Dynamic viscoelasticity and flow behavior of a polyoxyethylene glycol nonylphenyl ether/toluene/water system

Several samples of a ternary nonionic surfactant/ toluene/ water system at six compositions were characterized on the basis of their rheological and phase behaviors at 25 degrees C. Different self-association structures were identified: a dispersion of lamellar vesicles embedded in an isotropic phase (D-1), a further dispersion (D-2) consisting of an aqueous phase dispersed in a continuous medium whose structure is dominated by an incipient lamellar liquid-crystalline structure, three samples located in the lamellar mesophase (L-alpha) region and an L-2 sample. The latter exhibited Newtonian behavior and no viscoelasticity, both phenomena were attributed to the occurrence of reverse globular micelles. Linear dynamic viscoelasticity revealed that samples located well within the L-alpha, region showed mechanical and relaxation spectra typical of highly str uctured materials. Similar spectra were observed for a D-2 sample but with a lower plateau modulus, indicating that; the basic structure was the same as for standard L-alpha, samples but with weaker interactions among the liquid-crystalline monodomains. An L-alpha, sample located by the border of the L-2 and L-alpha regions showed more fluidlike viscoelastic properties. Relaxation spectra turned out to be quite sensitive to a change of composition. The different viscoelastic results found for the L-alpha samples studied were associated with a change of the so-called packing parameter with composition. Apparent viscosities derived from now curves were compared with complex viscosities. While shear flow provoked an order decrease in the L-alpha systems, it gave rise to a striking structural build-up process in the dispersions.