INFLUENCE OF SURFACTANT CONCENTRATION AND TEMPERATURE ON THE FLOW BEHAVIOR OF SUCROSE OLEATE AQUEOUS SYSTEMS

This paper deals with the flow behaviour of aqueous systems of a sucro se oleate with a high hydrophilic lipophilic balance (HLB, 15). Influe nces of temperature (10-45-degrees-C) and surfactant concentration (10 -45 wt.%) have been studied. The flow curves show both a limiting visc osity at low shear rates and a shear-thinning region after a critical shear rate that depends on temperature and sucrose oleate concentratio n. Experimental flow curves have been shifted on a master curve using the time-temperature superposition method. This master curve includes all the experimental flow curves obtained with the systems having a su crose oleate concentration between 10 and 30 wt.%. The shift factor sh ows a complex dependence on temperature, having two different Arrheniu s-like regions with two different activation energies. These results c an be explained on the basis of the existence of a micellar phase at l ow concentrations and temperatures and then a lamellar phase, complete ly developed for concentrations higher than 35 wt.% surfactant.