VISCOSITY OF A NONIONIC MICROEMULSION NEAR EMULSIFICATION FAILURE

The viscosity of a water-rich microemulsion phase composed of C(12)E(5 ), water, and decane has been measured. Attention has been focused on the concentration dependence of the viscosity along the emulsification failure boundary, where the microstructure of the system is that of o il-swollen spherical micelles. At high dilution, the concentration dep endence of the relative viscosity is consistent with the behavior of a suspension of spheres, with an effective micellar size characterized by its hydrodynamic radius. At higher concentrations, where interactio ns are important, a good correlation with colloidal hard-sphere system s is obtained if the apparent micellar size is characterized by the ha rd-sphere radius. With increasing temperature away from the emulsifica tion failure boundary, a significant increase in the viscosity is obse rved. The observed temperature dependence of the viscosity correlates with results obtained previously from H-2 NMR relaxation and self-diff usion experiments and is consistent with a micellar growth with increa sing temperature.