The role of the cationic surfactants in concentrated emulsions stabilized with globular protein

The rheology of highly concentrated emulsions stabilized with bovine serum albumin and the same protein with the addition of two different cationic surfactants was studied. These materials demonstrate non-Newtonian behavior with zero-shear-rate Newtonian viscosity and rather abrupt decrease of viscosity in a narrow shear stress range. Emulsions also possess elastic properties and storage modulus does not depend on frequency. The addition of low-molecular-mass surfactant leads to the modification of all theological properties: the viscosity, storage modulus, and yield stress decrease. Variation of the added surfactant in a very wide range shows that there is its threshold concentration, at which a surfactant substitutes protein in the interfacial layers. It was supposed that some peculiarities of emulsions under study are explained by their wide size distribution. As a result, these emulsions are possibly not compressed and their elasticity is mainly due to interlayer interactions rather than interfacial tension. (C) 2011 Elsevier B.V. All rights reserved.