  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.
