Apparent repulsion between equally and oppositely charged spherical polyelectrolytes in symmetrical salt solutions

Area of Science:

• Colloid and interface science
• Biophysical chemistry
• Computational physics

Background:

• Ion-mediated interactions are crucial for colloidal and biomacromolecular systems.
• Understanding these interactions is key to controlling material properties and biological functions.

Purpose of the Study:

• Investigate ion-mediated interactions between spherical polyelectrolytes (SPEs) in divalent electrolytes.
• Explore the influence of charge density, counterion size, and salt concentration on these interactions.

Main Methods:

• Utilized Monte Carlo simulations to model interactions between equally and oppositely charged SPEs.
• Developed and applied a modified Poisson-Boltzmann model to interpret simulation results.

Main Results:

• Observed unexpected apparent repulsion between SPEs at high divalent salt concentrations.
• Found repulsion intensifies with higher SPE charge densities and larger counterions.
• Linked repulsion to counterion over-neutralization and subsequent release upon SPE approach.

Conclusions:

• Ion-mediated interactions, particularly counterion condensation and release, significantly impact SPE behavior.
• The modified Poisson-Boltzmann model successfully reproduces the observed repulsion.
• Findings provide insights into controlling colloidal and biomacromolecular assembly through ionic environments.