Abstract:
The density variation and the driven flow of a model Uquid interacting via 12-
6 Lennard Jones potential in a nano-sized channel has been studied through
molecular dynamics simulations. The channel is unbounded in x and y directions through the use of periodic boundary condition and in the z direction
it is bounded by walls (lying in the x-y plane) on both sides and the separation between the walls is of the order of nanometers. Two types of wall have
been studied - a smooth structureless wall and an atomic wall. The smooth
wall is modelled by a Lennard Jones 10-4 potential. The atomic wall is composed of layers having 001 fee structure with wall atoms interacting with each
other through the Lennard Jones 12-6 potential of strength six times that
of the fluid-fluid interaction strength. Simulations are done for both static
and moving wall atoms. In the first case, wall atoms are assumed to have
infinite mass and therefore remain static at their original position throughout the simulation. In the second case, wall atoms have finite mass and are
allowed to move about their mean position. The density variation across the
channel is computed with the static wall. The simulated density profile is
compared with Koplik & Banavar (1988) and found to match very well. A
Poiseuille flow is simulated in the same system by imposing a constant body
force along the x direction on each fluid atom. The flow is simulated over
a range of the body force for which thermal equilibrium exists between the
wall and the fluid system. The simulated profiles at different body force are
fitted with Stokes profiles and viscosity values are estimated from the fitting
parameters. The viscosity values obtained from the present simulation lie
within the range estimated by KopUk k Banavar (1988). The shear viscosity
of the bulk liquid is calculated independently by non-equihbrium molecular
dynamics methods which yield viscosity values consistent with the estimates
from fitting the velocity profiles.
