Properties of sodium dodecyl sulfate/ n-butanol/ n-heptane/water microemulsion system

Phase diagrams of sodium dodecyl sulfate(SDS)/n-butanol/n-heptane/water microemulsion system with different R(ratio of water to SDS)at 25 ℃ were established.The appropriate mass fraction for the formation of microemulsion are n-butanol 25%～60% and n-heptane 0～80%.The system can form W/O mono-phase microemulsion region of rather wide range at room temperature.The impact of R on the area and position of microemulsion region is not significant.Based on the measurement of the electrical conductance of the system,it was observed that during the dilution of the system with water,the micro-structure of the system transforms from W/O to bicontinuous phase,virgulate liquid crystal,lamellar liquid crystal,bicontinuous phase and O/W subsequently.The structure parameters of the microemulsion were calculated and the results showed that,within a certain range,the water nucleus radius R_w increases with the increase of R and the volume of the water.As the water content increases,the free energy-ΔG~0_(c→i) reduces that is not advantageous to the stability of the system.The lower the content of water,the more advantageous to the formation of the microemulsion and its stability.