Salt and Water Uptake in Nanoconfinement under Applied Electric Field: An Open Ensemble Monte Carlo Study

Abstract

Permeation of electrolytes in nanoporous materials underlies many applications in energy and materials technologies. Wetting of apolar nanopores can be enhanced by electric field, attracting water and ions from unperturbed electrolyte bath. We study absorption of water and NaCl in the pores by Expanded Ensemble Grand Canonical Monte Carlo simulation, which implements particle insertions and deletions through incremental changes in particles’ coupling with the system. We determine the uptake of water and ions in the pores, and concomitant changes in pore thermodynamics, as functions of field strength in the pore and salinity in the external bath. Pressure increase and reduction of wetting free energy, σ, in the pore intensify near-quadratically with the field. Surprisingly, the influence of bulk salinity on σ can change qualitatively with pore width and field strength. Conforming to Gibbs adsorption isotherm, narrow pores with salt molality below that of the bath experience an increase in σ with rising bul...