Nanoparticle Diffusion in Polymer Melts and Hydrated Polymers

Nanoparticles (NPs) are combined with polymer matrices to modify mechanical, thermal, and optical properties, as well as to catalyze reactions in electrochemical devices. We recently developed a method for measuring NP diffusion coefficients in polymer melts by annealing trilayer samples and probing the NP concentration profile using time-of-flight secondary ion mass spectroscopy (ToF-SIMS). Previously, we established the role of NP size and surface chemistry on the nanoparticle diffusion coefficients and found good agreement with theory. Here, we report the diffusion coefficients of NOs grafted with bottlebrush polymers in melts of linear polymers. These bottlebrush polymer-grafted nanoparticles are comprised of large silica NPs (radius, 80 nm) grafted with various backbone degrees of polymerization and fixed polystyrene side chains (4.2 kDa), resulting in bottlebrush molecular weights ranging from 80 to 388 kDa. When the grafted bottlebrush polymers have a higher molecular weight than the matrix polymer, the core-shell model describes NP diffusion. Unexpectedly, when the grafted polymer is smaller than the matrix polymer, the NPs diffuse unexpectedly quickly, which we interpret as the onset of dewetting of the matrix from the grafted bottlebrush polymers and the disentanglement of the matrix polymers near the NPs. Disentanglement locally reduces the matrix viscosity, resulting in faster NP diffusion. We also explore the diffusion of catalytic nanoparticles in hydrated polymer electrolytes and the impact of nanoparticle diffusion on device performance.