Collision efficiency factor in Brownian coagulation (αBr): calculation and experimental verification

The collision efficiency factor in Brownian motion (αBr) has been calculated by Han et al. (J. Water Sci. Technol. 36 (1997) 69) including both hydrodynamic and interparticle forces. The sensitivity to each contributing parameter was investigated and a coagulation zone diagram in a graphical plane of surface potential and ionic strength was developed for a particle diameter of 2 μm. The current paper describes a set of experiments performed in a well-controlled laboratory to compare experimental and predicted regions in the Brownian coagulation zone diagram. A polystyrene Latex suspension (nominal diameter 3.12 μm) was used and the change of particle size distribution was measured over a wide range of surface potential (pH) and ionic strength. The total number of particles and the shift of the centroids of the particle size distribution curves were compared to quantify the degree of coagulation with time. An abrupt change of coagulation status was observed at a critical ionic strength. The critical ionic strength increased as the surface potential increased. The experimental results compared well with the theory.