Anomalous light scattering in liquid sulfur at the polymerization transition

Abstract

An anomalous increase of the forward light scattering in liquid sulfur is reported to occur in the 158-169 degrees C in which other physical properties of the liquid also show an anomalous behavior. The light scattering increases abruptly between 158 degrees C and 161 degrees C and then decreases and disappears at 169 degrees C, paralleling the behavior of the viscosity and the specific heat. The anomalous scattering effect is explained in terms of composition fluctuations generated at the onset of the ring-chain equilibrium transition which produce dielectric constant fluctuations. Following the theoretical model of polymerization developed by Tobolsky, it is proposed that these composition fluctuations may be produced by the peculiar dependence of the polymerization process on the temperature. The effect of thermal gradients is taken into account to explain the spatial distribution of the observed light scattering. It is shown how the anomalous light scattering can apparently increase the measured value of the absorption coefficient of the liquid. It is also discussed how it can be used to measure the polymerization temperature of liquid sulfur or similar systems.