Abstract
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,Φs=40%, a “nose-shaped” microemulsion region is observed. Below one-phase microemulsion region,Lαphase appears. The presence of NaCl decreases the domain size of1Φmicellar region whereas oxalic acid first decreases the domain belowΦw<18and then increases aboveΦw>18in the lower boundary of the phase diagram. The critical weight fraction of waterΦwcridecreases in presence of both electrolytes. However,Φwmaxincreases 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.
Highlights
Microemulsions (MEs) are optically transparent, thermodynamically stable, nanostructured mixture of oil and water stabilized by surfactant and cosurfactant [1]
Phase diagram of Gemini surfactant + 1-hexanol (1 : 5 molar ratio)/ oil/water or aqueous electrolyte systems were constructed by titration method and the phase boundaries of one-phase micellar region of the ternary systems were determined at fixed surfactant concentration, γ = 40%
At Φw > 15, Lα starts to appear in the lower portion of the phase diagram, and, the weight fraction of water (Φw ≈ 0–15) may be defined as the critical weight fraction of water Φwcri where phase transition occurs from 1Φ micellar region to Lα phase
Summary
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 microemulsions 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 be inferred. It allows comparison of efficiency of different surfactant for a given application. 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 [1,2,3] to construct
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