stability, and low price. Additionally, a large amount of these The dynamic properties of two kinds of aluminosilicate-based kinds of materials could be easily made, and they could electrorheological (ER) fluids were investigated under on-state possibly be developed into one of the best ER solid materials and off-state electric fields. The dynamic responsive (frequency if the appropriate conditions are found. Their steady and sweep spectrum and strain sweep spectrum) differences between dynamic shear properties under dc field have been studied these two ER suspensions were found under the off-state electric comprehensively (1-9) since the ER fluids are most likely field, whereas similarities were observed once an external electric operate under these conditions in devices. Many mechanical field was applied. Their dc conductances under an oscillatory memodels have been presented in an attempt to understand chanical field and their mechanical strengths under an oscillatory their mechanical behaviors and the operative mechanism. electric field were also examined. The periodically varied dc current in an oscillatory mechanical field and the decreased shear Nevertheless, the relationship between the microstructure of stress in an ac field were both found in these ER suspensions. The an ER fluid, its mechanical response under off-state and ondifferent in situ microstructures of these two ER fluids suggested state electric field, and its electric properties under a shear on the basis of the percolation model, as well as their different mechanical field are needed to further address, which is response times measured experimentally, were presented to underalso important for practical uses. In this paper, two kinds of stand the experimental observations. Our results have a direct alumino-silicate-based ER fluids were prepared for examinaimplication concerning the practical application of ER fluids. tion. Their mechanical responses under off-state field, dc