Time-dependent and nonlinear effects in electrorheological fluids

Abstract

An integral equation method is used to calculate particle-particle forces in electrorheological fluids. The method focuses on the gap region between particles where large electric-field concentrations occur. Effects due to time-dependent excitation and nonlinear ͑field-dependent͒ fluid conductivity are analyzed. It is found that the response to step-function changes in applied field closely follows a simple form that can be derived from the dipole approximation. Qualitatively different stress-vs-time curves are obtained for large dielectric mismatch ͑e.g., barium titanate/dodecane͒ relative to large conductivity mismatch ͑zeolite/silicone oil͒. In fluids where the conductivity is strongly field dependent, it is found that particle-particle forces scale linearly with applied field E 0 at large fields. Likewise, the shear yield stress scales as E 0 3/2 .

Electrorheologial properties of hematite/silicone oil suspensions under DC fields

“…For example, electrostatic forces (as manifested by, e.g., yield stress) are often found to vary as F el ∝ E n where n < 2 in contrast to the E 2 dependence predicted by the polarization model [21,22]. One explanation for this phenomenon is nonlinear conduction [23,24]: the electric field strength between closely spaced particles can be much larger than the nominal one.…”

Preparation of Stannum and Titanium Precipitation Particles and its High Electrorheological Properties

“…The high yield stress and its near-linear dependence on the electric field indicate that the behaviors of our STP ER fluid can be explained by the model of the polar molecule dominated ER (PM-ER) effect [15]. The PM-ER effect is based on the interaction of the polar molecule polarization charge between the particles, where the local electric field is much higher than that of the external field [16][17][18][19], and results in the polar molecules aligning in the direction of the electric field. Figure 3 shows the shear stress of STP ER fluid as a function of shear rate under various electric fields.…”

The electrode effect on polar molecule dominated electrorheological fluids

“…The behavior of conventional ER fluids [2][3][4][5][6][7] is based on the interaction of polarized particles in the electric field, of which the yield stress is usually less than 10 kPa. The low yield stress of such ER fluids has strongly limited their applications for decades.…”

“…However, PM-ER effect comes from the interaction of polar molecules adsorbed on the particles and the polarized charges of the neighboring particles in the gap between particles, where the high local field (about three orders higher than the applied electric field [4][5][6]) causes the polar molecules turning to the field direction [8]. The attractive force of the polar molecule-charge in PM-ER fluids can be orders higher than that of pure polarized particles in conventional ER fluids.…”