Elongation of confined ferrofluid droplets under applied fields

TL;DR

This paper investigates how ferrofluid droplets confined between plates elongate under an applied magnetic field, revealing a logarithmic relationship between elongation and aspect ratio, supported by experimental validation.

Contribution

It introduces a new understanding of droplet elongation behavior under confinement and applied fields, contrasting with unconfined droplet behavior.

Findings

Elongation varies logarithmically with aspect ratio.

Experimental results confirm theoretical predictions.

Confinement significantly alters droplet deformation behavior.

Abstract

Ferrofluids are strongly paramagnetic liquids. We study the behavior of ferrofluid droplets confined between two parallel plates with a weak applied field parallel to the plates. The droplets elongate under the applied field to reduce their demagnetizing energy and reach an equilibrium shape where the magnetic forces balance against the surface tension. This elongation varies logarithmically with aspect ratio of droplet thickness to its original radius, in contrast to the behavior of unconfined droplets. Experimental studies of a ferrofluid/water/surfactant emulsion confirm this prediction.