MATERIALS FOR ER FLUIDS

Recent improvements in the physical understanding of ER fluids have le d to the rational design of new ER materials with improved properties. This paper gives an overview of several recent developments in the fo rmulation of ER fluids, concentrating on new particulate phases for ER dispersions. Examples of homogeneous ER fluids are also discussed. Th e trend leading to designed ER dispersions is demonstrated by a new cl ass of electrorheological fluids based on non-aqueous polyurethane dis persions. The fluids exhibit an attractive combination of properties: low viscosity, high ER effect, and low conductivity. The dispersed pha se consists of a specially developed polyurethane elastomer which solv ates and stabilizes metal salts. The polymer network density influence s the mobility of the dissolved ions, allowing a surprising degree of control over the ER effect Properties such as the field strength depen dence of the ER-effect, switching response, and conductivity of these fluids correlate directly with changes in the polymer structure. Elect rorheological measurements in a couette viscometer (shear-mode) and in a model shock absorber (flow-mode) using a commercial polyurethane-ba sed fluid show that the ER effect is also dependent upon the shearing geometry.