Ionic asymmetry and solvent excluded volume effects on spherical electric double layers: a density functional...

Area of Science:

• Physical Chemistry
• Colloid Science
• Computational Physics

Background:

• Conventional theories for electrical double layers often neglect crucial factors like ion correlations and size asymmetry.
• Understanding ion distribution around macroions is vital for various applications, from biological systems to materials science.

Purpose of the Study:

• To develop and validate a classical density functional theory for electrical double layers of spherical macroions.
• To incorporate electrostatic ion correlations, size asymmetry, and excluded volume effects into the theoretical framework.
• To accurately predict ion density profiles and related properties around macroions.

Main Methods:

• Utilized a Hansen-Goos and Roth approximation for hard sphere excess free energy.
• Employed a functional Taylor expansion for ion density profiles.
• Applied the mean spherical approximation for multi-component charged hard sphere fluids to model electrostatic correlations.
• Validated the theoretical approach using Monte Carlo simulations.

Main Results:

• The developed theory effectively accounts for ion size asymmetry and solvent excluded volume effects, particularly at high ion concentrations.
• Monte Carlo simulations confirmed a good balance between accuracy and computational efficiency.
• Demonstrated the significant influence of solvent hard sphere diameter and density on ion distribution around macroions.

Conclusions:

• The new density functional theory provides a more accurate description of electrical double layers around spherical macroions.
• Results highlight the dominant role of solvent properties and ion size in counterion distribution, showing tight binding similar to the Stern model.
• The approach offers a valuable tool for studying complex electrolyte mixtures and macroion interactions.