Sodium dodecylsulfate/butanol-isopropanol/heptane/brine can form middle phase microemulsion. The effects of salinity and temperature on phase state of the microemulsion have been investigated. Microstructure of the microemulsion was determined by small angle X- diffraction, ESR and NMR. The difference of microstructure between the two surfactant-rich phases in four-phase microemulsion is compared. It can be concluded that three-phase and four-phase microemulsion can be formed under suitable conditions. Lamella liquid crystal appeared in both three-phase and four-phase microemulsion. The constituents and structure of two surfactant-rich phases in four-phase microemulsion are different. It is shown that microenvironment in the two surfactant-rich phases is different as detected by ESR, the constituents and average molecular ordering of water are also different as measured by ^2H NMR.

Key words: LAURYL SODIUM SULFATE, MICROEMUSION, PARAMAGNETIC RESONANCE, LIQUID CRYSTAL, N-BUTANOL, ISOPROPANOL