Nanostructured Microemulsion Phase Behavior Using AOT or Extended Surfactant Combined with a Cationic Hydrotrope

Khalid Kanan,Hala Yousef,Ibrahim Kayali

doi:10.4236/jsemat.2012.21010

Khalid Kanan, Hala Yousef + Show 1 more

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https://doi.org/10.4236/jsemat.2012.21010

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Abstract

The phase behavior for systems containing sodium bis (2-ethylhexyl sulfosuccinate) (AOT), with the cationic hydro-trope tetraethyl ammonium chloride (TEAC), in the presence of water and heptane were studied. Formulations of mi-croemulsion for such systems and for systems containing the so called “extended surfactant” were carried out at different salt concentrations. Anisotropy was detected using cross polarizers and polarized microscopy. Ultralow interfacial tension for microemulsion was measured, first theoretically using the Chun-Huh equation, and then experimentally using spinning drop experiments. The presence of short chain hydrotropes (TEAC) was found to destabilize the liquid crystalline region, observed in the AOT/water/heptane phase diagram. Ultralow interfacial tensions were observed for microemulsions formulated with surfactant concentrations as low as 0.5%, for both AOT and “extended surfactant” systems. The effect of temperature on the phase behavior of a microemulsion formed with AOT system was studied and found to behave in an opposite manner compared to the nonionic surfactant.

Highlights

IntroductionThe outstanding properties of microemulsions such as thermodynamic stability, high solubilizing capacity and ultralow interfacial tension (IFT) make them desirable for applications in many fields including enhanced oil recovery (EOR), surfactant enhanced aquifer remediation (SEAR), detergency, pharmaceuticals and cosmetic preparations [1,2,3]
The outstanding properties of microemulsions such as thermodynamic stability, high solubilizing capacity and ultralow interfacial tension (IFT) make them desirable for applications in many fields including enhanced oil recovery (EOR), surfactant enhanced aquifer remediation (SEAR), detergency, pharmaceuticals and cosmetic preparations [1,2,3].The high amount of surfactants required to formulate a microemulsion (20wt% or more) constitute a major problem for its usage
Ternary phase behavior was determined at 25 ̊C in our lab by using the cationic hydrotrope, tetraethyl ammonium chloride (TEAC), as a third component with the AOT/water system, where a single clear isotropic phase was obtained as AOT was present at 4.8wt%, the mixture turned rapidly to a single turbid phase at 9wt% AOT, and appeared to be very thick at 13wt% AOT .The addition of TEAC increases the solubility of AOT and causes the formation of the normal micelle L1 phase (Figure 1)

Summary

Introduction

The outstanding properties of microemulsions such as thermodynamic stability, high solubilizing capacity and ultralow interfacial tension (IFT) make them desirable for applications in many fields including enhanced oil recovery (EOR), surfactant enhanced aquifer remediation (SEAR), detergency, pharmaceuticals and cosmetic preparations [1,2,3]. The high amount of surfactants required to formulate a microemulsion (20wt% or more) constitute a major problem for its usage. The anionic surfactant Aerosol-OT, known as AOT, with its double tail can form microemulsions with no alcohols required. The phase diagram of brine/AOT/ decane system that was determined earlier showed that the reverse micellar solution L2, can dissolve large amounts of water forming bicontinuous or discrete droplet microemulsion [5]. AOT was found to change from hydrophobic to hydrophilic species with increasing temperature

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