Micellar structure changes in aqueous mixtures of nonionic surfactants

Rheology and small-angle neutron scattering are used to probe the structure of nonionic surfactant mixtures in water. Small amounts of a C 14 diol (Surfynol® 104) cause enormous structural and rheological changes when added to aqueous solutions of an ethylene oxide-propylene oxide-ethylene oxide triblock copolymer (Pluronic® P105). The C 14 diol is only soluble up to 0.1 wt % in pure water, but can be added in large quantities to aqueous solutions of the copolymer. The hydrophobic diol incorporates into the existing copolymer micelles and causes a cascade of changes in the micelle structure, with resultant changes in rheology. Particularly striking is the spherical to worm-like micelle transition, where the viscosity changes by a factor of more than 10 4 .