We analyze the effect of asymmetric finite ion size in nanoconfinement in the view of osmotic pressure and electrocapillarity. When the confinement width becomes comparable with the Debye length, the overlapped electric double layer is significantly deformed by the steric effects. We derive the osmotic pressure from the modified Poisson-Boltzmann equation in a nanoslit to examine the deviation from the ideal osmotic pressure and the repulsive force on the wall considering the asymmetry of ion sizes. Then the electrocapillarity due to the steric effect is investigated under constant potential condition with the flat interface assumption. Later, the deformation by the electrocapillarity is also considered in the first order approximation.

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 (Pnn) 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 (γ) and asymmetry of ions (ξ). The results show that the averaged normal stress on the walls (Pnn) and the averaged charge density in the channels (ρ) 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 (En) and average electrical stress (E 2 n ) on the channel wall, both of which are independent of the channel shape if the hydraulic radius is the same.