pH-Tunable wormlike micelles based on an ultra-long-chain “pseudo” gemini surfactant

Abstract

Smart surfactant wormlike micelles (SWLMs), responsive to external stimuli, are a particularly recent area of development, yet highly promising, given the versatility of the materials but simplicity of the design. Here, we developed a pH-switchable wormlike micellar system based on a “pseudo” gemini surfactant (named as EAMA) formed by a mixture of N-erucamido-N,N-dimethylamine (UC₂₂AMPM) and maleic acid with a molar ratio of 2 : 1, and compared the “pseudo” gemini worm system with UC₂₂AMPM in the presence of hydrochloric acid (EAHCl). It was found that both maleic acid and hydrochloric acid can protonate the ultra-long-chain tertiary amine into a quaternary ammonium surfactant, thereby forming wormlike micelles; however, much stronger viscoelastic behavior was evidenced in the maleic acid system because one protonated maleic acid molecule can “bridge” two quaternized UC₂₂AMPM molecules via electrostatic attraction. In contrast, the EAHCl system just shows a “mono” quaternary ammonium feature with a weak viscosity buildup. In addition, the maleic acid-based worm system was found to be more thermo-sensitive than conventional wormlike micelles, which also originates due to its “pseudo” gemini architecture.