Effect of matrix viscoelasticity on the electrorheological properties of particle suspensions

We have investigated the electrorheological properties of dispersions of se mi-conducting particles in oils and elastomers. We focused on how the dynam ic mechanical properties measured under oscillatory shearing change with th e viscosity of the oil or the elasticity of the elastomer. The dependence o n electric field and strain amplitude were also investigated. We found that the largest increment of the mechanical properties under electric fields w as obtained when using oils of low viscosity and elastomers of low elastici ty. The strain amplitude which produced the largest variation with electric field was found to be 0.1% for the elastomer systems, but significantly la rger (1%) for the oil systems. These results are interpreted in terms of a model based on the competition between the dipole-dipole electrostatic inte raction (which acts to maintain neighbouring particles together) and the sh earing force due to the deformation of the matrix (which acts to separate t he particles). We find that there are parallels between the electrorheologi cal behaviour of particles dispersed in elastomers and the behaviour of par ticles dispersed in oils. These results should find application in the sele ction of suitable matrix materials for electrorheological suspensions. (C) 1999 Elsevier Science B.V. All rights reserved.