Temperature evolution of the compressibility and correlation length in the vicinity of the lambda transition in sulfur

When heated above 159°C, the molecular liquid sulfur suddenly undergoes a partial and reversible polymerization transition, a phenomenon known as the “lambda transition” (λ-T). Despite the large number of experimental and theoretical studies devoted to this long-standing topic, the nature and origin of the lambda transition in sulfur are still elusive. The aim of this proposal is to accurately measure the temperature dependence of the isothermal compressibility KT and coherence length ξ in the vicinity of the lambda transition using small angle X-ray scattering (SAXS). This will be the first direct determination of the T dependence of KT and ξ that will, in turn, provide invaluable information on the underlying microscopic mechanism of the puzzling lambda transition. In particular, is there a diverging correlation length near the lambda transition?