Dielectric Criteria for the Electrorheological Effect

The suspended particles of an electrorheological (ER) fluid can be easily arrayed as a crystallite of a body-centered tetragonal (bct) lattice structure using an external electric field. Thus the entropy of this process, which is generally recognized as a first-order phase transition, would greatly decrease. From this fact, we theoretically derive that the dielectric loss tangent maximum value of the dispersed particles should be larger than 0.1, which agrees well with the currently observed experimental results; the negative ER effect becomes possible only when dε sp /d T < 0, where ε sp is the static dielectric constant of the dispersed particle material and T is temperature.