Predicting aggregation rates of colloidal particles from direct force measurements

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Materials Science

Background:

• Colloidal suspensions are ubiquitous in nature and industry.
• Understanding interparticle forces is crucial for controlling suspension behavior, such as aggregation.
• The Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory is a cornerstone for describing colloidal interactions.

Purpose of the Study:

• To directly measure forces between charged colloidal latex particles.
• To investigate the influence of cation valency on interparticle forces.
• To assess the predictive power of force measurements for colloidal aggregation rates.

Main Methods:

• Utilized the multiparticle colloidal probe technique with atomic force microscopy (AFM).
• Performed direct force measurements in aqueous solutions with varying inorganic monovalent and multivalent cations.
• Measured aggregation rates independently using light scattering.

Main Results:

• DLVO theory accurately described force profiles down to a few nanometers for monovalent and divalent cations.
• A significant non-DLVO attraction was observed at shorter distances.
• Highly charged cations induced a longer-ranged non-DLVO attraction, attributed to surface charge heterogeneities.
• Force measurements successfully predicted observed aggregation rates.

Conclusions:

• Direct force measurements effectively capture the primary interactions governing aggregation in colloidal suspensions.
• Non-DLVO forces play a critical role in colloidal interactions, especially at short distances and with multivalent cations.
• Surface charge heterogeneities can significantly influence interparticle forces and aggregation behavior.