Glasslike behavior in aqueous electrolyte solutions

Abstract

When salts are added to water, generally the viscosity increases, suggesting that the ions increase the strength of the water's hydrogen-bond network. However, IR pump-probe measurements on electrolyte solns. have found that ions have no influence on the rotational dynamics of water mols., implying no enhancement or breakdown of the hydrogen-bond network. Here, the authors report optical Kerr effect and dielec. relaxation spectroscopic measurements, which have enabled them to sep. the effects of rotational and transitional motions of the water mols. These data show that electrolyte solns. behave like a supercooled liq. approaching a glass transition in which rotational and translational mol. motions are decoupled. It is now possible to understand previously conflicting viscosity data, NMR relaxation, and ultrafast IR spectroscopy in a single unified picture. (c) 2008 American Institute of Physics.