Magnetofluidic based controlled droplet breakup: effect of non-uniform force field

TL;DR

This study investigates how a non-uniform magnetic field influences the controlled breakup of ferrofluid droplets in a microfluidic device, revealing a new mechanism for rapid, asymmetric droplet splitting useful in diagnostics.

Contribution

It introduces a novel magnetic field-driven droplet breakup mechanism that leverages internal convection and force asymmetry for controlled splitting in microfluidic systems.

Findings

Non-uniform magnetic fields induce asymmetric droplet splitting.

Internal convection within droplets triggers breakup at critical magnetic forces.

Larger daughter droplets form at the side with minimum flow time scale.

Abstract

We report the breakup dynamics of a magnetically active droplet (ferrofluid droplet) in a T-shaped LOC device under the modulation of a non-uniform magnetic field. We adhere to high-speed imaging modalities for the experimental quantification of the droplet splitting phenomena in the presence of a non-uniform force field gradient, while the underlying phenomena is supported by the numerical results in a qualitative manner as well. On reaching the T-junction divergence, the droplet engulfs the intersection fully and eventually deforms into the dumbbell-shaped form making its bulges to move towards the branches of the junction. We observe that the asymmetric distribution of the magnetic force lines, acting over the T-junction divergence, induces an accelerating motion to the left moving bulge (since the magnet is placed adjacent to the left branch). We show that the non-uniform force field gradient allows the formation of a hump-like structure inside the left moving bulge which triggers the onset of augmented convection in its flow field. We reveal that this augmented internal convection developed in the left moving volume/bulge, on getting coupled with the various involved time scales of the flow field, lead to the asymmetric splitting of the droplet into two sister droplets. Our analysis establishes that at the critical strength of the applied forcing, as realized by the critical magnetic Bond number, the flow time scale becomes minimum at the left branch of the channel, leading to the formation of larger sized sister droplet therein. Inferences of the present analysis, which focuses on the simple, wireless, robust and low-cost droplet splitting mechanism, will provide a potential solution for rapid droplet breakup, typically finds significant importance in point-of-care diagnostics.