721 research outputs found
Nanoscale simulations of directional locking
When particles suspended in a fluid are driven through a regular lattice of
cylindrical obstacles, the particle motion is usually not simply in the
direction of the force, and in the high Peclet number limit particle
trajectories tend to lock along certain lattice directions. By means of
molecular dynamics simulations we show that this effect persists in the
presence of molecular diffusion for nanoparticle flows, provided the Peclet
number is not too small. We examine the effects of varying particle and
obstacle size, the method of forcing, solid roughness, and particle
concentration. While we observe trajectory locking in all cases, the degree of
locking varies with particle size and these flows may have application as a
separation technique
Molecular dynamics of flows in the Knudsen regime
Novel technological applications often involve fluid flows in the Knudsen
regime in which the mean free path is comparable to the system size. We use
molecular dynamics simulations to study the transition between the dilute gas
and the dense fluid regimes as the fluid density is increased.Comment: REVTeX, 15 pages, 4 EPS figures, to appear in Physica
Hysteresis, force oscillations and non-equilibrium effects in the adhesion of spherical nanoparticles to atomically smooth surfaces
Molecular dynamics simulations are used to examine hysteretic effects and
distinctions between equilibrium and non-equilibrium aspects of particle
adsorption on the walls of nano-sized fluidfilled channels. The force on the
particle and the system's Helmholtz free energy are found to depend on the
particle's history as well as on its radial position and the wetting properties
of the fluid, even when the particle's motion occurs on time scales much longer
than the spontaneous adsorption time. The hysteresis is associated with changes
in the fluid density in the gap between the particle and the wall, and these
structural rearrangements persist over surprisingly long times. The force and
free energy exhibit large oscillations with distance when the lattice of the
structured nanoparticle is held in register with that of the tube wall, but not
if the particle is allowed to rotate freely. Adsorbed particles are trapped in
free energy minima in equilibrium, but if the particle is forced along the
channel the resulting stick-slip motion alters the fluid structure and allows
the particle to desorb
- …