Ferrofluid drops-based actuator in a narrow gap

Abstract

Directional transport of a liquid is an important issue in microfluidic systems and application purpose. Here, through combining the ideas of pressure-driven gas bubble-induced acoustic streaming flow and magnetic field-deformed ferrofluid drop, we study the ambient flow induced by an oscillating ferrofluid drop as an in situ actuator in a millimeter-sized gap environment. A drop squeezed by two parallel glass sheets, under the influence of a magnetic field, is discovered to undergo multimodal oscillations. The particle image velocimetry technique helps us to reveal the vortex-typed flow structure surrounding the oscillating drop. The shape changes of drop are found including the circular, elliptical, triangular, inverse-triangular, and circular shapes. We employ the numerical front-tracking method and analytical mixed-mode model to elucidate a drop-driven flow. We find that the pulsating, translational, and quadrupole mode oscillation of the drop is capable to describe most features of the flow distribution. Furthermore, we demonstrate an in situ pump by applying a spatially non-uniform pulsating magnetic field onto the arranged ferrofluid drops. The ferrofluid drop-based in situ pump shows the ability to produce a flow rate of 108 μl/min, which should be a great help in microfluidic pumping.