Measuring Nanoparticle Diffusion in Polymer Melts Using ToF-SIMS

Nanoparticle (NP) dynamics are important for understanding processing of polymer nanocomposites (PNCs) and tuning their membrane, optical, and mechanical properties. Previously, nanoparticle diffusion was measured with ion-beam spectroscopy and single-particle tracking methods that required highly specialized equipment and limited the range and resolution of diffusion measurements to ~500 nm. Here, we measure nanoparticle diffusion in strongly attractive PNC systems using time-of-flight secondary ion mass spectroscopy (ToF-SIMS) on length scales up to 20 μm, which is orders of magnitude larger than previous experiments. Tri-layer polymer-PNC-polymer samples were made, and the cross-section was measured to detect nanoparticle diffusion in polymer melts as a function of diffusion time, temperature, and NP loading. Raw ToF-SIMS data directly provide diffusion profiles that when fit to Fick’s 2^nd law finite source to semi-infinite medium solution results in a diffusion coefficient. Our findings match previously reported diffusion coefficients. Our ToF-SIMS method is more accessible and promises to determine molecular weight, particle loading, geometry, and chemistry effects on NP diffusion.