Collaborative Research: Spatial and Dynamic Heterogeneity and Nonlinear Viscoelastic Constitutive Behavior of Glasses and Their Nanocomposites as Probed by Nonlinear Spectroscopies

North Carolina State University, Raleigh NC

Investigators

Abstract

This research project will answer fundamental questions related to the performance of glassy polymers and their nanocomposites. These materials are important for a wide range of defense and commercial applications. Two mechanical spectroscopy techniques will be used to identify the unique “fingerprint” of these materials. Although normally used for soft materials, this research will employ this approach to investigate the nonlinear response of glassy polymers and their nanocomposites. The study combines experiment and computation to advance the science and engineering fundamentals of these advanced materials. The outreach programs at both universities provide opportunities for K-12 students and teachers to advance in their understanding and familiarity with STEM through activities exploring engineering, materials, and recycling. Students from underrepresented groups will be recruited to all activities of the work. The impact will be broadened by publication of results as well as technical presentation of the work at major conferences and incorporation of the findings in courses. The specific goals of the research are to use nanoparticle reinforced polymer glasses to elucidate the impact of different length scales and heterogeneity on the nonlinear viscoelasticity of polymer glasses and, simultaneously, their nanocomposites. The richness of the study arises from the facts that, in glass-forming systems including polymers, there is a consensus that the heterogeneities are on the scale of a few nanometers whereas in nanocomposites the size-scale range of interest can vary from that of the heterogeneity-scale of the polymer to the size of multiple particles, i.e., above 100 nm. There is significant evidence that properties of the polymer matrix itself are modified by the interphases and confinement effects, thus leading to a rich range of heterogeneity in these materials. The work uses the mechanical spectral hole burning (MSHB) and large amplitude oscillatory shear (LAOS) fingerprinting framework to elucidate the impact of different scales and heterogeneity on the nonlinear viscoelasticity of polymer glasses and their nanocomposites, something that has heretofore not been investigated. The intent is to systematically vary the scale and nature of the heterogeneity, to fingerprint it experimentally, and compare the results with computational models of behavior. The outcome will be a greatly improved understanding of how heterogeneity in glassy polymers and their nanocomposites impacts nonlinear behavior and, consequently, performance. 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.