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Surface potential

The relation between surface charge and surface potential can be expressed by the Grahame equation, derived from the Gouy-Chapman theory by assuming the electroneutrality condition, which states that the total charge of the double layer must be equal to the negative of the surface charge. Using the one-dimensional Poisson equation and assuming that, at an infinitely great distance, the potential gradient is equal to 0, the Grahame equation is obtained: σ = 8 c 0 ε ε 0 k B N A T sinh (z e ψ 0 2 k B T) {\displaystyle \sigma ={\sqrt {8c_{0}\varepsilon \varepsilon _{0}k_{\mathrm {B} }N_{A}T}}\sinh \left({\frac {ze\psi _{0}}{2k_{\mathrm {B} }T}}\right)} where c 0 {\displaystyle c_{0}} is the bulk concentration of the electrolyte, N A {\displaystyle N_{A}} Avogadro's constant, and T the absolute temperature.