Viscosity measurements in dense microemulsions

We report the results of a measurement of the shear viscosity as a function of the temperature and of the water volume fraction in a three-component sodium di(2-ethylhexyl)sulfosuccinate-decane-water microemulsion. The explored concentration range is 0{≤}{φ}{≤}0.73 and the packing fraction of the water-in-oil spherical droplets has been changed in order to obtain a very dense glass-forming liquid. Well-defined maxima in the relative viscosity have been observed at different concentrations and the corresponding temperature values decrease with increasing {φ}. The data are discussed considering the system as a colloidal one in which aggregation phenomena are present. In such a way, on the basis of a two-fluid model, we can consider two different contributions to the viscosity. One is directly connected to the repulsive interaction potential, while the second one is directly connected to the attractive interaction that contributes indirectly, through the formation of aggregates. The results are compatible with those previously obtained by light-scattering measurements that gives clear evidence of the presence of a large structural order at the glass transition.