Hard-magnetic liquid metal droplets with excellent magnetic field dependent mobility and elasticity

Abstract

Magnetic liquid metal droplets (MLMDs) have been proven to be very important in many fields such as flexible electronics and soft robotics. Usually, soft magnetic particles such as nickel (Ni) and iron (Fe) are mixed or suspended into the liquid metal to obtain soft MLMDs (S-LMDs), which can be easily manipulated under the magnetic field due to the favorable deformability and flexibility. In addition, hard magnetic particles such as neodymium iron boron (NdFeB) with a high residual magnetization can also be dispersed into the liquid metal and the hard MLMDs (H-LMDs) become more compact due to the interaction between internal particles induced by remanence. This work reports a kind of H-LMDs with high surface tension, high flexibility and mechanical robustness, whose electrical conductivity and strength are better than the S-LMDs. Under the magnetic field, the H-LMDs have a faster response time (0.58 s) and a larger actuating velocity (4.45 cm/s) than the S-LMDs. Moreover, the H-LMDs show excellent magnetic controllability, good elasticity and favorable mobility, as demonstrated by magnetically actuated locomotion, bounce tests and rolling angle measurements. Finally, the droplets can be further applied in wheel-driven motors and micro-valve switches, which demonstrates their high application potential in robotic manipulation and microfluidic devices.