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

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, τ_s, 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.