Fractal-chain transition of field-induced colloid structure

Electric-field-induced fractal and chain patterns formed by microspheres in liquid have been investigated. While conducting microspheres form fractal patterns, insulating microspheres form chains. The reversible fractal-chain transition is mainly controlled by the surface conductivity of microspheres. We have demonstrated the transition with glass microspheres coated with conducting and insulating films. Moreover, we observed that the suspended chains would aggregate to form columns under high field conditions. This aggregation, nevertheless, cannot be observed in the fractal case. © 1998 The American Physical Society.