ANIONIC SURFACTANT WATER-SYSTEMS - INFLUENCE OF LECITHIN ADDITION ON THE RHEOLOGICAL BEHAVIOR

The viscosity values of ternary systems containing anionic surfactant, lecithin, and water have been studied using sodium alkyl-ether-sulfate, sodium dodecyl-sulfate, and sodium dodecylbenzenesulfonate as surfactants. The highest concentrations of surfactant and lecithin studied were 30% and 3% in weight, respectively. The following conclusions may be drawn: (1) All the systems present Newtonian rheological behavior, except those containing: 30% sodium alkyl-ether-sulfate and 2% or more lecithin, 30% sodium dodecylsulfate and 3% lecithin. These non-Newtonian systems behave like pseudoplastic fluids. (2) The addition of lecithin improves the solubility of sodium dodecylsulfate in water, but diminishes the solubility of sodium dodecylbenzenesulfonate. (3) The systems containing sodium alkyl-ether-sulfate show an abnormal temperature dependence on viscosity, with maximum values at temperatures around 283–288 K. These viscosity maxima are related to the existence of ethylene oxide groups in surfactant molecules. (4) The addition of lecithin causes an increase in viscosity values of surfactant-water systems and also a shift of the maximum viscosity temperature toward higher values. © 1990, The Society of Rheology. All Rights Reserved.