Discriminative ionic capabilities on hydrogen-bond transition from the mode of ordinary water to (Mg, Ca, Sr)(Cl, Br)2 hydration

It has been a long pursuit to discriminate the ionic roles of mono- and di-valent salt solutions in modulating the hydrogen bonding network and solution properties. We attended this issue by examining the effect of concentrated YX2 (Y=Mg, Ca, Sr; X=CI, Br) solvation on O:H-O bonds transition from the mode of ordinary water to hydration in terms of the number fraction f(yx2) (C) and the segmental O:H-O bond phonon stiffness shift Delta omega(C) with C being the solute concentration. The invariant df(y)(C)/dC at C <= <0.05 suggests that the small Y2+ forms a constantly-sized hydration droplet with weak responding to interference of other ions because its hydrating H2O dipoles screen mostly its electric field. However, the number inadequacy of the highly-ordered hydrating H2O dipoles partially screens the large X. The X-<--> X- electrostatic repulsion weakens its electric field. The concentration-trend consistency of the f(yx2) (C), the solution conductivity sigma(yx2)(C), and surface stress (contact angle) theta(yx2)(C) for YX2 solutions clarifies their common origin of ionic polarization. However, the Jones-Dale notion disobedience of the viscosity eta(yx2)(C) suggests the dominance of the inter-ion repulsion. (C) 2019 Published by Elsevier B.V.