Electrolyte pore/solution partitioning by expanded grand canonical ensemble Monte Carlo simulation.

Area of Science:

• Physical Chemistry
• Computational Nanoscience
• Solution Chemistry

Background:

• Understanding ion and water behavior in confined environments is crucial for fields like geochemistry and materials science.
• Previous models often struggle with accurate calculations of anisotropic pressures and electrostatic cut-off effects in nanopores.

Purpose of the Study:

• To investigate the equilibrium partitioning of ions and water between apolar confinements and electrolyte solutions.
• To develop and apply a novel Monte Carlo approach for accurate simulations under anisotropic conditions.
• To analyze the impact of salt concentration on confinement properties, including layering, pressure, and wetting.

Main Methods:

• Developed a grand canonical Monte Carlo (GCMC) approach with fractional ion/water exchanges.
• Implemented a novel algorithm for self-consistent correction of non-electrostatic cut-off effects.
• Simulated partitioning in apolar confinements with varying pore widths and surrounding electrolyte concentrations.

Main Results:

• Salt molality inside confinements correlates with bulk phase but shows non-uniform width-dependence.
• Salt presence enhances layered structures and inter-wall pressure, while increasing solvation pressure repulsion.
• Wetting free energy of pore walls is modulated by salt concentration, depending on excess molality within the pore.

Conclusions:

• The study provides insights into salt-induced alterations of fluid behavior within nanopores.
• The developed GCMC method accurately captures complex interactions, including anisotropic pressures.
• While salt influences apparent hydrophobicity, it does not necessarily enhance the volatility of metastable liquids in pores.