Adsorption and Orientation of Ionic Liquids and Ionic Surfactants at Heptane/Water Interface

Molecular dynamics simulation of heptane/ionic-liquid/water system was performed to study the effect of hydrophobic and hydrophilic ionic liquids (ILs) on the interfacial structure of heptane/water as a model for oil/water systems. The results are compared with the simulated water/sodium-dodecyl-sulfate (SDS)/heptane interface. Also, the self-assembly and orientation of ILs and SDS molecules at heptane/vapor interface are studied. We observed that the behavior of these surfactants at heptane/water and heptane/vapor interfaces is very different. The computed density profiles provide a detailed view of the interfacial structure and a route to discuss quantitatively how the oil and water phases organize the surfactant molecules. The effect of ILs [C n mim]Cl and [C n mim]PF 6 (with n = 4, 8, and 12) and SDS on the interfacial tension of heptane/water was simulated and compared at T = 343.15 K. The results indicate that ILs with long alkyl chain could behave similar to a conventional surfactant.