A 3D-printed coaxial microfluidic device approach for generating magnetic liquid metal droplets with large size controllability

The monodisperse magnetic liquid metal droplets have been proven to be very important in soft robots or machines and flexible electronics. Unfortunately, the size and composition tunability is technically confined due to the scarce of the preparation method. This paper reports a 3D-printed coaxial microfluidic device to generate monodisperse magnetic liquid metal droplets (MLMDs) with droplets sizes varied in a large range of 650 to 1900 μm. Owing to the inner-dispersed iron/nickel (Fe/Ni) particles, the MLMDs with different magnetic contents possess unique magnetic field manipulation performance. The minimum magnetic flux density driven the MLMDs is only 24 mT and the relative average actuating velocity reaches as high as 5.1 cm/s, which means that the MLMDs can be precisely and rapidly manipulated. In addition, the manipulation of the MLMDs by an external magnetic field has been illustrated in two-dimensional crooked channels and three-dimensional spiral channels. The MLMDs move through the two kinds of channels smoothly and exhibit good magnetic maneuverability. Finally, the potential feasibility of the MLMDs is further confirmed in small-sized electrical switches with the sequential turning on of light-emitting diodes (LEDs).