Microstructural Changes in SDS Micelles Induced by Hydrotropic Salt

The addition of low concentrations of the hydrotropic salt p-toluidine hydrochloride (PTHC) to solutions of the anionic surfactant sodium dodecyl sulfate (SDS) promotes the transition from spherical to rodlike micelles. NMR measurements confirm that the hydrotrope adsorbs at the micelle-water interface, thereby screening electrostatic repulsions between the surfactant headgroups. The sphere-to-rod transition in dilute solutions is followed using quasielastic light scattering, and in the semidilute concentration range dynamic rheology is used to probe the viscoelastic nature of the solutions. The scaling of the zero-shear viscosity and the plateau modulus with surfactant concentration indicates the presence of electrostatic interactions between the micelles.