Observation of the structure and dynamics of water in aqueous alkaline chloride solutions under gigapascal pressure by neutron scattering

Jing, Z.*; Yamaguchi, Toshio*; Hattori, Takanori   ; Yamada, Takeshi*; Tamatsukuri, Hiromu   ; Matsuura, Masato*; Zhou, Y.*

We conducted high-pressure neutron diffraction and quasielastic neutron scattering on a series of aqueous alkaline chloride solutions and clarified that the pressure- and ion-induced modifications to the water structure and diffusion originate from distinct physical mechanisms. Applying gigapascal pressure transforms the tetrahedral hydrogen-bonded network structure of water into a dense random packing, due to the collapse of the second and third coordination shells and an increase in the number of interstitial water molecules, regardless of the ion species. On the contrary, dissolved ions disturb the second shell but preserve the inherent tetrahedral network structure of water at ambient pressure. The anomalous trend of water diffusion from Li to Cs under the ambient conditions disappears under the gigapascal pressure, and all the ions show a behavior of structure-making ions.