Equilibrium between two liquid structures in water: explicit representation via significant liquid structure theory

Abstract

We assumed that liquid water was mainly composed of two hydrogen-bonded liquid structures between which the transformation occurred resulting in the dynamic equilibrium of them. Implanting the significant liquid structure theory directly to a general thermodynamic expression for the mixture of certain two species, which are in equilibrium with each other, we obtained a partition function for the above water model. Using this method, we could represent two liquid structures of water more explicitly in the partition function compared to the previous work. The number of water molecules ( q) in a collective motion (the size of flickering cluster in liquid water) for the transformation between two liquid structures has been difficult to know, and it was estimated in this work by investigating which cases showed Arrhenius type of the transformation. This value was also confirmed by considering the temperature-dependent compressibility of water and it was roughly 10–25 (more exactly 15–20). Using the induced partition function with q=20, various properties of water were calculated and they showed a good agreement with experimental data. Especially, the density maximum at 4 °C was calculated without the parameter fitting intended for it.