Breaking of an emulsion under an ac electric field.

By using microfluidic chips, we investigate the stability regarding coalescence of droplet pairs under an electric field as a function of drop separation and ac field intensity. Three different regimes are found: stable, coalescence, and partial merging. From this, we identify the two breaking scenarios of a one dimensional train of droplets: in one case the coalescence front propagates; in the other case, in which pairs belong to the partial merging regime, the coalescence front can become heterogeneous. From these findings, we can propose a destruction mechanism for a macroscopic emulsion, which includes the packing condition for which total and immediate destruction is effective.