Structural transition in bidispersed electrorheological fluids.

We present results from finite element calculations on electrorheological fluids consisting of bidispersed dielectric microspheres and nanoparticles suspended in liquid, with one type much smaller than the other. The face-centered-cubic (fcc) structure of the larger microspheres is shown to be the ground state when the volume concentration of the nanoparticles is between 3-5 %. This is in contrast to the usual situation in which the body-centered-tetragonal (bct) structure is the lowest-energy state. As a function of the nanoparticles' concentration, the bct-fcc structural transition occurs when the nanoparticles' dielectric constant exceeds a threshold value, leading to the electrostatic energy curves of the two structures crossing each other.