Triple Ultrasensitive Wormlike Micelles from Cyclen-Based Oligomeric Surfactants

Stimuli-responsive wormlike micelles have attracted considerable interest in colloid and interface science owing to their reversible structural transitions and broad application potential in enhanced oil recovery, drug delivery, and nanomaterial synthesis. However, a systematic and quantitative understanding of how the number of alkyl tail chains in pseudo-oligomeric surfactants governs their self-assembly ability and stimulus-response performance has remained elusive, largely due to the lack of structurally well-defined homologous model systems. Herein, a homologous series of pseudo-oligomeric surfactants was constructed by coupling dodecylamine with cyclen-based polycarboxylates bearing two (DO2A), three (DO3A), or four (DO4A) carboxyl groups, and their assembly behavior was systematically investigated using steady/dynamic rheology, zeta potential measurements, and cryo-TEM. Increasing the dodecylamide chain count from two to four dramatically elevated the zero-shear viscosity from ∼3.2 mPa·s to ∼18,500 mPa·s at 2 wt %, consistent with packing parameter predictions. The optimal DO4A-based system exhibited an ultranarrow pH response window (ΔpH = 0.54) with a four-order-of-magnitude viscosity drop, high salt sensitivity with complete structural collapse at ∼10 mM hexanoic acid sodium, and an activation energy of 215 ± 17 kJ·mol–1 for the temperature response, indicating exceptionally high temperature sensitivity. The worm-to-vesicle morphological transitions induced by both pH and salt were inferred from the rheological results. This work not only provides the quantitative elucidation of the tail-number effect on pseudosurfactant assembly but also introduces cyclen polycarboxylates as inexpensive and readily available building blocks for smart viscoelastic fluids, with the cooperative protonation mechanism revealed here offering a new molecular design principle for next-generation stimuli-responsive soft materials.