Rheological Behavior of Highly Concentrated Oil-in-Water (o/w) Emulsions

Abstract

Oil-in-water (o/w) highly-concentrated emulsions have been studied in ternary water/polyethylene oxide -polypropylene oxide-polyethylene oxide (ABA block copolymer)/hydrocarbon systems in order to compare their rheological behavior with that of water-in-oil (w/o) highly concentrated emulsions. Viscoelastic measurements have been performed as a function of dispersed phase volume fraction and temperature. The structural parameters of the system, droplet size, interfacial tension and continuous phase viscosity have been determined in order to correlate these parameters with the rheological behavior. The shear modulus has been shown to depend on the volume fraction according to Princen's equation. The relaxation times were described using a Maxwell liquid model in which the viscosity is related to a reduced continuous phase viscosity. The effect of temperature on the shear modulus and relaxation time is significantly different from that observed for w/o highly concentrated emulsions. These differences in the rheological behavior of the emulsions weee discussed in terms of the chemical structure of the surfactants.