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Abstract

We have modeled an electrorheological (ER) fluid as hard-sphere particles, each with smaller hard-sphere ions constrained to roll on the sphere's inside surface. When the model E R fluid is placed in an electric field, each particle becomes polarized (due to rearrangement of the ions confined within the particle) with a dipole moment depending on both the field and interactions with its neighbors. Using NVT Monte Carlo simulations, we have shown that our model can display chain formation as seen in real ER fluids. Chaining occurred at a field where the net moment no longer varied linearly with the field. This model was extended to include particles shaped as ellipsoids of revolution. In the prolate case, slightly non-spherical particles were readily ordered by the field. In the oblate case, the induced dipole is roughly perpendicular to the symmetry axis. Oblate particles may then form a biaxial phase in an applied field. NPT and Gibbs ensemble Monte Carlo simulations were performed for spherical particles modified by an anisotropic potential of the form —4A£(