In recent years, X-ray photon correlation spectroscopy (XPCS) has emerged as a powerful tool for investigating the dynamic behavior of matter across the relevant length (nm to 100s of nm) and time scales (sub ms to 1000s). One of the major directions of XPCS research in polymer science is polymer nanocomposites (PNCs). The interaction of a coherent X-ray beam with electron density fluctuations between inorganic fillers and a polymer matrix produces a “speckle pattern”. From time series of speckle patterns, the dynamics of fillers are quantified via intensity-intensity autocorrelation functions. The technique is appliable to model PNCs as well as those created specifically for the unique and evolving needs of industrial manufacturing processes. These capabilities have led to efforts to link the nanoscale dynamics obtained from XPCS to the macroscopic response. Here, I present our recent XPCS results on the following three research topics: (i) filler dynamics during thermal cross-linking of industrial epoxy, (ii) filler dynamics in a dual-cure (UV/thermal) nanocomposite during direct ink write 3D printing including at the filament-filament interface, and (iii) collective nanoparticle dynamics associated with bridging network formation in model PNCs. Equilibrium and non-equilibrium dynamics of fillers are probed in-situ and linked to the thermal or mechanical macroscopic properties. At the same time, the XPCS results with the model PNCs allow us to perform a mode-coupling theory dynamical analysis that incorporates the static polymer-mediated bridging structure and collective motions of fillers over a wide range of length and time scales. These studies provide new insight into the correlation/decoupling between the microscopic dynamical properties and macroscopic properties and identify some outstanding remaining challenges for the theoretical understanding of complex soft materials.

X-ray photon correlation spectroscopy to establish the dynamics-property relationship in polymer nanocomposites

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.