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J Phys Chem B. 2013 May 2;117(17):5081-9. doi: 10.1021/jp402314f. Epub 2013 Apr 18.

Thermodynamically stable vesicle formation and vesicle-to-micelle transition of single-tailed anionic surfactant in water.

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  • 1Research and Development, Eco-Innovation Research, Kao Corporation, 1334, Minato, Wakayama-shi, Wakayama 640-8580, Japan. sakai.takaya@kao.co.jp

Abstract

The aggregation behavior of sodium 3,6,9,12,15-pentaoxa-heptacosanoate (AEC4-Na) in aqueous solution with increase of the concentration at 25 °C was investigated using differential scanning calorimetry, equilibrium surface tension, solubilization of an oil-soluble dye, steady-state fluorescence, dynamic light scattering, and freeze-fractured transmission electron microscopy. Vesicle formation of AEC4-Na preceded micelle formation below the critical micelle concentration (cmc). The vesicle-to-micelle transition was observed through a narrow concentration region above the cmc. The mean diameters of the vesicles and micelles were not affected by the concentration. All solutions over a wide range of concentrations were homogeneously transparent with a low Krafft point below 0 °C. These results indicate that the AEC4-Na vesicles have a thermodynamically stable structure. Vesicle formation may be caused by a pseudobinary mixed surfactant system composed of monomeric AEC4-Na and an acid soap that consists of a dimer complex formed between AEC4-Na and unneutralized AEC4-Na. The thermodynamic stability would then result from the inhibition of close intermolecular aggregation and flexibility of the molecular shape in the vesicles due to the oxyethylene units in AEC4-Na.

PMID:
23560707
DOI:
10.1021/jp402314f
[PubMed - indexed for MEDLINE]
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