Figure 5. Reversible phase transition of the liquid metal droplet robot between liquid state and solid state. (a) Schematic showing the magnetic field-controlled deformation of the liquid metal-based droplet robot in order to achieve different patterns. The robot is surrounded by air and located on a hydrophobic (spray coated) petri dish. (b) Photographs of the magnetic field-controlled deformation of the liquid metal droplet robot into the numbers 1 to 10. The experiment is performed on a liquid metal lyophobic surface. (c) Schematic showing the reversible phase transition of the liquid metal (Gallium) droplet robot between liquid state and solid state. (d) Photographs of the reversible phase transition of the liquid metal droplet robot between liquid state and solid state with different patterns generated by magnetic field on a silicon surface (SEM images of the surface morphology of the silicon surface is given in Figure S7, Movie S4).