Viscoelastic wormlike micellar solutions in mixed environmentally friendly nonionic surfactant systems

A study of the phase and theological behavior of polyoxyethylene(20)sorbitan monooleate (Tween 80)/monolaurin (ML)/water is presented at 25 degrees C. In water/surfactant binary system, Tween 80 forms an isotropic micellar solution over wide concentration range (similar to 42 wt%). With successive addition of ML to the aqueous Tween 80 solution, viscosity increases rapidly and a viscoelastic solution is formed. The viscoelastic micellar solution formed follows the Maxwell model typical of wormlike micellar systems at low-frequency region. With further addition of ML, the viscosity drops after a maximum and phase separation occurs. On increasing the concentration of Tween 80, micellar growth starts at a slightly lower concentration of ML. The micellar growth can be simply explained by reducing the effective area of Tween 80 head group upon addition of ML. (C) 2008 Elsevier B.V. All rights reserved.