Oil‐Induced Structural Change of Wormlike Micelles in Sugar Surfactant Systems

Abstract

Sucrose monofatty acid esters form spherical or short‐rod micelles in water. By combining the sugar surfactant with lipophilic monoglyceride or short‐EO‐chain, poly (oxyethylene) alkyl ether (C_mEO_n) one‐dimensional growth of micelles takes place, and the viscosity of the aqueous mixed nonionic surfactant solution dramatically increases due to the entanglement of elongated wormlike micelles. Upon addition of oil (decane or m‐xylene), the viscosity changes in the opposite way. With a slightly polar m‐xylene, the viscosity increases, but the viscosity is sharply decreased upon addition of the saturated hydrocarbon decane. It was confirmed by SAXS results that long wormlike micelles are more extended by m‐xylene because the m‐xylene molecules are solubilized in the surfactant palisade layer, whereas decane is solubilized in the core of micelles and makes an oil pool inside. Consequently, upon addition of decane, wormlike micelles become shortened and change to short fat micelles. The oil‐induced structural change in the micellar shape is highly related to the solubilized site of oil in the aggregates.

Keywords:

• Sucrose fatty acid ester
• wormlike micelle
• rheology
• small angle X‐ray scattering