Coacervation of dynamic covalent surfactants with polyacrylamides: properties and applications

Abstract

Dynamic covalent surfactants have been prepared from a mixture of 4-formyl-N,N,N-trimethylbenzenaminium iodide (FBA) with heptylamine (C₇A) or octylamine (C₈A) in alkaline aqueous solutions. The reversible pH-dependent nature of the imine bond is characterized by ¹H NMR and fluorescence analysis. The dynamic covalent surfactants self-assemble into micelles under alkaline conditions and exhibit coacervation with 10% hydrolyzed polyacrylamide (PAM) over a wide concentration range. The coacervate phase with a network structure was found to effectively extract the anionic dye Conge Red (CR). When the solution is adjusted to acidity, the imine bond is hydrolyzed, leading to the transition of the coacervates into a homogeneous and clear solution, and the precipitation of CR into purple-black solids due to the protonation of sulfonic groups. Thus, the extraction and release of CR molecules are realized with this dynamic covalent surfactant/PAM system. Moreover the initial components, FBA, amine, and PAM, can be easily regenerated with hydrochloric acid. This method shows potential applications in wastewater treatment.