H-bond and glassy state formation. A structural and dynamic study applied to aqueous solutions

Abstract

Aqueous electrolytic solutions MX·RH 2O, especially with LiCl as solute, are good at forming a glass. At some specific concentrations, compound formation can be bypassed on cooling the system. This occurs when the hydration number is such that the solution has lost the characteristic behaviour of water. Structural relaxation can be analysed easily in the three thermodynamic states: liquid, metastable (supercooled liquid) and out of equilibrium (glass). The local structural relaxation is given by neutron spin echo spectroscopy. The structural evolution can be followed efficiently also using neutron scattering. Indeed using isotopic substitution on nearly all the elements of the material Li, Cl and D we can derive the evolution of the short, medium and long range order in the three thermodynamic states. Correlated to the strong slowing down of the structural relaxation, is the ability of the supercooled and glassy states to construct characteristic H-bonded local configurations.