Exploring the minimum flow rate limit in electro co-flow

Abstract

Controlled generation of micron and sub-micron sized drops continues to be of strong interest for the scientific community due to the variety of applications in fields like cosmetics, food industry, and drug delivery among others. By flowing two immiscible liquids into a glass-based microfluidic device, we can make emulsion drops with a minimum size of the order of the tip size. Adding an external electric field, similarly to what it is done in the classical electrospray, allows the generation of droplets with sizes below the smallest geometrical characteristic of the device. In this work, we are focused on the region of small flow rates. There is a minimum flow rate below which a cone-jet cannot be formed regardless of the applied voltage. This limit marks the minimum drop size that could be generated. We study pairs of liquids with different viscosities and conductivities using high speed microscopy and current measurements. With these data we will try to understand this limit and the characteristics of the modes observed in this region.