Influence of Polydispersity and Thermal Exchange on the Flocculation Rate of O/W Emulsions

According to recent simulations [ Langmuir 16 , 7975 (2000)], the flocculation rate ( k f ) of concentrated oil in water (O/W) emulsions interacting through van der Waals forces, can reach values considerably higher than the one expected for a very dilute system of non-interacting spheres (5.49 2 10 -18 m 3 /s). Similar calculations at a volume fraction J =0.001 using 64 particles only, already show a k f =5.83 2 10 -18 m 3 /s, reasonably close to the theoretical prediction. In this report Brownian Dynamics (BD) simulations are used to study the effect of the volume fraction and the drop size distribution (DSD) on the flocculation rate. First, the dependence of k f with the maximum value of the thermal interaction between the particles and the solvent is studied. Following, the variation of the flocculation rate is studied as a function of polydispersity for J =0.15. As expected, there is a strong dependence of k f on J . Faster and slower aggregation rates are observed depending on the characteristics of the DSD.