Flocculation of weakly charged oil-water emulsions

This study concerns dodecane-water emulsions stabilized primarily by the no nionic surfactant decyl-beta-D-glucoside (C(10)beta Glu). The emulsions are stable with respect to coalescence and Ostwald ripening but unstable with respect to flocculation and creaming. Emulsions stabilized by monolayers of pure C(10)beta Glu flocculate and show rapid creaming. A sharp transition from a flocculated state to a nonflocculated state can be induced by the ad dition of small mole fractions of either the anionic sodium octadecylsulfat e or the cationic octadecyltrimethyIammonium bromide surfactants. The nonfl occulated emulsions show slower creaming and the discontinuous change in cr eaming rate can be used to detect the flocculation transition. We have meas ured the concentration of ionic surfactant required to induce the flocculat ion transition as a function of sodium chloride concentration in the contin uous aqueous phase. Using a model in which the colloidal interactions betwe en the deformable emulsion drops are taken to consist of electrostatic repu lsion, van der Waals attraction, and a abort-range repulsion modeled as a " hard wall", we show how the flocculation transition can be quantitatively p redicted using no adjustable parameters.