pH-switchable wormlike micelles with high viscoelasticity formed by pseudo-oligomeric surfactants

Abstract A pH-switchable wormlike micellar system with high viscoelasticity was prepared by mixing N-(3-(dimethylamino) propyl) stearamide (SAM) and phthalic acid (PA) at the molar ratio of 2:1. By simple in situ neutralization reaction, SAM and PA could dynamically combine to fabricate a pseudo-oligomeric surfactant without additional inorganic salts. Through the results of surface activity, rheology and Small-angle X-ray scattering (SAXS), it was found that the pseudo-oligomeric surfactant was readily to form viscoelastic wormlike micelles and showed remarkable thickening ability. The maximum zero shear viscosity (η0) was up to 9.4 × 103 Pa·s, which was higher than most of wormlike micelles formed by the conventional covalently linked oligomeric counterparts. The viscoelastic fluid formed by the pseudo-oligomeric surfactant was highly sensitive to pH, whose viscosity could be decreased to 0.001 Pa·s instantly by adding a small amount of acid or alkali.