Correlation of the Dielectric Properties of Dispersed Particles with the Electrorheological Effect

The Interfacial Polarization-Induced Electrorheological Effect

“…Phenomenologically, the ER effect, however, results not only from the highly polarized particle but also from the particle rearrangement, particle fi-brillation. The particle turning to a preferable position for facilitating fibrillation is recently thought to be an important process in the ER response, and the large dielectric loss is regarded as the only reason that the particles can possibly turn without aid by a shear field (9,10). Actually the ER effect becomes weak when the particle conductivity is beyond 10 Ϫ6 S/m, since the dielectric loss decreases with the particle conductivity increasing in this range.…”

“…However, the currently observed phenomena are not well understood using these models. For example, some materials have a comparatively large dielectric constant but do not display any ER effect (9, 10); the particle dielectric loss tangent around 0.10 at 1000 Hz is an essential requirement for a high performance ER fluid (9,10); the fluid with high conductive particles usually has a short response time (11); the strongest ER effect takes place in the suspension with the particle conductivity around 10 Ϫ7 S/m (12); and a high frequency electric field or a high temperature can improve the ER effect of some materials markedly (13,14), while weakening the ER effect of other materials dramatically (14 -16). In this paper, we try to systematically understand these ER phenomena using the Wagner model (17)(18)(19).…”

Electrorheological Fluids

“…By controlling the carbonating temperature and time, various oxidized polyacrylonitrile materials of different nitrogen and hydrogen content and thus different conductivity and dielectric constant can be obtained. They are ideal candidates for investigating the ER mechanism [40] and for making high-performance ER fluids. [61] The ER effect of oxidized polyacrylonitrile materials still has much room for improvement via chemical doping and surface modification.…”

“…Recently, criteria for screening materials to make high-performance ER fluids based on experimental and theoretical results were proposed. [40,122,123] According to the criteria, the dielectric loss tangent of the dispersed material should be larger than 0.1, and the dielectric constant ratio of the dispersed material to the dispersing medium should be between 50 and 60. Detailed information can be found in the papers cited.…”

The Effect of Polyaniline Content Deposited on Silica Gel Particles on the Electrorheology of Silicone-Oil Suspensions

“…The results obtained so far indicate that an appreciable ER effect occurs when the relaxation frequency, at which the relative dielectric loss factor 1::" has a local maximum, is in the frequency range 10-10 5 Hz corresponding to the interfacial polarization [2,[26][27][28]. The magnitude of polarization depends on the difference of dielectric constants e' below and above this frequency value.…”