Stability of emulsions of water in oil III. Flocculation and redispersion of water droplets covered by amphipolar monolayers

Abstract

Theoretical calculations demonstrate that emulsions of water in oil cannot be sufficiently protected against flocculation by an adsorbed layer of amphipolar molecules with an oleophilic chain of about 20 A. It is, however, expected that such flocculated emulsions can be redispersed by moderate rates of shear. This is confirmed by viscosity measurements. Non-Newtonian behavior found at low rates of shear is a consequence of flocculation. From the minimum rate of shear to reach the Newtonian region, i.e., to cause complete redispersion, the effective van der Waals' constant between the water droplets can be estimated. The rather low value of A = 0.4 × 10−14 erg is found.