtures. This is an interdisciplinary program, involving polymer physics, chemistry, interfacial science, thermodynamics and transport processes. It will include an ethnically diverse group, including under represented minorities, of undergraduates, PhD students and high school students. The program also includes an international collaborator in the area of materials synthesis. Outreach activities of the principal investigator include public lectures at technical meetings, retired groups and participation on various National Research Council studies and boards and technical society committees.