Does the State of the Art Knowledge on Water Structure Require Thinking About a New Thermodynamic Framework for Aqueous Solutions?

Abstract

In recent decades, old ideas of liquid water as a mixture of two distinct states, even at room temperature, resurged fueled by x-ray results that can be interpreted as fluctuating patches of high-density and low-density liquids. Isosbestic points in vibrational spectra indicate more strongly and more weakly hydrogen-bonded molecules, not necessarily patches. Despite mutual agreement among the fractions of the two states obtained from these experiments and with thermodynamic (two-state) and molecular models, chemical (example: water auto-dissociation) and interfacial (example: water surface tension) properties varying with temperature and salt content currently show opposite trends with the postulated fractions, which can therefore not be reconciled with a simple mixing model of the two states, whereas some physical properties (example: water static dielectric constant) can. Consequently, if the tale of two liquids were to be ultimately accepted and thermodynamic models for aqueous electrolyte solutions would need to be revised, then a simple mixing model would be insufficient with high probability.