In-situ Measurements of Electrorheological Response and Electric Properties of Ferroelectric Barium Titanate/Silicone Oil Suspension.

Electrorheological response of ferroelectric BaTiO3 / silicone oil suspension was experimentally studied with in-situ measurements of electric conductivity and dielectric permittivity in ranges of electric field strength (0-2kV/mm) and field frequency (100-5000Hz) under steady shear and shear stress sweep. In steady shear experiments, conducted at shear rates of 100 and 200s-1, shear stress increased with time accompanied by increases in the conductivity and the permittivity. The evolution of these electric properties suggested the growth of particle aggregation in the suspension. The shear stress at each time increased with field frequency, reached maximum value around 103Hz, and then declined. The change in the shear stress well corresponded to the change in the permittivity. An empirical relation of Δτ ∝(Δε rΕ )2 , observed for silica particle / silicone oil (Saimoto et al.,1999), was applicable to the present suspension, where Δτ is generated shear stress, Δεr generated dielectric permittivity, and Ε electric field strength. In the shear stress sweep experiments, hysteresis behavior was observed. Longer sweep period induced larger yield stress due to the growth of the aligned particles during the application of electric field. A drastic decrease in the permittivity around a yield point indicated collapse of the aggregative structure. A correlative behavior was observed between changes in the yield stress and the value of ΔεrΕ.