Structural relaxation in the aqueous solution LiCl ⋅ 6D2O by quasielastic neutron scattering

Abstract

The aqueous LiCl solution is often regarded as a model to study water, in particular, below the melting point. We report on the structural relaxation dynamics of a LiCl ⋅ 6D2O solution through quasielastic neutron scattering. Density fluctuations were measured at the structure factor peak of the solution over a wide temperature range from around 240 K up to 345 K in the frequency domain. At this wave vector the relaxation process is sensitive to collective density fluctuations on a next-neighbor distance. For all temperatures the Fourier transformed intermediate scattering function is well described by a stretched exponential decay function covering about two orders of magnitude in the ps time scale. Around T ≈ 300 K the relaxation times evidence a change from a high-temperature Arrhenius to a super-Arrhenius behavior upon cooling, similar to other glass forming molecular liquids. This transition can be described through an increasing activation energy, which is the result of an onset of cooperative particle dynamics. This enhanced slowing down in dynamics indicates the beginning of solidification in the molecular liquid at a temperature above the melting point of bulk water.