Crowded and Bimodal Size Nanoparticle Diffusion in Polymer Melts by ToF-SIMS

Nanoparticle (NP) diffusion in polymer nanocomposites (PNCs) is an important aspect in self-healing materials, drug delivery, and processing. NP size relative to matrix chains and NP loading are both well-studied factors that affect NP diffusion in polymer melts; however, methods like dynamic light scattering or single particle tracking are unable to access crowded NP regimes. Using time-of-flight secondary ion mass spectroscopy (ToF-SIMS), we investigate crowded and mixed nanoparticle systems in a poly(2-vinylpyridine) (P2VP) melt system on micron length scales. ToF-SIMS was used to measure cross-sectioned trilayer polymer-PNC-polymer samples to obtain 1D NP concentration profiles that are fit to obtain diffusion coefficients. We measure alumina and silica NPs of distinct sizes to obtain diffusion coefficients in low and high molecular weights matrices separately, then simultaneously in mixed-NP PNCs. With NPs of size < R_g and > R_g within the same PNC, two NP diffusion mechanisms are expected simultaneously, and we observe the effect of NP size and loading. This work provides insight into NP diffusion mechanisms in crowded and mixed-NP nanocomposites using the unique capabilities of ToF-SIMS.