of nonaqueous silica suspension is greatly enhanced upon We considered the electrorheological (ER) properties of an anapplication of a strong electric field (1). This behavior was hydrous suspension based on a semiconducting polymer. In order seen as instrumental in developing many mechanical applito investigate the effects of the electrical properties of polymeric cations, such as high-speed valves, reactive damping sysparticles on the ER phenomena, poly(p-phenylene) was synthetems, brakes, and miniature robotics joints due to the advansized and endowed with semiconductivity by doping with FeCl 3 tages of fast response time in ER phenomena (a few millisecsolutions. The dielectric behaviors of ER suspension revealed facilonds). As a result, development of high-performance ER itated interfacial polarization for the appropriately doped suspenfluid, followed by its optimization and tuning, has been a sion with intermediate conductivity of particle. These behaviors subject of considerable interest for practical application as were found to be closely related with the magnitude of dynamic yield stress, which showed a maximum and then decreased with a new electric-mechanical interface. increasing conductivity of particles. Therefore, we established an Because the conventional hydrous ER fluid having an adoptimum condition of FeCl 3 doping of poly(p-phenylene) showing sorbed layer of water on the particle surface has a relatively the maximum ER activity. Dynamic viscoelastic properties of the limited working temperature range, development of anhy-ER suspension were also characterized for the limited case. These drous ER materials has been pursued vigorously. These new experimental results give a clear relationship between the conducmaterials have intrinsic charge carriers in either bulk partitivity of semiconductive particles and their ER behaviors. Furthercles or their surfaces that can move locally under the electric more, effects of the interfacial polarization on yield stress behavfield (2, 3). The ER fluid based on the semiconducting iors were investigated using surfactant-activated ER suspensions. polymers is a novel, intrinsic ER system having several ad-Over a wide range of temperature, our suspensions show good ER vantages, such as a wide working temperature range, a reactivity while retaining the low current density that would broaden duced abrasion, and a relatively low current density. There the potential applicability of the ER fluids. แญง 1998 Academic Press have been several reports on the electrical and rheological Key Words: electrorheology; semiconductive poly(p-phenylene); FeCl 3 doping; yield stress; dielectric constants; high tempera-properties of anhydrous ER fluids composed of inorganic ture.
and polymeric materials (3-7). However, experimental studies on the detailed relationship between the electrical properties and rheological behaviors are still to be made in 1 To whom all correspondence should be addressed: telephone, /82 (42) 869 3923; telefax, /82 (42) 869 3910.