2013 Volume 20 Pages 29-39
In the extraction system using Aerosol OT (AOT) in isooctane, the distribution of AOT between the isooctane and aqueous phases depended on the concentration of inorganic electrolytes, salts and/or acids. A colored dye, neutral red, was selected as a probe molecule, which exists in red cationic and yellow nonionic forms in acidic and alkaline regions, respectively. The extraction was investigated in the acidic region in detail. At lower NaCl concentrations, the cationic neutral red existed in the aqueous phase. At higher NaCl concentrations, the cationic neutral red was extracted into the isooctane phase. At intermediate NaCl concentrations, a small amount of third phase appeared in the interfacial region and almost all of the cationic neutral red was extracted into it. Observation by optical microscopy gave geometric information about the third bicontinuous microemulsion phase as well as microemulsions or emulsions formed in the isooctane and aqueous phases.