VOLUMETRIC AND TRANSPORT-PROPERTIES OF WATER AOT N-HEPTANE MICROEMULSIONS

Density, ultrasonic velocity, viscosity, and electrical conductance of water/AOT/n-heptane microemulsions as a function of the volume fraction of the dispersed phase (0 < phi < 70) and of the molar ratio water/AOT = R (0 < R < 40) have been measured at 25-degrees-C. The density and the isentropic compressibility of the micellar phase are derived from the experimental data. The volumetric properties, at high R, exhibit a trend toward an enhanced water-like character of the dispersed phase. At low R there is evidence for a structural change in the hydrogen-bonded network of water filling the droplets. Electrical conductivity data show the existence of a percolation threshold depending on R. Below the percolation threshold, the specific conductance qualitatively and quantitatively agrees with the prediction of the droplet charge fluctuation model. Comparison of the viscosity and the electric conductance behavior with phi indicates that the processes for momentum and charge transfer, even if related to the droplets cluster formation, are different.