Migration of Ferrofluid Droplets in Shear Flow under a Uniform Magnetic Field

Abstract

Manipulation of droplets based on physical properties (e.g., size, interfacial tension, electrical, and mechanical properties) is a critical step in droplet microfluidics. Manipulations based on magnetic fields have several benefits compared to other active methods. While traditional magnetic manipulations require spatially inhomogeneous fields to apply forces, the fast spatial decay of the magnetic field strength from the source makes these techniques difficult to scale up. In this work, we report the observation of lateral migration of ferrofluid (or magnetic) droplets under the combined action of a uniform magnetic field and a pressure-driven flow in a microchannel. While the uniform magnetic field exerts negligible net force on the droplet, the Maxwell stresses deform the droplet to achieve elongated shapes and modulate the orientation relative to the fluid flow. Hydrodynamic interactions between the droplets and the channel walls result in a directional lateral migration. We experimentally study the effects of field strength and direction, and interfacial tension, and use analytical and numerical modeling to understand the lateral migration mechanism.

Department(s)

Mechanical and Aerospace Engineering

Comments

This work is partially supported by the National Science Foundation (Grant No. DMS-1818642).

Keywords and Phrases

Drops; Flow of fluids; Magnetic fields, Analytical and numerical models; Droplet microfluidics; Hydrodynamic interaction; Magnetic field strengths; Magnetic manipulation; Pressure-driven flows; Spatially inhomogeneous; Uniform magnetic fields, Shear flow

International Standard Serial Number (ISSN)

1744-683X; 1744-6848

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2019 Royal Society of Chemistry, All rights reserved.

Publication Date

01 Feb 2019

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