Binary fluids in planar nanopores: Adsorptive selectivity, heat capacity and self-diffusivity

Monte Carlo and molecular dynamics simulations are performed to study fluid adsorption of a two component fluid in slit pores of nanoscopic dimensions. The slit pores are immersed in a binary fluid bath, which is comprised of spherical molecules having a size ratio of 1.43, at constant temperature and composition. Pore width is varied to determine how the heat capacity and self-diffusion coefficient are linked to the composition and structure of the adsorbed fluid. In pores where the fluid structure is most pronounced, we observe: perfect (or near perfect) exclusion of one component by the other component, a heat capacity that rapidly oscillates and is of greater magnitude than in the fluid bath, and self-diffusion coefficients on the order of 10^–8 cm²/s. The behavior of the heat capacity and diffusion coefficients appears to arise from a near solid-like layering of OMCTS that occurs at certain favorable pore widths.