Dielectric criteria for the electrorheological effect

The suspended particles of an electrorheological (ER) fluid can be easily a rrayed as a crystallite of a body-centered tetragonal (bct) lattice structu re using an external electric field. Thus the entropy of this process, whic h 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 ne gative ER effect becomes possible only when d is an element of(sp)/dT < 0, where is an element of(sp) is the static dielectric constant of the dispers ed particle material and T is temperature.