Dynamic light scattering study of ionic KNO3-Ca(NO 3)2 mixtures

Abstract

We report spontaneous Brillouin and photon correlation spectroscopic results on the dynamics of the local density fluctuations in the ionic mixed salt xKNO3·Ca(NO3)2 with molar ratios 2:1, 3:2, and 1:1. For these mixtures, the density relaxation function g(t) changes from a stretched exponential (β = 0.47) near the glass transition temperature Tg, to an exponential (β = 1) form at high temperatures, whereas the composition dependence of the relaxation time τ reflects mainly differences between the Tg values. The 3:2 fragile glass (Tg = 60°C) is one of the few examples where g(t) is now known from the glass-like (60-90°C) to the liquid-like (T > 100°C) region through the application of various dynamic scattering techniques. The τ(T) and the evolution of the width β of the distribution are discussed in terms of the physical pictures implied by current models of the liquid and glass transition phase. © 1991 American Institute of Physics.