ABSTRACT
The electrorheological (ER) effects have mainly been studied with suspensions, and the technology for applications of many ER suspensions has been developed so far. The use of suspensions as an ER material often brings about a large increase of yield stress under an electric field, which should be useful for various applications. On the other hand, the development of ER materials having different rheological properties from those of suspensions may extend the potential use of ER fluids. Actually, some homogeneous ER fluids containing no solid particles have already been studied (e.g. Honda and Sasada 1977, Tanaka et al 1992). The noticeable feature of homogeneous ER fluids is their variety of response to an electric field. For example, the ER effect of a fluid based on liquid crystalline polymers are observed as an increase of viscosity without a yield behavior (Yang and Shine 1992, Inoue and Maniwa 1995). As another example, electrically induced decrease of viscosity was also reported for low molecular-weight liquid crystals (Fukumasa et al 1993), polymer solution (Uemura et al 1994), and lecithin-decane-water mixture (Shchipunov and Schmiedel 1996). The decrease of viscosity, or negative ER effect, is interesting because the opposite electro-responsive property to usual ER fluids may extend the possibility for applications.
