Condensation vs cavitation in water: A simulation study

Abstract

Condensation and cavitation in water play a crucial role in industry and atmospheric science. We employ molecular dynamics to investigate and compare both nucleation phenomena at 450 and 550 K, taking cavitation data mostly from our recent study [Lamas et al., J. Chem. Phys. 158, 124504 (2023)]. We obtain interfacial free energies across a wide range of supersaturation through direct coexistence, seeding, and, using a novel approach, also through spontaneous nucleation simulations. The consistency between these methods supports the validity of Classical Nucleation Theory even for nuclei as small as two molecular diameters in radius. Condensation at 550 K occurs several orders of magnitude faster than at 450 K due to the lower interfacial free energy. Unlike Lennard-Jones systems [Sanchez-Burgos et al., Phys. Rev. E 102, 062609 (2020)], cavitation and condensation are not governed by the same interfacial free energy trend. For condensation, interfacial free energy is nearly constant at 550 K and increases slightly at 450 K with nucleus size. For cavitation, in contrast, it decreases at both temperatures, leading to a higher cavitation rate. The kinetic pre-factor, influenced by the parent-phase density, further enhances the cavitation nucleation rate. Finally, the orientational ordering of interfacial molecules weakens with temperature and curvature, but no clear link between molecular structure and interfacial free energy is found. Our findings provide a comprehensive perspective on the thermodynamic and molecular factors governing nucleation in water, bridging the mechanisms of condensation and cavitation across different temperatures.