Electric percolation of water-in-oil microemulsions: The application of effective medium theory to system sodium dodecyl benzenesulfonate (DDBS)/n-pentanol/n-heptane/water

The electric conductive behavior of the system water/sodium dodecylbenzenesulfonate (DDBS)/n-pentanol/n-heptane has been studied. The results showed that the system has an intrinsic electric percolation phenomenon. The water induced percolation threshold, phi(d)(p), varies over a wide range and is higher than the theoretically predicted value of below 1/3. To use the changed form of the effective medium theory, a second-order polynomial relationship between sigma phi(d) and the conductivity sigma of system, is much better than to use the plot of sigma versus phi(d) in fitting the conductivity data of W/O microemulsion, where phi(d) is the volume fraction of the disperse phase. A linear equation exists when the volume fraction phi d of the disperse phase does not exceed percolation threshold phi(d)(p) much more. The content P of n-pentanol and DDBS affects the properties of the system significantly, but the influences on the limit conductivity of the disperse phase and that of the continuous phase are in the same tendency; also the distribution of alcohol among inner water core, surfactant shell, and continuous phase are changed. (C) 1996 Academic Press, Inc.