title: Characterization of Aqueous Oleic Acid/Oleate Dispersions by Fluorescent Probes and Raman Spectroscopy.
abstract: Oleic acid (OA) and oleates form self-assembled structures dispersible in aqueous media. Herein, the physicochemical properties of OA/oleate assemblies were characterized using fluorescent probes and Raman spectroscopy, under relatively high dilution (<100 mM of total amphiphile) at 25 °C. Anisotropy analysis using 1,6-diphenyl-1,3,5-hexatriene showed that the microviscosity of the OA/oleate assembly was highest at pH 7.5 (the pH range of 6.9-10.6 was investigated). The fluorescence spectra of 6-lauroyl-2-dimethylaminonaphthalene revealed the dehydrated environments on membrane surfaces at pH < 7.7. The pH-dependent Raman peak intensity ratios, chain torsion (S = I1124/I1096) and chain packing (R = I2850/I2930), showed local maxima, indicating the occurrence of metastable phases, such as dispersed cubic phase (pH = 7.5), vesicle (pH = 8.5), and dispersed cylindrical micelle (pH = 9.7). These results suggest that large-scale OA/oleate assemblies could possess particular membrane properties in a narrow pH region, e.g., at pH 7.5, and 9.7.
authors.affiliation: Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University 1-3 Machikaneyamacho, Toyonaka, Osaka 560-8531, Japan.
authors.forename: Keishi
authors.initials: K
authors.lastname: Suga
authors.affiliation: Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University 1-3 Machikaneyamacho, Toyonaka, Osaka 560-8531, Japan.
authors.forename: Dai
authors.initials: D
authors.lastname: Kondo
authors.affiliation: Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University 1-3 Machikaneyamacho, Toyonaka, Osaka 560-8531, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Otsuka
authors.affiliation: Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University 1-3 Machikaneyamacho, Toyonaka, Osaka 560-8531, Japan.
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Okamoto
authors.affiliation: Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University 1-3 Machikaneyamacho, Toyonaka, Osaka 560-8531, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Umakoshi