CHEMICAL AND STRUCTURAL TRANSFORMATION OF AGGREGATED AL-13 POLYCATIONS, PROMOTED BY SALICYLATE LIGAND

The chemical and structural consequences of the interaction between ag gregates made of Al-13 polycations and salicylate ligand were examined using adsorption isotherms, electrophoresis, infrared spectroscopy, F raunhofer light diffraction, and static light scattering spectroscopy. Drastic changes were observed for a pseudo equilibrium ligand concent ration equimolar to Al-13. Below this concentration, salicylate forms monodentate complexes with the charged aluminum sites, decreasing the electrostatic repulsion between Al-13 particles. A densification of th e aggregates is evident by an increase of the apparent fractal dimensi on from 1.8 to 2.9. No dissolution was observed in this concentration range. Above this ligand concentration, excess adsorption of salicylat e causes charge reversal, and dissolution of the aggregates, in the fo rm of soluble complexes and small clusters was observed. The consequen ces were a size reduction and loosening of the aggregates. In aquatic media, such radical in situ changes are able to strongly influence the transport of colloids and associated species.