Energetics of the contact minimum configuration of two hard spheres in water

Highlights: • A geometric approach accounts for two-cavity contact minimum energetics. • The driving force is the decrease in water accessible surface area. • This leads to a significant gain in translational entropy of water molecules. • The process is exothermic. Changes in thermodynamic functions for the formation of the contact minimum, cm, configuration of two hard spheres (i.e., two cavities) are calculated by means of a physically-based geometric approach over a large temperature range. The decrease in water accessible surface area due to cm formation causes a gain in translational entropy of water molecules, driving the process. This produces a negative Gibbs energy change, whose magnitude slightly increases with temperature. The process is exothermic due to the decrease in hydration shell size, but this enthalpy change is entirely compensated by a corresponding entropy contribution.