(631f) Solvent Effects on the Properties of Electric Double Layers with Surface Charge Regulation

The thermodynamically consistent representation of the
charge at the surface of an electric double layer is given by the chemical equilibrium
between the groups attached at the interface and the potential determining ions
in the solution (i.e., charge regulation). We report that this surface chemical
equilibrium is strongly coupled to the precise molecular structure of the
solution in near the charged interface that explicitly includes the solvent contribution,
also known as a ?civilized model?. Our analysis uses classical density
functional theory to obtain the molecular and ionic structure of an electric
double layer with surface charge regulation. The model suggests that the
excluded volume of the solvent is the main factor that couples the solution structure
to the surface chemistry, although attractive interactions may also play a role.
The Figure shows how the surface charge density depends on the relative size of
the solvent molecules in a Lennard-Jones type of electrolyte solution. The
different curves (top to bottom) are for increasing values of the Lennard-Jones
energy. The conclusion from our work is that an explicit account of the solvent
effects is necessary for quantitative description of an electric double layer with
surface charge regulation.