Phase Behavior of Pseudo-Ternary Gemini Surfactant + 1-Hexanol/Oil/Water Systems

Temperature dependent phase behavior of pseudo-ternary Gemini surfactant + 1-hexanol (1？:？5 molar ratios)/oil/water systems is reported from 0°C to 65°C. The influence of nature of hydrocarbon oil and type of electrolytes (weak as well as strong) has been investigated on the temperature induced phase behavior of the ternary system. At surfactant concentration, %, a “nose-shaped” microemulsion region is observed. Below one-phase microemulsion region, phase appears. The presence of NaCl decreases the domain size of micellar region whereas oxalic acid first decreases the domain below and then increases above in the lower boundary of the phase diagram. The critical weight fraction of water decreases in presence of both electrolytes. However, increases in presence of oxalic acid and remains constant in presence of NaCl as compared to salt-free system. Furthermore, when cyclohexane was replaced by a longer straight chain hydrocarbon, dodecane, the domain of the one-phase microemulsion region is tremendously increased. 1. Introduction Microemulsions (MEs) are optically transparent, thermodynamically stable, nanostructured mixture of oil and water stabilized by surfactant and cosurfactant [1]. Microemulsions have attracted great interest because of their unique physiochemical characteristics such as large stabilization capacity, ultralow interfacial tension, and a very large interfacial region, and because of their potential industrial applications such as enhanced oil recovery, biotechnology, nanotechnology, novel drug delivery, agriculture, beverages, and chemical reaction [2]. Phase behavior and structural organization of micro-emulsions are known to play key roles in its industrial and technological applications. Phase behavior studies provide information on the phase boundaries of different phases as a function of composition and temperature and more important structural organization of surfactant aggregates can also be inferred. In addition, it allows comparison of efficiency of different surfactant for a given application. The boundaries of one-phase micellar region can be easily accessed by visual observation of the sample of known composition. However, long equilibration is required in multiphase regions especially if a liquid crystalline phase is involved and this makes phase determination tedious, time consuming, and difficult [1–3] to construct. The phase behavior and structural organization of surfactant aggregates are highly dependent on the elastic properties of surfactant monolayer separating oil and water domains [4]. The natural curvature of