This research will develop new understanding of how polymers diffuse at surfaces and in confined geometries. The experiments will be based on using novel experimental platforms of fluorescence spectroscopy, sometimes with single-molecule resolution (FCS, fluorescence correlation spectroscopy), sometimes with FRAP (fluorescence recovery after photobleaching). As implemented, both experiments will yield spatially-resolved measurements with spatial resolution <0.5 mm. Many interesting and relevant variables will be performed, compared to available theory, and used to encourage the development of new theories. Two specific tasks are proposed. First, we will determine how surface diffusion depends on chain length and surface coverage for polymers adsorbed to solid surfaces from dilute solution. Second, we will study polymer melt diffusion over a wide range of controlled interfacial thickness, from nm to microns. These experiments will be enabled by a novel instrumental platform for integrating fluorescence experiments into a surface forces apparatus. Novel optical designs and exceptional dimensional stability will enable us to measure how lateral surface diffusion depends on thin film thickness. On the side of the solid surface, the critical role of the surface chemical composition will be explored. On the polymer side of the interface, we will focus on critical controlling aspects including the polymer chain length dependence, the polymer surface coverage, and in the case of molecularly-thin films, the film thickness, seeking to understand the universal aspects of this problem
NON-TECHNICAL SUMMARY: This research focuses on a central problem of polymer materials physics performance how polymers diffuse along the solid-liquid interface and in confined geometries. The scientific findings will develop new understanding that is fundamental in many scientific and technical applications, including adhesion, interdiffusion, friction, and the mechanical behavior of composite and nanocomposite materials. This work will import, into the field of polymer materials physics, fluorescence methods with single-molecule sensitivity that hold exceptional promise for this field. This will improve research infrastructure in the polymer field by developing new techniques not previously used in this discipline. The graduate and undergraduate students will be part of an interdisciplinary research group with other students from chemistry, chemical engineering, physics, and materials science.
