Computer Simulation of Flocculation Processes: The Roles of Chain Conformation and Chain/Colloid Concentration Ratio in the Aggregate Structures.

The flocculation of colloidal particles in the presence of adsorbing polymers is a key process in colloid science, as well as in the chemical and biological regulation of aquatic systems. Polymers can influence important physical properties of colloidal aggregates such as their densities and settling velocities, as well as their chemical properties, affecting the probability that two colloidal particles will stick together when they collide. The presence of polymers usually makes more difficult the application of a coagulation theory to colloidal suspensions and the interpretation of experimental observations. Knowledge of floc structures is a key factor in the understanding of flocculation processes, and simulation may provide useful insights required to interpret the results of experimental studies and elaborate new theoretical models. Although modeling leaves much room for more progress, researchers now find it indispensible from a fundamental point of view and for environmental applications. In this paper, we report a computer simulation study of a two- and three- dimensional model for bridging flocculation between large linear polymer chains and comparatively small colloidal particles. The floc structures are investigated as a function of chain/particle concentration ratio, chain conformation, and space dimension. The values of the sticking probabilities are chosen to emphasize colloid-chain interactions compared to colloid-colloid or chain-chain interactions. The results suggest that the floc morphology is strongly dependent on the chain conformation and to a slight extent on the chain/particle concentration ratio. In particular, colloid interactions with linear rods result in a network characterized by fractal dimensions significantly higher than those obtained on the basis of the Cluster-Cluster Aggregation models of colloids only, or by flocculation of colloids with coiled chains. Copyright 1998 Academic Press.