Attractive energy contribution to nanoconfined fluids behavior: the normal pressure tensor

Abstract

The aim of our research is to demonstrate the role of attractive intermolecular potential energy on normal pressure tensor of confined molecular fluids inside nanoslit pores of two structureless purely repulsive parallel walls in xy plane at z = 0 and z = H, in equilibrium with a bulk homogeneous fluid at the same temperature and at a uniform density. To achieve this we have derived the perturbation theory version of the normal pressure tensor of confined inhomogeneous fluids in nanoslit pores:. Assuming the truncated-LennardJones potential, the third term represents the attractive intermolecular potential energy contribution to the normal pressure tensor. We report solution of this equation for the truncated-Lennard-Jones confined fluid in nanoslit pores, and we demonstrate the role of attractive potential energy by comparing the results of Lennard-Jones and hard-sphere fluids. Our numerical calculations show that the normal pressure tensor has an oscillatory form versus distance from the walls for all confined fluids. The oscillations increase with reduced bulk density and decrease with fluidfluid attraction. It also becomes broad and smooth with pore width at constant temperature and density. In comparison with hard-sphere confined fluids, the values of the normal pressure for LJ fluids at all distances from the walls are less than the hard-sphere fluids. This analytic pressure tensor equation is a useful tool to understand the role of attractive and repulsive forces in the normal pressure tensor and to predict phase behavior of nanoconfined fluids.

Pressure Profile for an Associating Lennard-Jones Fluid Confined in a Spherical Cavity

“…Then, the pressure tensor P̃ can be derived by the relationship P̃ = −Π̃. In this way, one can find that for a confined fluid, the pressure tensor can be expressed as a summation of three parts by writing − where P̃ ext , P̃ kin , and P̃ int are the contributions due to external potential, kinetic part, and the configuration part, respectively.…”

“…For an inhomogeneous fluid, the pressure tensor depends explicitly on the position, and hence is called the local pressure tensor. The local pressure tensor of a confined fluid has, in addition to the above-mentioned two parts, an extra part contributed by either an external potential or fluid–pore interaction. − On the basis of these considerations, there have been many efforts over the last several decades to study the pressure tensor for confined fluids. ,− ,− …”

“…For instance, Hafskjold and Ikeshoji found that for a homogeneous hard-sphere (HS) fluid in spherical coordinates, the IK integral path can result in a uniform pressure, whereas with Harasima’s path it is not the case. So far, the local pressure tensor of a fluid under nanoconfinement has attracted increasing interest, which is mainly focused on simple fluids, such as an HS fluid and a Lennard-Jones (LJ) fluid. − …”

Thermodynamics, Structure, and Dynamic Properties of Nanostructured Water Confined into B-, N-, and Si-Doped Graphene Surfaces and Carbon Nanotubes

“…Depending on the CNT diameter, they predicted the formation of ice nanotubes with the square, pentagonal, hexagonal, and heptagonal cross sections. Mansoori and Keshavarzi and their co-workers − have comprehensively studied the structure, properties, and phase behavior of confined fluids. They also investigated phase transitions in nano systems and local pressure of confined fluids inside nano pores.…”