The stability boundaries of droplets of water/AOT/Dynol-604/isooctane mixed microemulsions

In this study, we investigated the volumetric properties of water/sodium 1,4-bis(2-ethylhexyl)sulfosuccinate(AOT)/ethoxylated-2,5,8,11-tetramethyl-6-dodecyne-5,8-diol(Dynol-604)/isooctane mixed microemulsions by density measurement at T = 303.15 K. It was observed that the volumetric interaction between the microemulsion droplets decreased with the increase of the content of Dynol-604 due to the reduction of electrostatic repulsion between the AOT head groups. The volumetric properties were analyzed by a proposed thermodynamic model to obtain the critical microemulsion concentrations and the maximum molar ratios ωd,max of water to surfactants, which are the stable boundaries of the microemulsion droplets to accommodate the maximal content of water in their cores. It was found that ωd,max increased from 62 to 77 as the mole fraction of Dynol-604 in mixed surfactants varied from 0 to 0.5. This result is further confirmed by conductivity measurements.