Phase-change Janus particles with switchable dual properties

We developed switchable Janus particles (JPs) fabricated by coating one hemisphere of silica microspheres with a phase-change film. We used the chalcogenide GeSbTe (GST), which exhibits a reversible phase change between a metal-like crystalline phase (c-GST) and a dielectric-like amorphous phase (a-GST). As a driving force for self-propelling the JPs, a perpendicular alternating current electric field was applied; the frequency dependence of the motion of an individual JP and that of inter-JP interaction were investigated. At lower frequencies (2-20 kHz), a-GST JPs were propelled with their silica side facing forward, which is similar to the behavior of Au-silica JPs propelled by the well-known induced-charge electrophoresis mechanism, whereas c-GST JPs were immobile because they adhered to the indium tin oxide substrate. At higher frequencies (50-300 kHz), both a-GST and c-GST JPs were propelled with their GST side facing forward and a substantial difference in inter-JP interaction was observed: repulsive collision for c-GST JPs but attractive stacking for a-GST JPs.