CAREER: Glass formation in strongly interacting polymers - predictive understanding from high-throughput simulation and theory

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NONTECHNICAL SUMMARYThis CAREER award supports theoretical and computational research, and education on soft materials. Transformational technologies ranging from vaccines that remain viable at room temperature to flexible and stable solar cells and electronics await the development of new polymeric materials, soft materials made from long molecular chains with repeating molecular units, that push the limits of material performance. Many of the most promising materials for these new technologies derive their potential from two shared features: they solidify without forming a crystal, through a process known as the glass transition; and their molecules possess strong interactions. At the same time that these features are key to the potential of these materials, they also present a challenge to rational materials design. A fundamental understanding of the physics of the glass transition, the central determinant of the properties of these materials, is still lacking. This problem is especially acute in strongly interacting polymers, because strong interactions are resistant to standard theoretical approaches and are difficult to efficiently capture in computer simulations. As a result, it has not been possible to study molecular behavior at sufficiently long time scales and in sufficiently diverse chemistries to both unravel the fundamental physics of these materials and guide their design.This project is aimed to overcome these challenges. The PI will combine new theoretical approaches and an improved strategy for simulating glass-forming materials to establish fundamental insights and design guidelines for strongly interacting glass-forming polymers. This strategy will enable access to very long time scales and tens of thousands of chemistries to identify common aspects of the molecular physics of these materials and translate them into predictive theories for their properties. This theoretical understanding, in turn, will guide selection of molecular structures yielding unique, targeted material properties. Success of this project will contribute to accelerating the development of materials with the potential to improve human health, enable a cleaner domestic energy economy, enhance the lightness and durability of auto and aircraft components, and broaden the versatility of electronics and solar cells.This research will be integrated with educational outreach activities that will advance a Science, Technology, Engineering, and Mathematics (STEM) pipeline focused on guiding outstanding students - especially those from socioeconomically underprivileged backgrounds - into STEM careers. Specific activities will include expanding a PI-initiated effort offering paid summer-to-fall research internships to high school students, engaging of undergraduates in laboratory research, and coordinating master's degree programs to cement the transition of undergraduate students into the STEM community. TECHNICAL SUMMARYThis CAREER award supports theoretical and computational research, and education on polymer glasses. Strongly interacting polymers can exhibit extreme properties with the potential to enable societally transformational technologies, such as room-temperature preservation of vaccines in hydrogen-bonding polymer glasses and flexible solar cells and electronics stabilized by extraordinarily impermeable glassy polymer films. The dynamic, mechanical, and transport properties that determine the performance of these materials are largely controlled by the details of their glass transition, both in the glassy state where the structure frozen in at the glass transition temperature "controls" these properties and at higher temperatures where the glass formation process can dominate behavior to hundreds of Kelvin above the glass transition temperature. Rational design of these materials therefore demands a predictive understanding of glass formation in strongly interacting polymers. However, an understanding of the glass transition sufficient to guide materials design remains a grand challenge of materials science. While molecular dynamics simulations have provided a valuable tool in the study of this phenomenon, they have been unable to yield a predictive understanding of its physics because their insufficient speed prohibits simulation in the deeply supercooled regime near the glass transition and prevents simulations from spanning the large sets of systems necessary to establish comprehensive structure/property relations. This problem is especially acute in strongly interacting polymers, in which simulations are substantially slower and standard theoretical approaches based only on van der Waals interactions break down. This research project is aimed to overcome these challenges and to accomplish two strategic goals:1) Identify universal mechanistic interrelations between static and dynamic properties associated with glass formation in strongly interacting polymers, including alpha relaxation time, glass transition temperature, fragility of glass formation, glassy modulus, configurational entropy, and free volume. 2) Establish mechanism-based structure-property relations predicting the dependence of these properties on the molecular structure of strongly interacting polymers.These goals will be achieved by employing a novel efficient protocol for molecular dynamics simulation of the glass transition, developed in the PI's group, to perform simulations that access the deeply supercooled regime and span large matrices of molecular properties in strongly interacting polymers. These simulation data will be employed to establish structure/property relations covering a large range of molecular properties based on molecular-level insights. Data from these simulations will also be combined with theoretical models of glass formation to establish new mechanistic understanding and theoretical descriptions of glass formation in strongly interacting polymers. Ultimately, by combining theory with high-throughput simulations, this project will establish structure/property relations to enable theory-based design of strongly-interacting glass-forming polymers. This research will be integrated with educational outreach activities that will advance a STEM pipeline focused on guiding outstanding students - especially those from socioeconomically underprivileged backgrounds - into STEM careers. Specific activities will include expanding a PI-initiated effort offering paid summer-to-fall research internships to high school students, engaging of undergraduates in laboratory research, and coordinating master's degree programs to cement the transition of undergraduate students into the STEM community.