NMR Relaxation Studies for Sodium and Potassium Ions and Water Molecules in Concentrated Aqueous Solutions of Dibutyl Phosphate

Abstract

Abstract The hydration and alkali-ion binding of an aggregate of the dibutyl phosphate (DBP) ion in its isotropic aqueous solution were investigated by measuring the nuclear magnetic relaxation times for 17O of H2O, and 23Na and 39K of hydrated alkaline metal ions at various temperatures. The relaxation rates for the 17O of H2O showed that the rotational motion of the water molecule is more restricted in the sodium system than that in the potassium system. Arrhenius plots also showed that the activation energy for the relaxation rate of the water molecule is larger in the sodium system. The dependences of the longitudinal relaxation rates for the alkali ions on the DBP concentrations in these systems showed that the sodium ion has an enhanced tendency, over the potassium ion, to interact with the dibutyl phosphate ion and to form ion-aggregates. Viscosity measurements showed that the appreciable restriction of the motion of the water molecules in DBP solutions corresponds to a great extent in the aggregation of DBP.