Perturbation analysis for the effects of ion correlations on the surface force and the specific capacitance in a nanochannel

Abstract

The room-temperature ionic liquids have unique chemical, electrochemical, and physical properties and they have wide range of applications. One of unique features of ionic liquids is the ion-ion correlation effect. In the present work, ion-ion correlation effects in the nanoslits or nanopores are investigated by both numerical and perturbation analyses. Especially, we pay attention to the effects on the disjoining pressure (surface force exerted on the unit area of the slit or pore surface) and the specific capacitance. The correlation effect is represented in terms the dimensionless correlation length δc=lc/κ−1, and a small parameter α≡1/δc is adopted for the cases of large correlation effects.The two kinds of boundary condition for the Bazant-Storey-Kornyshev model, the zero correlation boundary condition and the continuous electrical stress boundary condition are used and the results are compared. In both cases of boundary conditions, the negative disjoining pressure is observed and the specific capacitance shows maximum behavior in terms of the gap size or the pore diameter but they have different behaviors. Using perturbation analysis, the different behaviors of osmotic pressure and the specific capacitance of two boundary conditions are predicted analytically.