Influence of magnetic chain structures in micropillar array surface on the directional transport of droplets

Abstract

In recent years, significant advancements have been made in the study of magnetically responsive micropillars. However, the challenge of improving transport efficiency at a constant magnetic induction intensity still persists. In this paper, two types of micropillars were prepared: those with a vertical magnetic chain structure (MVMC) and those with an inclined magnetic chain structure (MIMC), by designing the distribution of magnetic nanoparticles within the micropillars. The droplet transport modes and capacities on the surfaces of the MVMC and the MIMC were different. With the same magnetic field, the MIMC exhibited a maximum bending angle of 87°, which was more favorable for droplet transport than that with the 72° angle achieved by MVMC. At the magnetic induction intensity of 160 mT, the MIMC surface facilitated rapid horizontal transport of a 2 μL droplet at the magnet moving velocity of 240 mm/s, which was 33 % faster than that at 180 mm/s achieved by MVMC. Furthermore, at the same magnet moving velocity of 130 mm/s, the MIMC surface was capable of transporting droplets up to 50 μL in volume, significantly surpassing the capacity of the MVMC surface, which could only transport up to 8 μL.