A model of the interface between an electrode and
the solution close to it. In this model a sheet
of one type of electrical charge surrounds the surface
of the electrode and a sheet of the opposite charge
surrounds the first sheet in the solution.
Helmholtz model the double layer is regarded as consisting
of two planes of charge, with the inner plain of ions
from the solution being caused by the charge on the
electrode and the outer plane being caused by oppositely
charged ions in the solution responding to the first
layer of ions.
In the Gouy-Chapman model thermal
motions of ions are taken into account.
model is completely successful since the Helmholtz
model exaggerates the rigidity of the structures of
the charges and the Gouy-Chapman model underestimates
the rigidity of the structure.
The Stern model improves
on both models by assuming that the ions next to the
electrode have a rigid structure, while taking the
second layer to be described by the Gouy-Chapman model.