Interactions between charged surfaces with ionizable sites.

Area of Science:

• Physical Chemistry
• Colloid and Surface Science
• Computational Nanoscience

Background:

• Surface charge density is critical for controlling interactions between surfaces in aqueous solutions.
• Surface charging occurs via titration of surface groups, dependent on dissociation constants and solution pH.

Purpose of the Study:

• To investigate the behavior of surface charge density and inter-surface forces in a system with explicitly described ionizable sites using Monte Carlo simulations.
• To compare simulation results with theoretical predictions for uniformly charged surfaces.

Main Methods:

• Utilized Monte Carlo simulations to model a system of two planar surfaces with ionizable sites in a salt solution.
• Focused on a specific surface density of ionizable sites (4.8 nm⁻²) representative of silica.

Main Results:

• Observed changes in surface charge density as surfaces approached due to interactions between ionizable groups.
• Detected an attractive force between surfaces above a threshold surface charge, consistent with uniform charge models.
• Found significant deviations in force compared to uniform charge models at close contact distances.

Conclusions:

• Explicitly modeled ionizable sites lead to distinct surface charge behaviors and inter-surface forces compared to simplified uniform charge models.
• The study highlights the importance of discrete charge effects in understanding surface interactions, particularly at nanoscale separations.