Phase behavior of epoxidized soybean oil-based ionic liquid microemulsions: Effects of ionic liquids, surfactants, and co-surfactants

Epoxidized soybean oil (ESBO)-based ionic liquid microemulsions are promising alternatives for petroleum-based lubricants. This study presents the phase behavior of these microemulsions through phase manifestation, and the areas of the single-phase domain were accordingly calculated to illustrate the phase-forming capacities of the designed microemulsions. Effects of ionic liquid anions and cations, surfactant and co-surfactant chain lengths on the phase behavior, and phase-forming capacities of ESBO-based ionic liquid microemulsions were investigated. Results showed that the phase-forming capacities of the ESBO-based ionic liquid microemulsions with different ionic liquid anions and cations showed the following sequence: Tf 2 N − -based   >   PF 6 − -based   >   BF 4 − -based, OMIM + -based   >   HMIM + -based   >   BMIM + -based   >   EMIM + -based. Given the presence of ionic liquid–ESBO amphiphilic balance in the designed systems, the ESBO–surfactant micelles achieved maximum solubilization capacity for 1-butyl-3-methyl-imidazolium tetrafluoroborate when the surfactant had approximately eight ethoxylated groups. In addition, ESBO-based microemulsion containing n -hexanol showed a higher phase-forming capacity than that containing n -butanol, and n -octanol caused a different phase behavior for the ESBO-based microemulsion because of its oilier nature than a co-surfactant.