Physics (Internal)

Peculiar Thermodynamics of Liquid Polyamorphism

This event is part of the Biophysics/Condensed Matter Seminar Series.

“Liquid polyamorphism” is the existence of two alternative amorphous structures in a single-component liquid. Liquid polyamorphism is found or predicted in a broad group of materials, such as triphenyl phosphite, phosphorus, sulfur, cerium, germanium, silicon, silicon dioxide, and hydrogen, usually at extreme conditions. In particular, this phenomenon is hypothesized in metastable, deeply supercooled water. Structure of supercooled water is supposed to exhibit two forms, a low-density liquid or a high-density liquid. The existence of these two alternative structures could, at certain conditions, result in metastable liquid-liquid separation in pure water. In this presentation a phenomenological approach, based on a “chemical reaction” between two alternative amorphous strictures, is formulated to quantitatively describe the phenomenon of liquid polyamorphism. The first fundamental question to be addressed is the peculiar interplay between thermodynamics and kinetics: a system with two inter-convertible fluid structures can be viewed as a single-component fluid if the time of observation is much longer than the time of conversion. In the opposite limit (slow conversion) the system can thermodynamically be treated as a two-component fluid mixture. An equation of state with a thermodynamic constrain imposed by “chemical- reaction” equilibrium between two inter-convertible fluid structures generically describes, within the same model, all the possible fluid phases (e.g. vapor and two liquids), stability limits, and thermodynamic anomalies. The results are compared with the behavior of p o p u l a r atomistic waterlike models.