CAREER: Modeling High Free Volume Polymers: Influence of Free Volume Element Distribution and Chain Dynamics on Physical Aging

About This Grant

NONTECHNICAL Summary This award supports computational research and education to advance understanding of physical polymer aging, the process where the configuration of atoms relaxes over time leading to changes the properties of polymers. Polymers are long chain molecules made of several repeating units. When these chains are tangled and randomly arranged without any order, the polymer is said to be ‘amorphous’. Below the glass transition temperature (the point at which the polymer changes from soft and flexible to hard and glass-like), amorphous polymers are widely used in applications ranging from storage and packaging to separation technologies. Owing to their low cost and ease of manufacturing, polymer membranes have the potential to dramatically reduce the energy required for industrial separations, which currently account for a substantial fraction of global energy consumption. Polymers of intrinsic microporosity are especially promising membrane materials because their loosely packed molecular structure creates extra internal space (also known as free volume), which increases how quickly and efficiently gas molecules can move through the material. However, these polymers are not widely used in industrial applications, because they undergo physical aging, a slow and irreversible process in which the polymer relaxes and densifies over time. This relaxation leads to reduced separation efficiency, loss of mechanical integrity, and ultimately diminished membrane performance. At present, physical aging in high free volume polymers like polymers of intrinsic microporosity is captured indirectly through changes in membrane performance, and the underlying structural changes at the molecular level remain poorly understood. This CAREER award addresses this critical knowledge gap by uncovering how polymer chains rearrange during aging and how these rearrangements affect membrane performance. Molecular simulations will allow the PI to directly observe these small-scale rearrangements over time, revealing how the material’s internal structure and movement change in ways that cannot be observed experimentally. By developing a predictive framework for aging behavior, this research will enable the rational design of polymer membranes that maintain their performance over long times, facilitating the transition of energy-efficient membrane technologies from the laboratory to industrial use. In addition to advancing membrane science, the project integrates education and workforce development. While molecular simulations are used across many science and engineering disciplines, access to simulation-based training at the K-12 and undergraduate levels remains limited. To address this gap, the project includes mentoring and training activities that are open to all students at the K–12 and undergraduate levels. In addition, the project will increase the accessibility of molecular simulations for blind and visually impaired students, enabling their early engagement in STEM research. Successful completion of these educational goals will broaden access to molecular simulation tools across multiple educational stages while also encouraging blind and visually impaired students to pursue STEM degrees and enter the STEM workforce. TECHNICAL Summary This award supports computational research and education to advance understanding of physical polymer aging with potential to help guide polymer design and discovery. Physical aging in amorphous polymers arises from the gradual relaxation of a non-equilibrium glassy structure toward a thermodynamically favorable state. In polymer membranes, these microscopic relaxation processes manifest as macroscopic declines in permeability and mechanical properties, limiting the long-term viability of state-of-the-art high free volume materials such as polymers of intrinsic microporosity. Despite their technological importance, the molecular mechanisms governing aging in these materials, including the roles of chain rigidity, cooperative dynamics, and free volume redistribution, remain poorly understood. This project uses atomistic molecular simulations in conjunction with glassy aging theories to elucidate the molecular origins of physical aging in high free volume polymer membranes. The research focuses on quantifying the interplay between monomer rigidity, segmental mobility, and free volume distribution, and on identifying the dominant relaxation modes that control aging behavior. Temperature jump protocols are employed in simulations to accelerate and probe aging dynamics, enabling systematic investigation of relaxation pathways that are inaccessible to conventional experimental techniques. The project further develops a computational protocol to predict aging behavior in high free volume polymers based on molecular-level descriptors. The outcomes of this research will bridge polymer physics and membrane science by providing a mechanistic framework for understanding aging in glassy polymers. The resulting insights will guide the design of rigid, solvent-cast polymer membranes with improved resistance to aging, advancing the fundamental understanding of non-equilibrium polymer dynamics while enabling the development of durable, energy-efficient separation technologies. 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.