Suspension of layered particles: an optimum electrorheological fluid for dc applications

A comparison is made between two types of solid particles used in electrorh eological fluids: particles with homogeneous electrical properties versus l ayered particles with a semi-conducting core surrounded by an outer layer o f lower conductivity, Rheological measurements of these suspensions under s teady sheer and d.c. electric field show that the layered particle system p roduces the same yield stress but with a substantially reduced electric cur rent. X-ray spectroscopic analysis confirms that these particles have a thi n layer of SiOx on the outer surface which causes the reduction in conducti vity. Measurement of the dielectric permittivity followed by analysis using the Maxwell-Wagner model of polarization indicates that the conductivity o f the outer laver is about 0.62 times that of the core region.