GouyChapmanModell

The Gouy-Chapman model, also known as the Gouy-Chapman-Stern model when referring to its more developed form, describes the structure of the electrical double layer at the interface between a charged surface and an electrolyte solution. Developed independently by Georges Gouy and David Chapman in the early 20th century, it provides a theoretical framework for understanding how ions in a solution arrange themselves in response to a charged electrode or colloid.

The core concept is that a charged surface in contact with an electrolyte will attract counterions (ions with opposite charge) and repel coions (ions with the same charge) from its immediate vicinity. Gouy and Chapman proposed that these counterions would not form a rigid layer but rather a diffuse, mobile layer extending into the bulk solution. The concentration of counterions would be highest at the surface and gradually decrease with distance, following a Boltzmann distribution. This diffuse layer effectively neutralizes the surface charge, creating a region of net charge in the solution.

The Gouy-Chapman model predicts that the thickness of this diffuse layer is dependent on the ionic strength of the solution and the temperature. Higher ionic strength leads to a compressed double layer, while lower ionic strength results in a thicker layer. While foundational, the original Gouy-Chapman model has limitations, such as neglecting the finite size of ions and specific adsorption. Later refinements, like the Stern model, incorporated these factors to provide a more accurate representation of the electrical double layer. The Gouy-Chapman model remains a crucial starting point for understanding interfacial phenomena in electrochemistry, colloid science, and membrane transport.