Quasielastic neutron scattering study of dynamics of CaCl2 aqueous solution confined in Vycor glass

Abstract

Quasielastic neutron scattering was used to probe the diffusion of water molecules in 2.3 molal CaCl₂ solution confined in 100% hydrated Vycor glass in the temperature range of 220 to 260 K. We observed a gradual transition from the restricted diffusion regime at lower temperatures to unrestricted diffusion regime at higher temperatures. The diffusion parameters were compared with the data on pure water confined in Vycor available in the literature. We found that the effect of dissolved ions onto the diffusion dynamics of the water molecules in the solution was amplified by confinement by at least an order of magnitude compared to bulk form, even though the dissolved ions were found to have little effect on the spatial characteristics of the restricted diffusion process of water molecules. At 260 K, the local diffusion coefficient of water molecules in the H₂O–CaCl₂ confined in Vycor was only 6% of the value reported for pure water confined in Vycor.