Visco-elastic studies on an electro-rheological fluid

Abstract

The fluid used for these studies consisted of lithium poly(methacrylate) dispersed in a chlorinated hydrocarbon oil. Shear wave propagation was employed to measure the storage and loss moduli at a frequency of 1200 rad s −1. The parameters varied were field strength, volume fraction and water content of the particles. Optical microscopy was used to measure the particle size distribution whilst electrophoresis was used to enable the electro-kinetic potential to be measured. This showed that the particles were positively charged with a potential of circa + 45 m V. Further characterisation of the suspensions was carried out by conductivity measurements and the conductivity of the systems was shown to be due to the counter-ions in the diffuse layer which balances the surface charge. The moduli of the suspensions were found to increase with applied field to a maximum value and then decrease. In addition, the storage moduli were much higher than the loss moduli for all samples at low applied fields, but at high fields both moduli were of similar magnitude. These experimental data will be discussed in terms of the inter-particle forces and the structure in the suspensions.