Direct observation of Brownian dynamics of hard colloidal nanorods

We synthesize monodisperse selenium (Se) colloidal rods, and the suspensions exhibit the smectic phase at a particle volume fraction (phi) of 0.28. Side-by-side rod clustering occurs at phi > 0.04. Cluster-size distributions and persistence times are determined for various phi. In dense suspensions (phi > 0.1), individual rods reveal characteristic fundamental motions, e.g., reptation and synchronized rotation. Mean-square displacements of the rods suggest a cage trapping and escape. Estimated translational and rotational diffusion coefficients show a large difference from predictions by computer simulations.