Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2022 / Paper 2 / Section B / 23 / iv

For an ideal electrolyte with species number densities $n_i$, valences $z_i$, solvent permittivity $ϵ$ and common temperature,Increasing salt concentration supplies more mobile charge to screen a surface perturbation, so a shorter distance is needed for the potential to decay. At fixed ion composition, permittivity and temperature, ${\lambda }_D\propto c^{-1/2}$.

A fivefold concentration increase therefore givesEquivalently, the inverse screening length grows by $\sqrt{5}$. Changing ion valence changes the ionic-strength weighting as well, and highly concentrated electrolytes can depart from this dilute-solution screening model.