Oscillation and collective conveyor of water-in-oil droplets by microfluidic bolus flow

TL;DR

This study reveals how water-in-oil droplets can be collectively transported and oscillate within microfluidic arrays through hydrodynamic effects, demonstrating a novel pattern formation mechanism in microfluidic systems.

Contribution

It introduces a hydrodynamic method for transporting droplets in microfluidics, highlighting collective oscillation and conveyor behavior driven by vortex-like flows.

Findings

Droplets exhibit back-and-forth oscillation near large droplet arrays.

Droplets are conveyed at the velocity of the large droplet array.

Multiple droplets can be transported as ordered clusters.

Abstract

Microfluidic techniques have been extensively developed to realize micro-total analysis systems in a small chip. For microanalysis, electro-magnetic forces have generally been utilized for the trapping of objects, but hydrodynamics has been little explored despite its relevance to pattern formation. Here, we report that water-in-oil (W/O) droplets can be transported in the grid of an array of other large W/O droplets. As each droplet approaches an interspace of the large droplet array, while exhibiting persistent back-and-forth motion, it is conveyed at a velocity equal to the droplet array. We confirm the appearance of closed streamlines in a numerical simulation, suggesting that a vortex-like stream is involved in trapping the droplet. Furthermore, more than one droplet is also conveyed as an ordered cluster with dynamic reposition.