Mixture of neutral and dipolar-hard spheres confined in a slit pore:   field-induced population inversion and demixing
  We study by Monte Carlo simulation a binary mixture of neutral and dipolar hard-spheres with non-additive diameters. With a view to understanding the interplay between population inversion for an open pore and the demixing phase transitions, the mixture is considered in the bulk and confined between two parallel hard-walls modeling a slit pore. A uniform field is applied in the pore in order to control its composition as shown previously. The demixing lines in the bulk and in the pore are studied by the Gibbs Ensemble Monte Carlo method. The open pore-bulk mixture equilibrium is studied by a combination of canonical/grand canonical simulations. A moderate electrostatic coupling is considered for remaining close to the conditions in which a jump in the adsorption of the minority species has been observed at zero field. Demixing lines are given in the bulk and for two different pore widths in parallel and normal fields, together with population inversion paths. Similarly to the effect of geometrical confinement, a normal field is found to favor the mixed state so that the population inversion does not interfere with demixing. A parallel field leads to more complex scenarios. Some indications for future work are briefly discussed. 
Charles Brunet, Jean Guillaume Malherbe and Said Amokrane
physics.class-ph cond-mat.soft