GROUND-STATE SYMMETRY OF AN ELECTRORHEOLOGICAL FLUID CONTAINING 2 TYPES OF PARTICLES

The ground state symmetry of an electrorheological fluid is studied nu merically using a finite element method. The free energies of body-cen tered cubic, body-centered tetragonal, simple hexagonal, hexagonal clo se-packed, simple cubic, simple hexagonal, and honeycomb structures ar e calculated for systems containing homogeneous particles with the die lectric constant greater or smaller than that of the base fluid. In ac cordance with other studies, the body-centered tetragonal symmetry was found to be the most favored lattice symmetry. The ground state of an ER system containing two types of particles, i.e., particles with the dielectric constant greater and smaller than that of the base fluid, was found to consist of separated particle columns each of which has o nly one type of particles. These separated particle columns preferred body-centered tetragonal symmetry. However, simple hexagonal and honey comb symmetries were found to be energetically quite close to a body-c entered tetragonal symmetry. In addition, simple hexagonal and honeyco mb symmetries do not need phase separation between different types of particles and are thus more likely to form. Dynamical effects were stu died using a point dipole model. Within the time-span studied the syst em seemed to form a polycrystalline structure.