Date/Time
Date(s) - 01/21/2025
3:00 pm - 4:00 pm
Location
Rhines 125
Categories
Abstract
The introduction of nanoparticles to elastomers and other polymers can greatly enhance mechanical rigidity and toughness, effects essential for diverse applications demanding mechanical robustness under load. Despite a century of use, the mechanism of this effect remains unsettled.
Here, we report on molecular simulations pointing to a leading-order understanding of the origin of nanoparticulate-driven elastomer reinforcement, from low strain to failure. At low strains, we find that a Poisson ratio mismatch between the elastomeric matrix and a co-existing percolated nanogranular solid governs reinforcement, causing the elastomer’s bulk modulus (order GPa) to contribute to the composite’s Young’s modulus (order MPa in neat elastomers). At intermediate strains, this mismatch effect leads to a situation wherein a normal compressive stress applied by the polymer to the filler preserves filler cohesion, enabling the emergence of a plastic nanogranular response under extensional strain. This plastic granular response, in turn, generates a large dissipative toughening effect.
Finally, our most recent results indicate that the consequences of this Poisson ratio mismatch, in the form of a massive internal stress buildup, play a central role in governing ultimate material failure. These findings tentatively provide a new foundation to design and understand elastomeric nanocomposites with exceptional mechanical properties.
Bio
David S. Simmons, Ph.D.
Professor, Chemical, Biological and Materials Engineering
University of South Florida
Dr. David S. Simmons is a Professor of Chemical, Biological, and Materials Engineering at the University of South Florida. The Simmons research group combines computer simulations, theory, AI, and experiments to understand and design polymers and soft materials from the molecule up, including nanostructured materials for applications from transportation to energy storage and sequence-controlled synthetic polymers with the potential to exceed the properties realized by nature itself.
Dr. Simmons’ work has been published in journals including Nature, Nature Physics, and PNAS and has been recognized by awards, including the NSF CAREER Award, the ACS Rubber Division Sparks-Thomas Award, and funding by the W. M. Keck Foundation.
Dr. Simmons received his B.S. and Ph.D. in Chemical Engineering at the University of Florida and the University of Texas at Austin, respectively, before completing an NRC Postdoctoral fellowship at NIST. He joined USF in 2018 after spending 6 years in the College of Polymer Engineering at the University of Akron. Earlier in his career, Dr. Simmons spent time at several biomedical industry startups, including in biomedical materials and device design.
Outside of his research roles, Dr. Simmons is President of the USF Faculty Senate and a member of the USF Board of Trustees.