Adsorption phenomena in particle transport through a fluid-filled nanochannel

G. Drazer, B. Khusid, J. Koplik and A. Acrivos
City College of New York, US

Keywords: molecular dynamics, nanochannel, colloidal particle, adsorption, slip, stick-slip

Abstract:
An important ingredient in future transport applications at the nanoscale will be the motion of suspensions of solid particles through channels. Calculations based on continuum dynamics and models are not reliable at this scale and atomistic calculations are needed to complement experiments and explore new phenomena. We report molecular dynamics simulations in the simplest case of a solid particle in a rigid channel, emphasizing the effects of tight confinement and wall interactions, and the domain of applicability of the macroscopic equations. We consider the motion of a closely fitting nanometer-size solid sphere in a fluid-filled cylindrical nanochannel at low Reynolds numbers, for a range of fluid-solid interactions corresponding to different wetting situations. For fluids that are not completely wetting we observe a novel adsorption phenomenon in which a solid sphere, initially moving along the center of the tube, meanders across the channel and is adsorbed onto the wall. Thereafter the adsorbed sphere either sticks to the wall and remains motionless on average; or else separates slightly from the tube wall and then either slips parallel to the tube axis or executes an intermittent stick-slip motion. In both cases the gap between the sphere and wall remains smaller than the size of a fluid molecule, so that the particle slides along the wall without the presence of an intervening fluid. At early times when the solid particle moves near the middle of the tube, the average particle velocity closely follows the continuum prediction, despite large thermal fluctuations.

NSTI Nanotech 2003 Conference Technical Program Abstract