Lateral migration of ferrofluid droplets in a microchannel under uniform magnetic fields

Manipulation of microfluidic droplets is an important step for applications in chemical and biological assays.  In this work, we experimentally studied the lateral migration of ferrofluid micro-droplets in a microchannel under uniform magnetic fields, where an aqueous ferrofluid works as the discrete phase and an oil works as the continuous phase.  When the uniform magnetic field is applied, the droplet is deformed and migrates laterally. The effect of the direction and strength of magnetic field, interfacial tension on the lateral migration of magnetic droplet is investigated.  The results show that the direction of droplet deformation and lateral migration depends on the direction of magnetic field. The degree of deformation and the net lateral migration depends on the strength of magnetic field. This method provides a simple and flexible means to manipulate and sort microfluidics droplets, as compared with other force-based manipulation techniques.