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

Abstract

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 noninteracting spheres ð5:49 3 10 218 m 3 =sÞ: Similar calculations at a volume fraction f 5 0:001 using 64 particles only, already show a k f 5 5:83 3 10 218 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 f 5 0:15: As expected, there is a strong dependence of k f on f. Faster and slower aggregation rates are observed depending on the characteristics of the DSD.

Role of the Secondary Minimum on the Flocculation Rate of Nondeformable Droplets

“…During the past decade, there has been significant progress in the solution of some of the problems outlined above. − Of all remaining limitations, the consideration of the coalescence mechanism in the case of deformable droplets is by far the most serious difficulty. The thinning of the film between large drops ( R i > 5 μm, where R i is the radius of the drop) involves at least six different steps. − These include the formation of a dimple, the generation of a plane-parallel film, the appearance and enhancement of surface oscillations, and either the final coalescence of the drops or the formation of long lasting films.…”

“…In previous papers, we used spherical nondeformable droplets in order to simulate the behavior of bitumen/water emulsions. − Unlike solid particles, these drops coalesce as soon as their interfaces touch. Because drops are not deformable, there is no transition between primary minimum flocculation and coalescence.…”

An Algorithm for Emulsion Stability Simulations: Account of Flocculation, Coalescence, Surfactant Adsorption and the Process of Ostwald Ripening

“…The data of Figure 3 corresponds to system #12 in Refs. [ 19 , 73 ]. The surfactant concentration in the system ( C s = 10 −5 M) is not enough to prevent the coalescence of drops during the course of the simulation.…”

“…It was observed that fluctuations as high as 10,000 k B T must be allowed in order to reproduce a mean square displacement equal to: 〈 r 2 〉 = 6D Δ t. Cut off thresholds in the value of the deviates corresponding to kinetic energies of 1000 k B T and 100 k B T fail to reproduce the correct value of 〈 r 2 〉. It was evident that values of the displacement corresponding to the outskirts of the Gaussian distribution are necessary in order to simulate the Brownian movement of the particles correctly [ 19 ].…”

Liquid–liquid microflows in micro-sieve dispersion devices with dual pore size

“…Emulsion droplet size and distribution significantly influence its properties (Ambrosone et al 2004;Klink et al 2011;Whitby et al 2007;Urbina-Villalba et al 2003). It is well known that microfluidic devices are effective platforms for producing monodispersed microdroplets or microbubbles (Marmottant and Raven 2009;Choi et al 2010).…”