Interaction forces, heteroaggregation, and deposition involving charged colloidal particles.

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Electrochemistry

Background:

• Understanding particle interactions is crucial in colloid science.
• The Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory is a cornerstone for describing interparticle forces.
• Asymmetric charging introduces complexities not fully captured by traditional symmetric models.

Purpose of the Study:

• To theoretically investigate force profiles, aggregation, and deposition rates for asymmetrically charged particles and surfaces in aqueous electrolytes.
• To analyze the influence of varying surface charge asymmetries, from symmetric to fully asymmetric and charged-neutral systems.
• To explore the critical role of charge regulation and boundary conditions in Poisson-Boltzmann modeling.

Main Methods:

• Theoretical calculations based on the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory.
• Electrostatic interactions modeled at the Poisson-Boltzmann (PB) level.
• Examination of different boundary conditions (constant charge vs. constant potential) for solving the PB equation.

Main Results:

• Asymmetric charging leads to distinct force profiles and altered aggregation/deposition rates compared to symmetric systems.
• Charged-neutral systems are particularly sensitive to boundary conditions, yielding either attractive or repulsive forces.
• Charge regulation significantly influences the critical coagulation concentration (CCC), with notable shifts observed in charged-neutral cases.
• In the presence of multivalent ions, systems resemble symmetrically charged ones, but deviations from the Schulze-Hardy limit are observed.

Conclusions:

• The degree of surface charge asymmetry and the applied boundary conditions critically determine particle interactions and stability.
• Charge regulation is a key factor affecting aggregation and deposition kinetics, particularly in charged-neutral colloidal systems.
• Existing theories may require refinement to accurately predict behavior in systems with significant charge asymmetry, especially concerning multivalent ion effects.