Flocculation versus coalescence

Flocculation versus Coalescence. The breaking of an emulsion is a two step process requiring the coalescence of the droplets after they are in contact.(17) If the system flocculates but is resistant to coalescence, the system will not phase separate. Over a period... 

They showed that the coalescence rate constant, K, increases while the flocculation rate constant decreases with increased demulsifier concentration. Flocculation is high at low demulsifier concentration. At increased concentration it breaks the interfacial film and promotes coalescence. A plot of initial coalescence rate constant versus dosage indicates that the demulsification of this system was in a flocculation-rate controlling state, within its environment. Aggregation is reversible and the drop identity is not lost. 

Smoluchowski distribution, Eq. (108), for k=. The model of Borwankar et al. (194) employs some assumptions, which make it more applicable to cases in which the flocculation (rather than the coalescence) is slow and is the rate-determining stage. This is illustrated by the curves shown in Fig. 22, which are calculated for the same rate of coalescence, but for two different rates of flocculation. For relatively high rates of flocculation (Fig. 22a) the predictions of the three theories differ, but the model of Borwankar et al. (194) gives values closer to that of the more detailed model by Danov et al. (175). For very low values of the flocculation rate constant, aj for which the coalescence is not the rate-determining stage, all three theoretical models (175, 193, 194) give results for versus time,... 

Macroemulsion stability between aqueous alkaline and acidic oil systems The rates of flocculation and/or coalescence can be inferred from plots of the ratio of the emulsion volume to the total volume, V /V.p, versus time as shown in Figures 11 and 12. 

On storage, several breakdown processes may occur that depend on the particle size distribution and the density difference between droplets and the medium. It is the magnitude of the attractive versus repulsive forces that determines flocculation. The solubility of the disperse droplets and the particle size distribution determines Ostwald ripening. The stability of the liquid film between the droplets determines coalescence phase inversion [1]. The various breakdown processes are illustrated in the figure 6.1. 

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