Interfacial Dynamics in Ultrathin Polymer Films

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NON-TECHNICAL SUMMARY:In many practical applications, polymers are in direct contact with solid surfaces so that polymer-substrate interactions and the presence of free interfaces induce drastic deviations from their bulk properties. Fundamental understanding of the origins of these deviations is still lacking. This research will employ specialized dielectric, microscopy, and thermal characterization experiments to gain in-depth understanding of the impact of nanoscale confinement and polymer/surface interactions on the bulk properties of polymers of different molecular architectures. A unique focus of this work is the development of new, more accurate experimental methods for probing dynamics at the immediate interface between polymers and solid surfaces. The fundamental understanding obtained from the planned research could provide a basis for deliberate and optimal design of polymers for many technological applications, such as batteries, fuel cells, and supercapacitors, where interfaces play a significant role in determining the overall functionality. In addition, the knowledge gained from this project concerning the impact of the chemistry of solid surfaces in contact with polymers, the type of polymer, extent of confinement and sample preparative conditions will provide fundamental understanding to the polymer science and engineering communities. An important component of this project also involves several integrated educational activities. The project will contribute to training and education of specialists in polymer nanotechnology and materials science through active involvement of graduate and undergraduate students in this research. The integrated research/educational program particularly emphasizes work with underrepresented groups and research experiences for high-school students.TECHNICAL SUMMARY:Polymers exhibit deviations from their bulk physical properties in the vicinity of solid interfaces due to changes in interfacial structure and dynamics. These changes lead to shifts in the distribution of microscopic relaxation times determining many physical quantities of polymeric materials relevant to numerous technological fields as adhesion, coatings, and nanocomposites. Predictive understanding of how these alterations in the polymer properties depend on the molecular structure, flexibility of the polymer chains, thickness of the polymer layers, chemistry of the substrates, as well as temperature, is still lacking, and reliable experimental techniques to directly probe the microscopic dynamics in confined polymers are limited. To address this gap, the planned project will employ atomic force microscopy, AC chip calorimetry, and especially broadband dielectric spectroscopy in combination with recently developed nanostructured electrode assembly featuring silica nanostructures and an air gap, to probe interfacial dynamics in model ultrathin polymer films. The main goal of the project is to unravel the impact of interfacial interactions on structural and chain dynamics in linear and architecturally complex polymers, beyond the mean relaxation times. The major objectives include: (i) to develop a fundamental understanding of the influence of solid substrates on dynamics of polymers at interfaces; (ii) elucidate the role of molecular weight, chain flexibility, and architecture on interfacial dynamics; and (iii) investigate the impact of polymer film thickness and temperature on the distribution of relaxation times at the interphases. The detailed fundamental understanding of the impact of one-dimensional confinement gained from this project will provide a scientific framework for the design of novel functional polymers with unique properties for numerous technologies, including coatings, polymer composites, and polymer electrolytes suitable for use in electrochemical power sources and devices..This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.