STRUCTURAL LIMITATION TO THE MATERIAL STRENGTH OF ELECTRORHEOLOGICAL FLUIDS

The variation of the dynamic modulus of a model electrorheological flu id with strain amplitude is shown to closely resemble that of traditio nal physical gels. Comparison of the in-phase stress component in each system indicates that the material strength of electrorheological flu ids in shear is limited by the small strain amplitude to structural fa ilure. An anisotropic network model is proposed for electrorheological fluids, in which the primary structure consists of chains of particle s spanning the electrode gap along the field direction, while many-bod y interactions form a secondary structure of short chains tilted with respect to the field direction and interconnecting the primary chains. A geometrical argument shows that the tensile strain in the secondary structure can be an order of magnitude larger than that in the primar y chains. This nonuniform strain distribution poses an inherent struct ural limitation on the shear material strength of electrorheological f luids. (C) 1997 American Institute of Physics.