Synergic Effect of the Mixed Cationic-Anionic Surfactants on the Interfacial Composition and Thermodynamics of W/O Microemulsions

Abstract

The interfacial composition, the solubility of the alcohol in the oil phase, and the standard free energy change of transferring alcohol from the continuous oil phase to the interfacial layer in the W/O microemulsion stabilized by cationic-anionic surfactants sodium dodecyl sulfate and 1-hexadecyl-3-methylimidazolium bromide were studied with the dilution method. The synergic effect exists between cationic and anionic surfactants on the formation of W/O microemulsion. The effects of different alcohols, oils, and brine on the formation of W/O microemulsions stabilized by cationic-anionic surfactants were also investigated. The alcohols with longer chain length have higher efficiency to form the W/O microemulsion. Long-chain alcohol was easier to penetrate into the interfacial layer and less alcohol was needed to form the stable W/O microemulsion. The effects of decreasing the carbon chain length of the alkane molecules and increasing NaCl concentrations are equivalent to that of increasing the carbon chain length of the alcohol molecules.

Keywords:

• Dilution method
• interfacial composition
• mixed surfactant
• thermodynamic property
• W/O microemulsion