Responsive wormlike micelles based on aspirin's reaction with hydroxylamine

Hydroxylamine converts sodium acetylsalicylate (the anionic form of aspirin) into salicylate, and in presence of hexadecyltrimethylammonium bromide (C₁₆TAB) can be used as a trigger to produce a responsive wormlike micelle system.

Dynamic oscillatory measurements were conducted to characterize the system's rheological evolution. In-situ FTIR, UV-Visible, and ¹H NMR spectroscopy were employed to accompany the chemical conversions, allowing the mechanism investigation of the whole process. Images obtained by using Cryo-TEM allow the identification of the wormlike micelles aggregates at the end of the reaction.

Hydroxylamine, introduced in the sulfate form, (NH₃OH)₂SO₄), is an effective chemical trigger for inducing the formation of responsive wormlike micelles in aqueous solutions containing CTAB and acetylsalicylate. The conversion of acetylsalicylate to salicylate effectively transforms an anionic species with low affinity for the micellar palisade into one with significantly higher affinity. The interfacial curvature of the micelles decreases due to the incorporation of salicylate, thereby promoting the elongation and entanglement of the wormlike micelles. The kinetics of micellar growth were probed through rheological measurements, enabling real-time monitoring of both micelle growth and the subsequent development of network entanglements. The evolution of the viscoelastic properties was quantitatively correlated with the in-situ formation of salicylate. Complementary spectroscopic techniques, including UV-Visible, FTIR and NMR, were employed to track the structural evolution of the self-assembled aggregates at the molecular level.