Surface tension and vapor-liquid phase coexistence of confined square-well fluid

Abstract

Vapor-liquid equilibrium and critical behavior of the square-well fluid of variable range: A theoretical study J. Chem. Phys. 123, 234513 (2005) Phase equilibria of a square-well fluid in planar slit pores with varying slit width are investigated by applying the grand-canonical transition-matrix Monte Carlo ͑GC-TMMC͒ with the histogram-reweighting method. The wall-fluid interaction strength was varied from repulsive to attractive such that it is greater than the fluid-fluid interaction strength. The nature of the phase coexistence envelope is in agreement with that given in literature. The surface tension of the vapor-liquid interface is calculated via molecular dynamics simulations. GC-TMMC with finite size scaling is also used to calculate the surface tension. The results from molecular dynamics and GC-TMMC methods are in very good mutual agreement. The vapor-liquid surface tension, under confinement, was found to be lower than the bulk surface tension. However, with the increase of the slit width the surface tension increases. For the case of a square-well fluid in an attractive planar slit pore, the vapor-liquid surface tension exhibits a maximum with respect to wall-fluid interaction energy. We also report estimates of critical properties of confined fluids via the rectilinear diameter approach.

Vapor-liquid critical and interfacial properties of square-well fluids in slit pores

“…29 The interfacial free energy of a 2D surface ͑with area A = LH͒ can be expressed with the system size according to Binder's formalism and is given by…”

“…29,46 In this approach, MC simulations are conducted in a standard grand canonical ensemble where the volume ͑V͒, chemical potential ͑ ͒, and temperature ͑T͒ are held constant and the particle number N ͑or density͒ and energy ͑U͒ fluctuates. During a simulation, attempted transitions between states of different densities are monitored.…”

“…Similar results were observed for SW fluid in slit pores in our previous work. 29 On the other hand, recent works on disordered and interconnected pores and narrow cylindrical pores have shown that capillary condensation cannot be considered as the first order transition, 30 which led to some debate. 16,17,23,31 The critical temperature estimation is an integral part in the calculation and understanding of phase equilibria, yet little work has been reported on the effect of fluid-fluid interaction range on phase equilibria and critical properties under confinement.…”

“…Although, fluidwall tension has been investigated by various authors, 32,33 vapor-liquid interfacial properties under confinement have not been studied well. In our previous study, 29 we examined different approaches to evaluate the surface tension under confinement. Following the prescribed scheme in the previous work, 29 our second aim is to investigate the surface tension, interfacial width, and structural properties of coexistence phases of variable SW fluids in variable slit pores.…”

Direct determination of fluid-solid coexistence of square-well fluids confined in narrow cylindrical hard pores

“…Many results are available for vapor-liquid phase behaviors for the SW model. [1][2][3][4] There are several techniques to determine the vapor-liquid coexistence, such as Gibbs ensemble Monte Carlo ͑GEMC͒, 5 Gibbs-Duhem integration ͑GDI͒, 6,7 grandcanonical transition-matrix Monte Carlo, 2,8 but less is known about the fluid-solid behavior. Pagan and Gunton 9 used the free energy calculation and GDI to determine the fluid-solid coexistence and the metastable fluid-fluid coexistence for a short range SW model.…”