Confinement and Interaction Effects on the Diffusion of Passive Particles - Selected Topics of Computational and Experimental Fluid Mechanics - page 369

Confinement and Interaction Effects
on the Diffusion of Passive Particles

A. Gonzalez, E. Diaz Herrera, M. Sandoval, M.A. Chavez Rojo
and J.A. Moreno Razo

Abstract We use Molecular Dynamics simulations to study the effect of interac-
tions and confinement (walls) on particle diffusion. We extend previous studies by
analyzing the mean squared displacement (MSD) of an interacting fluid constrained
to a circular, square and triangular cavity of nanometric size. The interactions among
particles and walls are modeled by means of three classic potentials namely, Lenard-
Jones (CLJ), soft Lenard-Jones (SLJ) and hard Lenard-Jones (HLJ) potentials. For
hard spheres, for all cavities, and for very diluted densities, diffusion is shown to be
less favorable in comparison with particles interacting with a CLJ. It is also observed
that HLJ particles do not show difference in their MSD with SLJ particles at these
densities. Confinement effects also appear at these densities and it is shown that dif-
fusion decreases in the following cavity shape order: triangular, square and circular.
For moderated densities, the combination of confinement and interactions shows a
non-trivial effect. It is observed that particles inside a triangular cavity interacting by
means of HLJ, reduce their MSD in comparison with CLJ or SLJ particles, since for
this cavity shape, hard collisions reduce the particles' speed. For higher densities,
another non-trivial effect appears. Once again, the combination of interactions and
confinement gives rise to order in the system that clearly reduces the system MSD.
It is also shown that order appears for SLJ particles but it is absent for CLJ or HLJ
particles.