Viscoelastic behavior corresponding to reptative relaxation times across the λ-transition for liquid elemental sulfur.

Abstract

Continued interest regarding the rheometric measurements of molten sulfur has persisted due to the need for industrial-scale transportation and handling of the material in a liquid phase. This has allowed for extended research developments to attain a fundamental understanding of the fluid. This work reports novel high temperature modulus data over the λ-transition region for liquid elemental sulfur, measured through the use of a modified Anton-Paar Modular Compact Rheometer 302. From these measurements, further insight was gained on the viscoelastic behavior and reptative relaxation times for liquid elemental sulfur. The slow relaxation time, τs, related to reptative behavior, was found to be between 0.24 s and 0.28 s at 190 °C. Utilizing the Maxwell relation, this was determined to correspond to an estimated viscosity range from 72 000 × 10-3 Pa s to 95 000 × 10-3 Pa s, which is in agreement with previous viscosity studies on liquid sulfur. A Cole-Cole plot of the experimental data also displayed characteristics of Debye-like relaxation, suggesting that the slow relaxation process was related to local S-S bond scission and recombination in sulfur chains and was not a relaxation coinciding with a polymeric chain mode. Finally, consecutive heating and cooling of the sulfur sample gave replicate values up to 210 °C on the third heating cycle, where an apparent structural change took place possibly due to cycling over the secondary transition, producing a thermal history, or sulfur reactions with trace impurities. This 210 °C temperature was found to have some recurrence within the literature.