Viscoelastic Wormlike Micelles of Long Polyoxyethylene Chain Phytosterol with Lipophilic Nonionic Surfactant in Aqueous Solution

We have studied the formation, structure, and rheological behavior of viscoelastic wormlike micelles in the mixed system of long polyxyethylene chain phytosterol (PhyEO(30)) and polyoxyethylene dodecyl ether (C(12)EO(n), n = 3 and 4) surfactants in water. Partial ternary phase diagrams of water/PhyEO(30)/C(12)EO(n), are constructed at 25 degrees C. Addition of C(12)EO(n) to the aqueous solution of PhyEO(30) in a dilute region increases the viscosity by several orders and forms viscoelastic micellar solution of entangled wormlike micelles showing the Maxwellian behavior at low shear frequencies. With successive addition of C(12)EO(n), ultimately a phase separation occurs with the formation of turbid solution of vesicular dispersion coexisting with the micellar phase. A rapid micellar growth has been observed when C(12)EO(3) replaces the C(12)EO(4). However, no viscosity maximum is seen with the C12EO3 system; the viscosity increases continuously until phase separation. The effect of temperature on water/PhyEO(30)/C(12)EO(3) system has also been studied. Small-angle X-ray scattering measurements have shown the one-dimensional micellar growth induced by C(12)EO(n) and well support the conclusions derived from rheometry.