The effect of discrete attractive fluid–wall interaction potentials on adsorption isotherms of Lennard-Jones fluid in cylindrical pores

Abstract

The dependence of the adsorption isotherm and phase behavior of Lennard-Jones (LJ) fluid in cylindrical pores on the fluid–wall interaction was investigated using a discrete attractive potential model and the density functional theory. The discrete attractive potential contains two parts, a deep well (dw) and a tail. The results show that the chemical potential corresponding to capillary condensation has a weak dependence on the deep well potential near the pore wall, but exhibits a strong dependence on the tail potential near the pore center. On the contrary, the chemical potential of the formation of the first monolayer is strongly dependent on the deep well potential but almost independent of the tail potential. The shape of the adsorption isotherm plotted as density versus chemical potential is determined by the shape of the fluid–wall interaction, namely εtail–εdw, rather than either the deep well potential or the weak tail potential separately. The critical temperature exhibits similar behavior in its dependence on εtail–εdw. There exists a region where layer transition and capillary condensation intersect. Adsorption isotherms, coexistence curves, and critical temperatures in this region exhibit distinct phase behaviors from other regions.