From self-assembly to controlled release: synthesis and properties of dynamic imine-based Gemini surfactants for...

Surfactants based on dynamic covalent bonds have attracted great interest in the past few decades due to the coexistence of covalent and non-covalent bonds. As a novel structure of surfactants, Gemini surfactants exhibit excellent surface activity and aggregation behavior. This work synthesized dicot quaternary ammonium salts containing aldehyde precursors, which can self-bind with primary amines of different chain lengths in water to undergo Schiff base reactions and generate pH responsive dynamic surfactants. Different linking groups and hydrophobic chain lengths were used to synthesize Gemini surfactants. The micelle aggregation behavior and surface activity of Gemini surfactants were systematically studied through surface tension, fluorescent probes, and conductivity. Particularly, the Gemini surfactant with 6 carbon atoms between amphiphilic groups and 10 carbon atoms in hydrophobic tail chain change the surface tension of water to 28.88mN·m^-1 with a critical micelle concentration of 0.117 mmol·L^-1.Products with different chain lengths and linking groups exhibit different micelle aggregation characteristics. Dynamic light scattering, rheology, and cryogenic transmission electron microscopy were used to study their high concentration aggregation behavior and the self-assembled vesicles and worm-like micelles of Gemini surfactants were revealed finally. The ability of micelles to encapsulate and release curcumin was studied by UV-visible spectroscopy and fluorescence spectroscopy, and it was found that they have excellent encapsulation ability for curcumin. Different from micelles, the aggregation behavior of Gemini surfactants changed with the concentration of them in aqueous solution increased.