Are nucleation bubbles in a liquid all independent?

TL;DR

This paper investigates the independence of nucleation bubbles in liquids, showing that spatially correlated bubbles form single density depressions, which impacts how bubble formation and liquid-to-vapor transition processes are understood and modeled.

Contribution

It introduces the concept of Low Density Regions (LDRs) as correlated bubble groups, altering the interpretation of nucleation events and improving modeling accuracy.

Findings

Correlated bubbles form single density depressions (LDRs).

LDRs should be counted as one event, not multiple.

Average number of LDRs relates to bubble-free probability.

Abstract

The spontaneous formation of tiny bubbles in a liquid is at the root of the nucleation mechanism during the liquid-to-vapor transition of a metastable liquid. The smaller the bubbles the larger their probability to appear, and even for moderately metastable liquid, it is frequent to observe several tiny bubbles close to each other, suggesting that they are not all independent. It is shown that these spatially correlated bubbles should be seen as belonging to one single density depression of the liquid due to fluctuations (called LDR for Low Density Region) and should be counted as one event instead of several. This has a major impact on the characterization of the bubble density in a liquid, with consequences (i) for understanding liquid-to-vapor transitions which proceed through growing and merging of these correlated bubbles, and (ii) for free energy profile and barrier calculations with molecular simulation techniques which require to convert the calculated size distribution of the largest bubble into the size distribution of any bubble. Remarkably, the average number of LDRs in a given volume simply relates to the probability of not having bubbles in the liquid.