Dielectric analysis of TiO₂-based electrorheological suspensions

Dielectric behaviors of titanium dioxide (TiO₂)-based electrorheological (ER) suspensions with different particle concentrations and TiO₂ polymorphs were investigated in the frequency range of 40 Hz to 110 MHz. Two relaxations in kilohertz and megahertz frequency range were attributed to interface polarization between TiO₂ and silicone oil and ion pair polarization between dissociated counterions and fixed charges on TiO₂ surfaces, respectively. Dipolar coefficient D, which is related to the construction or structure of the colloid, changes after critical volume fraction \(\phi _{\rm c} \approx \) 0.05, indicating that chain-like or network structures are formed by particles. Based on percolation model, the values of critical exponent suggest that particles may form two-dimensional percolation network. Furthermore, the effective dielectric mismatch parameter, \(\beta _{\rm eff}\), was calculated based on the obtained phase parameters. We found that rutile should have better ER activity than anatase. The main reason for weak ER activity of pure TiO₂ ER suspensions may due to poor conductivity properties of TiO₂ crystals.