Are nucleation bubbles in a liquid all independent?

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.