Effect of pressure on proton spin-lattice relaxation in several concentrated aqueous electrolyte solutions

Abstract

The pressure dependences of the proton nuclear spin-lattice relaxation times of the water molecules in concentrated 4.5 m aqueous solutions of CsBr, RbBr, KBr, LiCl, CaCl 2, and LaCl 3 have been measured at 25°C up to 2.5 kbars. The proton spin-lattice relaxation times of the aqueous solutions of the structure breaking electrolytes, CsBr, RbBr, and KBr, are longer than that of pure water and decrease with increasing pressure. For all these three solutions the pressure dependence of T 1 is very similar; however, under the same pressure and at the same temperature the structure breaking ability of the cations increases as K + < Rb + < Cs +. In concentrated solutions of LiCl, CaCl 2, and LaCl 3, the proton spin-lattice relaxation times, which are all shorter than T 1 of pure water at the same temperature, increase first to a maximum and then begin to decrease with increasing pressure. The structure-making ability of the cations increases as Li + < Ca ++ < La +3 which is parallel to the increase in charge-to-radius ratio of the cations.