Rubberlike Dynamics in Sulphur above theλ-Transition Temperature

Abstract

The high-frequency acoustic dynamics of sulfur across the liquid-liquid, lambda transition has been studied using inelastic x-ray scattering. The combination of these high-frequency data with lower frequency, literature data indicates that liquid sulfur develops, in the high-temperature, polymeric solution phase, some characteristic features of a rubber. In particular, entanglement coupling among polymeric chains plays a relevant role in the dynamics of this liquid phase.

A Brillouin light scattering study of the λ transition in liquid sulphur

“…The experimental results confirm the hypothesis [18] that the large increase in shear viscosity during the transition does not correspond to a slowing down of the main structural relaxation, but rather to the onset of an additional very low frequency relaxation, to be found below 10 kHz. Such a feature should be related to the increasing polymer mass fraction in the melt, and specifically to entanglement coupling between sulphur polymer chains.…”

“…Results for the real part of the longitudinal elastic modulus in liquid sulphur from BLS measurements are reported in the top graph, compared with literature data from recent inelastic Xray scattering measurements [18] and various ultrasonic works in literature [6][7][8][9]. The imaginary part of the longitudinal elastic modulus is shown in the bottom graph.…”

“…The main structural relaxation time appears unchanged by the transition, so an additional relaxation must be hypothesized [18], contributing to viscosity as an additional term in the Maxwell relation :…”

“…If the main structural relaxation time τ s remains in the ps scale during the λ transition, the first contribution to viscosity will be always in the order of 10 -2 Pa·s and the large part of the viscosity in the same temperature region must be provided by the second term. Given the value of G ∞1 , τ r should be at least larger than 10 -4 s to obtain a viscosity of 100 Pa·s during the transition [18].…”

“…The BLS study of liquid sulphur in the λ transition region reported thereafter is thus expected to provide valuable information on the structural dynamics in liquid sulphur. The results of this work will be discussed together with ultrasonic spectroscopy (US) data available in literature [6][7][8][9], reporting values of the sound speed in the 0.5-150 MHz frequency region, and recent inelastic X-ray scattering (IXS) results [18], accessing the collective dynamics of liquid sulphur in the THz range.…”