To grate a liquid into tiny droplets by its impact on a hydrophobic microgrid

We report on experiments of drop impacting a hydrophobic microgrid of typical spacing a few tens of micrometers. Above a threshold in impact speed, liquid emerges to the other side, forming microdroplets of size about that of the grid holes. We propose a method to produce either a monodisperse spray or a single tiny droplet of volume as small as a few picolitres corresponding to a volume division of the liquid drop by a factor of up to 10(5). We also discuss the discrepancy of the measured thresholds with that predicted by a balance between inertia and capillarity. (C) 2009 American Institute of Physics. [doi:10.1063/1.3275709]