Aggregation of polystyrene latexes stabilized with conventional, reactive, and polymeric surfactants

The aggregation process of the model latex systems, synthesized with conventional (Aerosol MA-80), reactive (TREM LF-40), and polymeric (poly(TREM)) surfactants was studied using viscosity measurement combined with light scattering and optical microscopy to determine rheological properties of the aggregates, correlated with aggregates sizes, and aggregate morphology. Calcium chloride (CaCl2) was used as the electrolyte to aggregate the latexes. The study mainly focused on the effect of particle concentration at the moderate solids content (15, 20, and 25%) on the aggregation.; In the electrostatic stabilized system (Aerosol MA-80), the aggregation was initiated at around 9 mM CaCl₂, and continued to grow as a function of electrolyte. At low electrolyte concentration, particles mostly formed a tight structure, indicating that the aggregation occurred in the primary minimum. At higher electrolyte concentration, shear-thinning behavior was observed, reflecting the breaking down of the loose aggregates formed in the secondary minimum. The onset of aggregation was found to decrease as the particle concentration increased, indicating the influence of interparticle distance. In case of the latex stabilized with reactive surfactant (TREM LF-40) where surfactant bound to the particle surface, and polymeric surfactant (poly(TREM)), a higher amount of electrolyte was required to initiate the aggregation, indicating a better stability achieved from electrosteric stabilization in these systems. Unlike the conventional system, the aggregates did not grow strongly as the electrolyte concentration increased. Only small aggregates, such as doublets or triplets were formed. The particle concentration showed some degree of influence on the onset of aggregation in the TREM system toward high % solids (25%), whereas no effect of particle concentration was found in the poly(TREM) system.; The DLVO theory has been used to explain the stability of the three model latexes at both intermediate and dilute particle concentration study. The calculated total energy of interaction between the particles revealed that the particles stabilized with TREM LF-40 and poly(TREM) have a higher energy barrier compared to the particles stabilized with Aerosol MA-80, arising from a higher in surface potential (dilute study), and the steric energy of the polymeric layer on the particle surface (intermediate study). This resulted in the need for a higher concentration of electrolyte to induce the aggregation. Overall, the theoretical calculation correlated well with the experimental results.