  We have determined the response time of dilute electrorheological fluids (ER)
in drag flow from the dynamic dielectric response. On the basis of a kinetic
rate equation a new formula was derived to approximate the experimental
time-dependent dielectric permittivity during the temporal evolution of the
microstructure. The dielectric response time was compared to the standard
rheological response time extracted from the time-dependent shear stress, and a
good agreement was obtained. We found that the dielectric method is more
sensitive to detect any transient during the chain formation process. The
experimental saturation value of the dielectric permittivity corresponding to
the equilibrium microstructure was estimated on the basis of formulas derived
from the Clausius-Mossotti equation.
