Temperature Dependence of the Pairwise Association of Hard Spheres in Water

Abstract

It is shown that the Gibbs energy change associated with the formation of the contact-minimum configuration of two hard spheres in water becomes more negative on increasing the temperature, at 1 atm, by extending the geometric approach previously developed [G. Graziano, Chem. Phys. Lett. 499, 79 (2010)]. This is because the decrease in water accessible surface area accompanying the association leads to a gain in translational entropy of water molecules. The process is exothermic, due to the release of some water molecules from the hydration shell to the bulk. This water reorganization is characterized by a complete enthalpy–entropy compensation and does not affect the Gibbs energy change.