Electrorheological properties of polyphenylene suspensions

Electrorheological (ER) fluids are currently being extensively investigated since their technical applications look very promising. The effect relies on rapid and reversible changes of viscosity of an ER fluid upon application of electric field. Doping of a conjugated polymer increases its electrical conductivity σ and dielectric constant ε. Since factors determining values of these two parameters are different, it is sometimes possible to prepare a material of high ε and low σ, which is the basic requirement for a main component of an ER fluid. Thus, conjugated polymers can be used in formulation of these fluids. Poly(p-phenylene) (PPP) treated with ferrous chloride was chosen and its bulk electrical properties were investigated by means of impedance spectroscopy. The values of ε were 40–130 and the values of σ were 10−8-10−6 S/cm. ER fluids were prepared from the polymer powder and silicone oil, and their ER properties were studied. The fluids exhibited Bingham-like behaviour. The magnitude of the ER effect increases with ε but saturation at dielectric constants exceeding 100 is observed. This saturation seems to be a general feature of any ER fluid. Correlations between material parameters of the doped bulk PPP and the ER effect are shown.