Fig. 3: Droplet size upon varying flow rates.

a Normalized bubble (air core) diameter \({d}_{b}/b\) versus \({k}_{1}\) for fixed \({k}_{2}\). Dots are experimental data, and the solid lines are the theoretical predictions of Eq. 1 with a multiplicative correction Factor ≈4. b Normalized oil (FC-40) droplet diameter \({d}_{o}/b\) vs. \({k}_{1}\) at different fixed \({k}_{2}\) values. c Normalized oil (FC-40) droplet diameter averaged over the investigated air pressure range \({\bar{d}}_{o}/b\) vs. \({k}_{2}\). d The ratio of the experimental production rate of hollow core double emulsion droplets, \({f}_{e}\), with the estimated rate of production of the resulting oil droplets, \(f={q}_{2}/{V}_{o}\), vs. \({k}_{1}\), at fixed \({k}_{2}\) values, the solid line stands for the constant value of 1. e Normalized shell thickness by the outer diameter of the hollow-core double emulsion, \(e/D\), plotted vs. the ratio \({q}_{2}/({q}_{1}+{q}_{2})\), the solid line is the linear line passing through the origin with a slope 1/6. Colors in (a), (b), (d) and (e) correspond to different \({k}_{2}\) values: \({k}_{2}=3.02\) (black); \({k}_{2}=2.27\) (red)\(;\) \({k}_{2}=1.81\) (blue); \({k}_{2}=1.42\) (green); \({k}_{2}=1.13\) (magenta)