Synergistic interactions in W/O microemulsions containing imidazolium based C12mimBr and sodium lauryl sulfate

Abstract

The physicochemical properties and synergistic effects of W/O microemulsion systems containing imidazolium based surfactant, 1-dodecyl-3-methylimidazolium bromide (C₁₂mimBr)-sodium lauryl sulfate (SLS)/ alcohol/alkane/ 5% NaCl solution at different molar ratios of water-to-surfactant (ω₀) are studied. The W/O microemulsions are formed at the molar fractions of SLS-to-C₁₂mimBr+SLS (X_SLS) ranges of 0.0-0.3 and 0.7-1.0. The synergism between C₁₂mimBr and SLS can be seen from the values of (mole fraction of alcohol in the oil phase), (mole fraction of alcohol in the interfacial layer) and  (the standard free energy change of transferring alcohol from the continuous oil phase to the interfacial layer). The increase in the values of  and , and the decrease in  values with ω₀ is attributed to the increasing hydrophilicity of the microemulsions. By increasing the carbon chain lengths of the alcohol molecules, or by increasing the salt concentrations, the values of  and  decrease, whereas that of  increases for the W/O microemulsions containing the mixed surfactants. On the other hand, the effect of the alkane carbon chain lengths is exactly the opposite of the effect of the alcohol carbon chain lengths on the these parameters.