Drop size control in electro-coflow

Abstract

We introduce electro-coflow as a way to generate emulsion drops with an average size that can be larger, comparable, and smaller than the smallest geometric feature of the device. The method relies on using three immiscible liquids, two of them having a finite electrical conductivity. There are three regimes of operation that allow the steady generation of drops: dripping, electro-dripping, and an electrically dominated regime. We transit from one to the other by increasing the applied voltage and describe the changes in drop size by balancing the relevant forces in each regime.

Capillary‐Based Microfluidics—Coflow, Flow‐Focusing, Electro‐Coflow, Drops, Jets, and Instabilities

“…In addition, microfluidic approaches based on surface acoustic waves and drop condensation and nucleation have neither been used to make uniformly small drops. To overcome drop size limitation in microfluidics, tip streaming induced by reduced surface tension and electro‐coflow may be employed.…”

Fluid Flows for Engineering Complex Materials

“…For liquids with electric conductivities of the order of 10 −3 S∕m, d min is of the order of 1 μm, but if K takes values of the order of 1 S∕m, then d min becomes of the order of 10 nm. On the other hand, since these highly charged droplets form upon the microjet breakup, the size distribution of these droplets is not as tight and monodisperse as droplets formed from an orifice (dripping), although there are regions within the (q, V) operating regime in which rather standard deviations from the droplet's mean size are smaller than 10%, as shown in the works by [34][35][36], among others.…”

“…Also, the values of liquid flow rates for electrodripping are usually much larger than those used in electrosprays, which leads to the generation of much larger droplets. Other modes of electrodripping are actually under investigation [36,[39][40][41].…”

Surface tension effects on submerged electrosprays

“…This produces disturbances in the electrical field surrounding the Taylor cone, which has crucial consequences to its stability. Gundabala et al 17,26 solved such situation by implementing the electrospray in a cylindrical co-flow system consisting of concentric capillaries.…”

“…It is nonetheless a problem that can be easily solved using a continuous external liquid flow as is the case in Gundabala et al 17 and others. 25,26 …”