Single Particle Tracking of Sticky and Non-Sticky Nanoparticles in Polymer Melts

While nanoparticle (NP) diffusion in polymer melts is important to the fabrication and applications of polymer nanocomposites, the influence of the NP/polymer interaction is poorly understood. Investigation of the weak NP/polymer interactions is experimentally challenging tendency for nanoparticle aggregation. Here, the diffusion coefficients of weakly attracting (methyl capped, CH₃ QDs) and strongly attracting (carboxylic acid capped, COOH QDs) nanoparticles (radius ~ 6.5 nm) in poly(propylene glycol) (PPG) melts were measured by single particle tracking (SPT). The mean-squared displacements and van Hove distribution of nanoparticle motion show Brownian motion of non-aggregated nanoparticle, in the long-time diffusion regime (~1s). For weakly interacting CH₃ QDs, the effective nanoparticle radius is independent of PPG M_W due to the absence of a bound layer. For strongly interacting COOH QDs, the effective radius of the nanoparticle increases with the PPG molecular weight as M_W^0.5, indicating a long-lived bound layer. By obtaining spatial and temporal diffusion behavior of single nanoparticles, SPT provides previously inaccessible information on the nanoparticle diffusion in polymer melts.