The effect of dispersed particle size and shape on the electrorheological behaviour of suspensions

Electrorheological (ER) and dielectric properties of suspensions of four inorganic powders (talc, magnesium hydroxide, aluminium hydroxide, and titanium dioxide) of different particle size and shape and polyaniline particles in silicone oil has been compared. It has been shown that the efficiency of ER effect expressed as a ratio of electroviscosity Deltaeta (an increase in suspension viscosity on the application of electric field) to the field-off viscosity, eta(0), in addition to dielectric phenomena of dispersed and continuous phase may be strongly influenced by the hydrodynamic properties of individual particles. The non-spherical or irregular particle shape can considerably increase rigidity of the structure formed in the electric field and enhance the ER performance. The main factor controlling the ER effect, however, is particle polarisability. Thus, the electroviscosity of suspensions of highly polarisable polyaniline particles proved to be much higher than that of suspension of the most ER-efficient inorganic powder. (C) 2003 Elsevier B.V. All rights reserved.