Universality of steric effects of electrolytes in nanoconfinements

Abstract

We analyze the steric effect of electrolyte on the normal stress exerted on a wall and the free charge density in a nanoconfinement using the modified Poisson-Boltzmann (mPB) equation. The outward normal stress exerted on the channel wall (P-nn) is calculated by solving the mPB numerically with a constant surface potential for various equilateral polygonal channels and compared with one-dimensional and circular channels by varying the steric factor (gamma) and asymmetry of ions (xi). The results show that the averaged normal stress on the walls ((P-nn) over bar) and the averaged charge density in the channels ((p) over bar) are almost independent of the channel shape, and are the same with those of the circular channel. From the numerical observation, we infer the universality of average electric field ((E-n) over bar) and average electrical stress (<(E-n(2))over bar>) on the channel wall, both of which are independent of the channel shape if the hydraulic radius is the same. Copyright (C) EPLA, 2018