Enhanced electrorheology of suspensions containing sea-urchin-like hierarchical Cr-doped titania particles

We developed a novel electrorheological (ER) suspension composed of Cr-doped titania particles with a sea-urchin-like hierarchical morphology, and demonstrated a distinct enhancement in ER properties. These hierarchical ER particles, which are easy to synthesize by a solvothermal approach, are nearly monodisperse and consist of high-density rutile Cr-doped titania nanorods assembled radially on the surfaces of particles. The specific surface area of the hierarchical Cr-doped titania particles is ∼ 65 m²/g, which is higher than that (5 m²/g) of the smooth non-hierarchical Cr-doped titania particles. Under electric fields, the ER properties of the suspension containing such hierarchical particles are investigated by steady shear viscosity and dynamic viscoelastic experiments. It is found that the suspension of hierarchical Cr-doped titania particles possesses a stronger ER effect compared to the corresponding suspension of smooth non-hierarchical Cr-doped titania particles. Its yield stress and ER efficiency are approximately twice as high as those of the smooth Cr-doped titania suspension. Meanwhile, a higher ER effect is also demonstrated for the hierarchical pure titania suspension in comparison with the smooth pure titania suspension. Furthermore, under electric and shearing fields the rheological and structuring processes of the hierarchical particle suspension is significantly different from that of the smooth particle suspension. In terms of the dielectric analysis and microscopy observation, the enhancement of ER effect of the suspension of hierarchical Cr-doped titania is likely attributed to the combined effects including improved interfacial polarization and increased interparticle interaction due to the presence of urchin-like nanostructures on the ER microparticles.