Shear‐Induced Structural Transitions in a Model Fabric Softener Containing an Esterquat Surfactant

Abstract

AbstractProcessing conditions must be rigorously controlled in the production of fabric softener because mechanical energy input during the mixing operation may provoke undesirable structural transitions. Hence, ability to control and modify rheological properties of surfactant systems is an important pre‐requisite for many applications of surfactant formulations. Mixtures of a commercial cationic esterquat‐type surfactant and different concentrations of salt (CaCl2) were rheologically and microscopically characterized. Shear‐induced microstructural transitions have been studied in order to control the formation of vesicles, which is undesirable. The addition of salt allows viscosity to be adjusted and provoked a lack of viscoelastic properties. In addition, a shear thickening effect above a specific value of critical shear rate, which is different for each salt concentration, was observed. This is related to the transition from lamellar bilayer to vesicles. This fact was confirmed by hysteresis‐loop experiments, which showed apparent antithixotropic behaviour. Start‐up flow tests indicated that a minimum value for shear rate and a certain shear time are needed for the formation of shear‐induced structures. After this test, the systems showed viscoelastic properties due to the formation of vesicles.