Diffusion power spectra as a window into dynamic materials architecture

Understanding molecular dynamics in heterogeneous environments is a foundational step in tuning macromolecular reactivity. This is especially important in the chemical recycling of commodity and specialty polymers, which is often undertaken in aqueous media using molecular or enzymatic catalysts. Yet, it remains a challenge study dynamic materials architectures without accurate discernment of the behavior of water in confining media to capture the complexity of the operative transport processes. Here, we develop experimental and analytical methodologies describing the complete set of diffusive eigenmodes that exist within time-varying, non-Euclidean boundary conditions—a situation commonly found in the reactive deconstruction of polymers. Diffusion power spectra, as discerned by an NMR-based method, yield frequency-domain velocity autocorrelation functions that are analyzed in the context of physical models parameterized with fractal mathematics. The results connect time-evolving local motion in polymers to chemical reactivity during acid-catalyzed deconstruction of elastomers. The fundamental understanding provided herein offers practical tools for engineering materials with tailored properties and behaviors, with particular attention to the design of reactive polymers that advance circular materials economies and sustainable chemistry practices.