Elongation of confined ferrofluid droplets under applied fields

Ferrofluids are strongly paramagnetic liquids. We study the behavior of fer rofluid droplets confined between two parallel plates with a weak applied f ield parallel to the plates. The droplets elongate under the applied field to reduce their demagnetizing energy and reach an equilibrium shape where t he magnetic forces balance against the surface tension. This elongation var ies logarithmically with aspect ratio of droplet thickness to its original radius, in contrast to the behavior of unconfined droplets. Experimental st udies of a ferrofluid-water-surfactant emulsion confirm this prediction. [S 1063-651X(99)00210-X].