  Wetting of a charged substrate by an electrolyte solution is investigated by
means of classical density functional theory applied to a lattice model. Within
the present model the pure, i.e., salt-free solvent, for which all interactions
are of the nearest-neighbor type only, exhibits a second-order wetting
transition for all strengths of the substrate-particle and the
particle-particle interactions for which the wetting transition temperature is
nonzero. The influences of the substrate charge density and of the ionic
strength on the wetting transition temperature and on the order of the wetting
transition are studied. If the substrate is neutral, the addition of salt to
the solvent changes neither the order nor the transition temperature of the
wetting transition of the system. If the surface charge is nonzero, upon adding
salt this continuous wetting transition changes to first-order within the wide
range of substrate surface charge densities and ionic strengths studied here.
As the substrate surface charge density is increased, at fixed ionic strength,
the wetting transition temperature decreases and the prewetting line associated
with the first-order wetting transition becomes longer. This decrease of the
wetting transition temperature upon increasing the surface charge density
becomes more pronounced by decreasing the ionic strength.
