Oppositely charged drops fail to coalesce above a critical field strength, despite the attractive force between opposite charges1.  Here we report a technique to externally control the extent to which charged droplets are allowed to coalesce. For sufficiently low conductivities, the degree of coalescence of water drops in oil depends sensitively on the applied field strength and droplet charge. Strikingly, in this regime the size of the daughter droplet is independent of the drop conductivity. We present evidence that the charge transfer is instead dominated by convection during the capillary-driven penetration of a vortex into the larger drop. Moreover, we demonstrate that the observed daughter droplet size accords with a model based on a balance between capillarity and electrostatic repulsion.  The results presented here should affect our understanding of any process involving charged liquid drops, including de-emulsification, atmospheric conduction and lab-on-a-chip manipulations.1Ristenpart et al., Nature 461, 377 (2009).

Coalescence on command: Electrically modulated partial coalescence of oppositely charged drops

241st National Meeting (2011)

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