FIELD-INDUCED STRUCTURES IN FERROFLUID EMULSIONS

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=1.33L0.37 for cell thickness 3≤L≤800 μm. A new theory, which treats the column shape more realistically, is developed to account for the results. © 1995 The American Physical Society.