Influence of droplet deformability on the coalescence rate of emulsions

In this article the influence of deformation on the coalescence rates of oil-in-water (O/W) emulsions is analyzed. Calculations for doublets and many-particles systems were performed based on a Brownian dynamics algorithm. Extensional and bending energies were included in order to quantify the effect of the changes in the surface geometry on the coalescence rates. Also, the hydrodynamic resistance due to the flat film was included through a correction to the diffusion coefficient in the lubrication limit. Results of two particles calculations were compared with previous analytical evaluations of the coalescence time in absence of highly repulsive barriers [Danov, Langmuir 9, 1731 (1993)]. Lifetime of doublets was calculated as a function of the particle radius from 100 nm to 100 microm. It was found that the doublets lifetime strongly depends on the interplay between the potential of interaction between the droplets and the hydrodynamic resistance. Depending on the repulsive barrier either a monotonous increase of the lifetime with the droplet size or a maximum value is observed. Finally, the evolution of O/W emulsions with a volume fraction of phi=0.10 was studied. For these many-particle systems, the results show a sensitive dependence of the aggregation behavior on the interfacial tension. The procedure reported here allows us to include Derjaguin-Landau-Verwey-Overbeek (DLVO) and non-DLVO forces and the film drainage velocity of many different systems.