Surface rolling active magnetic emulsions

Abstract

Active emulsions can exhibit chemotactic locomotion in fuel-rich conditions like their biological counterparts. However, possessing extensive control over the spontaneous motion of chemotactic droplets and achieving their locomotion in fuel-deficient environments remains as a challenge. Here, synthetic rotational flows are incorporated to augment droplets with on-demand surface rolling ability. These rotational flows arise from a freely rotating magnetic cluster encapsulated within an oil droplet and aid in locomotion in fuel-deficient regions. Combining autonomous and synthetic flows aids in switchable locomotion modes enabling active magnetic droplets to explore confined spaces by avoiding concentration gradient traps and entering narrow spaces. Finally, on-demand switchability between surface rolling and autonomous swimming modes allows the active magnetic droplets to locomote against chemotactic gradients, while transporting and manipulating surrounding micro/nanoscale entities.