The presence of significant amounts of adsorbed water on the particulate phase of most electrorheological (ER) materials is essential to their performance. This paper presents evidence showing that alumino-silicate particles, when used as the dispersed component, produce ER active fluids without the apparent need for any water, adsorbed or structured. It is suggested that these materials, by virtue of their unique chemistry and morphology, contain an intrinsic mechanism for producing their ER activity which does not require water. The ER activity and bulk conductivity of alumino-silicate based and silica gel based ER fluids are examined as a function of water content. Whereas the silica gel based fluid loses its ER activity between 1.5% and 6% H2O, the alumino-silicate based fluid continues to function at levels of HjO below FTIR detectability. Further, bulk current densities reach a constant value at around 0.5% HjO and below, but the fluids continue to operate without change. This suggests that models relying on increased interfacial polarization as a consequence of increased surface conductivity by “water coated” particles may not apply to Al-Si ER fluids. Most importantly it suggests that the ER activity of these materials is an inherent property of their chemistry and morphology. © 1990, The Society of Rheology. All rights reserved.
