COMPUTER-SIMULATION OF BRIDGING FLOCCULATION

A three-dimensional Monte Carlo model of a system of particles and polymer chains is used to simulate bridging flocculation of colloidal particles by adsorbing polymer molecules. Polymer chains are modelled as freely jointed off-lattice excluded-volume random chains of 50 segments. The polymer-particle interaction is described in terms of a single well-depth parameter expressing the strength of the segment-particle attraction in terms of a square-well pair potential. Numerical data are presented for the effect of the well depth on the configurations of the polymer chains and the structure of the resulting flocs. We observe that the simulated aggregates have a fractal-type structure with little short-range liquid-like order. There is a trend towards more compact flocs with closer particle-particle separations on increasing the adsorption strength. The large flocs rarely contain particles bridged by long dangling chains. The bridges mainly resemble a sort of polymeric 'glue' between particle surfaces separated by no more than a few segment diameters.