thickness of electrical double layer
The length characterizing the decrease with distance of the potential in the double layer = characteristic Debye length in the corresponding electrolyte solution = κ-1:
\[\frac{1}{\kappa } = \sqrt{\frac{\varepsilon_{\text{r}}\varepsilon_{0}RT}{F^{2}\sum _{i}c_{i}z_{i}^{2} }}\]
(rationalized four-quantity system)
\[\frac{1}{\kappa } = \sqrt{\frac{\varepsilon_{\text{r}}RT}{4\pi F^{2}\sum _{i}c_{i}z_{i}^{2} }}\]
(three-quantity electrostatic system)
where ɛ = static permittivity = ɛr.ɛ0, ɛr = relative static permittivity of solution; ɛ0 = permittivity of vacuum, R = gas constant, T = thermodynamic temperature, F = Faraday constant, ci = concentration of species i, ci = ionic charge on species i.
PAC, 1972, 31, 577. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry' on page 619 (