Complexes of humic acid with cationic surfactants support the supramolecular view of extracted humic matter

Environmental context The molecular organisation of humic substances is key to understanding various natural and engineered processes, such as metal speciation bioavailability. Two main models have been proposed: polymeric supramolecular organisation. A physicochemical approach, based on the interaction acid with increasing amounts cationic surfactants, leads a sequence structures that provides support view Abstract structural extracted matter, or supramolecular, has long-standing controversial issue. In this paper, we show between reference material, Suwannee River Humic Acid (SRHA), homologous series surfactants (n-alkyl trimethyl ammonium chloride) insights resolve controversy. By combining measurements turbidity, electrophoretic mobility, surface tension cryogenic transmission electron microscopy, that: (i) binding surfactant anionic initially triggered by electrostatic interactions; (ii) contrasting evolution turbidity–surfactant concentration curves implies alkyl chain interacts hydrophobic moieties matter from very low concentrations surfactant; (iii) drastic restructuring occurs binding, which brings out supplementary sites; (iv) in presence C12 surfactant, SRHA spontaneously forms stable nanoscale unilamellar vesicles, which, addition high activity complexes, could be interest remediation oil-contaminated environments; (v) obtained C12-cationic – humic-rich aggregates, surfactant-rich vesicles bears striking similarities phase behaviour aqueous mixtures thus supporting structure.