Colloid polymer interactions and aggregation in aqueous mixtures of polystyrene latex, sodium dodecyl sulfate, and a hydrophobically modified polymer:: A dynamic light scattering study

The kinetics of clusters formed in the flocculation process of polystyrene latex particles (PSL) in the presence of hydrophobically modified ethyl(hydroxyethyl)cellulose (HM-EHEC) and sodium dodecyl sulfate (SDS) in the concentration interval of 2-4 mmolal have been investigated with the aid of dynamic light scattering measurements at different temperatures. For this system (HM-EHEC/SDS/PSL) we observe an intriguing time-dependent cluster growth over a restricted (2-4 mmolal) surfactant concentration range. The rate of flocculation and the aggregation mechanism are affected by both the level of surfactant addition and temperature. The value of the homogeneity exponent lambda, used to characterize the aggregation mechanism, depends on temperature and concentration of surfactant. Flocculation behaviors between the reaction-limited and diffusion-limited regimes are observed. The picture that emerges is that polymer-surfactant complexes are adsorbed onto the PSL particles in form of fuzzy layers with hydrophobic stickers. The sticking probability seems to be influenced by temperature and the level of surfactant addition. Upon collision, these particles form aggregates through hydrophobic interactions, and macroscopic flocs are evolved at long times. When the sample is exposed to ultrasonic perturbation, the flocs break up, but a rapid reformation of flocs is found upon removal of the ultrasonic perturbation.