COMPUTER-SIMULATION OF BRIDGING FLOCCULATION PROCESSES - THE ROLE OF COLLOID TO POLYMER CONCENTRATION RATIO ON AGGREGATION KINETICS

The flocculation of colloidal particles by adsorbing polymers is one o f the central issues of colloid science and a very important topic in many industrial, biological, and environmental processes, We report a computer simulation study of a 2- and 3-dimensional model for bridging flocculation between large linear polymer chains and comparatively sm all colloidal particles, where the structure and growth kinetics of cl uster formation are investigated, This model was developed within the framework of the cluster-cluster aggregation model using mass and frac tal dimension dependent diffusion constants, where bridging flocculati on is seen as a case of heterocoagulation in which, in addition, macro molecule configurations and lengths play an important role. The simula tion of aggregate structure and formation kinetics obtained at differe nt (i) relative particle concentrations, (ii) polymer chain conformati ons, and (iii) sticking probabilities are described from a qualitative ly and quantitative point of view, The results suggest that the format ion of large aggregates is a slow process, controlled by the reactivit y of the clusters, even when the reaction between microcolloids and ma crochains is very fast, Aggregation kinetics are strongly dependent on the particle/chain concentration ratio and on the configurational pro perties of the chains, It is shown that the scaling laws which are val id for homocoagulation processes are also applicable to the kinetics o f bridging flocculation, The corresponding scaling exponents have been calculated. (C) 1996 academic Press, Inc.