Factors affecting emulsion stability, and the HLB concept

Abstract Tbe optimum stability of O/W emulsions stabilized by 1:1 molar ratios of Spans and Tweens is due to association between the emulsifier molecules adsorbed at the oil—water interface. Emulsion stability is related to both surface elasticity and surface viscosity, as derived from interfacial rheological measurements, with a greater dependence on the first named parameter. Discrepancies between activation energies calculated from the temperature dependence of emulsion stability and of surface elasticity suggest that some additional factor is also involved in globule coalescence, e.g., dehydration of the Tween polyoxyethylene chains. Coalescence may be due to the force pressing adjacent globules together giving rise to a compressive stress which increases with time. When it exceeds a critical value, which will be related to the maximum deformation which the globules can withstand, the interfacial film around the globules begins to break down and coalescence begins.' The various analytical procedures for determining HLB values of emulsifiers do not account for interaction between the emulsifiers and the aqueous and oil phases. It may be possible to derive more meaningful values from phase inversion temperature determinations on the emulsions.