Opposed flow focusing: evidence of a second order jetting transition

TL;DR

This paper introduces a new microfluidic opposed-flow geometry that enables a second order jetting transition, producing sub-micron emulsions and colloidal clusters, unlike traditional coflowing methods.

Contribution

The authors present a novel opposed-flow microfluidic design that achieves a second order jetting transition, allowing for finer emulsions than conventional methods.

Findings

Jet radius vanishes as a power law at critical pressure.

Achieved sub-micron silicone oil emulsions.

Produced colloidal clusters from tiny droplets.

Abstract

We propose a novel microfluidic "opposed-flow" geometry in which the continuous fluid phase is fed into a junction in a direction opposite the dispersed phase. This pulls out the dispersed phase into a micron-sized jet, which decays into micron-sized droplets. As the driving pressure is tuned to a critical value, the jet radius vanishes as a power law down to sizes below 1 $\mu$m. By contrast, the conventional "coflowing" junction leads to a first order jetting transition, in which the jet disappears at a finite radius of several $\mu$m, to give way to a "dripping" state, resulting in much larger droplets. We demonstrate the effectiveness of our method by producing the first microfluidic silicone oil emulsions with a sub micron particle radius, and utilize these droplets to produce colloidal clusters.