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Issue 11, 2011
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Structure and rheology of reverse micelles in dipentaerythrityl tri-(12-hydroxystearate)/oil systems

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Abstract

We report the formation of reverse rod-like micelles and their rheological properties in novel nonionic surfactant, dipentaerythrityl tri-(12-hydroxystearate) (designated as WO-6)/oil systems without external water addition. Small-angle X-ray scattering (SAXS) was used to investigate the structure of the micelles and their flow properties were studied by rheological measurements. We found that WO-6 spontaneously self-assembles into reverse micelles in a variety of organic solvents at ambient conditions, their structure depending on solvent molecular architecture, surfactant concentration, and temperature. Rod-like micelles with a maximum length of ca. 12 nm and a cross section diameter of ca. 2 nm were observed in cyclohexane. When cyclohexane was replaced with a linear chain octane, the length and the cross section diameter were simultaneously increased. With a further increase of hydrocarbon chain length of solvent oils from octane to hexadecane, the rod-like micelles grew axially, keeping the cross section diameter (ca. 3 nm) virtually constant. Increasing surfactant concentration also favored one-dimensional micellar growth. On the other hand, micelles shrunk with the rise of temperature, which is similar to a rod-to-sphere transition, and is essentially the opposite temperature dependence to that often observed in aqueous micellar systems. A structural picture drawn by SAXS is well supported by rheology; the relative (zero-shear) viscosity of the WO-6/oil systems was found to be markedly greater than that expected for a dispersion of spherical particles due to the elongated micellar structure, despite quantitative inconsistency with semi-empirically predicted values for rigid rod-like particles.

Graphical abstract: Structure and rheology of reverse micelles in dipentaerythrityl tri-(12-hydroxystearate)/oil systems

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Publication details

The article was received on 04 Oct 2010, accepted on 10 Feb 2011 and first published on 18 Feb 2011


Article type: Paper
DOI: 10.1039/C0CP02024A
Citation: Phys. Chem. Chem. Phys., 2011,13, 4911-4918
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    Structure and rheology of reverse micelles in dipentaerythrityl tri-(12-hydroxystearate)/oil systems

    L. K. Shrestha, T. Sato, R. G. Shrestha, J. Hill, K. Ariga and K. Aramaki, Phys. Chem. Chem. Phys., 2011, 13, 4911
    DOI: 10.1039/C0CP02024A

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