  The three-phase contact line formed by the intersection of a liquid-vapor
interface of an electrolyte solution with a charged planar substrate is studied
in terms of classical density functional theory applied to a lattice model. The
influence of the substrate charge density and of the ionic strength of the
solution on the intrinsic structure of the three-phase contact line and on the
corresponding line tension is analyzed. We find a negative line tension for all
values of the surface charge density and of the ionic strength considered. The
strength of the line tension decreases upon decreasing the contact angle via
varying either the temperature or the substrate charge density.
