Multifaceted role of bound chains in reinforcement of polymer nanocomposites - structural and dynamical analysis*

The addition of nanoparticles (NPs) to polymer matrices is a powerful route to improve mechanical and other properties and design next-generation engineering materials. This presentation focuses on a nanoscale understanding of mechanical property enhancement in polymer nanocomposites (PNC). A key is ascribed to polymer chains adsorbed on the NP surface that acts as polymer bridges between neighboring NPs, leading to a network-like microstructure that reinforces the PNC.

The first topic is to probe the NP network’s structures and dynamics (10^-3 < t < 10³ s) using X-ray photon correlation spectroscopy. Silica NPs dispersed in attractive poly(2-vinyl pyridine) melts are used. We map out the structures and dynamics as a function of the probed length scale, NP loadings, temperature, and molecular weight. In addition, we employ the dynamical mode-coupling theory that incorporates the effect of bridging microstructure on the structures/dynamics.

The second topic is to reveal the structural and dynamical features of bound polymer (BP) chains that are not in bridges, but rather at the level of individual chains. A carbon black (CB) filled polybutadiene (PB) system is used. We prepare the BP chains composed of hydrogenated PB using a solvent-based approach, and the “BP coated CB fillers” are then embedded into a deuterated PB matrix, resulting in a strong contrast between a matrix and the BP for neutron scattering and spectroscopy experiments. In addition, molecular dynamics simulations are performed to complement the experimental results and to unravel details that are not accessible experimentally.

These experimental, theoretical, and computational results are then linked to the mechanical properties. The details will be discussed in the presentation.