title: Dynamic polarizability of rotating particles in electrorheological fluids.
abstract: A rotating particle in electrorheological (ER) fluid leads to a displacement of its polarization charges on the surface which relax toward the external applied field E0, resulting in a steady-state polarization at an angle with respect to E0. This dynamic effect has shown to affect the ER fluid properties dramatically. In this paper, we develop a dynamic effective medium theory (EMT) for a system containing rotating particles of finite volume fraction. This is a generalization of established EMT to account for the interactions between many rotating particles. While the theory is valid for three dimensions, the results in a special two-dimensional configuration show that the system exhibits an off-diagonal polarization response in addition to a diagonal polarization response, which resembles the classic Hall effect. The diagonal response monotonically decreases with increasing rotational speed, whereas the off-diagonal response exhibits a maximum at a reduced rotational angular velocity omega0, compared to the case of isolated rotating particles. This implies a way of measurement on the interacting relaxation time. The dependencies of the diagonal and off-diagonal responses on various factors, such as omega0, the volume fraction, and the dielectric contrast, are discussed.
authors.affiliation: Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China. jjxiao@phy.cuhk.edu.hk
authors.forename: J J
authors.initials: JJ
authors.lastname: Xiao
authors.forename: J P
authors.initials: JP
authors.lastname: Huang
authors.forename: K W
authors.initials: KW
authors.lastname: Yu