Pattern transitions induced by the surface properties of suspended microspheres in electrorheological fluid

In our previous Letter [Phys. Fluids 8, 2789 (1996)] we reported a new kind of netlike structure formed by metal microspheres suspended in silicon oil. In this paper we present further experimental results showing that different patterns are formed depending on whether metal, semiconducting, or dielectric microspheres are presented in the electric field. In addition, several experiments are performed on the surface properties of suspended microspheres and it is found that a pattern transition occurs when the surface conductivity of the solid phase is changed. This phenomenon can also be observed in a glass/oil ER fluid if the glass particles absorb enough water. (C) 1997 American Institute of Physics.