Vesicles as rheology modifier

Fernandez P, Willenbacher N, Frechen T, Kühnle A. Vesicles as rheology modifier. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2005;262(1-3):204-210.Vesicles are self-assembled spherical aggregates of amphiphilic molecules with rich structural variety. They have attracted increasing attention due to their possible applications in pharmaceutics and cosmetic fields, but also from a more fundamental point of view. In this work, we present vesicle formation from mixtures of commercial surfactants. We show how mixing of two non-ionic surfactants can lead to vesicle formation by adjusting the packing parameter of the mixture. High-frequency viscosity data can be described in terms of an effective hard sphere system applying the Lionberger-Russel model. Thus, we were able to estimate the hydrodynamic volume of the vesicles and hence their average size, which agrees well with the structures observed by transmission electron microscopy. Finally, we show that oil-in-water emulsions prepared with the adjusted surfactant mixture have two orders of magnitude higher viscosities compared to similar emulsions stabilised with an anionic surfactant, demonstrating the significant impact of the vesicles on the rheological and hence creaming behaviour of emulsions. (c) 2005 Elsevier B.V. All rights reserved