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 p olymers is a key process in colloid science, as well as in the chemica l and biological regulation of aquatic systems. Polymers can influence important physical properties of colloidal aggregates such as their d ensities and settling velocities, as well as their chemical properties , affecting the probability that two colloidal particles will stick to gether when they collide. The presence of polymers usually makes more difficult the application of a coagulation theory to colloidal suspens ions and the interpretation of experimental observations. Knowledge of flee structures is a key factor in the understanding of flocculation processes, and simulation may provide useful insights required to inte rpret the results of experimental studies and elaborate new theoretica l models. Although modeling leaves much room for more progress, resear chers now find it indispensible from a fundamental point of view and f or environmental applications. In this paper, we report a computer sim ulation study of a two- and three- dimensional model for bridging floc culation between large linear polymer chains and comparatively small c olloidal particles. The hoc structures are investigated as a function of chain/particle concentration ratio, chain conformation, and space d imension. The values of the sticking probabilities are chosen to empha size colloid-chain interactions compared to colloid-colloid or chain-c hain interactions. The results suggest that the flee morphology is str ongly dependent on the chain conformation and to a slight extent on th e chain/particle concentration ratio. In particular, colloid interacti ons with linear rods result in a network characterized by fractal dime nsions significantly higher than those obtained on the basis of the Cl uster-Cluster Aggregation models of colloids only, or by flocculation of colloids with coiled chains. (C) 1998 Academic Press.