The Droplet Evaporation/Condensation Transition in a Finite Volume

A fluid in the NVT ensemble at T less than the critical temperature T c and ρ = N/V somewhat in excess of ρ coex (1) (density of the saturated gas in the gas-liquid transition) is considered. For V → ∞, a macroscopic liquid droplet coexists with surrounding saturated gas according to the lever rule. For finite V, droplets can only exist if they exceed a minimum size. A (rounded) first order transition of the system occurs when the droplet evaporates into the supersaturated gas. Simulation evidence for this transition is given for a Lennard-Jones model and interpreted by a phenomenological theory. At the transition, the chemical potential difference µ t – µ coex scales like L - d/(d+1) for a cubic volume V = L d in d dimensions, as L → ∞.