Rheological and Microstructural Behavior of a Model Concentrated Fabric Softener

Abstract

Shear-induced microstructural transitions in aqueous systems of a cationic commercial esterquat-type surfactant used in concentrated fabric softeners were rheologically and microscopically characterized. Binary (surfactant/water) and ternary (surfactant/CaCl2/water) systems were studied. The obtained flow curves demonstrated the shear-thickening behavior in ternary systems at high shear rates, provoked by shear-induced transitions from surfactant bilayers to multilamellar vesicles. This fact was confirmed by hysteresis-loop experiments which proved that a critical shear rate was required to observe apparent antithixotropic behavior in the ternary systems. Start-up flow tests indicated that the increase of shear stress with shear time was more marked as the shear rate was increased. Finally, a comparative aging study of ternary systems with a surfactant used in concentrated fabric softeners and the ternary systems with a surfactant utilized in diluted and semiconcentrated fabric softeners was performed.