Molecular dynamics study of fluids confined in a nanopore and microflows perturbed by upward-force

Abstract

The confined fluids have different structural and dynamical characteristics compared to the homogeneous bulk fluids whose transport is isotropic in all directions. These fluids provide useful information on the mechanism of spreading, melting, lubrication, and friction of microporous media. We employ the molecular dynamics (MD) technique to understand the structure and dynamics of the confined fluids at the atomistic level. The wall model employed in this study is a structureless thermal wall. This type of wall controls temperature through a stochastic boundary condition. When a particle passes across a thermal wall, it is reentered inside of the cylinder by applying the thermalization mechanism designed by Tennenbaum et al [1]. We examine transport properties of simple fluids confined in 2- and 3-dimensional nanopores with various fluid density and pore size. We also study the behavior of the velocity auto-correlation function depending on both the density and the pore size and compare it with the prediction by the hydrodynamic theory. Further, we observed flow patterns in two-dimensional microfluid by using MD simulation. Convection patterns are induced by upward-force perturbations which are applied on fluid molecules passing through a specific area in the center of the system. We observed thermodynamic and transport properties of microflows. The convection patterns in flows have chiral property in that each vorticity has its own direction, clockwise or counterclockwise. Research on a new separation method of chiral molecules has been suggested in a microfluidic flow with spatially variable vorticity. It induced thermal fluctuating motion of the molecules on velocity field which is expressed in terms of a scalar stream function. We use MD simulation to confirm that this new chiral separation method is valid by observing its separation ratio.