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

Abstract

Computer simulation studies of a square-well fluid in a slit pore. Spreading pressure and vapor-liquid phase equilibria using the virtual-parameter-variation method J. Chem. Phys. 112, 5168 (2000) Vapor-liquid phase equilibria of square-well ͑SW͒ fluids of variable interaction range: = 1.25, 1.75, 2.0, and 3.0 in hard slit pores are studied by means of grand-canonical transition-matrix Monte Carlo ͑GC-TMMC͒ simulation. Critical density under confinement shows an oscillatory behavior as slit width, H, reduced from 12 to 1 . Two linear regimes are found for the shift in the critical temperature with the inverse in the slit width. The first regime is seen for H Ͼ 2.0 with linear increase in the slope of shift in the critical temperature against inverse slit width with increasing interaction range. Subsequent decrease in H has little consequence on the critical temperature and it remains almost constant. Vapor-liquid surface tensions of SW fluids of variable well extent in a planar slit pore of variable slit width are also reported. GC-TMMC results are compared with that from slab based canonical Monte Carlo and molecular dynamics techniques and found to be in good agreement. Although, vapor-liquid surface tension under confinement is found to be lower than the bulk surface tension, the behavior of surface tension as a function of temperature is invariant with the variable pore size. Interfacial width, , calculated using a hyperbolic function increases with decreasing slit width at a given temperature, which is contrary to what is being observed recently for cylindrical pores. Inverse scaled interfacial width ͑ / H͒, however, linearly increases with increase in the scaled temperature ͑T c,bulk − T͒ / T c,bulk .

Effect of surface-screening parameter of the Yukawa potential model on vapour–liquid phase coexistence and critical-point properties of confined Yukawa fluid

“…The parameter b is also known as the order parameter critical exponent. In the current investigation, we have not used Binder's fourthorder cumulant approach [50] or much better mixed-field finite-size scaling approach to evaluate the pore critical temperature, but a recent study using finite-size scaling approach [51] for the estimation of critical point of LJ fluid in hard slit -pore confinement shows similar behaviour as reported in some other recent work [27,48,49] using the current technique. The critical temperature,T c , estimated from Equation (3) is used to calculate the critical density, r c r c , from the least square fit of the following equation [52]:…”

“…However, the other effective method that uses finite-size scaling approach has shown similar trend of critical-point properties, T c and r c , under slit-pore confinement [51] as depicted by the use of simple rectilinear law approach and current simulation technique in some other work. [27,48] Therefore, the critical-point data obtained using current simulation technique and with simple rectilinear law are reasonably good for qualitative comparisons.…”

“…The detailed methodology is described in the earlier work. [46,48] The simulation cell size in z-direction 2 S.K. Singh (confined direction), L z is kept fixed at a value 8 in all simulations.…”

Thermodynamics phase changes of nanopore fluids

“…In addition, comparison with another classical EOS, such as PR, is shown. A thorough literature survey (Didar and Akkutlu, 2013;Singh et al, 2009;Morishige et al, 1997;Morishige and Shikimi, 1998;Zarragoicoechea and Kuz, 2004;Vishnyakov et al, 2001;Ortiz et al, 2005;Jana et al, 2009;Devegowda et al, 2012) is performed to collect the critical shifts obtained from experiments and molecular simulation.…”

A grand canonical Monte Carlo simulation study of argon and krypton confined inside weakly attractive slit pores

“…Figure 3(a) shows that at 246 K for the pore with slit height of h ¼ 9 Å , the density profiles are uniform and coincident at both the pressures (50 and 200 atm) whereas in the larger pore (h ¼ 15 Å ) at the lower pressure of 50 atm, a uniform profile is noted; though at the higher pressure of 200 atm, a depletion region near the wall is followed by a 'sticking tendency' at the centre of the pore. This 'sticking tendency' has also been observed by Jana et al [53] in confined SW fluids (a hard core fluid model) in walls modelled using a hard potential. The effect of increase of temperature to 300 K on the density profiles is shown in Figure 3(b).…”