Size of the smallest jet drops from bursting bubbles
In plain words
When a bubble bursts at a liquid surface, a thin jet shoots up and breaks into tiny droplets that carry sea salt and microbes into the air. How small the first droplet can be, as a function of liquid properties and bubble size, is disputed.
Precise statement
For a bubble of radius $R_b$ bursting at the free surface of a liquid with viscosity $\mu$, density $\rho$ and surface tension $\sigma$, the first jet-drop radius $r_d$ depends on $\mathrm{Oh} = \mu/\sqrt{\rho \sigma R_b}$ and $\mathrm{Bo} = \rho g R_b^{2}/\sigma$. Determine the scaling of $r_d/R_b$ near the critical Ohnesorge number $\mathrm{Oh}*$ (a few times $10^{-2}$, approximately) at which the jet is thinnest, and the minimum $r_d$ as $\mathrm{Bo} \to 0$.
What would settle it
High-speed imaging and simulations resolving $r_{d}$ over a decade in Oh around $\mathrm{Oh}*$ with $\mathrm{Bo} < 10^{-2}$.
Status in the literature
Competing scaling laws proposed since 2017 differ near Oh*.