Effect of aromatic acid on the rheological behaviors and microstructural mechanism of wormlike micelles in betaine surfactant

The rheology and microstructural behaviors of viscoelastic surfactant solutions induced by different organic acids are fascinating. However, the viscosity and viscoelasticity behavior of some surfactants such as oleyl amidopropyl betaine (OAPB) surfactant is very poor even at high concentrations. To improve these properties at low concentrations, a system of OAPB and phthalic acid (OPA) at a mass ratio of 3:2 has been developed. The rheological behaviors and microstructural aggregations of the OAPB/OPA system were measured by rheometer, transmission electron microscopy (Cryo-TEM), and dynamic light scattering (DLS). The experimental results showed that the addition of OPA significantly increases the viscoelasticity and viscosity properties of the OAPB viscoelastic micelle solutions at 25 degrees C. The improvements of these properties are attributed to the formation of a micellar network due to the addition of OPA. The rheology and micellar properties were found to transform a transparent viscous water like a fluid at pH 7 to a viscoelastic fluid at pH 2.9. The zero-shear viscosity and relaxation times declined exponentially with an increase of temperature indicating a reduction in the average micellar lengths. The properties changes were attributed to the strength of electrostatic attractions, hydrophobic effects, and hydrogen bonding between OAPB and OPA molecules. Since the current system can be easily tuned by pH for at least 3 circles without deterioration of its properties, the system unlocks the significant prospect for designing stimuli-responsive smart materials for various industrial applications. (C) 2021 Elsevier B.V. All rights reserved.