We report measurements of the static shear modulus of electrorheological (ER) fluids consisting of water-wetted silica microspheres in silicone oil. A shear-annealing method, using creep-recovery (CR) cycles under an external electric field, is used to enhance ER properties of the fluid. The shear-annealing method enables the silica spheres in the ER fluid to form better aligned and denser column microstructures. A stable state with elastic shear deformation is obtained after a sufficient number of CR cycles, with an optimal combination of stress duration and shear strength. Static shear modulus is obtained by measuring the elastic deformations at different shear stresses for an electric field frequency from $10\text{to}1000\mathrm{Hz}$. A water-bridge model is proposed to explain the enhanced shear modulus.

• Received 26 July 2005

DOI:https://doi.org/10.1103/PhysRevE.73.051501