Biomedical and Chemical Engineering Seminar

Modeling the Molecular Mechanisms of Mediating of Nonlinear Viscoelasticity in Recyclable Self-Assembling Polymer Networks

Dr. Thomas O'Connor

Assistant Professor, Materials Science and Engineering

Carnegie Mellon University

The outsized need to eliminate plastic waste has stimulated advances in polymer chemistry to design reprocessable that replace strong covalent bonds with reversible self-assembling bonds that can be triggered to degrade through environmental cues. While exciting, such reprocessable polymers are of little use if we do not know how to process them in the first place.  Many industrial polymer processes elongate polymer liquids at rates much faster than the molecules can relax, driving large changes in chain conformations and viscoelastic stresses. Understanding these nonequilibrium dynamics is essential for developing and controlling manufacturing process, but our best viscoelastic models rely on mean-field approximations that fail when applied to self-assembling polymers. This has made it difficult to adopt and reliably process these sustainable polymer alternatives.

Our group is harnessing new nonequilibrium molecular simulation techniques that permit direct prediction of self-assembling chain dynamics in strong nonlinear flows with arbitrary flow geometries and flow histories. This has enabled us to bypass the need for constitutive models and directly apply MD simulations to predict both the macroscopic rheology and microscopic dynamics of a wide variety of architecturally complex synthetic and bio-inspired polymer systems. Here, I'll present molecular simulations for synthetic and self-assembling polymers undergoing nonlinear shear and extensional flows, which I will compare to analogous experimental systems. In all cases, coarse-grained MD simulations reproduce the rate-dependent nonlinear rheology observed in experiments, even when constitutive models fail. Simulations also reveal the exotic chain dynamics and molecular mechanisms that mediate rate-dependent flow behaviors critical to processability.

Bio:

Thomas O’Connor is an Assistant Professor of Materials Science and Engineering at Carnegie Mellon University. His research group applies molecular and continuum simulations to design sustainable polymer materials and improve soft material manufacturing methods. O’Connor is particularly interested in learning how nature can guide the design of new polymer processing and manufacturing methods by studying how insects, spiders, and worms have naturally evolved to manipulate macromolecules as adhesives and webbing. O’Connor is a recipient of the 2024 DOE Early Career Research Program Award, which supports his labs efforts to understand the mechanistic origins of self-healing in polymer materials.

Prior to joining Carnegie Mellon, O'Connor was a Harry S. Truman Fellow at Sandia National Laboratories, where he developed an open-source platform for modeling multiphase processing flows (LAMMPS/RHEO).  He remains an active developer for Sandia’s LAMMPS software for molecular simulations. O'Connor is an officer within the U.S. Society of Rheology and the Division of Polymer Physics of the American Physical Society, where he coorganizers major outreach events including the Annual Squishy Science Sunday at the APS March Meeting.