Fig. 1. (a) Schematic diagram of the preparation process of magnetic liquid metal. (b) Optical images of the pure liquid metal droplet (LMD), magnetic liquid metal droplet with Fe particles (S-LMD), large-sized NdFeB particles (H-LMD1) and small-sized NdFeB particles (H-LMD). (c) The magnetic hysteresis loops of the three kinds of MLMDs.

Fig. 2. SEM images of (a) small-sized NdFeB particles and (b) the particles dispersed in the H-LM. (c) EDS mapping of the H-LM. (d) The impacts of shear rates on the viscosity of the H-LM under different magnetic fields. The inset shows schematic illustrations of the Physica MCR302 test system. (e) The impacts of magnetic fields on the viscosity of the three magnetic liquid metal at a constant shear rate of 1 s-1. (f) The electrical conductivity of the S-LM, H-LM and LM.

Fig. 3. (a) Images of the contact angle measuring experiment for S-LMD, H-LMD and LMD on silicon wafer, glass, and PDMS substrates. Scale bar =1 mm. (b) The static contact angles of the three kinds of droplets. (c) The changes of droplet morphology under different magnetic flux density. Scale bar =1 mm. (d) Schematic diagram of contact angle test under the magnetic field. (e) The changes of contact angles for H-LMD and S-LMD on silicon substrate under the magnetic field. (f) The changes of contact lines for H-LMD and S-LMD on silicon substrate under the magnetic field.

Fig. 4. (a) Schematic diagram of the rolling test on the inclined substrate. (b) Image of the droplet rolling on the platform with an adjustable tilt angle. (c) The critical rolling angles of the LMD, H-LMD and S-LMD with different sizes on the silicon wafer substrate. (d) The rolling velocities of the S-LMD, H-LMD and LMD when rolling at an inclined angle of 30°. (e) Images of the position for the LMD, H-LMD and S-LMD at the same time when rolling from the silicon wafer substrate at an inclination angle of 30°.

Fig. 5. (a-c) High-speed images demonstrating different behavior of the H-LMD, S-LMD and LMD after impacting the substrate from a height of 10 cm. Scale bar = 5 mm. (d) Bouncing tracks of the three different types of droplets. (e) The rebound height of S-LMD, H-LMD and LMD falling from different heights on the silicon substrate. (f) Scheme of fatal jump of liquid metal droplets. High speed images demonstrating different regimes of the three kinds of droplets upon impacting on the substrate from different heights. Scale bar = 2 mm.

Fig. 6. (a) Magnetic controllability testing system. (b) Schematic of force analysis for a droplet moving on the glass substrate. (c) The relationship between the sizes of the droplets and the max actuating distance. (d) The magnetic flux density versus to the distance away from the magnet surface. (e) Distribution of magnetic lines of induction around the magnet. (f) The relationship between the sizes of the droplets and the average actuating velocity.

Fig. 7. (a) Schematic diagram of the actuating delay time experiment. (b) High-speed images from the movement of the magnet to the movement of S-LMD and H-LMD. (c) Schematic diagram of the wheel model. (d) Actuating process of the wheel. The wheel was placed on a glass substrate and actuated by a magnet.

Fig. 8. (a) Schematic diagram of the fabrication of the microfluidic chip used in fabricating micro-valve. (b-c) Structure of the liquid metal droplet-based micro-valve. (d) The open and close process of the micro-valve by manipulation of the H-LMD with an applied magnetic field. (e) Comparison of the efficiency for the micro-valve when the inlet flow rate is changed from 1 mL/h to 6 mL/h.