Effect of the Charge of a Small Amount of a Cosurfactant on the Viscoelasticity of Zwitterionic Wormlike Micelles

The rheological properties and structure of aqueous solutions of wormlike micelles of a zwitterionic surfactant in the presence of an ultra-small amount of a cosurfactant with a similar structure, the charge of which depends on the pH, are studied. It is shown that the transition of the cosurfactant from the cationic form to the uncharged form leads to an increase in the viscosity, relaxation time, and elastic response of solutions by an order of magnitude. The formation of wormlike micelles in the case of charged and uncharged forms of cosurfactants is confirmed by small-angle neutron scattering. It is shown that even a small amount of charged cosurfactant leads to a decrease in the average contour length of wormlike micelles in comparison with a neutral cosurfactant. Thus, pH-sensitive viscoelastic solutions based on a zwitterionic surfactant in the presence of an ultra-small amount of a cosurfactant, the charge of which depends on the pH, are investigated.