Polypyrrole-coated Pickering-type droplet as light-responsive carrier of oily material

Polystyrene particle-stabilized Pickering-type paraffin droplets were successfully coated by polypyrrole overlayers by aqueous chemical oxidative polymerization of pyrrole, and the thickness of polypyrrole overlayer could be controlled simply by changing pyrrole concentration in the polymerization media. Remote motion control of the droplets was realized on a planar air–water surface by site-selective near-infrared light irradiation, due to light-to-heat photothermal property of the polypyrrole. Furthermore, motion control of the paraffin droplet was also possible using sunlight focused using a magnifying glass. A Marangoni flow induced by site-selective light irradiation of the droplet could work as a driving force to move the droplet on the air–water surface, and the direction and timing of irradiation could control those of the motion on demand. Path length, velocity, and decay time of the droplet motions became longer and larger with an increase of thickness of polypyrrole overlayer, which was confirmed by numerical analyses.