Immiscible impact dynamics of droplets onto millimetric films

The impact of liquid droplets onto a film of an immiscible liquid is studied experimentally across a broad range of parameters [Re= O(10 ¹- 10 ³) , We= O(10 ²- 10 ³) ] with the aid of high-speed photography and image analysis. Above a critical impact parameter, Re^{1 / 2}We^{1 / 4}≈ 100 , the droplet fragments into multiple satellite droplets, which typically occurs as the result of a fingering instability. Statistical analysis indicates that the satellite droplets are approximately log-normally distributed, in agreement with some previous studies and the theoretical predictions of Wu (Prob Eng Mech 18:241–249, 2003). However, in contrast to a recent study by Lhuissier et al. (Phys Rev Lett 110:264503, 2013), we find that it is the modal satellite diameter, not the mean diameter, that scales inversely with the impact speed (or Weber number) and that the dependence is d_mod∼ We^{- 1 / 4}.