Aluminum Polyphosphate Thermoreversible Gels: A Study by31P and27Al NMR Spectroscopy

摘要: Abstract The formation of thermoreversible gels from aqueous aluminum polyphosphate solutions was previously assigned to hydration-dependent interionic associations, but these were not elucidated. In the present work, aluminum-phosphate interactions examined by 31 P- and 27 Al-NMR spectroscopy gels, at various P/Al ratios temperatures. fraction phosphate groups actually involved in sol–gel transition is small, as evidenced comparison spectra temperatures, which only minor spectral changes are associated with gel formation. Chemical responsible for network mainly Al- (H 2 O) 4 (PO 3 ) groups, ligands chain-ends. Within a large total found hexaquoaluminum ions, spectra; on other hand, P-NMR show that most ions associated. These data indicate bonding bridging involve both inner- outer-coordination sphere interactions. former depend ligand exchange reactions half-life order magnitude few seconds, explains time dependence transformations, this system.