Wormlike micelles in poly(oxyethylene) surfactant solution: Growth control through hydrophilic-group size variation

Viscoelastic micellar solutions are formed in poly(oxyethylene) cholesteryl ether (ChEOm, m=15m=15, 30) aqueous solutions on addition of tri(ethyleneglycol) mono n-dodecyl ether (C12EO3). The steady-shear and dynamic rheological behavior of the systems is characteristic of wormlike micellar solution. In either system, the plateau modulus (G0G0) and relaxation time (τ) are found to increase with increasing cosurfactant mixing fractions. The plateau modulus of the ChEO30–C12EO3 system at the maximum viscosity region is found to be higher than that in the ChEO15–C12EO3 system at the maximum viscosity region, whereas for the relaxation time the opposite relation is found. The maximum viscosities obtained in the two systems are of the same order of magnitude. In the ChEO30–C12EO3 system, the maximum viscosity is obtained at a higher cosurfactant mixing fraction than that in the ChEO15–C12EO3 system. It is concluded that decreasing the head-group size of the hydrophilic surfactant favors micellar growth. Monolaurin, another hydrophobic surfactant known to induce growth in some systems, is found to cause phase separation before significant micellar growth occurs in ChEOm solutions, although the effect of head-group size of ChEOm is found to be similar to the ChEOm–C12EO3 systems.

The one-dimensional micellar growth occurring on addition of hydrophobic cosurfactant to solutions of hydrophilic surfactant can be controlled by changing the head-group sizes of the hydrophilic surfactant over a large range.Figure optionsDownload as PowerPoint slide