CAREER: Fundamental Studies of Glassy Polymer Mechanics

University Of South Florida, Tampa FL

Investigators

Abstract

NONTECHNICAL SUMMARY This CAREER award supports computational and theoretical research, and education in the field of glassy polymer mechanics. The industrial importance of understanding strength and failure of polymeric materials, such as structural plastics, has made quantitatively predicting their entire range of mechanical response an important goal of physical polymer science. Polymeric materials are composed of long chain molecules with repeating chemical units. Chemically different polymers exhibit dramatically different mechanical properties; large differences in mechanical responses play a major role in determining the stability of these materials against fracture. Understanding these different mechanical responses is critical to developing new high-performance materials as well as predicting the failure behavior and operational lifetime of existing systems, yet progress towards understanding them has been slow. Explaining the variety of behaviors observed has remained an open problem and microscopic, physics-based models are so far unsatisfactory at a predictive level. While computer simulations can provide essentially complete information on phenomena occurring during deformation of model systems, physical interpretation of this information can be difficult in the absence of an overarching theoretical framework. Recently developed candidate frameworks that have not yet been tested by simulation provide an opportunity for transformative advance. The research involves coordinated modeling that will exploit this opportunity and other opportunities that have emerged from recent experimental work. Progress toward the long term goals of this project will facilitate development of strong, lightweight structural plastics that can be used in applications ranging from automobiles to armaments. This project contributes to training two students in polymer physics, statistical mechanics, and computer simulations and contributes to developing a modern materials workforce. This award also contributes to enhance access of underrepresented minority students, including African Americans, Hispanics, and Native Americans, to higher degrees in physics through participation in the American Physical Society Bridge Program. The PI plans to assume primary responsibility for local Bridge student recruitment, admissions, and mentoring, as well as teaching a Science and Technology Engineering and Mathematics Professional Development course. The PI will also continue developing non-cognitive criteria for admissions and work to ensure their implementation within the Bridge Program and the local Applied Physics PhD program. TECHNICAL SUMMARY This CAREER award supports computational and theoretical research, and education in the field of glassy polymer mechanics. The project includes a program of simulations and analytical modeling that will significantly enhance basic physical understanding of how the mechanical properties of polymer glasses relate to their microscopic interactions and mesoscale order. Simulations will systematically relate differences in mechanical response to differences in micro- and meso-structure by varying local chain stiffness, sample preparation protocol, and deformation history, including temperature. Systems will be deformed to fracture in order to determine how these factors influence ultimate mechanical properties, such as ductility and toughness. The relatively low computational cost of the coarse-grained approach will be exploited to explore relevant parameter spaces far more broadly than is feasible for chemically detailed models. Analytical work will both complement the simulations and extend recently developed microphysics-based theories of polymer mechanics, through an iterative process wherein simulation uncovers problems with theories, the theories are improved as needed, and then used to make new predictions that will be tested by carefully designed follow-up simulations. This combined approach is designed to contribute maximally to the community's long term goal to obtain a level of physical understanding sufficient to develop predictive materials design principles to tailor mechanical response. Progress toward the long term goals of this project will facilitate development of strong, lightweight structural plastics that can be used in applications ranging from automobiles to armaments. This project contributes to training two students in polymer physics, statistical mechanics, and computer simulations and contributes to developing a modern materials workforce. This award also contributes to enhance access of underrepresented minority students, including African Americans, Hispanics, and Native Americans, to higher degrees in physics through participation in the American Physical Society Bridge Program. The PI plans to assume primary responsibility for local Bridge student recruitment, admissions, and mentoring, as well as teaching a Science and Technology Engineering and Mathematics Professional Development course. The PI will also continue developing non-cognitive criteria for admissions and work to ensure their implementation within the Bridge Program and the local Applied Physics PhD program.