Glasslike Behavior in Aqueous Electrolyte Solutions

TL;DR

This study reveals that aqueous electrolyte solutions exhibit glasslike behavior with decoupled rotational and translational motions, unifying previous conflicting observations from viscosity, NMR, and infrared spectroscopy.

Contribution

The paper introduces optical Kerr-effect and dielectric relaxation measurements to distinguish rotational and translational water motions, revealing glasslike dynamics in electrolyte solutions.

Findings

Electrolyte solutions show decoupled rotational and translational motions.

Solutions behave like supercooled liquids near a glass transition.

Unified explanation for viscosity, NMR, and infrared spectroscopy data.

Abstract

When salts are added to water, the viscosity generally increases suggesting the ions increase the strength of the water's hydrogen-bond network. However, infrared pump-probe measurements on electrolyte solutions have found that ions have no influence on the rotational dynamics of water molecules implying no enhance-ment or breakdown of the hydrogen-bond network. Here we report optical Kerr-effect and dielectric relaxa-tion spectroscopic measurements, which have enabled us to separate the effects of rotational and transitional motions of the water molecules. These data show that electrolyte solutions behave like a supercooled liquid approaching a glass transition in which rotational and translational molecular motions are decoupled. It is now possible to understand previously conflicting viscosity data, nuclear magnetic resonance relaxation, and ultrafast infrared spectroscopy in a single unified picture.