Department of Mechanical Engineering, Stanford University, 450 Serra Mall, California 94305, USA.
Soft Matter. 2018 Jan 31;14(5):681-692. doi: 10.1039/c7sm01973d.
We present a microfluidic platform for magnetic manipulation of water droplets immersed in bulk oil-based ferrofluid. Although non-magnetic, the droplets are exclusively controlled by magnetic fields without any pressure-driven flow. The fluids are dispensed in a sub-millimeter Hele-Shaw chamber that includes permalloy tracks on its substrate. An in-plane rotating magnetic field magnetizes the permalloy tracks, producing local magnetic gradients, while an orthogonal magnetic field magnetizes the bulk ferrofluid. To minimize the magnetostatic energy of the system, the water droplets are attracted towards the locations on the tracks where the bulk ferrofluid is repelled. Using this technique, we demonstrate synchronous generation and propagation of water droplets, study the kinematics of propagation, and analyze the flow of the bulk ferrofluid. In addition, we show controlled break-up of droplets and droplet-to-droplet interactions. Finally, we discuss future applications owing to the potential biocompatibility of the droplets.
我们提出了一种用于在浸入 bulk oil-based ferrofluid 的水中操控水滴的微流控平台。尽管是非磁性的，但这些水滴完全可以通过磁场进行控制，而无需任何压力驱动的流动。这些流体被分配到一个亚毫米级的 Hele-Shaw 腔中，该腔的基底上包括坡莫合金轨道。一个面内旋转磁场使坡莫合金轨道磁化，产生局部磁场梯度，而一个正交磁场则使 bulk ferrofluid 磁化。为了使系统的静磁能最小化，水滴被吸引到 bulk ferrofluid 被排斥的轨道位置。通过这种技术，我们演示了水滴的同步生成和传播，研究了传播的运动学，并分析了 bulk ferrofluid 的流动。此外，我们还展示了受控的液滴破裂和液滴之间的相互作用。最后，我们讨论了由于水滴潜在的生物相容性而带来的未来应用。
