Connecting the Anomalous Rheology of Poly(2-vinylpyridine)/Octa(aminophenyl)silsesquioxane to Intermediate Polymer Relaxations

A molecular-level understanding of the rheology of polymer nanocomposite melts is critical for their use in high-throughput and advanced manufacturing techniques, but it is challenging due to the complex interplay between components and their geometry. To this end, polyhedral oligomeric silsesquioxane (POSS) provides an ideal platform for nanocomposite study because its extremely small size (~ 2 nm) makes the polymer matrix effectively "all-interfacial". In particular, such all-interfacial nanocomposites with attractive interactions (e.g., poly(2-vinylpyridine)/octa(aminophenyl) POSS: P2VP/OAPS) are known to reach ~ 50 vol% loading without OAPS aggregations. Recent works revealed that the significant increase in glass transition temperature in P2VP/OAPS could be explained well by the contributions of hydrogen bonds. However, there are unsolved questions regarding their anomalous rheological properties such as: 1) disappearance of entanglement plateau, 2) relatively small change in viscosity at high temperatures. This talk will share our recent systematic study of small amplitude oscillatory shear rheology with a wide range of molecular weights in P2VP/OAPS nanocomposites. We will explain the observed rheological behavior using the "slower process" of P2VP (relaxation mode between segmental and entire chain). The insights obtained in this study will be crucial to establishing property-processing rules for the next generation of nanocomposite materials.