An investigation of structure transition in sodium dodecyl trioxyethylene sulfate/n-butanol/n-octane/water system by dielectric relaxation spectroscopy method

The phase diagram of the quaternary system of sodium dodecyl trioxyethylene sulfate (SDES)/n-butanol/n-octane/water was obtained at (30.0 +/- 0.1)degreesC. There exists a clear, isotropic, and low-viscosity L phase, which can be divided into W/O, bi-continuous (B. C.) and O/W microemulsions by conductivity measurement results. Dielectric Relaxation Spectroscopy (DRS) measurements, including permittivity, conductivity, relaxation strength, characteristic relaxation time, dielectric parameters, phase parameters, etc.. were applied to investigating the microstructures of the system mentioned above. For the samples with a fixed SDES/n-butanol mass ratio of 4/6 including 20% (mass fraction) of n-octane. DRS indicated a structure transition from a W/O to an O/W via a B.C. microemulsion with the increase of the water content. For the samples with a fixed (SDES/20%n-octane)/H2O mass ratio of 5/5, DRS presented that there only exists a onefold structure of a W/O microemulsion as the (n-butanol/20%n-octane) content increases. The results obtained from DRS are in good agreement with those from the phase diagram.