Negative electrorheological responses of mono-dispersed polypyrrole-SAN copolymer suspensions

The mono-dispersed polypyrrole (PPy)-poly(acrylonitrile-co-styrene) (SAN) copolymer particles were synthesized by emulsion polymerization and the electrorheological (ER) behavior of their suspensions was investigated. The suspensions of the mono-dispersed PPy-SAN copolymer particles showed negative ER effects. It was quite unexpected to negative ER effects for ER suspensions of conducting polymers or conducting polymer composites. The ER responses decreased with increasing electric field strength and particle size. A power-law dependence on the particle size and the electric field strength, τ(E)-τ0=−103.95 d−2E, showed a reasonable fit to the dynamic yield stress differences. It was observed that particles separated between the electrodes during experiments under the applied electric field. The migrations due to charge injection, by which the gap between the electrodes devoid of particles, seem to play a role in the yield stress decrease, leading to the negative ER response. [graphic not available: see fulltext]