According to the dielectric design, a new kind of rare-earth (RE)-doped TiO2 particle was synthesized by means of sol-gel technique for use in electrorheological (ER) fluids. A distinct enhancement in the yield stress under dc electric field was found by using such particles, when compared with that of pure TiO2. The yield stress of typical cerium-doped TiO2 suspension was about 5.0 kPa at 3 kV/mm and 7.0 kPa at 4 kV/mm, which were 10 times higher than that of a pure TiO2 suspension. The yield stress showed a marked dependence on RE-doping degree. Substitution of 10mol% cerium or 8mol% lanthanum for Ti could obtain the highest yield stress. These were well explained by the dielectric measurements that showed an increase in the dielectric loss and the dielectric constant at low frequency and their regular change with rare earth content. The lattice distortion and defects in the TiO2 crystal caused by substitution for Ti with large-radius RE ions may be responsible for the obvious improvement noted above.

A new kind of mesoporous rare-earth-doped TiO2 particle with a well-defined crystalline framework was synthesized under a general temperature state for use as electrorheological (ER) active material. The neutral surfactant dodecylamine (DDA) was used as a template to direct the mesoporous structure. The low-angle X-ray diffraction peak showed that the mesoporous rare-earth-doped TiO2 had an interlayer distance of about 3.4 nm and the highangle peaks showed that the material possessed an anatase crystalline framework. ER properties of the suspension based on this material and silicone oil were measured in a dc electric field. It had been shown that the extraordinary high yield stress over 8.1 kPa could be induced when a 3 kV/mm electric field was applied. It was 20 times higher than that of pure TiO2 ER suspension and twice as high as that of single-doped TiO2 ER suspension as reported in our previous works. Interestingly, the shear stress of this suspension was found to continuously increase with temperature elevation in the range 10-100 ℃. These improvements were attributed to the pursuit of slow polarization and suitable conduction properties of this mesoporous-doped TiO2 suspension in terms of the measured results of dielectric and conduction properties. The present experimental result suggests that both the active internal structure and interface or surface structure of ER particles, which merit the pursuit of suitable dielectric and conduction properties, are the key to high ER activity.

We have used laser diffraction methods to demonstrate that water-in-oil microemulsions and emulsions under an electric field present diffraction patterns and optical activity, which can be tuned by the external electric field. When the optical rotation angle increases with the electric field, the electric vector of incident polarized light rotates clockwise. It is thought that the spatial ymmetry breaking of the distribution of the droplets and the charges induced by the applied electric field is the origin of the phenomena in the complex fluids.