A creaming study of weakly flocculated and depletion flocculated oil-in-water emulsions

The creaming of weakly flocculated and depletion flocculated oil-in-water emulsions was investigated and the data compared with theory. The Stokes equation was applicable provided the average droplet diameter was less than 13 μm. The creaming data for emulsions containing excess added ionic surfactant (i.e. depletion flocculation) exhibited a minimum with respect to added ionic surfactant concentration which may be ascribed to formation of an emulsion gel phase. The oil phase employed in this work was kerosene. The emulsion preparation conditions simulated those used industrially for ‘Quick-break’ emulsions. Non-ionic surfactants of the type CxEy, (C and E represent alkyl and alcohol–ethoxylate moieties, respectively) and ionic surfactants (e.g. sodium dodecylsulfate (SDS) and cetyltrimethylammonium chloride (CTAC)) were employed. An extension of the Stokes equation was used to estimate the droplet diameter from the creaming rate data for the emulsions. The analysis suggested that the as-made emulsions were weakly flocculated. Theoretical analysis of depletion flocculation showed that the electrostatic exclusion region between micelles and droplets greatly increases the attractive interaction.