Surfactant solution flow behavior is of great importance to both the chemical and consumer product industries. Most studies on the flow behavior of surfactant solutions, however, have focused on the dilute regime. Seldom reported is rheology in the highly concentrated regime where typically these surfactants are processed and delivered. First, we present here the phase diagram for the ternary system: water and two anionic surfactants (sodium salt of lauric and oleic acid) at different temperatures. Then, we present both linear viscoelastic and steady shear flow results in the high (70 to 90%) surfactant regime. We find that high values of the shear modulus are directly dependent on the quantity of surfactant crystals and that the formation of a lamellar liquid crystal phase at 45°C affects both modulus and flow of the system. Lamellar crystals create a stiff network resulting in wall slip at large shear strain. Using serrated plates removes slip at the wall and we find a shear rate where microfractures localize in a preferential plane and the material flows. This behavior is reversible.
Bibliographical noteFunding Information:
This project was partially supported by a Tri-Council grant to J.P. Smol, as well as a research
grant from the Natural Sciences and Engineering Research Council of Canada. We thank Brian F. Cumming for critical reviews of earlier drafts of this manuscript, as well as M. Sullivan and two anonymous reviewers. Chantal Vis at the University of Montreal and the Government of Quebec Ministry of Environment provided some of the environmental data. John R. Clew provided the map of sample locations.
- Highly concentrated anionic surfactants
- Lamellar phase
- Liquid crystals