Estimation of bubble cavitation rates in a symmetrical Lennard-Jones mixture by NVT seeding simulations

Abstract

The liquid-vapour transition starts with the formation of a sufficiently large bubble in the metastable liquid to trigger the phase transition. Understanding this process is of fundamental and practical interest, but its study is challenging because it occurs over timescales that are too short for experiments but too long for simulations. The Seeding method estimates cavitation rates by simulating a liquid in which a bubble is inserted, thus avoiding the long times needed for its formation. In one-component systems, in the NpT ensemble the bubble grows or redissolves depending on whether its size is larger or smaller than the critical size, whereas in the NVT ensemble the critical bubble can remain in equilibrium. Provided that a good criterion is used to determine the bubble size, this method, combined with Classical Nucleation Theory (CNT), gives cavitation rates consistent with those obtained by methods independent of CNT. In this work, the applicability of NVT Seeding to homogeneous cavitation in mixtures is demonstrated, focusing on a partially miscible symmetrical binary Lennard-Jones (LJ) liquid at a temperature within the mixing regime. At the same stretching pressure, cavitation rates are higher in the binary than in the pure liquid due to the lower interfacial free energy of the mixture. Curiously, the cost of creating a bubble is similar in the pure and binary LJ liquids at the same metastability, \Delta \mu/\Delta \mu_{spin}, with \Delta \mu being the difference of chemical potential between the metastable liquid and coexistence, and \Delta \mu_{spin} between the spinodal and coexistence.

The water cavitation line as predicted by the TIP4P/2005 model

“…The lowering of γ by moving away from coexistence is a common feature with other systems like the Lennard-Jones fluid in the cavitation/condensation transition [28][29][30]33 or ice nucleation in water. 45,67 In our case, both the curvature of the interface and the pressure of the surrounding fluid change by moving away from coexistence.…”

“…Computer simulations can bridge this gap, and they have been extensively used to study cavitation in model systems like the Lennard-Jones fluid. [26][27][28][29][30][31][32][33] By contrast, simulation work for water cavitation is more scarce, due to the technical difficulty of studying a rare event like cavitation-which requires the use of special simulation methods-in a costly system from a computational point of view due to the presence of electrostatic interactions. Reference 3 pioneers in the simulation work on water cavitation.…”

Does Maxwell's hypothesis of air saturation near the surface of evaporating liquid hold at all spatial scales?

“…2023; Lamas et al. 2023). Since cavitating bubbles are created with zero radii, Tolman's length – no matter how small – may affect the whole ‘trajectory’ of their growth.…”

“…The asymptotic structure of the solution of the two models should be similar, and the results obtained in the present paper should make the analysis of the Enskog-Vlasov equation much easier. (vii) Note that, strictly speaking, the surface tension depends on the drop's curvature (Tolman's effect), which can have a profound influence on, say, cavitation (Menzl et al 2016;Magaletti, Gallo & Casciola 2021;Aasen et al 2023;Lamas et al 2023).…”

Special Topic Preface: Nucleation—Current understanding approaching 150 years after Gibbs

“…They find consistency with the classical nucleation theory, direct molecular dynamics, and seeding but not with FFS calculations. Lamas et al 49 demonstrate the applicability of the seeding technique in the (N, V, T) ensemble, combined with the classical nucleation theory (CNT), to investigate cavitation rates in a symmetric and partially miscible binary Lennard-Jones mixture. They report good agreement with the predictions based on CNT-independent methods and find that the energetics of bubble formation is similar for the binary and pure liquid cases when computed at the same measure of metastability.…”