Molecular Dynamics Study of the Surface Tension of a Binary Immiscible Fluid
V Simmons, Joseph B. Hubbard
The planar interface between two liquids having two degrees of affinity to mix has been studied by molecular dynamics simulations. The surface tension is calculated from the normal, PN, and transverse, PT, components of the pressure tensor P for a wide range of temperatures. An unusual increase in surface tension with increasing temperature is attributed to a pressure induced void transfer mechanism which is justified by basic thermodynamic arguments. This effect is diminished on the addition of a modest attractive potential between the two species, and there is a turnover point at higher temperatures beyond which surface tension decreases with increasing temperature. An order parameter is identified as the gradient of the mole fraction distribution through the interfacial region. An additional effect is the dramatic inversion of the kinetic and potential contributions to the PN profile as the temperature is varied. It is found that a commonly used approximation for P, the Irving-Kirkwood 1 or (IF1) method, results in a relatively modest unphysical variability in PN that weakly violates the condition of local mechanical stability. However, this artifact does not prevent the (IK1) method from producing an interfacial tension which is identical to that derived from the complete IK formula with no additional approximations.
Journal of Chemical Physics
molecular dynamics, order parameter, surface tension
and Hubbard, J.
Molecular Dynamics Study of the Surface Tension of a Binary Immiscible Fluid, Journal of Chemical Physics
(Accessed June 3, 2023)