(374c) Nanoparticle Dispersion in Hard Porous Media As a Model of Composites

The transport of sub-micron particles in complex and highly confined porous media impacts processing of polymer nanocomposites. Specifically, attaining the optimal thermal, mechanical, electrical, and/or optical properties of polymer nanocomposites requires excellent control over the distribution of nanoparticles during processing in polymer solutions or melts. In the limit of strong confinement, in which the size of nanoparticles is comparable to typical length scales within the complex confining medium, the local mechanisms that influence nanoparticle transport remain poorly understood. Here, we use optical microscopy to probe the diffusive and transport properties of particles of size 200—400 nm in hard porous media that serve as models of fibers or other stiff components in a composite. We fabricate arrays of nanoposts that are arranged in a square lattice and employ both particle-tracking and differential dynamic microscopy to obtain information on the nanoparticle dynamics from microscopy movies. In both quiescent diffusion and in flow-driven transport through hard media, we generally find that the dynamics of the nanoparticles become increasingly slowed and stretched as the particles are more strongly confined within the post arrays. Under strong confinement, nanoparticles preferentially disperse along rather than normal to the direction of flow; this finding deviates from the dispersion behaviors observed for small solute molecules. These results have important implications for processing of nanocomposites, as the particle size will strongly affect the ability of nanomaterials to be uniformly dispersed in a composite matrix.