(387h) Critical Properties of Fluids in Nanopores: Crossover From 3D to 2D

We study the effect of surface attraction on simple SW-fluid in slit pores of varying slit width from quasi 3D to 2D regime, by means of grand-canonical transition-matrix Monte Carlo (GC-TMMC) simulation. Our investigations indicate that various equilibrium and critical properties, under confinement of attractive slit pores, show very rich and interesting behaviors. Critical properties under confinement are found to vary rather interestingly as slit width is reduced from 40 molecular diameters (quasi-3D) to 1 molecular diameter (pure-2D). Critical temperatures are found to vary monotonically and approaches the bulk value as slit width becomes infinitely large. Moreover, around five different linear regimes are found for shift in the critical temperature with inverse of the slit width, for different attractive slit pores. On the other hand shift in the critical density and the critical pressure does not show any specific trend. Nevertheless, critical density and pressure show the sign of approaching towards 3D bulk value for infinitely large slit width in some interesting manner. Critical properties, below the slit width of 2 molecular diameters have insignificant effect on the surface characteristics and it behaves as quasi2D system. In this investigation, it has been observed that vapor pressure (spreading pressure) under confinement shows positive and negative deviation around bulk saturation pressure, with change in the slit pore width. Vapor-liquid surface tensions of the fluid for different attractive planar slit-pore of variable slit-widths are also compared. The role of different attractive surfaces on the vapor-liquid surface tension becomes insignificant for slit width less than 3 molecular diameters. But at a larger slit width, surface with lower attraction to the fluid molecules has shown comparatively larger surface tension value. Vapor-liquid Interfacial width is found to increase with decreasing slit width at a given temperature and wall-fluid interaction, which is contrary to what is being observed for fluids confined under hard cylindrical pores. We also present a similar study on cylindrical pores.