title: Phase behavior of phytosterol ethoxylates in an imidazolium-type room-temperature ionic liquid.
abstract: The temperature-concentration phase behavior of nonionic surfactants in an aprotic imidazolium-type room-temperature ionic liquid (RT-IL) was evaluated on the basis of a combination of visual appearance, polarized optical microscopy, and small angle X-ray scattering data. Phytosterol ethoxylates (BPS-n, where n denotes oxyethylene chain lengths of 5, 10, 20, and 30) were used as surfactants in the RT-IL, 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF₆). The two component mixtures yielded various phases such as discontinuous cubic, hexagonal, and lamellar phases. An increased tendency toward formation of lesser-curved molecular assemblies was observed at higher BPS-n concentrations, at lower temperatures, and for shorter oxyethylene chain surfactants. These trends are similar to those observed in aqueous BPS-n systems; however, notable differences in the phase states of the aqueous system versus the BmimPF₆ system were evident. Comparison with the water system showed that the BmimPF₆ system yielded fewer phases and generally required higher BPS-n concentrations to induce phase transitions. Evaluation of the effects of addition of a third component (e.g., 1-dodecanol and dodecane) to the binary system on the phase behavior showed that at a given composition ratio of BPS-20 to BmimPF₆, the addition of 1-dodecanol generally results in the phase transition to lesser-curved assemblies whereas dodecane generated no significant effects. The observed phase change is satisfactorily rationalized by localized solubilization of the third component into the binary surfactant assemblies.
authors.affiliation: Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science. k-sakai@rs.noda.tus.ac.jp
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
authors.forename: Takanori
authors.initials: T
authors.lastname: Saitoh
authors.forename: Takeshi
authors.initials: T
authors.lastname: Misono
authors.forename: Koji
authors.initials: K
authors.lastname: Tsuchiya
authors.forename: Kenichi
authors.initials: K
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
mesh_terms: D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D009821:Oils / Q000737:chemistry; D044367:Phase Transition; D010840:Phytosterols / Q000737:chemistry*; D013696:Temperature
chemical_list: C412621:1-butyl-3-methylimidazolium hexafluorophosphate; D007093:Imidazoles; D052578:Ionic Liquids; D009821:Oils; D010840:Phytosterols