Volumetric and transport properties of water/AOT/n-heptane microemulsions

Abstract

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 < Q < 70) and of the molar ratio water/AOT = R (0 < R < 40) have been measured at 25 O 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 4 indicates that the processes for momentum and charge transfer, even if related to the droplets cluster formation, are different.

Electrical Conductivity of Water/Sodium Bis(2-ethylhexyl) Sulfosuccinate/n-Heptane and Water/Sodium Bis(2-ethylhexyl) Phosphate/n-Heptane Systems: The Influences of Water Content, Bis(2-ethylhexyl) Phosphoric Acid, and Temperature

“…For the system with the water content in the range of 0 to 60, the AOT + HDEHP reverse micelles distinguish themselves with their very low conductivity. The κ-W 0 curves of H 2 O/(AOT, HDEHP)/n-heptane systems appear bell-shaped with a maximum conductivity in each plot, similar to that of AOT reverse micelles (17)(18)(19)(20)(21). What differentiates the AOT + HDEHP system from the AOT system is that, at room temperature, no percolation phenomena can be observed in the AOT + HDEHP system within the range of water solubilization capacity, whereas percolation conductance occurs in AOT reverse micelles/microemulsions (17).…”

Physicochemical Properties of Copper(II) Bis(2-ethylhexyl) Sulfosuccinate Reversed Micelles

“…2 the plot of D for the water/Cu(DEHSS) 2 / greater coefficient for f V ), (ii) solvation of the micelles CCl 4 system as a function of R is shown. For comparison (involving an effective volume fraction greater than the stoithe trend observed for the water/NaDEHSS/n-heptane syschiometric one), and (iii) formation of transient clusters of tem is also shown (21). As can be clearly seen, both trends micelles held together by short-range intermicellar interacshow a bell shape and maxima are seen at two different R tions resulting from the DEHSS -anion exchange process values.…”

“…2 simply indicates that more water is needed to achieve the complete hydration of the ionic head of Cu(DEHSS) 2 . n-heptane systems as a function of R are shown (21 can be seen, both trends show an initial rapid increase with involved in the formation of the hexahydrate complex but R followed by a broad maximum. Taking into account that also by the chemical species lying in the second solvation the initial water addition involves hydration of the surfactant shell.…”

Structure and phase behaviour of the ternary system water, n -heptane and the nonionic surfactant Igepal ® CA520

“…7 and 8) indicate that there is a structural transition at a water content of about 2 wt%. Several studies of the aggregate structure in reversed micellar solutions by dynamic light scattering have been published recently [17][18][19][20][21][22]. The results of dynamic light scattering measurements in fairly dilute systems indicate clearly the formation of very small, spherical aggregates.…”