Vegetable Oil Microemulsified Ionic Liquids as Renewable Biolubricant Basestocks: The Interface Nature

Vegetable oil microemulsified ionic liquids are promising renewable lubricant systems. In the present study, the interfacial composition and thermodynamic properties for castor oil, glycerol trioleate, and epoxidized soybean oil microemulsified ionic liquids were researched by dilution method. The effects of the cationic chain length of ionic liquids, the oxyethylene groups' number of surfactants, the carbon chain lengths of co-surfactants and temperature on those above mentioned parameters were further detailed. The results showed that with the increase of temperature, the cationic chain length of ionic liquids and the oxyethylene groups' number of surfactant, less co-surfactant at the interface was required to form the stable ionic liquid microemulsions. However, the requirement of co-surfactants at the interface was gradually increased with the increment of the carbon chain lengths of co-surfactants. The standard Gibbs free energy changes for the transfer of co-surfactant from oil phase to the interface were negative in all investigated ionic liquid microemulsions, and the standard enthalpy and entropy changes for the transfer process depended largely on the types of oil and the various thermal conditions.