(604b) Diffusion and Transport of Nanoparticles in Arrays of Nanoposts

We study the diffusive dynamics and convective transport of nanoparticles of diameter 200—400 nm in microfabricated arrays of cylindrical nanoposts using differential dynamic microscopy and single particle tracking. Posts of diameter 500 nm and height 10 μm were spaced by 1.2—10 μm on a square lattice. First, we measured dynamics of nanoparticles in quiescent dilute dispersions. As the spacing between posts was decreased, the diffusive dynamics slowed and on all length scales were best represented by a stretched exponential function. Both the relative diffusivity and the stretching exponent decreased linearly with increased confinement and, equivalently, with decreased void volume. Second, we measured the dispersion of nanoparticles as they flowed through the nanopost arrays. The distributions of particle velocity in the longitudinal and transverse directions exhibited distinct scaling behaviors with increasing confinement. Moreover, with increasing confinement the transverse dispersion became progressively non-Gaussian and increasingly important relative to the longitudinal dispersion. The appearance of non-Gaussian and stretched dynamics suggests that the transport properties of nanoparticles become increasingly cooperative when strongly confined.