On the origin of the $\lambda$-transition in liquid Sulphur

TL;DR

This study introduces a new infrared photon correlation spectroscopy technique to investigate the lambda transition in liquid sulfur, revealing a chain relaxation process that clarifies its viscoelastic behavior.

Contribution

It presents a novel experimental method using infrared radiation to study sulfur's lambda transition, overcoming previous optical limitations and confirming the Maxwell relation's applicability.

Findings

Revealed a chain relaxation process with millisecond timescale.

Validated the Maxwell relation in liquid sulfur.

Explained the viscoelastic behavior during the lambda transition.

Abstract

Developing a novel experimental technique, we applied photon correlation spectroscopy using infrared radiation in liquid Sulphur around $T_\lambda$, i.e. in the temperature range where an abrupt increase in viscosity by four orders of magnitude is observed upon heating within few degrees. This allowed us - overcoming photo-induced and absorption effects at visible wavelengths - to reveal a chain relaxation process with characteristic time in the ms range. These results do rehabilitate the validity of the Maxwell relation in Sulphur from an apparent failure, allowing rationalizing the mechanical and thermodynamic behavior of this system within a viscoelastic scenario.