Viscoelastic wormlike micellar solutions in mixed environmentally friendly nonionic surfactant systems

A study of the phase and rheological behavior of polyoxyethylene(20)sorbitan monooleate (Tween 80)/monolaurin (ML)/water is presented at 25 °C. In water/surfactant binary system, Tween 80 forms an isotropic micellar solution over wide concentration range (∼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.