Nucleation and Cavitation of Spherical, Cylindrical, and Slab-Like Droplets and Bubbles in Small Systems
Luis G. MacDowell, Vincent K. Shen, Jeffrey R. Errington
We employ a capillary drop model and obtain analytical results that allow us to predict the shape of subcritical isotherms inside the coexistence region of small finite-sized systems. We find that depending on system size, there exist different sequences of structural transitions between condensed or cavitated domains. For large systems, we find a sequence of transitions involving spherical, cylindrical and slab-like domains. As the system size decreases, those domains with larger curvature are gradually suppressed, such that condensation (or cavitation) involves a transformation between a homogeneous fluid and a cylindrical domain, or between a homogeneous fluid and a slab-like domain. Eventually, for very small system sizes, no condensation occurs at all, and a full mean field van der Waals loop is observed. These qualitative predictions are tested against computer simulation results for the Lennard--Jones system, and good agreement is found. For very small system sizes, we observe that the simulated isotherms closely resemble the mean-field isotherm up to the spinodal points and also inside the 'unstable' portion of the van der Waals loop. Employing an accurate mean-field equation of state, together with surface tensions obtained from simulation, we find that the capillary drop model provides excellent agreement down to very small system sizes. We discuss the nature of the extrema of the finite size loops and show that they are more related to bubble and dew points than to the spinodal. Our results are of relevance to phase transitions in nanopores and provide first order corrections to nucleation energies measured in finite closed systems.
, Shen, V.
and Errington, J.
Nucleation and Cavitation of Spherical, Cylindrical, and Slab-Like Droplets and Bubbles in Small Systems, Journal of Chemical Physics
(Accessed May 28, 2023)