Ground state of a dipolar fluid film

The ground state of a simple dipolar fluid film is approximately determined as a function of the sample thickness and the volume fraction, for low volume fraction. A model involving analytic and numerical analysis is employed. The body-centered-tetragonal internal structure is found to be consistently lower in energy than face-centered-cubic. In the absence of polydispersity, the ground-state columns are approximately square in cross section. Interestingly, reflection symmetry breaking occurs due to the repulsion of the bound charges at the ends of the columns. A transition to a "stripe" phase is seen at higher volume fraction. The possibility is raised that the columnar structures seen in magnetorheological fluid experiments are far from equilibrium. [S1063-651X(98)01511-6].