Surface charge#Gouy-Chapman

That the Gouy -Chapman double layer model is a further development of the simple model of an electrical double layer according to Helmholtz. New is that the thermal motion of the solvent molecules and the ions is taken into account, which refute the idea of ​​a rigid ion layer of the Helmholtz between model. This thermal motion causes a diffuse layer forms, which is more extensive than a molecular layer. Here, a statistical distribution of the ions is assumed as early as the Debye- Hückel theory ( Debye-Hückel - Onsager theory ) has also been postulated. According to these considerations, it follows on the diffuse layer across an exponential decay of the potential. Since the ions are assumed in this theory as a point, they can reach as close to the surface of the respective phase. With this description, the real case of ions with their own expansion was not enough done. A further development of the double layer theory that takes into account in this case, the star bilayer after Otto star.