Gouy-Chapman Picture

Synonyms

Gouy-Chapman picture of the electrical double layer

Definition

The Gouy-Chapman picture of the electrical double layer describes the charge and potential distribution at a charged interface. The surface charge σ _o is compensated by unequal distribution of counterions (opposite in charge to the surface) and co-ions (same sign as the surface) which extend to some distance from the surface. The potential ψ decays exponentially with distance x. At low potentials, $\psi = \mathop{\psi }\nolimits_{\rm o} {\rm exp} - (\kappa \rm x)$, where ψ_o is the surface potential. When x = 1/κ, ψ _x = ψ _o/e; 1/κ is referred to as the “thickness” of the “double layer”. The double-layer extension depends on electrolyte concentration and valency of the counterions: $\left(\frac{1}{\rm K}\right) = \left( {{{\varepsilon _r \varepsilon _o kT} \over {2n_o Z_i^2 e^2}}} \right)$;ε _r is the permittivity (dielectric constant), 78.6 for water at 25 °C. ε _ois the permittivity of free space. k is the...