Liquid polymorphism, density anomaly and H-bond disruption in an associating lattice gases

TL;DR

This study explores how hydrogen bond distortions and proton degeneracy affect the thermodynamics of a minimal associating liquid model, revealing persistent liquid phases and density anomalies despite these modifications.

Contribution

It demonstrates that liquid phases and density anomalies remain unaffected by bond distortion or proton degeneracy, and links hydrogen bond density reduction to density anomalies.

Findings

Presence of two liquid phases persists under modifications.

Density anomaly correlates with a steep reduction in hydrogen bond density.

Increasing degeneracy lowers critical temperatures and steepens the coexistence line.

Abstract

We have investigated the effects of either distorting hydrogen bonds or removing proton degeneracy on the thermodynamic properties of a minimal model for associating liquids. The presence of two liquid phases and a density anomaly is unaffected in both cases. Increasing the degeneracy of bonded structures leads to lower temperature critical points and a steeper liquid-liquid coexistence line, implying a low density liquid of larger entropy. Analysis of the hydrogen bond net accross the phase diagram indicates that the density anomaly is accompanied by a steep reduction of hydrogen bond density, which introduces a restriction on a correlation which has been preconized long ago. This feature is present independent of bond distortion or of the presence of proton entropy.