Vibrational dynamics and structural relaxation in aqueous electrolyte solutions in the liquid, undercooled liquid and glassy states

Abstract

In very concentrated aqueous electrolyte solutions, the competition between dipolar and ionic forces and most of the system properties, are finely monitored by the concentration. For LiCl, RH2O (R being the number of water moles per mole of salt) two domains of concentration exist around even hydration numbers R = 6 and R = 4, which can be reversibly undercooled from the liquid to the glassy state. At other concentrations, for [MATH], metastability is achieved only in a restricted temperature range. The collective behaviour as well as individual atomic motions, have been studied by neutron inelastic scattering in the metastable state of LiCl, 6H2O and LiCl, 4H2O down to the glass transition. The study of the structural relaxation by neutron spin echo (NSE) allows us to show that the temperature dependence of the response of the system follows a scaling relation with a cross-over at a phase transition present in the liquid phase.