Fluid enhancement of particle transport in nanochannels

We investigate the effect that fluid density has on the mobility of a spherical nanoparticle moving through a cylindrical nanochannel. The solid nanoparticle, the channel wall, and the fluid are described at the molecular level, and we use molecular dynamics simulations to study their behavior. We consider densities ranging from a few fluid molecules to a relatively dense fluid inside the channel. The inhomogeneous distribution of the fluid molecules inside the channel results in the competition of two effects as the fluid density is increased. The fluid molecules adsorb on the channel surface, and thus reduce the friction with the wall and enhance the mobility of the particle. On the other hand, the addition of fluid molecules increases the viscous drag on the particle and thus reduces its mobility. The outcome of these competing effects depends on the strength of the interaction between the atoms in the particle and those in the wall. We examine three different cases, i.e., intermediate, strong, and weak interaction energies. For an intermediate interaction, two distinct peaks are observed in the mobility of the particle as the first two adsorbed fluid layers form. On the other hand, a monotonously increasing mobility is found for a strong interaction energy, and a nearly constant mobility is observed for a weak interaction. (c) 2006 American Institute of Physics.