Manipulation of the viscosity behavior of wormlike micellar gels by changing the molecular structure of added perfumes

• Significant effect of perfume solubilization on viscosity of wormlike micellar solutions.
• Smaller penetration in palisade layer for branched or cyclic high polarity molecules.
• Larger penetration in palisade layer for branched or cyclic low polarity molecules.

We studied the effect of a trace amount of perfumes and oils on the rheological properties of micellar solutions formed in a water/sodium dodecyl sulfate (SDS)/tri(oxyethylene) dodecyl ether (C12EO3) system which gives a maximum zero-shear viscosity as a function of surfactant mixing fraction due to wormlike micelle formation. By adding high-polarity perfumes and oils (9-decen-1-ol, 1-decanol, l-menthol, geraniol and α-terpineol), the viscosity peak shifts to lower hydrophobic surfactant composition and the degree of the viscosity peak shift is the largest for the linear-chain molecules and smaller for the branched or cyclic molecules. Dynamic frequency tests show that the zero-shear viscosity behavior for different high-polarity perfume and oil systems varies due to the change in the relaxation time behavior. The linear-chain molecules can penetrate well in the palisade layer of micelles and the penetration could be interrupted by branched or cyclic molecular architecture. On the other hand, by adding low-polarity perfumes and oils (p-cymene, hexahydrocumene, butylbenzene, d-limonene and decane), the behavior of the viscosity curve is quite different for decane and for other molecules, i.e. decane decreases the viscosity peak without shift of surfactant mixing fraction whereas other molecules behave as high-polarity molecules.

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