An electrical double layer model with spatial variation of the permittivity

Interaction between a charged surface and an electrolyte solution causes the formation of an electrical double layer (EDL), which has been a subject of extensive studies for more than a century. The present paper provides a simple EDL model, based on the idea that the dipole moments of water molecules at the charged surface are predominantly oriented towards the surface while all orientations are equally probable for water dipoles far away from the charged surface. Therefore, the model takes into account the spatial variation of the permittivity near the charged surface as well as the finite size of counterions and builds an analogy to the Stern Model.