Rheological Properties and Microstructure Transition in Mixture of Zwitterionic Surfactant, Anionic Surfactant and Salts in Sorbitol/H₂O Solvent: 2. Effect of Salts and Sorbitol

Abstract

The impact of mixed salts and sorbitol on the viscoelastic properties of a multi‐component system, made of a zwitterionic surfactant cocoamidopropyl betaine (CAPB), an anionic surfactant sodium lauryl sulfate (SLSS) and mixed salts (tetrasodium pyrophosphate, sodium acid pyrophosphate, saccharin and sodium fluoride) in sorbitol/H2O mixed solvent are systematically investigated by steady state and dynamic rheology. As reported previously, the viscosity of the mixed system passes through a maximum with increase in the SLSS mass fraction (XSLSS) at a fixed total surfactant concentration, salt concentration (Csalt) and mass ratio of sorbitol in mixed solvent (R). The shape of the XSLSS‐dependent viscosity curve does not change regardless of Csalt and R, but adding salts or sorbitol has different effects on the rheological properties of this system. The former due to a high screening effect plays an important role in the elongation and entanglement of the wormlike micelles, facilitating the enhancement of rheological properties and the formation of Maxwell fluids. The latter has a dual effect on the rheological properties and phase behavior of the mixtures. A certain amount of sorbitol can promote the formation entangled wormlike micelles, while the effect is reversed if the sorbitol content is too large. The electrostatic and hydrophobic interaction between CAPB and SLSS are the prerequisite for the aggregate formation and transition. Meanwhile, the aggregation behaviors are strongly influenced by the balance between low dielectric constant, strong solvophobic interaction and steric effect of sorbitol with the ability to form hydrogen bonds which favors the growth of micelles, and appearance of aqueous two‐phase systems with smaller amounts of wormlike micelles in CAPB‐rich regions which oppose enhancement of rheological properties. Our findings provide a new insight and approach to control and adjust the phase behavior of such a complicated applied multi‐component system.