Sedimentation behaviour of hierarchical porous TiO₂ microspheres electrorheological fluids

Increasing the specific surface area of particles improves the suspension stability of electrorheological fluids. In this study, we introduced three TiO₂ electrorheological materials, namely, mesoporous TiO₂: Ce⁴⁺, hollow TiO₂: Ce⁴⁺ and mesoporous hollow TiO₂, all of which possess better sedimentation stability than pure solid TiO₂ electrorheological materials. We aim to highlight the advantages of nanostructured materials with large surface area in improving the sedimentation stability of electrorheological fluids. The results indicated that the suspension composed of Ce-doped mesoporous TiO₂ particles in silicone oil exhibited a strong electrorheological effect. The yield stress of a typical Ce-doped TiO₂ electrorheological fluid was approximately 5.0 kPa at 1.5 kV/mm and 6.0 kPa at 2 kV/mm, which were 10 times higher than that of pure TiO₂ electrorheological fluid. Hollow TiO₂: Ce⁴⁺ spheres using the polymer polystyrene as the hollow template not only showed good electrorheological effect but also greatly increased settleability. The specific surface area of the mesoporous TiO₂ hollow spheres was twice that of the mesoporous TiO₂ and thus showed better suspension stability.