Field-Induced Structures in Ferrofluid Emulsions.

Abstract

The field-induced structure in a monodisperse ferrofluid emulsion is studied. An applied magnetic field induces a magnetic dipole moment in each droplet. When the dipole-dipole interaction energy exceeds the thermal energy, a phase transition occurs as the fluid of randomly dispersed droplets changes to a solid of nearly equally sized and spaced columns. Our results show that the column spacing follows a relation ${d\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.33L}^{0.37}$ for cell thickness $3\ensuremath{\le}L\ensuremath{\le}800\ensuremath{\mu}\mathrm{m}$. A new theory, which treats the column shape more realistically, is developed to account for the results.