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 towards the external applied field E0, resulting in a steadystate polarization at an angle with respect to E0. This dynamic effect has shown to affect the ER fluids 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 an increasing rotational speed, whereas the off-diagonal response exhibits a maximum at a reduced rotational angular velocity ω0 comparing 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 ω0, the volume fraction, and the dielectric contrast, are discussed.

Alternating-current relaxation of a rotating metallic particle

“…Therefore, we try to use Eq. (20) to fit the experimental data, by using more accurate relaxation times, as listed in Tables 1 and 2 explicitly. It is found that the relaxation times τ R always take the values with the same order of magnitude for the current systems.…”

“…[36] By using Eq. (20), we obtain a fitting of Tao and Lan's experimental data of a rotating metallic particle (made of copper of dielectric constant 6) and a stationary metallic one (Fig. 2) or a stationary dielectric one (Fig.…”

“…The structures of various systems, such as colloidal suspensions including electrorheological fluids, [1][2][3] magnetorheological suspensions, [4][5][6][7] ferrofluids, [8][9][10][11] living cells suspensions, [12] and so on, are very sensitive to the change of interparticle forces. Unfortunately, some shearing flow that is inevitable in experiments and natural environments can cause the rotation of the colloidal particles, [13][14][15][16][17][18][19][20][21][22][23] thus reducing the interparticle force to some extent. An interaction between a rotating electric field and suspended particles or cells can also lead to a rotational motion of the particles.…”

“…From upper to bottom: R = 19.314 mm (or gap =0.254 mm) and E 0 = 100 V/mm; R = 19.441 mm (or gap =0.381 mm) and E 0 = 100 V/mm; R = 19.441 mm (or gap =0.381 mm) and E 0 = 80 V/mm; R = 19.568 mm (or gap =0.508 mm) and E 0 = 80 V/mm. According to our theory [Eq (20)…”

Geometrical study of electrorheological activity with shape-controlled titania-coated silica nanomaterials

“…The rheological changes in ER fluid are very fast and reversible. The ER fluids have many desirable rheological characteristics including simple mechanics, low power consumption, rapid response time, and reversible change in rheological properties [8][9][10][11][12][13][14].…”