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 [ R e = O ( 10 1 - 10 3 ) , W e = O ( 10 2 - 10 3 ) ] with the aid of high-speed photography and image analysis. Above a critical impact parameter, R e 1 / 2 W e 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 ∼ W e - 1 / 4 .