Nonionic surfactant mixtures in an imidazolium-type room-temperature ionic liquid.
The physicochemical properties of nonionic surfactant mixtures in an aprotic, imidazolium-type room-temperature ionic liquid (RT-IL) have been studied using a combination of static surface tensiometry, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM). The surfactants used in this study are phytosterol ethoxylates (BPS-n, where n is an oxyethylene chain length of either 5 or 30) and the selected RT-IL is 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)). The shorter chain oxyethylene surfactant (BPS-5) exhibits greater surface activity in BmimPF(6) than BPS-30; hence, BPS-5 is a major component in driving the interfacial adsorption and molecular aggregation of the mixed system. The surface tension data demonstrate that an increased mole fraction of BPS-5 results in a decreased critical aggregation concentration (cac) and negatively increased Gibbs free energies estimated for molecular aggregation (ΔG(0)(agg)) and interfacial adsorption (ΔG(0)(ads)). Indeed, the compositions of the monolayer adsorbed at the air/solution interface and the molecular aggregate formed in the bulk solution are enriched with BPS-5. The combination of the DLS and cryo-TEM results demonstrates the spontaneous formation of multi-lamellar vesicles resulting from the BPS-5-rich composition of the molecular aggregates.
Department of Pure and Applied Chemistry, Tokyo University of Science, Japan. k-sakai@rs.noda.tus.ac.jp
Hideki
H
Sakai
Takanori
T
Saitoh
Takeshi
T
Misono
Koji
K
Tsuchiya
Kenichi
K
Sakai
Masahiko
M
Abe
D000327:Adsorption; D005026:Ethylene Glycols / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D010840:Phytosterols / Q000737:chemistry; D012542:Scattering, Radiation; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature
C412621:1-butyl-3-methylimidazolium hexafluorophosphate; D005026:Ethylene Glycols; D007093:Imidazoles; D052578:Ionic Liquids; D010840:Phytosterols; D013501:Surface-Active Agents