Rectifying jet breakup by electric forcing

Abstract

The high-throughput production of monodisperse droplets is paramount in most of the applications in droplet microfluidics. In a flow-focusing junction, a straightforward way to increase droplet production rate is to increase the flow rates. However, at a critical flow velocity, the droplet monodispersity breaks down due to a transition from the dripping to the jetting regime. As a result, a much more polydisperse droplet population is generated. The change from monodisperse to polydisperse droplet production emerges from the intrinsic properties of the instabilities of jets. In the jetting regime, droplet pinch-off is governed by a convective instability which amplifies random noise when traveling down the jet leading to an irregular breakup.We show that with the use of an amplitude-modulated electric signal, we select the breakup frequency of the jet. Matching the perturbation frequency close to the natural breakup frequency of the jet, we increase the monodispersity of the droplet population. This method is applicable to droplet production at a high throughput, that is, beyond the dripping to jetting threshold, including an active control since the frequency, and hence droplet sizes, are determined by the forcing frequency.

Drop-On-Demand Microdroplet Generation under Charge Injection by Corona Discharge

“…In the realm of microfluidic technologies, electric field-controlled methods have gained popularity for their precision and eco-friendliness in generating microdroplets. − The interaction between an electric field and the surface charges (including polarized and free charges) induced by the differences in electrical properties between the continuous and dispersed phases plays a crucial role. , This interaction generates additional electrical forces, known as Maxwell stresses, at the fluid interface. Appropriately distributing the electric field within microfluidic devices can harness these Maxwell stresses to promote interface instability, facilitating the breakup of droplets from the dispersed phase .…”