Relaxation Dynamics of Liquid Sulfur Across the λ-Transition

Liquid sulfur exhibits the famous λ-transition at T = 432 K, changing from a liquid mainly consisting of eight-membered rings into a liquid with chains of different lengths. This transition is accompanied by an increase in viscosity that reaches four orders of magnitude. We present a neutron-scattering study conducted throughout the transition to elucidate the slow relaxation dynamics. The data are analyzed within the frequency domain and, after Fourier transformation, in the time domain as well. The relaxation dynamics between 1 ps and 140 ps deviate strongly from simple exponential decay and can be accurately described as stretched exponential decay. The relaxation times demonstrate a change to faster dynamics above the transition at a wave vector corresponding to nearest-neighbor distances. At smaller wave vectors, however, and hence greater length scales, the relaxation times increase with an increasing temperature, evidencing a significant change in dynamics. The Q-dependence of the relaxation rate above the λ-transition agrees with predictions for polymer melt dynamics. The relaxation dynamics at these length scales are dominated by chain-like structures, and the observed polymer-like dynamics might be the microscopic origin of the increase in viscosity.