Brillouin-scattering study of the liquid-glass transition in supercooled aqueous lithium chloride solutions: Generalized hydrodynamics and mode-coupling analyses

Abstract

Brillouin scattering in aqueous LiCl solutions was investigated in the concentration range 5–36 mol % at temperatures between 375 and 78 K. The polarized spectra were found to be accurately described by generalized hydrodynamics with a single-relaxation-time structural-relaxation process. The relaxation times obey the Arrhenius relation above ∼200 K with activation energies between 2.5 kcal/mol at 36% and 6 kcal/mol at 5%. The transverse-acoustic mode that was observed in the depolarized spectra was qualitatively analyzed with a simple viscoelastic form for the transverse-current correlation function. The polarized spectra were also compared to preliminary predictions of the mode-coupling theory as formulated by Bengtzelius et al., and showed qualitative agreement but significant quantitative disagreement. Both the LA and TA sound velocities exhibit discontinuous slope changes in their temperature dependences at the glass transition.