The structure and properties of vicinal water: Lessons from statistical geometry

Abstract

In earlier works the properties of water near surfaces (vicinal water) have been shown to differ from those of the bulk. For instance, the density of water in 14 nm diameter silica pores is 3% lower that of the bulk, while the heat capacity is 25% greater than that of the bulk. Etzler has proposed a statistical thermodynamic model for vicinal water which has predicted previously unmeasured thermodynamic properties of vicinal water. This model is based on earlier calculations by Stey, who found the distribution of single particle enthalpies in liquid water to be bimodal. Here we explore the microscopic implications of Stey's distribution. Specifically, it is found that the distribution of molecular (Voronoi) volumes is bimodal in SPC/E water at 298 K. This result is consistent both with the earlier work of Stey and with Röntgen's hypothesis (1892), which states that water exists in “bulky” and “dense” states. Furthermore, the results of this work are probably relevant to the understanding of liquid water at negative pressures and at supercooled temperatures.