FIELD-INDUCED STRUCTURE OF CONFINED FERROFLUID EMULSION

Field-induced phase behavior of a confined monodisperse ferrofluid emu lsion was studied using optical microscopy, light transmission, and st atic light scattering techniques. Upon application of magnetic field, randomly-dispersed magnetic emulsion droplets form solid structures at lambda = 1.5, where lambda is defined as the ratio of the dipole-dipo le interaction energy to the thermal energy at room temperature. The n ew solid phase consists of either single droplet chains, columns, or w orm-like clusters, depending on the volume fraction, cell thickness an d rate of field application. For the column phase, an equilibrium stru cture of equally-sized and spaced columns was observed. Our measuremen ts taken for cell thickness 5 mu m less than or equal to L less than o r equal to 500 mu m and volume fraction 0.04 show the column spacing t o be reasonably described by d = 1.49 L(0.34).