Speaker
Description
Charged water drops are more widespread than commonly acknowledged. For example, raindrops typically carry charges of order Q~1 pC, while routine pipetting in the laboratory produces drops with Q~50 pC. Here, we show that such modest charging can spontaneously generate periodic Coulomb fissions for evaporating water drops on lubricated surfaces. The drop periodically elongates over a timescale of seconds and subsequently emits small droplets with more than 60 successive cycles observed over 30 min. Interestingly, the underlying instability can be quantitatively predicted by a model taking into account two fissility thresholds: one marking the onset of drop elongation and another triggering fission. The drop shape undergoes a supercritical bifurcation that culminates in a fission where a fine liquid jet is expelled within microseconds, which disintegrates into 40-50 microdroplets. The phenomenon spans an extraordinary range of length scales (from millimetres to microns) and
time scales (hour to microseconds), with broad potential applications ranging from nanoscale fabrication to electrospray ionization.