## thickness of electrical double layer

https://doi.org/10.1351/goldbook.T06343
The length characterizing the decrease with distance of the potential in the double layer = characteristic @[email protected] length in the corresponding electrolyte solution = $$\kappa^{-1}$$:
 $\frac{1}{\kappa } = \sqrt{\frac{\varepsilon_{\text{r}}\varepsilon_{0}RT}{F^{2}\sum _{i}c_{i}z_{i}^{2} }}$ (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 $$\varepsilon$$ = static @[email protected] = $$\varepsilon_{\text{r}}\varepsilon_{0}$$, $$\varepsilon_{\text{r}}$$ = relative static @[email protected] of solution; $$\varepsilon_{0}$$ = @[email protected], $$R$$ = @[email protected], $$T$$ = @[email protected], $$F$$ = @[email protected], $$z_{\text{i}}$$ = concentration of species $$i$$, $$z_{\text{i}}$$ = ionic charge on species $$i$$.
Source:
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 [Terms] [Paper]