Entropy crossover from molecular to macroscopic cavity hydration

The entropies of hydrating molecular and macroscopic non-polar surfaces differ in sign at room temperature, suggesting a size scale at which hydration transitions between these behaviors. Following a curvature expansion for the surface tension, we derive an expression for the radius of a cavity-like solute at which the solvation entropy is zero. This expression accurately predicts the crossover radii observed in a simulation/scaled-particle theory analysis of cavity solvation in water and n-hexane along their saturation curves. Our results indicate differences between water and organic solvents are encoded in the temperature dependence of the surface tension and its leading curvature correction.