Population inversion of a NAHS mixture adsorbed into a cylindrical pore

A cylindrical nanopore immersed in a nonadditive hard sphere binary fluid is studied by means of integral equation theories and Monte Carlo simulations. It is found that at low and intermediate values of the bulk total number density the more concentrated bulk species is preferentially absorbed by the pore, as expected. However, further increments of the bulk number density lead to an abrupt population inversion in the confined fluid and an entropy driven prewetting transition at the outside wall of the pore. These phenomena are a function of the pore size, the nonadditivity parameter, the bulk number density, and particles relative number fraction. We discuss our results in relation to the phase separation in the bulk.