Structural relaxation in supercooled glass-forming solutions: a neutron spin-echo study of LiCl,6D2O

Abstract

We have performed neutron spin-echo measurements on the supercooled glass-forming system ⁷LiCl,6D₂O above its glass transition temperature (T_g=135 K). This investigation has permitted us to determine the time dependence of the density correlation function phi (Q, t) between 2 ps and 2 ns at the maximum of the structure factor (Q=1.9 AA^-1). We have shown for the viscosity, the existence of two temperature domains limited by two critical temperatures (fixed points). This crossover from the stable liquid to the metastable liquid might be related to a change in the multiplicity of the microscopic interactions. In this study we show that the dynamics of the structural relaxation is consistent with the two scaling laws of the viscosity. Both the average relaxation time and the stretched exponential behaviour indicate a crossover regime around 210 K. However, the scaling of the density correlation function differs, in the lower-temperature regime, from the scaling of the shear viscosity. For the supercooled liquid dynamics, the results are more or less correlated to the mode-coupling theory.