Rectifying jet breakup by electric forcing

Droplet microfluidics is a technology used in a wide range of applications relying on the production of droplets uniform in size. Monodisperse droplets are produced by a flow focusing junction in the dripping regime. Increasing the throughput of production by increasing the flow rate eventually leads to a transition from the dripping to the jetting regime. A fluid jet is unstable to external perturbations resulting in a polydisperse emulsion. Imposing external perturbations on a jet can alter the break-up dynamics resulting in a more monodisperse emulsion. Electric fields have been shown to be a method which offers a fast way to affect the behaviour at the flow focusing junction in the dripping regime.

We experimentally investigate how an amplitude modulated electric field imposes a local perturbation on a hydrodynamic jet in a flow focusing junction. We manufactured four electrodes symmetrically around the flow focusing junction. By modulating the electric field applied to the upstream electrodes, we impose an interfacial perturbations, controlled externaly. We investigate the effect of the modulation frequency and amplitude on the break-up frequency of the jet and find that the monodispersity of the produced droplets is increased when the modulation frequency is close to the natural break-up frequency of the jet. Further we find that this increase relates directly to the amplitude of the electric field. We are able to decrease the standard deviation of the distrubtion of the droplet diameter a 3.5-fold as compared to unperturbed jet.

The results indicate that perturbing a jet by amplitude modulated electric fields is an efficient method to increase the monodispersity of droplets produced in the jetting regime. This method could be further integrated in high-throughput droplet production systems.