Nanoparticle Diffusion in Crowded Polymer Nanocomposite Melts.

This study examines nanoparticle diffusion in crowded polymer nanocomposites by diffusing small Al₂O₃ nanoparticles (NPs) in SiO₂-loaded P2VP matrices. Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measures Al₂O₃ NP diffusion coefficients within a homogeneous PNC background of larger, immobile SiO₂ NPs. By developing a geometric model for the average interparticle distance in a system with two NP sizes, we quantify nanocomposite confinement relative to the Al₂O₃ NP size with a bound layer. At low SiO₂ concentrations, Al₂O₃ NP diffusion aligns with the neat polymer results. In more crowded nanocomposites with higher SiO₂ concentrations where the interparticle distance approaches the size of the mobile Al₂O₃ NP, the 6.5 nm Al₂O₃ NPs diffuse faster than predicted by both core-shell and vehicular diffusion models. Relative to our previous studies of NPs diffusing into polymers, these findings demonstrate that the local environment in crowded systems significantly complicates NP diffusion behavior and the bound layer lifetimes.