Electrical method to control the running direction and speed of self-powered tiny liquid metal motors

The motion control of small motors in solution is significant for various applications, ranging from microfluidics, smart machines, to tiny robot. Here, we propose an electrical controlling method to flexibly manipulate liquid metalmotors powered with aluminium. It was discovered that adding aluminium to liquid metal droplets would significantly magnify its electric controlling capability, which provides dozens of times' driving force compared to pure GaIn10 droplets. After switching on the electrical field, the aluminium powered liquid metal droplet would accelerate its running speed to an extremely high magnitude, e.g. 43 cms^-1 under 20V voltage, as measured in a channel with 1 cm width and filled with aqueous solution. In addition, we also observed that the motion trajectories of the motors in the free space of a Petri dish nearly reflect the electric field lines in the electrolyte, which suggests an important and straightforward way to visualize such complex physical property. Lastly, the oscillating motion behaviour of the motor under a small electrical voltage and its continuous running modality were experimentally discriminated and interpreted. The current findings on the Al-Ga-In motors generate profound impact on developing future microfluidic systems or tiny soft robots that are hard to achieve otherwise through conventional strategies.