title: Reverse micelle microstructural transformations induced by surfactant molecular structure, concentration, and temperature.
abstract: We have investigated the microstructural transformations of nonionic surfactant reverse micelles induced by surfactant molecular architecture, surfactant concentration, and temperature in nonaqueous media. The investigations were based on small-angle X-ray scattering (SAXS) and rheometry techniques. Polyglycerol polyoleic acid esters spontaneously self-assembled into reverse micelle in n-decane under ambient conditions, whose shape, size, and internal structure could be controlled by the surfactant molecular architecture, concentration, and temperature. The maximum size of the micelles was found to increase with an increase in the hydrophilic headgroup size of the surfactant. On the other hand, an opposite trend was observed with an increase in the number of oleate chain per surfactant molecules, which was well supported by rheology data; viscosity decreased with the number of oleate chain per surfactant molecule. The SAXS and rheology data have shown a clear evidence of one dimensional micellar growth with increase in the surfactant concentration. The relative viscosity, eta(r), of the reverse micelle exhibited steeper concentration dependence behavior than those predicted for a dispersion of spherical particles based on the Krieger-Dougherty relation which provided a clear evidence of the presence of elongated micelles at higher concentration. An ellipsoidal prolate-to-sphere type transition was observed upon heating.
authors.affiliation: Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8501, Japan.
authors.forename: Rekha Goswami
authors.initials: RG
authors.lastname: Shrestha
authors.forename: Lok Kumar
authors.initials: LK
authors.lastname: Shrestha
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Ariga
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe