title: Effect of water on interfacial chemical properties of nonionic surfactants in hydrophobic ionic liquid bmimPF6.
abstract: We studied the effect of water addition on interfacial properties and aggregate behavior of nonionic surfactants (polyoxyethylene alkyl ether; CnEm) in an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate; bmimPF₆). When a small amount of water was added to mixtures of CnEm and bmimPF₆, two breaking points (cac1, cac2) were observed in the surface tension/CnEm concentration plots, suggesting the formation of two kinds of aggregates. This two-step aggregate formation was also confirmed by the fluorescence probe method using pyrene. The particle size of the aggregates measured by dynamic light scattering (DLS) was around 200 nm at cac1, and decreased to 4 nm above cac2. These results, together with freeze-fracture TEM observations, showed that the aggregate formed at cac1 was water in bmimPF₆ emulsions, which then transformed to micelles solubilizing water in the palisade layer above cac2. This concentration-dependent aggregate formation was supported thermodynamically by studying the dependence of cacs on temperature and alkyl and POE chain lengths of the surfactant.
authors.affiliation: Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, Yamazaki, Noda, Chiba, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Misono
authors.forename: Kenichi
authors.initials: K
authors.lastname: Aburai
authors.forename: Takeshi
authors.initials: T
authors.lastname: Endo
authors.forename: Kenichi
authors.initials: K
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
mesh_terms: D000371:Agglutination; D055598:Chemical Phenomena; D004655:Emulsions; D057927:Hydrophobic and Hydrophilic Interactions; D007093:Imidazoles; D052578:Ionic Liquids; D008823:Micelles; D010316:Particle Size; D011092:Polyethylene Glycols / Q000737:chemistry*; D012995:Solubility; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics; D014867:Water
chemical_list: C412621:1-butyl-3-methylimidazolium hexafluorophosphate; D004655:Emulsions; D007093:Imidazoles; D052578:Ionic Liquids; D008823:Micelles; C495681:Sanonic SS-90; D013501:Surface-Active Agents; D014867:Water; D011092:Polyethylene Glycols