Stretching Folding Instability and Nanoemulsions

TL;DR

This paper investigates a folding-stretching instability in a microfluidic device, demonstrating high-speed imaging of oscillating fluid threads and droplet formation, including the creation of sub-micrometer droplets.

Contribution

It reveals a novel folding-stretching instability in microfluidics and captures detailed high-speed dynamics of droplet pinch-off and formation.

Findings

Oscillating oil thread observed in microfluidic focusing.

Droplet formation occurs with high repeatability.

Sub-micrometer droplets are produced.

Abstract

Here we show a folding-stretching instability in a microfluidic flow focusing device using silicon oil (100cSt) and water. The fluid dynamics video demonstrates an oscillating thread of oil focused by two co-flowing streams of water. We show several high-speed sequences of these oscillations with 30,000 frames/s. Once the thread is decelerated in a slower moving pool downstream an instability sets in and water-in-oil droplets are formed. We reveal the details of the pinch-off with 500,000 frames/s. The pinch-off is so repeatable that complex droplet patterns emerge. Some of droplets are below the resolution limit, thus smaller than 1 micrometer in diameter.