Study of the electrical conductivity of four-component critical microemulsions

Abstract

Experimental data for the electric conductivity are reported for two microemulsions of n-dodecane, water, n-pentanol, and sodium dodecylsulfate with lower critical solution points along a critical line ending at a critical end point (CEP). One microemulsion (C) had a lower critical solution point (LCSP) close to the CEP. For the other microemulsion (A), the LCSP was away from the CEP. For a third microemulsion (D′) with a composition close to that of C, measurements were carried out near an upper critical solution point (UCSP) about 6 °C below the LCSP of sample C. For all three cases, an anomalous behavior was observed near the critical point. The anomaly for sample A can be well described in terms of a power law with Ising exponent values. This is not possible for sample C (near the CEP), where the anomalous behavior of σ can be better described with an expression recently proposed by Rebbouh and Lalanne [J. Chem. Phys. 90, 1175 (1989)] on the basis of a microscopic model for the merging of dynamic clusters near the CEP. On the basis of our additional results for the microemulsion D′, we can find no evidence for the influence of critical fluctuations near the UCSP on the anomaly in σ at the LCSP of sample C.