Characterization of Aqueous Oleic Acid/Oleate Dispersions by Fluorescent Probes and Raman Spectroscopy

Keishi Suga, Dai Kondo, Yoko Otsuka, Yukihiro Okamoto, Hiroshi Umakoshi

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)7606-7612
Number of pages7
JournalLangmuir
Volume32
Issue number30
DOIs
Publication statusPublished - 2016 Aug 2
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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