CAREER: Novel Coarse-Grained Simulations to Study Relationships Linking Morphology and Plastic Resistance in Semi-Crystalline Polymers

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This Faculty Early Career Development (CAREER) program will support fundamental research on how material structure at the molecular scale affects macroscopic physical properties of semi-crystalline plastics, facilitated by the creation of a new multiscale methodology for accelerated computational simulations. Plastics are used in a vast range of products for their excellent properties including high strength to weight ratio, chemical resistance, and durability. Plastics are made of organic polymers, long molecules composed of many repeating units, whose structure and chemistry dictate the material properties. At the nanoscale, semi-crystalline polymers are composed of a mixture of regions in which long molecular chains are either highly ordered or disordered. The significantly different mechanical properties of these different phases can, when combined, lead to remarkably tough and stiff materials. Over the past decades, costly empirical efforts have been predominantly employed to progressively search for improved chemistries and material processing in order to create stronger and tougher plastics. Accurate and efficient simulation methods are needed to replace these empirical efforts, a critical step in shortening today?s 10-20 year materials development cycle. Therefore, results from this research will foster new innovation in plastics manufacturing, one of the few U.S. manufacturing sectors with a trade surplus, ultimately benefiting the U.S. economy and society. Furthermore, the integration of educational and outreach activities with this research effort will help to address national challenges in meeting future demands for an abundant, diverse, and talented engineering workforce. For example, efficient learning will be facilitated through an adaptive and intelligent web-based educational system and cooperative learning, the latter of which will also be used to identify mentors for focused high school student workshops. Coarse-grained molecular models are limited in the extent to which they can describe polymer mechanics due to well-known problems of representability and transferability. Furthermore, their usage has been typically limited to simulations of single phase materials such as polymer melts or polymer glasses. The scientific objective of this research effort is to create and validate a multiscale computational framework that provides a systematic approach for generating coarse-grained molecular models of semi-crystalline polymers, which are optimized so that they preserve the essential kinematic details of relevant inelastic deformation mechanisms. The research team will develop and train coarse-grained models, and conduct verification and validation of the models to ensure that the spectrum of relaxation timescales is preserved across the coarse-grained transformation. The team will also exercise the newly developed models to identify relationships between interphase structure and mechanical properties such as slip resistance.